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RSS2020 Vol. 32, No. 4
The modern particle accelerators have developed greatly over the last 100 years. This article provides an overview of all main types of particle accelerators. Simple charts are given to exhibit conceptual and technological evolutions of major particle accelerators. It also briefly introduces the basic types, fundamental principles, technological approaches, and typical technical features of various types of particle accelerators.
To study the application and development of stretched wire technology in accelerator alignment and survey, the principle of stretched wire technology is summarized firstly, then the development history of stretched wire alignment method in accelerator is reviewed, and the latest development trend of stretched wire alignment method is introduced. Finally, the advantages and disadvantages of various alignment methods and their suitable environments are discussed, and the development differences between domestic and foreign alignment methods are compared. The development direction of the stretched wire alignment method is pointed out, and the direction of the accelerator alignment and survey is given.
In measurement of magnetic axis of solenoid, there are some key difficulties to overcome, such as precision measurement of tuat-wire vibration and position, reducing measurement signal distortion, and separative data processing for offset and tilt signal in magnetic axis of solenoid. One kind of signal detect and measurement principle of extracting the useful faintness signal via subtracting the high offset level signal from the total measurement signal is adopted to meet the above need. The method of constant current driving the detector is also adopted to obtain more stable and anti-jamming signal. The measurement system has been developed for directly obtaining the pure vibration signal of the tuat-wire. The problems of obtaining completely exact measurement signal by simply using an AC coupling amplifier or band-pass filter are resolved and the faint signal can be obtained without aberration. The influence produced by tilt and ups-and-downs in low frequency component of base line signal is eliminated ulteriorly. The separative data processing for offset and tilt signal is also achieved to some extent. The measurement sensitivity has been improved maximumly by about an order of magnitude.
Flashover across the insulator in induction cavity with electron beam load once occurred frequently, which affected the performance parameters and stability of the high voltage high current devices and equipment. This paper studies the vacuum surface flashover across the insulator in the induction cavity of a linear induction accelerator under debugging. After excluding design and fabrication of the insulator as well as cleanness and vacuum degrees, it is found that the electrons from the plasma induced by high energy electrons interacting with the gas adsorbed on the inner cavity wall might play the key role of flashover. These thermal electrons move randomly and some of them will reach and stay on the insulator surface for some time, and flashover happens when high electric field is applied across the insulator with accumulated electrons.
In order to greatly improve the quality factor (Q) of a Nb superconducting cavity and reduce its power loss, we performed high-temperature nitrogen doping (N-doping) on the superconducting cavity, which is the most widely used method in the world. Based on the needs of large-scale accelerators at home and abroad, the Institute of High Energy Physics, Chinese Academy of Sciences, carried out researches on 1.3 GHz 1-cell superconducting cavities, including standard post-processing and N-doping. After data analysis and comparison, it can be found that the Q values of two 1.3 GHz 1-cell fine-grain superconducting cavities have been significantly improved. At the same time, the abnormal behavior of Q value depending on acceleration gradient (Eacc) was observed in low-temperature vertical test, which is called the "anti-Q-slope" phenomenon.
Vertical test is an important method for characterizing the performance of superconducting cavities. We designed an superconducting cavity vertical test system based on digital self-excited algorithm and the technology of low-level radio frequency, which could improve the vertical test efficiency of superconducting cavities. The RF front-end and clock distribution system of the vertical test system adopts the second up-and-down conversion scheme. To some extent, the working frequency of the digital self-excited loop of the vertical test system can be set flexibly, and the working bandwidth of the test system is increased. The test results of the pass-band frequency of the 1.3 GHz 9-cell superconducting cavity show that the vertical test system has strong frequency resolution (＜800 kHz) to ensure the smooth progress of the multi-cell superconducting cavity pass-band test.
