Limitations of Heavy Ion Synchrotron Acceleration for Inertial Fusion

The potential benefits from heavy ion inertial fusion motivate the rapid development of a program to test the principle.1,2,3 To define the program, accelerator parameters which have not hitherto been commonly considered must be studied interactively with basic questions of space charge limitations and charge exchange. Beam lifetime and power output efficiency may ultimately lead to a linear accelerator as the choice for an ignition device. For proof of principle, however, at power levels way beyond present inertial fusion experience, synchrotrons may have applicability at lower cost. The power and energy which can be delivered by the accelerating system to the reaction chamber are limited by space charge defocussing and intra beam charge exchange scattering, both of which are beam density dependent. These put constraints on linac injector energy, synchrotron aperture, synchrotron magnetic rigidity, acceleration time, ion species and charge to mass ratio. The accelerator system considered is classical. A linear accelerator injects into a synchrotron which accelerates the ion beam to the full energy delivered to the target. The maximum energy deliverable by a synchrotron is treated in section I. The targetting parameters and the energy gained through synchrotron acceleration completely determine the synchrotron aperture. These are discussed in sections II and III. The ion range in material is treated in section IV. The problem of intrabeam scattering is considered in section V. Finally, in section VI is a discussion of examples to meet specified goals.     

Choice of basic parameters for high-energy linear electron accelerators

The choice of basic operating parameters for high-energy linear electron accelerators is analyzed. The length of the accelerator, the number of sections, the required power supply, and the cost of construction and operation are considered as functions of the electric field strength along the axis of the waveguide, the sections of which are supplied independently by radiofrequency sources. The minimum costs of accelerator construction and operation are independent of the final electron energy. It is shown that it is most desirable to use radio-frequency sources of highest possible power (greater than 20 megawatts) for supplying the accelerator section. Consideration is given to the problem of increasing the length of the useful part of the radiofrequency pulse.Reported at the All-Union Conference on High-Energy Particle Physics, 1956.     

用于预测带电粒子非线性行为的新型神经网络层

基于加速器高阶传输映射的非线性效应解析分析,具有物理图像清晰、守辛、准确的优点,但其缺点是适用范围较窄。为了扩展非线性效应解析分析的适用范围,提出一种模拟李指数运算过程的神经网络层并构建了用于预测带电粒子非线性行为的新型神经网络。经过大量粒子跟踪数据的学习,可用于预测带电粒子复杂的非线性运动行为,并从中提取线性传输矩阵与表征非线性运动的指数因子。为了验证该新型神经网络的有效性,跟踪一段由薄透镜磁铁组成的磁聚焦结构得到大量的训练数据,并对所提出的神经网络进行训练。训练后的神经网络在测试数据集上表现良好,测试数据的损失函数方均根小于8×10-4,达到了预测带电粒子非线性行为的目的。     

用于回旋加速器射频低电平系统的通用DSP固件程序设计

针对回旋加速器射频系统幅度、相位、启动逻辑、联锁保护、在线参数修改等控制需求,编写了一种基于有限状态机的通用DSP固件程序。该固件程序将射频系统启动过程划分为5个状态:封锁RF信号、搜索腔体谐振点、提升射频功率、匹配相位、幅相闭环控制。该固件程序通过串口与本地上位机和远程控制机进行实时通信,支持在线修改射频系统启动参数;采用异步事件驱动方式,实现对打火和反射功率过大等异常情况快速响应。该固件程序成功应用于CYCIAE-100回旋加速器射频低电平系统中,在CYCIAE-100回旋加速器调束过程中,完成了射频系统的启动控制和设备保护,满足加速器控制系统的需求。     

Ranges and stopping power of KeV electrons in the solid hydrogens

1–3 keV electron ranges and stopping power in the solid hydrogens have been investigated by the Monte Carlo simulation method on the basis of experimental thin film measurements. In the simulation, elastic scattering cross sections are calculated exactly using the single-atom crystalline potentials. Inelastic processes for gold are treated by modifying Gryziński's semiempirical expression for each core and valence electron excitation. For H₂ the ionization cross section from Green and Sawada is applied together with the gas phase stopping power from Parks et al. Simulations of electron penetration in a layer of solid hydrogen on a gold substrate with normal incidence and reflection from bulk hydrogen with different angles of incidence are fitted to experimental measurements by adjusting the stopping power of electrons in solid hydrogen. It is found to be 0.75 times the stopping power for the gas phase. The mean path length and mean penetration depth of electrons in solid hydrogen are determined from the simulations with this modified stopping power. Also the full penetration depth distributions are presented as well as their Gaussian parametrizations. The previously determined measured projected range is almost equal to the calculated mean path length.     

