Heavy-current accelerator based on a transformer

The operating principles of a direct-action accelerator designed to acceIerate electrons to an energy of 1.5 MeV with a mean beam power of tens of kilowatts and an efficiency of around 90% are described. The electron-current pulse length can be varied from 0 to g msec, and the repetition frequency up to 50 times per sec. The mean current im may reach 1/6 of the maximum current in the pulse. Magnetic lenses are installed in order to focus electron currents of up to 100 mA into a beam a few mm in diameter in the accelerating tube. Heavy-metal screens are placed close to the axis of the tube in order to protect the gas gaps and other electrically-stressed parts of the accelerator from radiation arising inside the tube.The construction of a system for producing an electron beam with an energy of 1.5 MeV and a mean power of 25 kW (i_m = 17 mA) is described.Translated from Atomnaya Énergiya, Vol. 20, No. 5, pp. 385–392, May, 1966.     

System for Measuring the Beam Position in a Racetrack Microtron-Recuperator

The system described is intended for studying the positions (at 29 points) of the beam trajectory where electrostatic pickups are placed as sensors. The frequency of particle injection into the microtron-recuperator can vary from 20 kHz to 22.5 MHz with 1-nsec bunches. The system makes it possible to measure the position of the accelerated and delayed beams which are both present in the resonator gap. The measurement method is based on simultaneous measurement of the amplitudes of the pulsed signals from four pickup plates using a fast ADC.     

Linear induction accelerator

The construction and operating principles of a heavy-current linear induction accelerator yielding 3-MeV electrons and pulse currents up to 200 A are described. Results obtained on one section of this accelerator are presented. The electron current is 180 A (pulsed) with an energy of 485 keV; the pulse duration at a level of 0.95 is 0.35 sec.Translated from Atomnaya Énergiya, Vol. 21, No. 6, pp. 439–445, December, 1966.     

DG系列大功率工业辐照电子加速器

中国科学院近代物理研究所成功研制了DG系列中频变压器型工业电子加速器,其中DG-2.5型加速器能量范围1.0-2.5 MeV,最大束流功率90 kw,束流扫描有效宽度1000 mm,适用于各种辐照领域;DG-1.2型能量范围0.8-1.2 MeV,最大功率50 kw;这两种型号加速器均通过了长时间测试,工作稳定、故障率低,采用计算机自动控制,并可与束下传动系统连锁,完全达到了工业应用的标准.     

高平均束流功率辐照加速器加速结构的研究

本文介绍了10 MeV/100 kW的高平均束流功率工业辐照加速器束流动力学模拟结果及其加速结构的优化设计结果。加速器采用驻波双周期轴耦合结构,1个加速腔和1个耦合腔构成1个加速单元,其工作频率为325 MHz,工作模式为π/2,加速腔和耦合腔之间通过耦合狭缝在轴向以磁耦合的方式耦合在一起。使用SUPERFISH优化加速腔的有效分路阻抗、Kilp系数等关键参数。束流动力学方面,使用PARMELA模拟论证在粒子源提供2.5 keV、500 mA的电子束后,通过6个加速腔可得到10 MeV/100 kW的平均束流功率。加速腔优化完成后使用CST对耦合腔进行了设计,此时由6个加速单元组成的加速结构有效分路阻抗为23.9 MΩ/m、无载品质因数为29 347,各加速腔与相邻的耦合腔耦合系数为4.7%,工作模式与其相邻模式的最小频率间隔为2 MHz,每个加速单元功耗为290 kW。     

Linear Accelerator for Multiply-Charged Ions at 8 MeV/nucleon – Injector in the TWA Accelerator Complex

The terawatt accumulator at the Institute of Theoretical and Experimental Physics is in the physical startup phase. A new high-current linear accelerator-injector must be developed to achieve design parameters 10¹¹ particles/sec on target; this injector should give at the entrance of the accelerator ring a heavy-ion beam with current 15–20 mA and energy ~7–8 MeV/nucleon with the required charge-to-mass ratio. To this end, a linear accelerator with rf quadrupole focusing at the working frequency 81 MHz was developed; it will accelerate Al¹¹⁺ or Co²⁵⁺ from a laser source before the synchrotron. The accelerator will consist of two sections. The first section with spatially uniform quadrupole focusing will accelerate the beam up to 1.6 MeV/nucleon. A new structure with rf quadrupole focusing and period length 2 is proposed for the second accelerating section. Preliminary numerical simulation of this structure showed that 7 MeV/nucleon with minimum beam losses and accelerating gradients 3.5 MV/m will be achieved on it. Construction of the first section with spatially uniform quadrupole focusing has begun.     

