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RSS2007 Vol. 19, No. 06
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Particle simulation and experimental study of subnanosecond millimeter wave backward wave oscillator
2007,
19.
Abstract:
The particle simulation of the subnanosecond millimeter wave backward wave oscillator was carried out by KARAT code, the experiment was done under the condition of the electron beam with voltage 200 kV, current 500 A, pulse width 1.65 ns, and guiding magnetic field 1.7 T. The output millimeter wave with millimeter wave power 40 MW, pulse width 500 ps, frequency 37.6 GHz, repetition rate 10 Hz and radiation mode TE11 was acquired by the experiment.
The particle simulation of the subnanosecond millimeter wave backward wave oscillator was carried out by KARAT code, the experiment was done under the condition of the electron beam with voltage 200 kV, current 500 A, pulse width 1.65 ns, and guiding magnetic field 1.7 T. The output millimeter wave with millimeter wave power 40 MW, pulse width 500 ps, frequency 37.6 GHz, repetition rate 10 Hz and radiation mode TE11 was acquired by the experiment.
2007,
19.
Abstract:
An optimized X-band relativistic backward wave oscillator (RBWO) based on superradiance mechanism of short electron beam was designed and simulated numerically. The simulation results indicate that the RBWO can realize microwave radiation with high peak power and high power conversion efficiency under superradiace mechanism. A small narrow pulse electron accelerator is build based on a compact Tesla pulse source along with design of a resistance conversion section, a diode and a magnetic system. The preliminary experiment was performed at low magnetic field condition. For guiding magnetic field 0.73 T, beam voltage 380 kV, beam current 4.5 kA and pulse width 3.1 ns, microwave pulses with about 360 MW peak power, 1.10 ns pulse width and 800 ps risetime were generated, and the conversion eff
An optimized X-band relativistic backward wave oscillator (RBWO) based on superradiance mechanism of short electron beam was designed and simulated numerically. The simulation results indicate that the RBWO can realize microwave radiation with high peak power and high power conversion efficiency under superradiace mechanism. A small narrow pulse electron accelerator is build based on a compact Tesla pulse source along with design of a resistance conversion section, a diode and a magnetic system. The preliminary experiment was performed at low magnetic field condition. For guiding magnetic field 0.73 T, beam voltage 380 kV, beam current 4.5 kA and pulse width 3.1 ns, microwave pulses with about 360 MW peak power, 1.10 ns pulse width and 800 ps risetime were generated, and the conversion eff
2007,
19.
Abstract:
By means of the 2-D simplified model，the dynamic process of the exploding tube of MFCG is simulated. The simulation results show that the expanding angle can be varied with the radial position(or different time) due to the radial velocity variation with the radial position(or different time). In order to compare the simulated expanding angle with the results of the experiments, the velocity should take an average over time(or position). The ending effect on the expanding velocity is given by simulation results and it may be useful to improve experimental results. The simulation results suggest that using high density metal material may reduce the sliding effect because the high density causes big ratio of radial velocity to axial velocity. The simulated expanding angles of 2-D model are c
By means of the 2-D simplified model，the dynamic process of the exploding tube of MFCG is simulated. The simulation results show that the expanding angle can be varied with the radial position(or different time) due to the radial velocity variation with the radial position(or different time). In order to compare the simulated expanding angle with the results of the experiments, the velocity should take an average over time(or position). The ending effect on the expanding velocity is given by simulation results and it may be useful to improve experimental results. The simulation results suggest that using high density metal material may reduce the sliding effect because the high density causes big ratio of radial velocity to axial velocity. The simulated expanding angles of 2-D model are c
2007,
19.
Abstract:
A cyclotron was designed using the 2.5 dimensional particle simulation code KARAT in the paper. Transverse momentum of the electrons was imparted by a kicker. By using intense coupling and optimized length of the interaction space, the device could generate microwave pulse with a peak power of 7 MW, an operating frequency of 38.5 GHz with the diving electron beam of 250 kV, 200 A and 1 ns. The peak power conversion reached 14%. The peak power had a square relationship with the beam pulse width during certain range, which was in accordance with the character of superradiance.
A cyclotron was designed using the 2.5 dimensional particle simulation code KARAT in the paper. Transverse momentum of the electrons was imparted by a kicker. By using intense coupling and optimized length of the interaction space, the device could generate microwave pulse with a peak power of 7 MW, an operating frequency of 38.5 GHz with the diving electron beam of 250 kV, 200 A and 1 ns. The peak power conversion reached 14%. The peak power had a square relationship with the beam pulse width during certain range, which was in accordance with the character of superradiance.
2007,
19.
Abstract:
The effects of the plasma generated from the air ionzation on the output characteristic of microwave are given. Keeping the external wave constant, the diode current increases, the diode voltage decreases, and the microwave frequency decreases with the increase of air pressure. The space charge neutralization introduced by the plasma ion and the microwave energy absorption produced by the plasma electron will affect the beam-wave interaction simultaneously. In certain range of air pressure, the advantage of space charge neutralization leads to the increase of the output power. However, when the pressure is higher, the compact plasma electron will strongly absorb the microwave energy, and lower the output power, even result in pulse shortening. On the other hand, due to the presence of the
The effects of the plasma generated from the air ionzation on the output characteristic of microwave are given. Keeping the external wave constant, the diode current increases, the diode voltage decreases, and the microwave frequency decreases with the increase of air pressure. The space charge neutralization introduced by the plasma ion and the microwave energy absorption produced by the plasma electron will affect the beam-wave interaction simultaneously. In certain range of air pressure, the advantage of space charge neutralization leads to the increase of the output power. However, when the pressure is higher, the compact plasma electron will strongly absorb the microwave energy, and lower the output power, even result in pulse shortening. On the other hand, due to the presence of the
2007,
19.
Abstract:
The cutoff characteristic of waveguide is theoretically analysed in this paper, as well as the feasibility and accuracy in measuring the output power of HPM using the characteristic. It was used to measure the output microwave power of a magnetically insulated transmission line oscillator(MILO) operating at 1.75 GHz in far-field region. The experimental results show that a 2.3 GW high power microwave of TM01 mode is detected from the MILO device. The detected radiation pattern agrees with that of the simulation well. The microwave pulse width is more than 40 ns, and there is no obvious microwave power breakdown. It is good to use the cutoff characteristic of waveguide to prevent the power breakdown of the receiving horn and improve the measuring accuracy.
