Electromagnetic Oscillations in a Spherical Conducting Cavity with Dielectric Layers. Application to Linear Accelerators

We present an analysis of electromagnetic oscillations in a spherical conducting cavity filled concentrically with either dielectric or vacuum layers. The fields are given analytically, and the resonant frequency is determined numerically. An important special case of a spherical conducting cavity with a smaller dielectric sphere at its center is treated in more detail. By numerically integrating the equations of motion we demonstrate that the transverse electric oscillations in such cavity can be used to accelerate strongly relativistic electrons. The electron’s trajectory is assumed to be nearly tangential to the dielectric sphere. We demonstrate that the interaction of such electrons with the oscillating magnetic field deflects their trajectory from a straight line only slightly. The Q factor of such a resonator only depends on losses in the dielectric. For existing ultra low loss dielectrics, Q can be three orders of magnitude better than obtained in existing cylindrical cavities.

Optimization of the S-band side-coupled cavities for proton acceleration

The proton beam with energy around 100 MeV has seen wide applications in modern scientific research and in various fields.However,proton sources in China fall short for meeting experimental needs owing to the vast size and expensive traditional proton accelerators.The Institute of Nuclear Science and Technology of Sichuan University proposed to build a 3 GHz side-coupled cavity linac(SCL)for re-accelerating a 26 MeV proton beam extracted from a CS-30 cyclotron to 120 MeV.We carried out investigations into several vital factors of S-band SCL for proton acceleration,such as optimization of SCL cavity geometry,end cell tuning,and bridge coupler design.Results demonstrated that the effective shunt impedance per unit length ranged from 22.5 to 59.8 MX/m throughout the acceleration process,and the acceleration gradient changed from 11.5 to 15.7 MV/m when the maximum surface electric field was equivalent to Kilpatrick electric field.We obtained equivalent circuit parameters of the biperiodic structures and applied them to the end cell tuning;results of the theoretical analysis agreed well with the 3D simulation.We designed and optimized a bridge coupler based on the previously obtained biperiodic structure parameters,and the field distribution un-uniformness was\1.5%for a two-tank module.The radio frequency power distribution system of the linac was obtained based on the preliminary beam dynamics design.

Ultrahigh accelerating gradient and quality factor of CEPC 650 MHz superconducting radio-frequency cavity

Two 650 MHz single-cell superconducting radio-frequency(SRF)cavities used for the Circular Electron Positron Collider(CEPC)were studied to achieve a high accelerating gradient(E_(acc))and high intrinsic quality factor(Q_(0)).The 650 MHz single-cell cavities were subjected to a combination of buffered chemical polishing(BCP)and electropolishing(EP),and their E_(acc) exceeded40 MV/m.Such a high E_(acc) may result from the cold EP with more uniform removal.BCP is easy,cheap,and rough,whereas EP is complicated,expensive,and precise Therefore,the combination of BCP and EP investigated in this study is suitable for surface treatments of mass SRF cavities.Medium temperature(mid-T)furnace baking was also conducted,which demonstrated an ultrahigh Q_(0) of 8×10^(10) at 22 MV/m for both cavities,and an extremely low BCS resistance(R_(BCS))of~1.0 nΩwas achieved a2.0 K.

Radiation Shielding Design for a 10 MeV Rose-like Electron Irradiation Accelerator

This article focuses on the radiation shielding research of the coaxial cavity electron accelerator,a petal-shaped electron accelerator independently developed by the Institute of Modern Physics at the Chinese Academy of Sciences.This study aims to provide reference for the radiation shielding design of similar devices in the future.The coaxial cavity electron accelerator mainly consists of an electron gun,a resonant cavity,nine external bending magnets.

Design, fabrication, and testing of low-group-velocity S-band traveling-wave accelerating structure

To implement the Tsinghua Thomson Scattering X-ray Source upgrade plan and the Very Compact Inverse Compton Scattering Gamma-ray Source (VIGAS) program, a new 1.5-m traveling-wave accelerating structure was designed to replace the old 3-m SLAC-type structure with the aim of increasing the accelerating gradient from15 to 30 MV/m. The new type of structure works in the 3π/4 mode with a comparatively low group velocity varying from 0.007c to 0.003c to increase the accelerating gradient at a given power. An elliptical iris was employed to reduce the surface field enhancement. The filling process of the low-group-velocity structure was analyzed using a circuit model. After fabrication, the structure was precisely tuned using the non-contact tuning method, followed by detailed low-power radiofrequency measurements. The structure was first installed and utilized at a beamline for the terahertz experiment at Tsinghua University. After 120 h of conditioning, it is now operating at a gradient of 24.2 MV/m and a 20.7-MW input power, with the klystron operating at its full power. It is expected to generate an accelerating gradient of 30 MV/m when the klystron power is upgraded to 30 MW in the near future.

Study on hysteresis phenomenon in the acceleration phase of supercavitation vehicle

This paper aims to explore cavity shape variation regularity in the acceleration phase of supercavitat- ing vehicle. According to the theory of Homogenous Equilibrium Flow,with Mixture Multiphase Model,by setting up the flow speed at the inlet boundary as a function of time,this study carried out the experiments for the supercavitation vehicle's numeral model and obtained the variation regularity of cavity shape,the viscous drag coefficient and the cavity hysteresis time when the supercavitating vehicle was in the phase of acceleration. Results show that when the vehicle is in the phase of acceleration,at the same cavitation number,the cavity size decrease with the increase of acceleration. With the decrease of cavity number,the effect of acceleration on cavity shape is smaller,but the viscous drag increases along with the increase of acceleration. On the condition when the velocity reaches equality uniform status,the cavity hysteresis decreases as the acceleration becomes smaller. On the condition of the same acceleration,the cavity hysteresis time decreases as the velocity increases.