Development of an electron linac at PNC for transmutation studies

Various methods have been examined to transmute long-lived fission products using accelerators at PNC. The present paper describes the development of a high power continuous wave (CW) electron linac which was started in 1989 to study the feasibility of nuclear waste transmutation. Transmutation by photonuclear reaction using an electron accelerator has the advantage of producing a relatively small amount of secondary radioactive waste. It is also deemed to broaden the base of accelerator technology.

The PNC high power CW electron accelerator, which is designed to accelerate energies up to 10 MeV and an average beam current of 20 mA and has a normal conducting traveling wave resonant ring (TWRR) disk-loaded accelerating tubes, was pre-commissioned with an injector and the first accelerating tube.

In December 1995, the accelerator had been partially built and the pre-commissioning of the injector began. We have been successful to produce electron beams with 3 msec pulse width, 100 mA peak, and about 2.9 MeV energy. The facility construction will be completed in March 1997, followed by the commissioning of the entire 10 MeV linac.     

350keV电子高压加速器研制

加速器辐照装置用于辐照生产医用输液塑料袋原膜材。所研制的350keV电子高压加速器具有以下特点：在静电加速器中采用高压倍压电源代替输电带，此新型结构加速器可输出低能大功率电子束，且体积小、自屏蔽，适于在线辐照加工；一般高压倍压电源采用50Hz供电，而在此装置中由14kHz中频电源供电，高压电源体积小。加速器空载高压达370kV，电子束350keV/20mA，扫描宽度70cm，辐照剂量不均匀性好于7%。该加速器辐照装置已投入运行，并已生产出合格医用输液袋膜材投放市场，产品填补了国内医用输液袋膜材市场的空白。     

北大4.5MV静电加速器束流脉冲化系统

４．５ＭＶ静电加速器是北大设计和建造的单级静电加速器。为了能够利用飞行时间法进行中子能量测量，需要把连续束变成短脉冲束。为此，在该器上配置了束流脉冲化系统。文章主要介绍４．５ＭＶ静电加速器束流脉冲化系统所采用的９ＭＨｚ射频聚束器和１．５ＭＨｚ射频切割器及有关的电子学线路、粒子纵向运动的模拟、对横向聚焦的要求。实验结果表明，可以获得的脉冲宽度为１．８ｎｓ。     

4.5MV静电加速器离子聚束电路的设计

在加速器中产生脉冲中子源需要对离子源脉冲化。采用10MHz聚束和2.5MHz扫描频率，通过在交叉场分析器设置直流偏置电压和变频切割电压，改变离子束脉冲频率，使之从2.5MHz到39KHz可调。本文介绍了脉冲频率可调，幅度可调的脉冲化电路的改进设计及初步实验结果，并给出功放热设计参考。     

Energy-spread measurement of triple-pulse electron beams based on the magnetic dispersion principle

The method of energy dispersion in magnetic field is used to analyze the energy spread of the triple-pulse electron beam generated by the Dragon-II linear induction accelerator.A sector magnet is applied for energy analysis of the electron beam,with a bending radius of 300 mm and a deflection angle of 90°.For each pulse,the time-resolved and integral images of the electron position at the output port of beam-bending line are recorded by a streak camera and a CCD camera,respectively.Experimental results demonstrate an energy spread of less than ±2.0%for the electron pulses.The cavity voltage waveforms obtained by different detectors are also analyzed for comparison.     