The cutoff characteristic of waveguide is theoretically analysed in this paper, as well as the feasibility and accuracy in measuring the output power of HPM using the characteristic. It was used to measure the output microwave power of a magnetically insulated transmission line oscillator(MILO) operating at 1.75 GHz in far-field region. The experimental results show that a 2.3 GW high power microwave of TM01 mode is detected from the MILO device. The detected radiation pattern agrees with that of the simulation well. The microwave pulse width is more than 40 ns, and there is no obvious microwave power breakdown. It is good to use the cutoff characteristic of waveguide to prevent the power breakdown of the receiving horn and improve the measuring accuracy.
2007,
19.
Abstract:
A new kind of slow-wave circuit, tunnelplane, is put forward. The tunnelplane circuit was similar to tunneladder slow-wave circuit, but the support between the ring and the metal wall is a metal plane. The tunnelplane was analyzed by field method. The discrepancy of dispersion between the analysis and CST was within 1.5%. The analysis shows that the tunnelplane structure has relatively broader band than the tunneladder structure, and both of the structures have high interaction impedance.
A new kind of slow-wave circuit, tunnelplane, is put forward. The tunnelplane circuit was similar to tunneladder slow-wave circuit, but the support between the ring and the metal wall is a metal plane. The tunnelplane was analyzed by field method. The discrepancy of dispersion between the analysis and CST was within 1.5%. The analysis shows that the tunnelplane structure has relatively broader band than the tunneladder structure, and both of the structures have high interaction impedance.
Primary study on spatial powers combining of parallel and intersectant beams of high power microwave
2007,
19.
Abstract:
Considering that the phases are hard to controll accurately for the high power microwaves, the spatial powers combining of both parallel beams and intersectant beams is investigated. It is concluded that when a small solid angles range adjacent to the main direction in the far field is considered, the parallel beams combining of compact antenna arrays has its priority if the phases can be controlled,and the parallel beams combining of sparse antenna arrays has its priority if the phases can not be controlled. When a small area in the far field is considered, the parallel beams combining of compact antenna arrays has its priority if the phases can be controlled, and the intersectant beams of sparse antenna arrays has its priority if the phases can not be controlled. On the account of the en
Considering that the phases are hard to controll accurately for the high power microwaves, the spatial powers combining of both parallel beams and intersectant beams is investigated. It is concluded that when a small solid angles range adjacent to the main direction in the far field is considered, the parallel beams combining of compact antenna arrays has its priority if the phases can be controlled,and the parallel beams combining of sparse antenna arrays has its priority if the phases can not be controlled. When a small area in the far field is considered, the parallel beams combining of compact antenna arrays has its priority if the phases can be controlled, and the intersectant beams of sparse antenna arrays has its priority if the phases can not be controlled. On the account of the en
2007,
19.
Abstract:
In this paper, the finite-difference time-domain(FDTD) method was employed to simulate the linear coupling processes of the microwave pulse into the nested cylindrical cavities system with narrow rectangular slots. The influence of the position of the inner slot on the coupling characteristics of outer cavity and inner cavity was analyzed. Except the region near the inner slot, the influence on the coupling characteristics of outer cavity is very small and it can be neglected. However, the influence on the coupling characteristics of inner cavity is significant. The shielding property of the inner cavity is determined jointly by the distribution of coupling field inside the outer cavity and the position of the inner slot.
In this paper, the finite-difference time-domain(FDTD) method was employed to simulate the linear coupling processes of the microwave pulse into the nested cylindrical cavities system with narrow rectangular slots. The influence of the position of the inner slot on the coupling characteristics of outer cavity and inner cavity was analyzed. Except the region near the inner slot, the influence on the coupling characteristics of outer cavity is very small and it can be neglected. However, the influence on the coupling characteristics of inner cavity is significant. The shielding property of the inner cavity is determined jointly by the distribution of coupling field inside the outer cavity and the position of the inner slot.
2007,
19.
Abstract:
With the 2.5D fully electromagnetic particle-in-cell code, a P-band hybrid magnetically insulated transmission line oscillator(MILO) was proposed and investigated by using the advantages of both tapered MILO and load-limited MILO. For the hybrid MILO, one extractor vane is taken place by three ones with tapered depth to form a taper section in the load-limited MILO. This provides a better match between the electric field of the main slow wave structure and the electric field of the output coaxial transmission line in order to increase the output microwave power. The simulation results show that a 640 MHz, 4.27 GW high power microwave in TEM mode can be obtained when the beam energy is 550 keV and current is about 57 kA. The efficiency is about 13.6%. The MILO starts to oscillate at 4 ns, a
With the 2.5D fully electromagnetic particle-in-cell code, a P-band hybrid magnetically insulated transmission line oscillator(MILO) was proposed and investigated by using the advantages of both tapered MILO and load-limited MILO. For the hybrid MILO, one extractor vane is taken place by three ones with tapered depth to form a taper section in the load-limited MILO. This provides a better match between the electric field of the main slow wave structure and the electric field of the output coaxial transmission line in order to increase the output microwave power. The simulation results show that a 640 MHz, 4.27 GW high power microwave in TEM mode can be obtained when the beam energy is 550 keV and current is about 57 kA. The efficiency is about 13.6%. The MILO starts to oscillate at 4 ns, a
2007,
19.
Abstract:
The small-signal theory of the gyro-TWT, a pinch-point analysis based on the theory of Briggs and Bers combining the cold analysis of the dielectric-loaded waveguide are employed to analysis the threshold current of the operating mode and critical oscillation lengths of the spurious mode under different load condition. The analysis concludes that the improvement of the dielectric loss, through altering the load condition, can enhance the threshold current and critical oscillation lengths. The cold analysis of the dielectric-loaded waveguide and a smooth waveguide dispersion relation is used to analyse the small signal gain of the dielectric-loaded gyro-TWT. Through numerical calculation, the analysis gives the gain-frequency response of a dielectric-loaded gyro-TWT.
