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基于DRS4测试板的数字波形分析方法
No full text<span style="color: rgb(51, 51, 51); font-family: arial, helvetica, sans-serif; font-size: 13px; line-height: 22px; background-color: rgb(248, 248, 248);">使用不同的方法来确定LaBr_3晶体信号的到达时间。在文中信号经过光电倍增管的放大之后由DSR4测试板进行数字采集,其中DRS4是由瑞士PSI研究所生产的高带宽、低功耗以及快读出时间的开关电容阵列。这些优势使得DRS4很具有吸引力,很多实验将传统的ADC与TDC替换为DRS4。采集的波形可以通过不同的方法进行后续处理。其中包括:(1)恒分甄别、(2)波形拟合、(3)PMT脉冲模型法以及(4)均值过滤法。文中实现的恒分甄别的时间分辨与使用模拟电路获取的平均时间分辨相比没有提高。高斯波形拟合法虽然与数字CFD的结果相当,但是却更加耗时。均值滤波法虽然容易实现,但是通过这个方法得到的时间分辨与采样时间在一个量级。而PMT脉冲模型法得到的平均时间分辨为195.4 ps,优于模拟信号的恒分甄别的时间分辨254.7 ps.</span><span style="color: rgb(51, 51, 51); font-family: arial, helvetica, sans-serif; font-size: 13px; line-height: 22px; background-color: rgb(248, 248, 248);">Various digital methods were examined for determining the relative arrival times of pulses from Ф20 mm* 5 mm LaBr_3 scintillators. In this study, pulses from the photomultiplier tubes(PMTs) were digitized by DRS4 evaluation board, a switched capacitor array(SCA) produced by the Paul Scherrer Institute(PSI). The high bandwidth, low power consumption and short readout time make DRS4 attractive for many experiments, replacing traditional ADCs and TDCs. The sampling signals were post processed with multiple techniques. These techniques include:(1) constant-fraction discrimination(CFD),(2) pulse-shape fitting,(3) mean PMT pulse model and(4) median filtered zero crossing method. The implemented CFD in the digital regimes did not improve the resolution of using analog equipment with average time resolution. The pulse-shape fitting yielded as good resolution as digital CFD, however, is much more time consuming. The median filtered method were easy to implement, and had a resolution on the order of sampling time. Average timing resolutions of 195.4 ps were obtained with mean PMT pulse model, which is better than the analog constant-fraction-zero-crossing with average resolution of 254.7 ps.</span
Beam experiments with a non-intercepting beam induced fluorescence profile monitor for the ADS LINAC
No full text<span style="color: rgb(51, 51, 51); font-family: arial, helvetica, sans-serif; font-size: 13px; line-height: 22px; background-color: rgb(248, 248, 248);">An accelerator-driven subcritical system (ADS) project was launched in China in 2011, aiming to design and build an ADS demonstration facility with the capability of more than 1000 MW thermal power. The driver linac is defined to be a 10 mA current of high energy protons at 1.5 GeV in continuous wave operation mode. To meet the extremely high power and intense beam accelerator requirements, non-interceptive monitors for the beam transverse profile are required for this proton linac. Taking advantage of the residual gas as active material, the Beam Induced Fluorescence (BIF) monitor exploits gas-excited fluorescence in the visible spectrum region for transverse profile measurements. The advantages of this non-intercepting method are that nothing is installed in the vacuum pipe, component design is compact and there is no need for expensive signal processing electronics. Beam experiments have been performed under constant beam conditions. The helium spectrum has been verified with different optical filters, showing that a proper optical band-pass filter covering 400-500 nm is necessary for fluorescence experiments with helium. By changing gas pressure, it is shown that gas pressure is proportional to the signal amplitude but has no influence on detected profile width. Finally, a comparison experiment between the BIF monitor and a wire scanner shows that the detected profile width results of both methods agree well.</span
The development of a room temperature electron cyclotron resonance ion source (Lanzhou electron cyclotron resonance ion source No. 4) with evaporative cooling technology at Institute of Modern Physics
No full textStudy of dielectronic recombination at the CSRm using lithium-like Ar15+ions
No full text<span style="color: rgb(51, 51, 51); font-family: arial, helvetica, sans-serif; font-size: 13px; line-height: 22px; background-color: rgb(248, 248, 248);">The main cooler storage ring (CSRm) of the HIRFL facility in Lanzhou, China is equipped with an electron-cooler and denotes an ideal platform for dielectronic recombination (DR) experiments. In order to fully understand our DR experimental setup and especially the electron energy detuning system, we have performed a DR calibration experiment using the Li-like argon ions at the CSRm because Ar15+ has a simple electronic structure and the DR spectrum can be calculated with an ultra-high precision and be compared with the existing experimental data. The experiment was carried out over the center-of-mass energy range 0-32 eV that includes all DR resonance associated with 2S(1/2) -> 2p(1/2) and most of the 2S(1/2) -> 2p(3/2) excitations. We present the details of the experimental technique and the DR experimental resonance spectrum of the Ar15+.</span