On peak current in atmospheric pulse-modulated microwave discharges by the PIC-MCC model

Pulse modulation provides a new way to tailor the electron density,electron energy and gas temperature in atmospheric radio-frequency (rf) discharges.In this paper,by increasing the rf frequency to several hundreds of MHz,or even much higher to the range of GHz,a very strong peak current in the first period (PCFP) with much larger electron energy can be formed during cthe power-on phase,which is not observed in the common pulse modulation discharges at a rf frequency of 13.56 MHz.The PIC-MCC model is explored to unveil the generation mechanism of PCFP,and based on the simulation data a larger voltage increasing rate over a quarter of a period and the distribution of electron density just before the power-on phase are believed to play key roles;the PCFP is usually produced in the rnicroplasma regime driven by the pulsed power supply.The effects of duty cycle and pulse modulation frequency on the evolution of PCFP are also discussed from the computational data.Therefore,the duty cycle and pulse modulation frequency can be used to optimize the generation of PCFP and high-energy electrons.     

Determination of prompt-neutron decay constant from phase shift between beam current and neutron detection signals for an accelerator-driven system in the Kyoto University Critical Assembly

A unique power spectral analysis for a subcritical reactor system driven by a pulsed 14 MeV neutron source was carried out at the Kyoto University Critical Assembly (KUCA). In this analysis, a complex cross-power spectral density between time-sequence signal data from an accelerator beam ammeter and a neutron detector was measured to determine the prompt-neutron decay constant of an accelerator-driven system (ADS) from the phase data of the spectral density. Assuming the one-point kinetics model, in theory, the decay constant can be arithmetically derived from the phase at the integral multiples of the pulse repetition frequency. However, the actual derivation from the phase at a pulse repetition frequency of 20 Hz considerably underestimated the prompt-neutron decay constant, compared with that obtained by a previous pulsed neutron experiment, and the derived decay constant apparently decreased with an increase in the multiple of the pulsed repetition frequency. Considering a lag time in detector response, the above underestimation and the above apparent decrease were solved to obtain the consistent decay constant. While both previous power spectral analysis and Feynman-α analysis for pulsed neutron source require non-linear least-squares fits of the respective complicated formulae, the present analysis makes the fitting unnecessary except at regular calibration of the lag time. This feature is advantageous for a robust online monitoring of subcritical reactivity of an actual ADS.     

Design and Development of a Power Supply System for NBI Test Stand of EAST

A neutral beam injector (NBI) test stand was constructed to develop a multi-megawatt prototype ion source as an auxiliary heating system on experimental advanced superconducting tokamak. A power supply system for the NBI test stand components such as a set of dc power supplies for plasma generator, a dc high voltage power supply of a tetrode accelerator, a transmission line and a surge energy suppressor. Stable arc discharges of the plasma generator with hydrogen gases for 100 s long pulse have been produced by six Langmuir probes feedback loop regulation mode to control the arc power supply. The 4 MW hydrogen ion beam of 1 s is extracted with beam energy of 80 keV and the beam current of 52 A. The dc high voltage power supply for the plasma grid of the prototype ion source was designed to contribute maximum voltage of 100 kV and current of 100 A. The high voltage power output is continuously adjustable to satisfy with plasma physics experiment in operation frequency of 10 Hz. To prevent damage of the beam source at high voltage breakdown, core snubber using deltamax soft magnetic materials have been adopted to satisfy the input energy into the accelerator from the power supply can be reduced to about 5 J in the case of breakdown at 80 kV. For the transmission line, a disc shape multi cable coaxial configuration was adopted and which the dimension of the diameter is 140 mm at the core snubber. The major issues of discharge characteristics with long pulse and beam extraction with high power for the prototype ion source were investigated on the NBI test stand.     

基于100 MeV紧凑型强流质子回旋加速器的束流切割器研制

通过理论分析和仿真模拟对中国原子能科学研究院一台100 MeV强流质子回旋加速器的束流切割器进行了优化设计,并同时研制出两套束流切割器进行实测对比,选定最佳方案。该切割器波形选择为回旋加速器高频频率的16分频28 MHz正弦波,具有结构紧凑体积小、螺旋谐振器Q相对较高、加载切割电压较高且功率损耗低、无需水冷等特点,同时配套研制了一套开口形状为正方形的选束狭缝装置。最后在实验终端成功获得了能量为100 MeV、重复频率为56 MHz的脉冲质子束。该切束器的成功研制不仅满足了核数据测量的应用需求,还极大地推动了回旋加速器束流脉冲化技术的发展。     

A Pulsed Neutron Source for Thermal Reactor Physics

A compact 200 kV Cockcraft type pulsed neutron source was designed and constructed as a versatile tool for various pulsed neutron experiments in thermal reactor physics. Special care was taken to obtain the maximum peak intensity of pulsed neutrons against the average background neutrons induced from accelerator operation. To this end, two particular design features have been adopted. One is pulsing of the R-F ion source probe voltage combined with pulsing of the deflector voltage of the post accelerated D⁺ ion beam. The other feature is the use of a beam analyzing magnet to the accelerated beam. With these devices, a peak to background ratio of 10⁵ was obtained.