The small-signal theory of the gyro-TWT, a pinch-point analysis based on the theory of Briggs and Bers combining the cold analysis of the dielectric-loaded waveguide are employed to analysis the threshold current of the operating mode and critical oscillation lengths of the spurious mode under different load condition. The analysis concludes that the improvement of the dielectric loss, through altering the load condition, can enhance the threshold current and critical oscillation lengths. The cold analysis of the dielectric-loaded waveguide and a smooth waveguide dispersion relation is used to analyse the small signal gain of the dielectric-loaded gyro-TWT. Through numerical calculation, the analysis gives the gain-frequency response of a dielectric-loaded gyro-TWT.
2007,
19.
Abstract:
The analysis uses the mode-matching technique to generate a parameter matrix which can be cascaded for computing the resonant frequency and Q value of a complex cavity consisting of a series of waveguide sections is introduced. Program was designed to calculate the parameter matrix to get the eigenvalue parameters of a cavity. The result indicates that the simulation results of an input cavity obtained by the program are in good agreement with the cold-test results. The analysis provides useful information for further study of beam-wave interaction and design of gyrotrons.
The analysis uses the mode-matching technique to generate a parameter matrix which can be cascaded for computing the resonant frequency and Q value of a complex cavity consisting of a series of waveguide sections is introduced. Program was designed to calculate the parameter matrix to get the eigenvalue parameters of a cavity. The result indicates that the simulation results of an input cavity obtained by the program are in good agreement with the cold-test results. The analysis provides useful information for further study of beam-wave interaction and design of gyrotrons.
2007,
19.
Abstract:
The generalized expression of Fermat’s principle is introduced through defining generalized refractive index on the basis of the comparison of the definition between left handed materials(LHMs) and right handed materials(RHMs). The concrete expression of generalized refractive index is derived from electromagnetic theory. The refractive index represents positive or negative refraction of the perfect and composite materials by medium electrical parameters, and the theory obtained can be used to depict the steady electromagnetic or optical system effectively with variable refractive index consisting of LHMs and RHMs. The high frequency forms of refractive index and negative refractions are discussed.
The generalized expression of Fermat’s principle is introduced through defining generalized refractive index on the basis of the comparison of the definition between left handed materials(LHMs) and right handed materials(RHMs). The concrete expression of generalized refractive index is derived from electromagnetic theory. The refractive index represents positive or negative refraction of the perfect and composite materials by medium electrical parameters, and the theory obtained can be used to depict the steady electromagnetic or optical system effectively with variable refractive index consisting of LHMs and RHMs. The high frequency forms of refractive index and negative refractions are discussed.
2007,
19.
Abstract:
The gyroklystron is a high power, high gain, and high efficiency millimeter wave amplifier. Its circuit usually comprises of 4 or 3 stagger-tuned cavities. The input coupler is the first cavity of the circuit and must exhibit reasonable coupling strength between the TE10 mode in rectangular waveguide and the desired TE011 or TE021 circular cavity mode with high purity. The theoretical analysis and HFSS simulation of the input coupler are presented. Mode matching technology is used to calculate the size of coaxial and cylindrical cavities. A new method, combining theory and HFSS, is presented to calculate the purity of working mode. Some results are obtained through the study of the orientation, width and length, angular offset of the apertures. The results show that 45°orientation is bett
The gyroklystron is a high power, high gain, and high efficiency millimeter wave amplifier. Its circuit usually comprises of 4 or 3 stagger-tuned cavities. The input coupler is the first cavity of the circuit and must exhibit reasonable coupling strength between the TE10 mode in rectangular waveguide and the desired TE011 or TE021 circular cavity mode with high purity. The theoretical analysis and HFSS simulation of the input coupler are presented. Mode matching technology is used to calculate the size of coaxial and cylindrical cavities. A new method, combining theory and HFSS, is presented to calculate the purity of working mode. Some results are obtained through the study of the orientation, width and length, angular offset of the apertures. The results show that 45°orientation is bett
2007,
19.
Abstract:
Resonant condition of this new cavity resonator is different from that of the traditional cavity resonators for its total phase shift need not be a positive integral multiple of 180°. The left-handed transmission line(LHTL) which can realize a negative phase shift is a resonant-slot coupled cavity chain, while the right-handed transmission line(RHTL) which realizes a positive phase shift is a coaxial waveguide, and resonant condition can be satisfied as long as the total phase shift keep zero. Because of its larruping resonant condition, the theory and simulation prove the length of the cavity resonators can be much smaller than that of the traditional cavity resonator.
Resonant condition of this new cavity resonator is different from that of the traditional cavity resonators for its total phase shift need not be a positive integral multiple of 180°. The left-handed transmission line(LHTL) which can realize a negative phase shift is a resonant-slot coupled cavity chain, while the right-handed transmission line(RHTL) which realizes a positive phase shift is a coaxial waveguide, and resonant condition can be satisfied as long as the total phase shift keep zero. Because of its larruping resonant condition, the theory and simulation prove the length of the cavity resonators can be much smaller than that of the traditional cavity resonator.
2007,
19.
Abstract:
The power capacity of a 36-element high power helical array antenna fed from double-layered radial waveguide is investigated. Two breakdown conditions are discussed, which are breakdown under vacuum condition and breakdown on the medium surface. Based on those breakdown threshold values, the power capacity of the antenna is analyzed theoretically and qualitatively and simulated. The simulation results are presented and the reasons for capacity debasement are analyzed. Methods for improving the power capacity are discussed. The results show that the power capacity of the improved antenna can reach 1 GW.
The power capacity of a 36-element high power helical array antenna fed from double-layered radial waveguide is investigated. Two breakdown conditions are discussed, which are breakdown under vacuum condition and breakdown on the medium surface. Based on those breakdown threshold values, the power capacity of the antenna is analyzed theoretically and qualitatively and simulated. The simulation results are presented and the reasons for capacity debasement are analyzed. Methods for improving the power capacity are discussed. The results show that the power capacity of the improved antenna can reach 1 GW.
2007,
19.