Ten Insert Devices (IDs) had been installed in the Shanghai Synchrotron Radiation Facility (SSRF) storage ring. The ID gaps were repeatedly adjusted for the scientific experiments during the user time. The residual quadrupole errors beyond the ID feedforward disturbed the beam optics, including the betatron tune deviations that spoiled machine performance and brightness stability. A tune feedback system was developed and implemented in the SSRF storage ring to resolve the deterioration. The tune stability of ±0.001 in 2 weeks was reached. Another important function of this feedback system is finding out slow drift in the power supplies of dipole or quadrupole by observing the correction current changes in the feedback. To prove this feedback’s feasibility, we compared variations of the beam parameters, including the injection efficiency, the beam life-time, the horizontal beam size and the beta-beatings.
A high-speed real-time dynamic power control system based on an open source platform has been developed to satisfy the multi-platform energy extraction requirements of the main loop dynamic power supply in a proton therapy facility. The control system uses a Beaglebone based open-source platform as the top-level hardware interface, the controller with Field Programmable Gate Array (FPGA) as the core as the underlying hardware interface, and uses a distributed Experiment Physics and Industrial Control System (EPICS) for remote control. This system can transmit the output reference current waveform data of any dynamic power source in real time, and controls the dynamic power source to output according to the preset current waveform combined with the timing system and the interlocking system, and realizes the energy extraction of multiple platforms. Experimental results show that the control system can achieve a maximum of 100 000 instructions per second and zero error rates for millions of data transmissions. In addition, the system structure is flexible and extensible, and it can be served as a universal control platform.
Scanning lidar is widely used in atmospheric remote sensing detection and target capture. To realize the effective detection of lidar, this paper studies four common scanning modes of lidar: raster scanning, Lissajo scanning, spiral scanning and hexagonal scanning. The corresponding scanning equation is deduced, and the physical meaning and adjustment method of parameters are discussed. Aiming at the requirement of fine scanning in atmospheric remote sensing detection, the distribution of spot under raster scanning and hexagonal scanning is studied. The leakage rate and overlap rate of these two scanning modes are simulated and analyzed. The results show that under the same scanning condition, the leakage area of hexagonal scanning mode is the smallest. The physical image and scan pattern of scanning control system based on the above research are presented. Finally, the characteristics of these four scanning modes are summarized, and their application and suggestions are given.
Using the theory of free radical concentration fluctuation combined with the effect of optical tweezers, this paper studies the linewidth of femtosecond laser two-photon polymerization multiple-fast-scanning processing theoretically. According to the relationship between the change of free radical concentration and time in the two-photon photopolymerization processing, considering the influence of the optical tweezers on the free radical distribution range, it obtains the formula of the linewidth of multiple-rapid-scanning processing. It also presents the relationship between linewidth and scanning speed, laser power, and interval time. The results can be regressed to the general formula of single-scanning and are in good agreement with the experimental results in the literature. The study provides a new idea for studying the femtosecond laser two-photon processing to obtain a smaller processing linewidth, and provides a theoretical basis for the femtosecond laser multiple-rapid-scanning processing.
To provide significant parameters for fast ignition coupling efficiency and density diagnosis for higher compression, a ps-duration X-ray backlighter has been produced with ps-duration laser on Shenguang-Ⅱ updated facility. The radiation properties such as backlighting image resolution and the photons arriving at the image plate have been successfully measured. Based on the conformed conditions, density diagnosis of an indirectly-driven fast ignition target using ps-duration backlighting has been carried out. The obtained short-pulse backlighting radiography shows that the imploded shell shape agrees well with that of simulation and the areal density exceeds 50 mg/cm2. The short-pulse backlighting radiography also shows the hydrodynamic instability which might be caused by the asymmetric compression. Further investigations and attempts to improve implosion performance to a higher density are in progress.
This paper firstly determines the main factors affecting its the efficiency of multi-injection electron beam introduction and preliminary structural parameters through theoretical analysis. Secondly, the Ka-band relativistic multi-beam diode model is established by three-dimensional particle simulation software to optimize the structural parameters. The final efficiency of electron beam introduction can reach 89%. An experimental study on the generation and transmission of electron beams was carried out to verify the results of particle simulation. Under the condition of electron beam voltage 502 kV, beam current 4.34 kA, axial magnetic induction strength 0.76 T, the electron beam introduction efficiency reached 72%. The electron beam pattern obtained by electron beam bombardment of the nylon target indicates that the shape of the electron beam is not distorted during generation and transmission. The generated electron beam diameter is about 2 mm. The simulation and experimental results show that the designed high-current multi-beam diode can generate high-quality electron beams and achieve efficient electron beam introduction.