~(71)Ga(n,γ)~(72)Ga和~(180)Hf(n,γ)~(181)Hf反应截面的测量与评价

为解决目前71 Ga(n,γ)72 Ga反应和180 Hf(n,γ)181 Hf反应截面实验数据的分歧,在中国原子能科学研究院的600kV高压倍加器和5SDH-2串列加速器上用活化法在0.5～3MeV能区内测量了这两个反应在4个能点的反应截面。并对国内外0.01～4MeV范围内的实验数据进行了修正和评价,最终给出了这两个反应在此能区范围内的推荐值。     

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.     

Mathematical modeling of acceleration in a racetrack microtron at 50 MeV with a limited number of orbits

A mathematical model of a racetrack microtron at 50 MeV is described. A special feature of the accelerator is that the transverse dimensions of the accelerating section of the microtron are substantial. To bypass this section in the first revolution, the acceleration factor is increased to four. Another feature of the accelerator is that the beam is injected directly into the accelerating section with comparatively low energy. The frequency of the accelerating section is 1500 MHz, the increment to the beam energy in one revolution is ∼10 MeV, the number of revolutions is 5, and the injection energy is 0.75–0.88 MeV. Modeling showed that the phase-energy region from which particles are trapped in an accelerating regime is large, which makes it possible to obtain an intense accelerated beam at the exit. __________ Translated from Atomnaya énergiya, Vol. 104, No. 5, pp. 307–310, May, 2008.     

Experimental Investigation of Models of a Cascade Blanket in an Electronuclear System

Using in an electronuclear system a two-section blanket with unilateral neutron coupling of the sections (cascade-type blanket) can decrease substantially the power requirements for the accelerator. Theoretical work confirms this supposition, but there are no experimental data in this field. An experimental investigation of cascade-type blankets is planned at the All-Russia Scientific-Research Institute of Experimental Physics. The results of a computational substantiation of models of a cascade blanket (primarily with a central section consisting of ²³⁷Np), which are suitable for performing experiments, are presented. The models chosen for the blanket are deeply subcritical (k _eff = 0.5–0.6) and contain a relatively small amount of fissioning materials. These models satisfy the nuclear-safety requirements and at the same time ensure that the experiments yield adequate information.     

多能量档电子直线加速器用栅控电子枪电源研究

本文介绍了一种应用于多能量档电子直线加速器栅控电子枪的专用电源。根据栅控电子枪的工作需求,电子枪的阴极处于-50 kV高压上,电源的3路输出,包括灯丝电源、偏压电源和栅控脉冲电源,均通过高压隔离变压器,将信号输送到高压端的灯丝、阴极和栅极上。利用主控计算机精确调节了电子枪发射束流的大小和脉冲宽度,以满足加速器多能量输出的需求。高压端均为无源器件,以降低故障率。此电源结构简单、调节方便、工作稳定,已在多能量档电子直线加速器上连续工作近4 a,运行状态良好。     

X波段2MeV行波电子直线加速管的物理设计

在模拟计算程序LINE-ACC/PC基础上，结合单一搜索方法和非线性最小二乘算法编程，实现一个X波段2MeV行波加速管的物理设计。应用此方法可以有效缩短加速管的优化设计时间。文章给出的优化计算可应用于一类常相速周期结构的加速管设计。文章同时给出了纵向粒子动力学、盘荷波导的几何尺寸及加速管的工作特性等方面的计算结果。     

CSRe分子离子研究装置低能传输线物理设计

本文完成了CSRe分子离子研究装置低能传输线的物理设计。采用Poisson/Superfish软件对150 kV倍压型高压加速器的电场分布进行了模拟,结果显示,加速器各区域空间电场强度均远低于击穿电场强度限值。利用Beampath程序对离子源引出的分子离子束在高压加速器中的传输进行了模拟,束流包络显示,加速区电场对分子离子束具有较强的聚焦作用,加速管出口束斑尺寸较小。采用Trace-3D程序设计了高分辨能力的磁分析系统和RFQ加速器的注入匹配段。通过Beampath程序的模拟,分析出了质量数为150的分子离子束,并由三单元四极透镜实现了分析束流与直线加速器RFQ的注入匹配。     

基于IOT放大器的微波功率源在超导直线加速器上的应用

中国工程物理研究院太赫兹自由电子激光装置（CTFEL）的直线加速器由两个4-cell超导加速腔构成,每个加速腔的激励由1套基于感应输出管（IOT）放大器的L波段微波功率源（25 kW）提供。本文介绍了微波功率源的基本原理、组成结构和调试过程,以及微波功率源在功率耦合器老炼平台和超导直线加速器上的一些实验结果。微波功率源安装调试后工作稳定,两套微波功率源的主要参数均达到设计要求。超导直线加速器的幅值稳定度和相位稳定度分别为0.04%和0.08°,优于设计指标。     

Experimental Confirmation of the Concept of Two-Section Cascade-Type Blankets

In the last ten years, Russia and other countries have been showing a great deal of interest in two-section blanket reactors with unilateral neutron coupling of the sections (cascade-type blankets). These setups are intended to operate in power and transmutation electronuclear facilities, for which they permit decreasing substantially the required power of the proton accelerator. Theoretical and design works have been done on cascade-type blankets, but until very recently there were no experimental works.The results of the first experiment of this type, performed at the All-Russia Scientific-Research Institute of Experimental Physics, on compact deeply subcritical uranium–neptunium assemblies are presented. The experiment has confirmed the theoretical conclusion that cascade blankets have positive properties and ²³⁷Np is effective as a means for achieving unilateral coupling of the sections.     