Abstract:
In design of the waveguide-stripline-coaxial line directional coupler, the solution of the field distribution in the stripline is essential. Using the Schwarz-Christoffel transformation function, the perfect stripline is transformed into a parallel-plate capacitor, and the field distribution in the stripline is derived. The coupling coefficient, directivity and the relationships between coupling coefficient and geometric dimension are obtained by the coupling theory of small hole. The comparison between the calculated coupling coefficient and the measured one of couplers manufactured by us shows little difference as 1.04 dB.
In design of the waveguide-stripline-coaxial line directional coupler, the solution of the field distribution in the stripline is essential. Using the Schwarz-Christoffel transformation function, the perfect stripline is transformed into a parallel-plate capacitor, and the field distribution in the stripline is derived. The coupling coefficient, directivity and the relationships between coupling coefficient and geometric dimension are obtained by the coupling theory of small hole. The comparison between the calculated coupling coefficient and the measured one of couplers manufactured by us shows little difference as 1.04 dB.
2007,
19.
Abstract:
According to demand of the double anode magnetron injection gun for gyroklystron amplifier, many factors influencing electron gun performance, such as electrode shape, magnetic distribution, beam current, first anode voltage, second anode voltage, were discussed, The results show that the transverse to longitudinal velocity ratio of beam increases and the trans-velocity spread decreases when the first anode voltage increases or magnetic induction at the cathode decreases, when the first anode obliquity reduces and cathode obliquity increases, the transverse to longitudinal velocity ratio of beam increases and the trans-velocity spread will decrease. Quality of electron beam is improved by adjusting the distance between the cathode and the first anode and the first anode voltage properly. A
According to demand of the double anode magnetron injection gun for gyroklystron amplifier, many factors influencing electron gun performance, such as electrode shape, magnetic distribution, beam current, first anode voltage, second anode voltage, were discussed, The results show that the transverse to longitudinal velocity ratio of beam increases and the trans-velocity spread decreases when the first anode voltage increases or magnetic induction at the cathode decreases, when the first anode obliquity reduces and cathode obliquity increases, the transverse to longitudinal velocity ratio of beam increases and the trans-velocity spread will decrease. Quality of electron beam is improved by adjusting the distance between the cathode and the first anode and the first anode voltage properly. A
2007,
19.
Abstract:
The propagation of high power microwave (HPM) can produce nonlinear effect in lower ionosphere. In this paper, the analytical interaction effect of HPM in lower ionosphere, and the relation of interaction factor with the initial electric field and microwave frequency are analyzed when HPM propagates in lower ionosphere. Based on the study, the relationship between the amplitude cross modulation depth and the delay time of two pulses at different conditions are discussed and simulated numerically. The conclusion is that the rule of variety of the amplitude cross modulation depth changes with the different delay time, and the ratio of the initial electric field amplitude of interference waves to the plasma electric field amplitude should be controlled below “ten” when HPM propagates in low
The propagation of high power microwave (HPM) can produce nonlinear effect in lower ionosphere. In this paper, the analytical interaction effect of HPM in lower ionosphere, and the relation of interaction factor with the initial electric field and microwave frequency are analyzed when HPM propagates in lower ionosphere. Based on the study, the relationship between the amplitude cross modulation depth and the delay time of two pulses at different conditions are discussed and simulated numerically. The conclusion is that the rule of variety of the amplitude cross modulation depth changes with the different delay time, and the ratio of the initial electric field amplitude of interference waves to the plasma electric field amplitude should be controlled below “ten” when HPM propagates in low
2007,
19.
Abstract:
A novel mode converter with slow-wave structures is investigated. The circular waveguide is separated into two regions by a metal plate. One is a regular 180° sector waveguide, the other is inserted with slow-wave structures. The input circular TM01 mode excites two sector TE11 modes which propagate at different phase velocities in the two regions. Adjusting the parameters of the SWSs, the two sector TE11 modes have various phase difference. At the end of the plate the two sector TE11 modes with 180° phase difference couple into the circular TE11 mode to finish the TM01-TE11 mode conversion. The input and output is aligned on the same axis, which is helpful for the compactness of the microwave lunching systems. Numerical simulations reveal that at the operating frequency of 1.8 GHz the c
A novel mode converter with slow-wave structures is investigated. The circular waveguide is separated into two regions by a metal plate. One is a regular 180° sector waveguide, the other is inserted with slow-wave structures. The input circular TM01 mode excites two sector TE11 modes which propagate at different phase velocities in the two regions. Adjusting the parameters of the SWSs, the two sector TE11 modes have various phase difference. At the end of the plate the two sector TE11 modes with 180° phase difference couple into the circular TE11 mode to finish the TM01-TE11 mode conversion. The input and output is aligned on the same axis, which is helpful for the compactness of the microwave lunching systems. Numerical simulations reveal that at the operating frequency of 1.8 GHz the c
2007,
19.
Abstract:
The electric-magnetic vibrator combined ultrawideband antenna consist of three parts: feed-in system,TEM horn radiation unit and current loop radiation unit. Applying CST electromagnetic software, the relation between physical structure and port S parameter and the radiation characteristic in time domain of the electric-magnetic vibrator combined ultrawideband (UWB) antenna were investigated. The results indicate that when the TEM horn radiation unit and current loop radiation unit are divided three parts, the antenna has smaller port S parameter, larger power on main axis and it has better direction.
The electric-magnetic vibrator combined ultrawideband antenna consist of three parts: feed-in system,TEM horn radiation unit and current loop radiation unit. Applying CST electromagnetic software, the relation between physical structure and port S parameter and the radiation characteristic in time domain of the electric-magnetic vibrator combined ultrawideband (UWB) antenna were investigated. The results indicate that when the TEM horn radiation unit and current loop radiation unit are divided three parts, the antenna has smaller port S parameter, larger power on main axis and it has better direction.
2007,
19.