A novel half rectangular-ring helix slow-wave structure (SWS) is proposed for the design of wide bandwidth and high power traveling-wave tubes. The numerical calculation by 3D electromagnetic simulation software HFSS shows that proper dispersion and coupling impedance can be obtained by reasonably setting the geometrical parameters of the SWS. Meanwhile, compared with the half circular ring helix slow wave structure, slight variation in dispersion and remarkable improvement in coupling impedance have been observed in the numerical calculation of the half rectangular ring helix SWS. The half rectangular-ring helix slow-wave structure has the combined advantages of flatten dispersion, high interaction impedance, easy fabrication and convenience for interaction with sheet beam.
Aiming at the research requirements of multi-physical effects mechanism of devices in complex electromagnetic environment, a parallel computing program for semiconductor multi-physics effects, JEMS-CDS-Device, is developed. This paper introduces the architecture design and implementation technology of JEMS-CDS-Device. The program is based on the unstructured grid parallel framework—JAUMIN. It uses the finite volume method (FVM) to discretize and uses the Newton method to get fully coupled solution of the “electric-carrier transport-thermal” problem. The program which adopts the “kernel ＋ algorithm library” form architecture, supports 2D/3D unstructured mesh, and can solve problems of tens of millions of degrees of freedom parallelly. It supports extended development of physical effect equations, discrete algorithms, material physics models, etc.
In this paper, the rationality of Electromagnetic Compatibility（EMC）design of Printed Circuit Board (PCB) is evaluated in advance through electromagnetic simulation. The purpose of this method is to reduce the chances that the Electromagnetic Interference (EMI) of PCB does not meet GMW 3097 standard in EMC test. Firstly, the 3D electromagnetic field simulation of the Peripheral Component Interconnect express (PCIe) module on the PCB is performed. Then the field simulation is dynamically linked with the circuit simulation of the Simulation Program with Integrated Circuit Emphasis (SPICE) model of chip on the PCIe module, so that the co-simulation of field and circuit is performed. According to the experimental test, the accuracy of this simulation method is within 6 dBμV, which satisfies the deviation of PCB processing technology and the uncertainty of the experimental test. Thus, this simulation method meets the accuracy requirements. Therefore, the EMI of PCB can be evaluated and the PCB design can be optimized by this simulation method. After the 33 Ω resistors on the PCIe module was replaced by magnetic beads, the EMI of the PCB at 1.6 GHz is reduced by 13.4 dB. According to the 1-m method specified in the CISPR 25 standard for testing, the EMI of PCB becomes −3.4 dBμV, which is lower than the GMW 3097 standard requirement. Therefore, the effectiveness of this measure is verified.
In this paper, CFBR-II fast neutron reactor (China's second fast neutron pulse reactor) and Co-60 device are used to carry out experiments on different sequential neutrons/gamma irradiated bipolar transistors. Under the condition that the collector-emitter voltage is constant, the variation curve of the bipolar transistor current gain with the collector current is measured, and the influence of different irradiation order of neutron/ gamma on the current gain of the bipolar transistor is studied. The experimental results show that when the collector-emitter voltage is constant and the collector current is extremely low, the current gain degradation of the bipolar transistor is relatively large, and the current gain increases with the collector current. The degradation of the current gain of the bipolar transistor caused by the gamma irradiation after the neutron pre-irradiation would be greater than that of the neutron irradiation after the gamma pre-irradiation, and the difference is more obvious in PNP transistor than in NPN transistor. This paper presents a preliminary discussion on the related mechanism.