SSC-LINAC重离子RFQ动力学模拟与研究
No full text<span style="color: rgb(51, 51, 51); font-family: arial, helvetica, sans-serif; font-size: 13px; line-height: 22px; background-color: rgb(248, 248, 248);">采用多粒子跟踪程序BEAMPATH 对SSC-LINAC 重离子RFQ 直线加速器进行动力学模拟,分别对RFQ 的接受度、高频特性、束流稳定性、空间电荷效应等进行了分析。该RFQ具有很大的纵向接受度,有利于束流在RFQ中的传输;高频特性研究表明,翼间电压设定在理论值以上时,该RFQ都能保持较好的束流特性;束流稳定性分析结果表明,该RFQ具有很大的束流失配容忍度;空间电荷效应研究表明,当束流强度低于0.5 mA时,束流传输不受影响。综合研究结果表明,53.667 MHz重离子RFQ具有较好的动力学特性,满足SSC-LINAC直线加速器的设计要求。</span><span style="color: rgb(51, 51, 51); font-family: arial, helvetica, sans-serif; font-size: 13px; line-height: 22px; background-color: rgb(248, 248, 248);">The RFQ beam dynamics of a heavy ion linac was investigated in this paper and the BEAMPATH code was employed in this study. The main research was focused on the beam performances depending on longitudinal acceptance, RF properties, beam instability and space charge effect. The RFQ has large longitudinal acceptance in design, which brings the beam performances well. In the RF parameter study, the beam can keep good transmission in the acceleration even the vane voltage is larger than the theoretical value. It is also shown that the RFQ has a large robustness for the mismatch of the input beam by the analysis of the beam instability. Furthermore, the beam evolution is independent on the space charge effect when the beam current is less than 0.5 em A. The preliminary analysis of the beam dynamics shows that the 53.667 MHz heavy ion RFQ has a promising performance, which meets the requirements of SSC-LINAC.</span
Nanoindentation on V-4Ti alloy irradiated by H and He ions
No full textV-4Ti and V samples were irradiated by H/He ions with various energies to produce a damage plateau in the region from surface to the depth of 1.5 um at room temperature. Nanoindentation was performed to investigate the hardening behavior of the two materials under irradiation. It is found that the relation of maximum depth of plastic zone and indentation depth is not a fixed value. The maximum depth of plastic zone decreases with increase of damage level. Nix and Gao model was used to fit the measured hardness to obtain a hardness value H-o excluding indentation size effect (ISE), which can be used to characterize the hardening effect induced by irradiation. After fitting the data of H-o, it is found that there is an exponential relation between the H-o and damage level for both the V-4Ti and V materials. When the damage level is higher than similar to 0.2 dpa, the hardness increases slowly, this indicates a slow increase of pinning centers in samples at this damage level. Comparing the hardening fraction of V-4Ti and V samples, significant hardening can be seen for V sample, and it becomes severe especially at damage higher than similar to 0.2 dpa. The irradiation hardening resistance property of V-4Ti alloy is better than that of pure V. (C) 2015 Elsevier B.V. All rights reserved
Design of RF coupler for C-ADS injector II RFQ
No full textThe coupler, which belongs to the field of proton linear accelerator technology, was designed for a four-vane radio frequency quadrupole (RFQ) accelerator as a high power coupling device. It adopts a new bowl-shaped ceramic window structure specially, and its reasonable structural design provides a good solution to transmission impedance matching. The coupler consists of inner conductor, outer conductor, ceramic window, coupling loop and complicated water cooling channels. And the nitride titanium coating on the surface of ceramic window can prevent temperature rising from multipacting phenomenon. The radio frequency (RF) power achieved rated value of 120 kW through two identical compact couplers on the RFQ cavity in July 2014, and the measured results meet the requirements of original dynamics design of 2.1 MeV output energy and 10 mA beam current. The design of the coupler structure provides an abundant technical reference for the RF design of couplers with the similar power and frequency scale in civil related field. ©, 2015, Atomic Energy Press. All right reserved