Abstract:
The carbon-fiber cathode with CsI was substituted for the stainless steel cathode in the reflex triode virtual cathode oscillator experimental device. The carbon-fiber cathode vircator output microwaves with pulse width over 200 ns, which was about 30% longer than that of stainless steel cathode, and the ratio of the pulse areas was about 2.273, which meant the energy of single pulse of the former was double the latter’s. It was analysed that the complex emission mechanism, characteristic and configuration of the carbon fiber cathode slowers the plasma expansion velocities and lowers the temperature, thus extends the output pulse width and enhances the output energy.
The carbon-fiber cathode with CsI was substituted for the stainless steel cathode in the reflex triode virtual cathode oscillator experimental device. The carbon-fiber cathode vircator output microwaves with pulse width over 200 ns, which was about 30% longer than that of stainless steel cathode, and the ratio of the pulse areas was about 2.273, which meant the energy of single pulse of the former was double the latter’s. It was analysed that the complex emission mechanism, characteristic and configuration of the carbon fiber cathode slowers the plasma expansion velocities and lowers the temperature, thus extends the output pulse width and enhances the output energy.
2007,
19.
Abstract:
In order to study the basic physical process and energy conversion mechanism of helical magnetic flux compression generators (HMFCG) of the two-stage cylinder-taper configuration, a series of HMFCG models were simulated and analyzed using the code MFCG(Ⅴ). The influence of the magnetic pressure on the radial velocity and the expanding process of the armature were particularly analyzed. The simulation results show that during most time of the magnetic flux compression process, the radial velocity of the expanding armature is determined by detonation pressure, but with the current increase the effects of magnetic pressure become more and more important, which should be considered in designing the second stage of the HMFCG.
In order to study the basic physical process and energy conversion mechanism of helical magnetic flux compression generators (HMFCG) of the two-stage cylinder-taper configuration, a series of HMFCG models were simulated and analyzed using the code MFCG(Ⅴ). The influence of the magnetic pressure on the radial velocity and the expanding process of the armature were particularly analyzed. The simulation results show that during most time of the magnetic flux compression process, the radial velocity of the expanding armature is determined by detonation pressure, but with the current increase the effects of magnetic pressure become more and more important, which should be considered in designing the second stage of the HMFCG.
2007,
19.
Abstract:
In order to research Dense Plasma Focus device (DPF), a kind of scintillation neutron detector is introduced in this paper. The detector consists of a ST401-plastic scintillation and a XP2262B-photoelectric electron-multiplier tube. With a silver activation detector, the DT neutron sensitivity of the scintillation detector is calibrated as 0.022 5 pC per neutron, the neutron yield measurement range is from 109 to 1011 per pulse.
In order to research Dense Plasma Focus device (DPF), a kind of scintillation neutron detector is introduced in this paper. The detector consists of a ST401-plastic scintillation and a XP2262B-photoelectric electron-multiplier tube. With a silver activation detector, the DT neutron sensitivity of the scintillation detector is calibrated as 0.022 5 pC per neutron, the neutron yield measurement range is from 109 to 1011 per pulse.
2007,
19.
Abstract:
In the experiment of gas laser pumped by electron beam, large area uniform electron beam is important to generate high efficiency laser output. The experimental study on generation of large area uniform electron beam with SPG-200 pulsed power generator is introduced. SPG-200 is an all-solid-state components pulsed power generator based on SOS, and its open voltage is more than 350 kV. The cathode have the area of 24 mm×294 mm, and the anode-cathode(A-C)gap spacing is adjustable from 0 to 49 mm. The electron beam of cathode emission is transported to the laser chamber through the diode pressure foil, which separates the vacuum chamber from the laser chamber. Velvet and graphite cathodes are studied, each generates large area electron beam. The diode parameters are presented, and the unifor
In the experiment of gas laser pumped by electron beam, large area uniform electron beam is important to generate high efficiency laser output. The experimental study on generation of large area uniform electron beam with SPG-200 pulsed power generator is introduced. SPG-200 is an all-solid-state components pulsed power generator based on SOS, and its open voltage is more than 350 kV. The cathode have the area of 24 mm×294 mm, and the anode-cathode(A-C)gap spacing is adjustable from 0 to 49 mm. The electron beam of cathode emission is transported to the laser chamber through the diode pressure foil, which separates the vacuum chamber from the laser chamber. Velvet and graphite cathodes are studied, each generates large area electron beam. The diode parameters are presented, and the unifor
2007,
19.
Abstract:
ν/γ is an important physical parameter. ν，γ, are the Budker parameter and the relativistic mass factor, respectively. In this paper, its basic physical sense is expounded from three aspects of Lawson and Humphries formula and energy storage in intense relativistic electron beam. It can be expressed as the ratio of transverse electro-magnetic energy in the beam to its axial motion kinetic energy. For ν/γ closed to or greater than 1, there is an important self field effect in intense relativistic electron beam transport.
ν/γ is an important physical parameter. ν，γ, are the Budker parameter and the relativistic mass factor, respectively. In this paper, its basic physical sense is expounded from three aspects of Lawson and Humphries formula and energy storage in intense relativistic electron beam. It can be expressed as the ratio of transverse electro-magnetic energy in the beam to its axial motion kinetic energy. For ν/γ closed to or greater than 1, there is an important self field effect in intense relativistic electron beam transport.
2007,
19.
Abstract:
The 3.5 MeV foilless injector is the electron source of dragon-Ⅰ linear induction accelerator(LIA). In beam tuning, the variety range of magnetic field is approximately determined by simulation. Based on the beam current waveforms at injector exit, the magnetic field profile of diode is decided by experiments. By measureing some beam parameters, the layout of magnetic field for the whole injector is obtained. The tuning experimental results show that this injector has achieved prospective guide line with an output beam energy of 3.5 MeV, a beam current of 2.8 kA and a normalized emittance of 1 040 mm·mrad.
The 3.5 MeV foilless injector is the electron source of dragon-Ⅰ linear induction accelerator(LIA). In beam tuning, the variety range of magnetic field is approximately determined by simulation. Based on the beam current waveforms at injector exit, the magnetic field profile of diode is decided by experiments. By measureing some beam parameters, the layout of magnetic field for the whole injector is obtained. The tuning experimental results show that this injector has achieved prospective guide line with an output beam energy of 3.5 MeV, a beam current of 2.8 kA and a normalized emittance of 1 040 mm·mrad.
