Quality quantification in pulsed power supply for synchrotron magnet
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摘要: 同步加速器中，磁铁励磁电流高频的纹波误差能够引起磁场纹波，进而导致束流接受度降低。励磁电流低频的跟踪误差会影响磁场与束流能量的匹配程度，同时会引起束流闭合轨道畸变。为了从以上两方面评估励磁电流误差对于束流的影响，研究了HIAF BRing二极磁铁磁场纹波与励磁电流纹波之间的关系，并提出了一套基于高低频分离的脉冲励磁电流质量量化方法。该方法利用高斯平滑处理得到励磁电流低频的跟踪误差分量和高频的纹波误差分量，采用三倍标准差作为励磁电流跟踪性能及纹波质量的量化指标。方法中低通滤波器参数由磁铁磁场纹波与励磁电流纹波的响应关系确定，该方法同时准确地量化评估了磁场纹波质量。此外，由该方法得到的电流跟踪误差波形能够应用于同步加速器励磁电源的给定修正，进而提高磁场与束流能量匹配程度。Abstract: In synchrotrons, the high-frequency ripple error of magnet excitation current causes magnetic field ripple, which leads to decreased beam acceptance. The low-frequency tracking error of the excitation current would affect the matching degree of magnetic field and beam energy, which would cause the closed orbit distortion of the beam. The correlation between magnetic field ripple and excitation current ripple of HIAF BRing dipole magnet is studied in this paper. The current quality quantification methods based on high and low-frequency separation are proposed, which evaluate the effect of excitation current error on the beam. The low-frequency tracking error and high-frequency ripple error of the excitation current are obtained by Gaussian smoothing. Three times the standard deviation is used as the quantification indicator of the excitation current in terms of ripple and tracking error. Since parameters of the low-pass filter are determined by the response relationship between magnetic field ripple and excitation current ripple, this method could accurately quantify the magnetic field ripple. Th current tracking error waveform could be used to adjust the reference waveform of synchrotron pulse power supplies, improving the matching degree of magnetic field and beam energy.
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Key words:
- tracking error /
- ripple error /
- quantification method /
- pulse power supply /
- synchrotron
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图 1 BRing二极铁电源样机典型工作波形、电流输出、电流误差、跟踪误差
Figure 1. Typical operating waveform, output current, current error and tracking error of the BRing dipole-magnet power supply prototype
图 2 电流纹波与跟踪质量以及磁场纹波质量量化方法流程图
Figure 2. Flow chart of ripple and tracking quantification method for the current and ripple quantification method for the magnetic field
图 3 恒流励磁实验与脉冲励磁实验平台示意图
Figure 3. Schematic diagram of constant current excitation and pulse current excitation experiment platform
图 4 归一化磁场慢漂消除，1.6 kHz滤波前后归一化磁场与电流纹波及纹波直方图变化（E13运行模式）
Figure 4. Low-frequency drift elimination of normalized magnetic field, and variation of ripple and histograms of normalized magnetic field and excitation current before and after filtering with cut-off frequency of 1.6 kHz
图 5 五种工作模式下磁场纹波和励磁电流纹波量化指标重复测试结果 (1.6 kHz截止频率低通滤波)
Figure 5. Repeated testing result of quantification indicators of magnetic field and excitation current ripple under 5 operation mode (low pass filtering with cut-off frequency of 1.6 kHz)
图 6 不同PI参数下电流给定波形、电流误差波形及电流跟踪误差波形
Figure 6. Current reference waveforms, current error waveforms, and current tracking error waveforms under different PI regulator parameters
图 7 不同PI参数下输出电流波形、电流纹波误差波形
Figure 7. Output current waveforms, current ripple error waveforms under different PI regulator parameters
图 8 不同PI参数下的电流纹波误差及电流跟踪误差三倍标准差指标
Figure 8. Three times the standard deviation of current ripple error and tracking error under different PI regulator parameters
表 1 BRing二极铁电源样机设计参数
Table 1. Design parameters of BRing dipole-magnet power supply prototype
maximum current $ {I}_{\mathrm{m}\mathrm{a}\mathrm{x}} $/A maximum current rise rate $ {\dot{I}}_{\mathrm{m}\mathrm{a}\mathrm{x}} $/(A/s) load inductance $ {L}_{\mathrm{M}} $/mH load resistor $ {R}_{\mathrm{M}} $/mΩ ＞ 3900 ＞ 38000 116 36.4 
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表 2 磁场与励磁电流质量测量实验参数
Table 2. Test parameters of magnetic field and excitation current quality measurement
test parameter constant current excitation tests pulse excitation tests excitation current amplitude 400 A 3900 Arated magnetic field of dipole-magnet
deflection radius of dipole-magnet
deviation angle of dipole-magnet1.58 T
21.5 m
7.5°1.58 T
21.5 m
7.5°deflection angle of the magnetic coil 10.14° / effective area of the magnetic coil ($ {s}_{\mathrm{c}} $) 0.017 m2 / number of turns of the magnetic coil ($ {n}_{\mathrm{c}} $) 20 turns / sampling rate of ADC 200 kHz 100 kHz bits of ADC 24 bit 18 bit voltage range of ADC [−10, 10] V [−10, 10] V measuring current range of DCCT [0, 4000 ] A[0, 6000 ] Acurrent voltage ratio of DCCT 400 A/V 600 A/V
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