Pulsed neutrons of 14 MeV can be generated at pulse widths from 0.13 μs 500 ms, with a neutron yield of 3.7×10⁴–2×10⁹ n/pulse. The repetition rate of the pulses can be changed independently of the pulse width. An arrangement for long focusing beam adjustment provides for selection of the target position in a wide range.     

Development of Thin-wall Vacuum Chamber for Heavy Ion Medical Accelerator

Heavy Ion Medical Machine (HIMM), developed by the Institute of Modern Physics, Chinese Academy of Sciences, is the first medical heavy ion accelerator with independent intellectual property rights in China. Because the RAMPING mode was used for high frequency pulse dipole magnets of HIMM and the rising rate of magnetic field is 1.6 T/s, the vacuum chamber installed in the high frequency pulsed magnet is a thin-wall stainless vacuum chamber with reinforcing ribs to reduce the influence of eddy current on the ion beam stability. However, the gap size of magnet occupied by thin-wall stainless vacuum chamber with reinforcing ribs is too large, and it not only causes the high cost of magnets, but also greatly improves the maintenance cost. Based on these reasons, a new thin-wall vacuum chamber (0.3 mm) with ceramic lining was put forward and the prototype was designed and manufactured. The test results show that the obtained pressure of the prototype is in the order magnitude of 10^-10 Pa, and the magnet gap can be effectively reduced. And it is the development direction of thin-wall vacuum chamber of accelerator in the future.     

医用重离子加速器薄壁真空室研制

中国科学院近代物理研究所研制的医用重离子加速器装置是我国第1台拥有自主知识产权的医用重离子加速器,其高频脉冲二极磁铁使用RAMPING工作模式且磁场上升速率为1.6 T/s,所以安装在高频脉冲磁铁内的真空室采用一种薄壁加筋结构不锈钢真空室以减少涡流对离子束稳定性的影响。然而由于薄壁加筋不锈钢真空室占用磁铁气隙尺寸偏大,不仅造成了磁铁造价成本偏高,更是提高了运维成本。基于以上原因,本文提出陶瓷内衬薄壁（0.3 mm）真空室,并研制了原理样机。测试结果表明：样机真空度进入了10^-10 Pa量级范围,并可有效减小磁铁气隙,是未来加速器薄壁真空室的发展方向。     

Investigations of the performance of gas-discharge counters with a controlled pulsed power supply

With a pulsed power supply for gas-discharge counters, counting errors, determined by the dead time, are eliminated. Because of this, the possibility arises of using hodoscope systems of counters with a controlled pulsed power supply in experiments carried out with accelerators having a large background of extraneous radiation. In the present work the counting characteristics were investigated, and also measurements were carried out of the efficiency and the resolving power of self-quenching factory-produced counters with a controlled pulsed power supply. It is found that in the case of short-duration pulses (pulse length 10^–6 sec) the counters can work under over-voltages of up to 2 kv. At the same time there is no necessity to amplify the pulses in the hodoscope channel or to use a discriminator to obtain their coincidences with the control pulse. Each channel, in this case, in addition to the counter contains a load resistance and a neon lamp. The considerable simplification of the system, by comparison with the usual type of hodoscope, and also the reliable performance of counters with pulsed power supplies, make such systems also useful for the study of cosmic radiation.In conclution, the author express their gratitude to A. N. Sinaev for help during the work.     

小型无损探伤电子直线加速器BP神经网络稳频系统

作为小型探伤电子直线加速器功率源的磁控管 (工作频率为 93 70MHz) ,其主要缺点是自身振荡频率的稳定性差 ,且磁控管在工作中由于各种原因会产生打火、跳谱和散谱现象 ,从而造成加速器工作不稳定 ,因此 ,必须采用频率稳定系统。为了更好地解决上述问题 ,应用BP神经网络方法 ,以保证工作频率稳定。