2007,
19.
Abstract:
The physical mechanism for producing keV level X-radiation via high power Z-pinch and a two-level model for K-shell radiation scaling of the imploding Z-pinch plasma were investigated, and the results of the numerical simulation by the two-level model were given in detail. The performance parameters of Qiangguang-Ⅰ generator for driving Z-pinch loads, the configuration and parameters of double-shell neon gas puff load and aluminum wire array were described, and the experimental arrangement was introduced. The waveform of X-ray measured by special X-ray diode for Qiangguang-Ⅰ with neondouble gas puff indicated that a good result of keV level characteristic X radiation could be obtained when the initial pressure of neon is 0.8 MPa.
The physical mechanism for producing keV level X-radiation via high power Z-pinch and a two-level model for K-shell radiation scaling of the imploding Z-pinch plasma were investigated, and the results of the numerical simulation by the two-level model were given in detail. The performance parameters of Qiangguang-Ⅰ generator for driving Z-pinch loads, the configuration and parameters of double-shell neon gas puff load and aluminum wire array were described, and the experimental arrangement was introduced. The waveform of X-ray measured by special X-ray diode for Qiangguang-Ⅰ with neondouble gas puff indicated that a good result of keV level characteristic X radiation could be obtained when the initial pressure of neon is 0.8 MPa.
2007,
19.
Abstract:
The operation principle of integral construction of Tesla transformer and PFL was investigated in Tesla-transformer-type accelerator. Experiment was carried out on Tesla transformer’s secondary winding to study the impulse voltage distribution while PFL was discharging. The regularities of turn-ground voltage distribution and interturn voltage distribution were summarized. Voltage distribution within PFL was calculated and it was compared with the experimental result. Structural winding of parallel coils in the head, parallel coils in the end and shading ring were used to improve voltage distribution and that was testified by experiment. The results indicate that taper winding doesn’t effect electric field within PFL, the turn-ground voltage appears linearly, the interturn voltage fluctu
The operation principle of integral construction of Tesla transformer and PFL was investigated in Tesla-transformer-type accelerator. Experiment was carried out on Tesla transformer’s secondary winding to study the impulse voltage distribution while PFL was discharging. The regularities of turn-ground voltage distribution and interturn voltage distribution were summarized. Voltage distribution within PFL was calculated and it was compared with the experimental result. Structural winding of parallel coils in the head, parallel coils in the end and shading ring were used to improve voltage distribution and that was testified by experiment. The results indicate that taper winding doesn’t effect electric field within PFL, the turn-ground voltage appears linearly, the interturn voltage fluctu
2007,
19.
Abstract:
A method based on Creedon’s laminar flow theory is got to predict MITL operating point changing, which is resulted from the so called electron re-trapping. The method gives exact numerical solutions for MITL total current, cathode current and voltage, i.e., operating point, behind the reflected front when forwards operating point and diode impedance are given. The result with the method is consistent with PIC simulation and could be used to estimate the maximum effective current, which is useful to generate X-ray for radiography, transmitted from MITL to under-matched diode.
A method based on Creedon’s laminar flow theory is got to predict MITL operating point changing, which is resulted from the so called electron re-trapping. The method gives exact numerical solutions for MITL total current, cathode current and voltage, i.e., operating point, behind the reflected front when forwards operating point and diode impedance are given. The result with the method is consistent with PIC simulation and could be used to estimate the maximum effective current, which is useful to generate X-ray for radiography, transmitted from MITL to under-matched diode.
2007,
19.
Abstract:
The synchronizer trigger system of Flash Ⅱ accelerator gas switch is designed and debugged. The system is composed of a synchro-control and a high voltage pulse generator, and the process includes the selection of synchronizer signal, filter, fast comparator, forestage trigger pulse formation, and the high voltage trigger pulse output. By filter circuit, the high frequent noise signal of Marx current is removed. By the fast comparator and the forestage trigger pulse circuit, the working point is accessed and a trigger signal is generated. The operating mode of the high voltage pulse generator switch is field distortion and preioniaztion, and its time response is 50 ns, jitter less than 5 ns. The experimental results indicate that the synchronizer system can generate a 100 kV pulse with ri
The synchronizer trigger system of Flash Ⅱ accelerator gas switch is designed and debugged. The system is composed of a synchro-control and a high voltage pulse generator, and the process includes the selection of synchronizer signal, filter, fast comparator, forestage trigger pulse formation, and the high voltage trigger pulse output. By filter circuit, the high frequent noise signal of Marx current is removed. By the fast comparator and the forestage trigger pulse circuit, the working point is accessed and a trigger signal is generated. The operating mode of the high voltage pulse generator switch is field distortion and preioniaztion, and its time response is 50 ns, jitter less than 5 ns. The experimental results indicate that the synchronizer system can generate a 100 kV pulse with ri
2007,
19.
Abstract:
The high power pulse technology, which is used in the ionic excimer, excimer and soft X-ray lasers, is introduced. The electrical parameters required by the three types of lasers are given respectively. In order to obtain soft X-ray laser, ten-stage Marx generator and Blumlein transmission line are used to build the capillary discharge device with maximum current of 40 kA and rise-time of 26.6 ns. The soft X-ray laser is observed with the device. The electron beam device with voltage of 600 kV and current of 20 kA is used to pump the ionic excimer and the resonator effects are obtained. The narrow voltage pulse of 29.2 ns is realized to excite S2 excimer.
The high power pulse technology, which is used in the ionic excimer, excimer and soft X-ray lasers, is introduced. The electrical parameters required by the three types of lasers are given respectively. In order to obtain soft X-ray laser, ten-stage Marx generator and Blumlein transmission line are used to build the capillary discharge device with maximum current of 40 kA and rise-time of 26.6 ns. The soft X-ray laser is observed with the device. The electron beam device with voltage of 600 kV and current of 20 kA is used to pump the ionic excimer and the resonator effects are obtained. The narrow voltage pulse of 29.2 ns is realized to excite S2 excimer.
2007,
19.