Based on the self-developed nanosecond pulsed test platform with output voltage of 30 ns risetime and 100 ns half width, and the standard dielectric strength DC tester, the breakdown characteristics of four liquid dielectrics (transformer oil, glycerol, deionized water and Galden HT200) under DC and nanosecond pulses were experimentally studied and compared. The following conclusions were obtained: (1)Under both DC and nanosecond pulse, Galden HT200 has the highest breakdown field strength which is more than 40% higher than that of the transformer oil. (2) Under the nanosecond pulse, the breakdown field strength of Galden HT200 and transformer oil both increased by 6.5-7 times than those under DC. And it took the shortest time(nanosecond scale) for Galden HT200 to breakdown, followed by the transformer oil(20 ns), then glycerol(45 ns) and deionized water(70 ns). (3) After multiple breakdowns, a lot of carbonized discharge products were accumulated at the electrode gap in the glycerol which has the largest viscosity coefficient. However, there are no obvious breakdown traces in the Galden HT200 and deionized water, which both have the smaller viscosity coefficient. But obvious shock waves were observed in the Galden HT200 and deionized water, which make the gap electrodes loose.
Characteristics of electrohydraulic shockwave are the keys to the application of electrohydraulic disintegration of rocks (EHDR). Mathematical models are used to characterize the generation and propagation of the shockwave, an integrated experimental platform is established, the measured and simulated results of typical shockwave characteristics are analyzed. The simulated results of characteristics of shockwaves under different charge voltage are given, and the influence of charge voltage on the shockwave characteristics are analyzed. The results show that the peak pressure and energy of shockwave is 2.67 MPa and 27.30 J respectively, the wave front time is 2.16 μs, the loading rate is 1.24 MPa/μs, when the charge voltage is 11 kV. The peak value and energy of shockwaves increase, the wave front time decreases, the loading rate of shockwaves increases, while the efficiency of electrical energy transfer into shockwave energy decreases, when the charge voltage of capacitor rises. Characteristics of shockwaves can be predicted from the parameters of discharge circuit via simulation, thus to provide theoretical basis for further study on the morphology and effect of EHDR.
To construct a 5 MW neutral beam heating beamline for HL-2M device, the development of the discharge chamber of the hot cathode arc discharge ion source for neutral beam heating was carried out. The neutral beamline contains four sets of 80 kV/45 A/5 s ion sources, and the discharge chamber design index is 850 A/5 s. Firstly, the electromagnetic studio in CST software was used to simulate the cusp magnetic field of the discharge chamber with specific geometric structure, and the cusp magnetic field distribution was obtained, which verified the rationality of cusp magnetic field layout. To solve the problems in the process of the discharge chamber and the localized arcing in the experiment, the structure of the discharge chamber was improved. The side wall of the discharge chamber changed from 40 rows of cusp magnets to 7 rings of cusp magnets, the cathode structure changed from the filament plate structure to the ceramic kovar structure, and a ceramic shield was added between the discharge chamber and the accelerator. Normal arc discharge was obtained in both the cathode plate discharge chamber and the cathode ceramic kovar discharge chamber. The final shaped discharge chamber adopted 7-ring cusp magnets and ceramic kovar cathode structure. The arc discharge index of the 5 MW neutral beamline ion source was achieved in the final shaped discharge chamber. The arc discharge time was close to 5 s, and the maximum arc discharge current reached 1 000 A.
In this work, an efficiency calibration function model is presented to calculate the efficiency of segment in segmented gamma scanning (SGS) for 200 L nuclear waste drum. Discrete SGS efficiencies are simulated with MCNP for different densities and gamma ray energies. Parameters of function are determined by using multivariate nonlinear regression method with the efficiencies. The SGS efficiency calibration function is constructed to calculate the efficiency matrix. Aluminum silicate with density of 0.310 g·cm−3, wood fiber of 0.595 g·cm−3, point sources 137Cs with activity of 3.110×105 Bq and 60Co of 1.371×105 Bq are used to construct samples of drum for SGS analysis. Result shows: for the extremely heterogeneous radioisotope distribution of only a point source placed at 8 different positions in the drum, errors of reconstructed activities are −37.68%～31.52%. Overall, the reconstructed activity is in agreement with the true activity. This method effectively and accurately achieves SGS efficiency calculation and reconstruction of activity.