束流发射度和亮度与束流密度分布的关系

束流发射率和束流亮度是表征加速器束流品质的主要指标。理论和实验研究都已发现,它们与束流空间电荷的非均匀分布有密切关系。     

中国散裂中子源强流质子加速器设计、研制及调试运行

中国散裂中子源（CSNS）是基于强流质子加速器的大科学装置,通过高功率质子束流轰击重金属靶产生高通量中子用于开展中子散射研究,CSNS是世界上第四台、发展中国家第一台脉冲型散裂中子源。CSNS包括高功率强流质子加速器、中子靶站和中子谱仪以及相应的配套设施等。加速器由80 MeV负氢直线加速器、1.6 GeV快循环同步加速器及相应的束流输运线组成。CSNS加速器是我国第一台中高能强流高功率质子加速器,本文将介绍CSNS加速器的设计、关键技术、设备研制以及束流调试过程和其中关键问题。     

高能电子单粒子效应模拟实验研究

本文基于2 MeV自屏蔽电子加速器和10 MeV电子直线加速器,开展了电子单粒子效应实验研究,并分析了其机理。在保持入射电子能量不变的情况下,在±20%范围内改变器件的工作电压进行了单粒子翻转实验。实验结果表明：45 nm SRAM（额定工作电压1.5 V）芯片在电子直线加速器产生的高能电子照射下能产生明显的单粒子翻转,单粒子翻转截面随入射电子能量的变化趋势与文献数据相符合;电子引起的单粒子翻转截面随器件工作电压的变化趋势与理论预期一致,即工作电压越小,单粒子翻转临界电荷越小,翻转截面也越高。     

Analysis of double stub tuner control stability in a phased array antenna with strong cross-coupling

Active stub tuning with a fast ferrite tuner (FFT) has greatly increased the effectiveness of fusion ion cyclotron range of frequency (ICRF) systems (50–100 MHz) by allowing for the antenna system to respond dynamically to changes in the plasma load impedance such as during the L–H transition or edge localized modes (ELMs). A high power waveguide double-stub tuner is under development for use with the Alcator C-Mod lower hybrid current drive (LHCD) system at 4.6 GHz. The amplitude and relative phase shift between adjacent columns of an LHCD antenna are critical for control of the launched n_|| spectrum. Adding a double-stub tuning network will perturb the phase and amplitude of the forward wave particularly if the unmatched reflection coefficient is high. This effect can be compensated by adjusting the phase of the low power microwave drive for each klystron amplifier. Cross-coupling of the reflected power between columns of the launcher must also be considered. The problem is simulated by cascading a scattering matrix for the plasma provided by a linear coupling model with the measured launcher scattering matrix and that of the FFTs. The solution is advanced in an iterative manner similar to the time-dependent behavior of the real system. System performance is presented under a range of edge density conditions from under-dense to over-dense and a range of launched n_||. Simulations predict power reflection coefficients (Γ²) of less than 1% with no contamination of the n_|| spectrum. Instability of the FFT tuning network can be problematic for certain plasma conditions and relative phasings, but reducing the control gain of the FFT network stabilizes the system.     

HYPER (Hybrid Power Extraction Reactor): A system for clean nuclear energy

The Korea Atomic Energy Research Institute (KAERI) has been performing accelerator driven system related research and development (RID) called HYPER (HYbrid Power Extraction Reactor) for the transmutation of nuclear waste and energy production through the transmutation process. HYPER program is within the frame work of the national mid and long-term nuclear research plan. KAERI is aiming to develop the elemental technologies for the subcritical transmutation system by the year of 2001 and build a small bench scale test facility (5 MW) by the year of 2006. Some major features of HYPER have been developed and employed. On-power fueling concepts are employed to keep system power constant with a minimum variation of accelerator power. A hollow cylinder-type metal fuel is designed for the on-line refueling concept. Lead–bismuth (Pb–Bi) is adopted as a coolant and spallation target material. 1 GeV 16 mA proton beam is designed to be provided for HYPER. HYPER is to transmute about 380 kg of TRU a year and produce 1000 MW of power. The support ratio of HYPER for LWR units producing the same power is believed to be 56.