Abstract:
The measurement on the static breakdown voltages for two kinds of pseudospark switches with different electrode structures is presented. A newly designed pseudospark switch with two electrodes of 1 mm-wide annular slots was tested. Comparing the experimental results with that of a typical structure with eight equally-spaced 2 mm-diameter boreholes, it is found that the static breakdown voltage of the former is obvious higher than that of the latter under the same experimental conditions. A maximum hold-off voltage of 41 kV has been demonstrated for the annular-slot structure. Furthermore, the stability of the annular-slot structure is much better than the multihole one evidently.
The measurement on the static breakdown voltages for two kinds of pseudospark switches with different electrode structures is presented. A newly designed pseudospark switch with two electrodes of 1 mm-wide annular slots was tested. Comparing the experimental results with that of a typical structure with eight equally-spaced 2 mm-diameter boreholes, it is found that the static breakdown voltage of the former is obvious higher than that of the latter under the same experimental conditions. A maximum hold-off voltage of 41 kV has been demonstrated for the annular-slot structure. Furthermore, the stability of the annular-slot structure is much better than the multihole one evidently.
2007,
19.
Abstract:
For a high current diode composed of a small disk type ceramic insulator water/vacuum interface, the design of radial insulation structure is presented. According to the theory of vacuum flashover and the design rules for radial insulation, a “cone-column” anode outline and the cathode shielding rings were adopted. The electrostatic field along the insulator surface was obtained by FEA simulation. By adjusting the outline of the anode and the shielding rings, the electric fields were well distributed and the field around the triple junction was controlled. A high voltage test was carried out on a water isolated spiral pulse forming line(PFL) accelerator with 200 ns pulse width, and the results show the diode can work stably in 400 kV, 200 ns conditions.
For a high current diode composed of a small disk type ceramic insulator water/vacuum interface, the design of radial insulation structure is presented. According to the theory of vacuum flashover and the design rules for radial insulation, a “cone-column” anode outline and the cathode shielding rings were adopted. The electrostatic field along the insulator surface was obtained by FEA simulation. By adjusting the outline of the anode and the shielding rings, the electric fields were well distributed and the field around the triple junction was controlled. A high voltage test was carried out on a water isolated spiral pulse forming line(PFL) accelerator with 200 ns pulse width, and the results show the diode can work stably in 400 kV, 200 ns conditions.
2007,
19.
Abstract:
This paper studies the pulsed magnetizing property of annealing metglass and silicon steel core with polymer foil between layers fitted to the linear transformer driver(LTD). The capacitor fast discharge method was used to acquire a pulse with about 20 ns rise time and mearsure the magnetizing properties of annealing metglass 2605SA1 and silicon sted DG6. Through measuring primary current and secondary coil opened voltage, magnetic core hysteresis loops have been drawn. After the experiment, relative permeability was obtained in different dB/dt. The results indicate that the relative permeability is decreased with the increase of dB/dt. The relative permeability of annealing metglas 2605SA1 is less than 1 000 when dB/dt is more than 20 T/ms and that of silicon steel DG6 is less than 1 000
This paper studies the pulsed magnetizing property of annealing metglass and silicon steel core with polymer foil between layers fitted to the linear transformer driver(LTD). The capacitor fast discharge method was used to acquire a pulse with about 20 ns rise time and mearsure the magnetizing properties of annealing metglass 2605SA1 and silicon sted DG6. Through measuring primary current and secondary coil opened voltage, magnetic core hysteresis loops have been drawn. After the experiment, relative permeability was obtained in different dB/dt. The results indicate that the relative permeability is decreased with the increase of dB/dt. The relative permeability of annealing metglas 2605SA1 is less than 1 000 when dB/dt is more than 20 T/ms and that of silicon steel DG6 is less than 1 000
2007,
19.
Abstract:
Surface flashover switch have been investigated as a low inductance, low pulsed rate and low jitter command triggered switch. The development and mechanism of surface flashover switch are introduced in this paper. Experiments was carried out to study optically induced surface flashover characteristics. The Nd:YAG laser (wavelengthes are 1 024, 532, 355 nm) was used to induce flashover in the experiment. The DC flashover phenomena induced by laser with different wavelength, energy and focus shape were described. Experimental results indicated that the delay time and jitter was decreased at constant surface electric field strength with laser energy increase, and the range of triggering voltage was extended at the meantime. The jitter was decreasing with the decreasing laser wavelength. The f
Surface flashover switch have been investigated as a low inductance, low pulsed rate and low jitter command triggered switch. The development and mechanism of surface flashover switch are introduced in this paper. Experiments was carried out to study optically induced surface flashover characteristics. The Nd:YAG laser (wavelengthes are 1 024, 532, 355 nm) was used to induce flashover in the experiment. The DC flashover phenomena induced by laser with different wavelength, energy and focus shape were described. Experimental results indicated that the delay time and jitter was decreased at constant surface electric field strength with laser energy increase, and the range of triggering voltage was extended at the meantime. The jitter was decreasing with the decreasing laser wavelength. The f
2007,
19.
Abstract:
A high voltage pulse source with 300 kV peak voltage and less than 3 ns risetime was developed. The peaking circuit which consists of a peaking capacitor and an output switch is the key part of this source. The primary requirement of the peaking circuit is decreasing its stray inductance as low as possible for getting a fast risetime. Compact structures were designed especially for the peaking capacitor, the output switch and their connection. The peaking capacitor is made of three coaxial foil capacitors connected in series and the special gap structure at the end of each electrode is designed for improving its insulating ability. This capacitor can endure more than 300 kV pulse voltage with 17 ns risetime. The output switch is a SF6 gas switch with high pressure (up to 1.0 MPa) and small
A high voltage pulse source with 300 kV peak voltage and less than 3 ns risetime was developed. The peaking circuit which consists of a peaking capacitor and an output switch is the key part of this source. The primary requirement of the peaking circuit is decreasing its stray inductance as low as possible for getting a fast risetime. Compact structures were designed especially for the peaking capacitor, the output switch and their connection. The peaking capacitor is made of three coaxial foil capacitors connected in series and the special gap structure at the end of each electrode is designed for improving its insulating ability. This capacitor can endure more than 300 kV pulse voltage with 17 ns risetime. The output switch is a SF6 gas switch with high pressure (up to 1.0 MPa) and small
2007,
19.
Abstract:
Two surface discharge radiation sources with slope structure and plane structure respectively are introduced. The discharge characteristics of these two sources were studied with 1.0 μF and 1.5 μF storage capacitance and 15~30 kV charging voltage. From the experiment, some conclusions are drawn: the discharge resistance and inductance increase with the increase of the electrode distance of the slope structure, the discharge circuit area becomes larger; the discharge current and deposition power of the slope structure source are smaller than those of the plane structure source while the deposition efficiency is larger under the same charging voltage and capacitance; the use of 1.5 μF capacitor can enhance the deposition efficiency of the same source and it matches the discharge circuit e
Two surface discharge radiation sources with slope structure and plane structure respectively are introduced. The discharge characteristics of these two sources were studied with 1.0 μF and 1.5 μF storage capacitance and 15~30 kV charging voltage. From the experiment, some conclusions are drawn: the discharge resistance and inductance increase with the increase of the electrode distance of the slope structure, the discharge circuit area becomes larger; the discharge current and deposition power of the slope structure source are smaller than those of the plane structure source while the deposition efficiency is larger under the same charging voltage and capacitance; the use of 1.5 μF capacitor can enhance the deposition efficiency of the same source and it matches the discharge circuit e
2007,
19.
Abstract:
In this paper, the output voltage on a resistive load of a capacitor discharging circuit is numerically calculated based on Rompe-Weizel's formula for spark dynamic resistance. With the same electrical parameters, the calculated peak voltage is 54 kV, and the rise time is 2.0 ns, while the published experimental data are 55 kV and 2.3 ns respectively. Both results agree well basically. Based on Braginskii's formula for spark dynamic resistance, the nonlinear dynamic resistance of a spark gap used in a transmission line discharging circuit is calculated under the assumption of constant conductivity and variable conductivity. The comparison between calculated results(0.5~0.8 Ω) and existent measured data(0.7~0.9 Ω) indicates that the model of spark dynamic resistance with variable conducti
In this paper, the output voltage on a resistive load of a capacitor discharging circuit is numerically calculated based on Rompe-Weizel's formula for spark dynamic resistance. With the same electrical parameters, the calculated peak voltage is 54 kV, and the rise time is 2.0 ns, while the published experimental data are 55 kV and 2.3 ns respectively. Both results agree well basically. Based on Braginskii's formula for spark dynamic resistance, the nonlinear dynamic resistance of a spark gap used in a transmission line discharging circuit is calculated under the assumption of constant conductivity and variable conductivity. The comparison between calculated results(0.5~0.8 Ω) and existent measured data(0.7~0.9 Ω) indicates that the model of spark dynamic resistance with variable conducti
2007,
19.
Abstract:
In this paper a Blumlein line in folded parallel-plates configuration using Kapton film as dielectrics is investigated. The characteristic parameters of this Blumlein line were analyzed theoretically, and the electromagnetic field distribution and the process of the wave transmitting in the transmission line are simulated. According to the results of the theoretic analysis and simulation, a Blumlein line in folded parallel-plates configuration with output voltage of 600 kV, pulse duration of 40 ns, characteristic impedance of 5 Ω was designed and manufactured. The chamber of the Blumlein line is 1.2 m long, 0.4 m wide and 0.4 m high. The experimental results demonstrated the wave transmitting process in Blumlein line and gave the voltage waveform of 400 kV and the current waveform of 40
In this paper a Blumlein line in folded parallel-plates configuration using Kapton film as dielectrics is investigated. The characteristic parameters of this Blumlein line were analyzed theoretically, and the electromagnetic field distribution and the process of the wave transmitting in the transmission line are simulated. According to the results of the theoretic analysis and simulation, a Blumlein line in folded parallel-plates configuration with output voltage of 600 kV, pulse duration of 40 ns, characteristic impedance of 5 Ω was designed and manufactured. The chamber of the Blumlein line is 1.2 m long, 0.4 m wide and 0.4 m high. The experimental results demonstrated the wave transmitting process in Blumlein line and gave the voltage waveform of 400 kV and the current waveform of 40
2007,
19.
Abstract:
A rep-rate fast pulse hard X-ray generator is developed. The specialties in principle and structure is described, and the experiment parameters of running voltage, current and X-ray radiation field are measured and analyzed. The stability of the source is investigated. The results show that the generator has flexible structure and running mode and can produce a medium intense rep-rate nanosecond or sub-nanosecond pulse hard X-ray radiation field, whose parameters of upper limit of energy, spectrum, intensity, pulse width, etc, are on-line controlled.
A rep-rate fast pulse hard X-ray generator is developed. The specialties in principle and structure is described, and the experiment parameters of running voltage, current and X-ray radiation field are measured and analyzed. The stability of the source is investigated. The results show that the generator has flexible structure and running mode and can produce a medium intense rep-rate nanosecond or sub-nanosecond pulse hard X-ray radiation field, whose parameters of upper limit of energy, spectrum, intensity, pulse width, etc, are on-line controlled.
2007,
19.
Abstract:
This article describes the design and performance of a rep-frequency pulsed-current source. The scheme for rep-frequency pulse current source is based on the new type reversely switching dynistor(RSD). The pulsed-current source, which mainly consists of RSD switch with the diameter of 52 mm, fast thyristors and magnetic switch and etc, is capable of working at single shot, rep-frequency of 1, 10 and 100 Hz. The pulsed-current source can deliver a pulse current with peak current about 62 kA, with a pulse width up to 10 μs, current rate of rise of 18 kA/μs and at working voltage of 1 kV.
This article describes the design and performance of a rep-frequency pulsed-current source. The scheme for rep-frequency pulse current source is based on the new type reversely switching dynistor(RSD). The pulsed-current source, which mainly consists of RSD switch with the diameter of 52 mm, fast thyristors and magnetic switch and etc, is capable of working at single shot, rep-frequency of 1, 10 and 100 Hz. The pulsed-current source can deliver a pulse current with peak current about 62 kA, with a pulse width up to 10 μs, current rate of rise of 18 kA/μs and at working voltage of 1 kV.