Nitrogen doping/infusion of 650 MHz cavities for CEPC

The nitrogen doping/infusion of 650 MHz cavities for the circular electron positron collider(CEPC)is investigated in this study.Two 650 MHz 1-cell cavities are first treated via buffered chemical polishing(BCP),followed by nitrogen doping.A"2/6"condition is adopted,similar to that for 1.3 GHz cavities of Linear Coherent Light Source II.The quality factor of both cavities improved to 7×10^(10)in low fields,i.e.,higher than that obtained from the baseline test.One 650 MHz two-cell cavity is nitrogen infused at 165℃for 48 h with a BCP surface base.The intrinsic quality factor(Q0)reached6×10^(10)at 22 MV/m in the vertical test,and the maximum gradient is 25 MV/m,which exceeds the specification of the CEPC(4×10^(10)at 22 MV/m).

Design and commissioning of a wideband RF system for CSNS-Ⅱ rapid-cycling synchrotron

The China Spallation Neutron Source(CSNS) upgrade project(CSNS-Ⅱ) aims to enhance the beam power from 100 to 500 kW. A dual-harmonic accelerating method has been adopted to alleviate the stronger space-charge effect in rapid-cycling synchrotrons owing to the increased beam intensity. To satisfy the requirements of dual-harmonic acceleration, a new radiofrequency(RF) system based on a magnetic alloy-loaded cavity is proposed. This paper presents design considerations and experimental results regarding the performance evaluation of the proposed RF system through high-power tests and beam commissioning. The test results demonstrate that the RF system satisfies the desired specifications and affords significant benefits for CSNS-Ⅱ.

DTL cavity design and beam dynamics for a TAC linear proton accelerator

A 30 mA drift tube linac （DTL） accelerator has been designed using SUPERFISH code in the energy range of 3-55 MeV in the framework of the Turkish Accelerator Center （TAC） project. Optimization criteria in cavity design are effective shunt impedance （ZTT）, transit-time factor and electrical breakdown limit. In geometrical optimization we have aimed to increase the energy gain in each RF gap of the DTL cells by maximizing the effective shunt impedance （ZTT） and the transit-time factor. Beam dynamics studies of the DTL accelerator have been performed using beam dynamics simulation codes of PATH and PARMILA. The results of both codes have been compared. In the beam dynamical studies, the rms values of beam emittance have been taken into account and a low emittance growth in both x and y directions has been attempted.

直线感应加速器加速腔物理设计与研究

简要介绍直线感应加速器（ＬＩＡ）加速腔物理设计的几个关键问题．讨论了加速电压及其平顶和腔参数的关系．对腔的耦合阻抗与束流不稳定性的关系作了概念性介绍，分析了降低耦合阻抗的途径．并给出两个加速腔设计原型．

兰州重离子加速器冷却储存环高频加速系统

文章介绍兰州重离子加速器冷却储存环主环用于加速粒子的高频加速系统。加速系统的频率范围为0．25～1．7MHz，最高峰值电压为8．0kV。高频腔体的固有谐振频率通过调节绕在腔体加载的铁氧体材料上的偏磁电流来改变，所加载的铁氧体材料为600HH。高频腔体内的真空度达到3×10^-9 Pa，高频发射机的最大输出功率为30kW，高频系统的控制采用基于PCI总线技术，它提供所有高频系统控制及监测功能。

Microwave Cold Test Debug of an S-Band 2MeV on-Axis Coupling SW Accelerator

This paper presents the model cavity tune and cold test of an S-band 2MeV on-axis coupling SW accelerator. The measurement of the model cavity's frequency,degree of coupling,Q value and on-axis field distribution are described in detail.In addition,the results of cavity tune and cold test of the accelerating tube are given.The frequency consistency of the accelerator is within±0.3MHz,the coupling degree in the supersaturation state 1.14,the quality factor of the accelerator 12000±200,and the field distribution ratio 1:2.2:2.All the results observed show that the accelerator satisfies the physics design with microwave debugging.

小型微波谐振腔用于蛋白质微波辅助酶解

采用微波谐振腔对细胞色素c以及牛血清白蛋白进行微波辅助酶解,通过电喷雾三级四极杆质谱对得到的肽段进行分析,证明该方法可用很低的微波功率将蛋白质彻底酶解为多肽.通过调整微波条件可以使蛋白质的酶解效率基本达到100%,细胞色素c和牛血清白蛋白的序列覆盖率分别为45%和26%.该方法不但可将蛋白酶解时间由传统方法的16 h缩短为20min,还将功率由使用微波炉时的数百瓦降至20 W.

感应加速腔横向阻抗测量

描述了采用脉冲双线法测量感应加速腔横向阻抗的原理、方法和步骤。测量结果显示 ,新设计的真空腔和绝缘腔的横向阻抗特性优于以前设计的原形腔 ,而且加速间隙由于采用了类同轴结构 ,绝缘腔的低频模式被有效抑制 ,在 753 MHz测得其横向阻抗为 82 0 Ω/m。

楔形体入水冲击响应的试验研究及应用

结构物在入水过程中会受到较大的冲击载荷,严重影响结构和结构内部人员的安全,因此入水问题的研究在航空航天和军事领域具有实际意义。以简单的楔形体为研究对象,进行了垂直入水的冲击试验,采用高速摄像机采集了楔形体入水过程的图像,并且考察楔形体入水过程的加速度的响应,通过滤波消除高频信号,得到合理的加速度响应值。结果表明:楔形体密闭空腔对加速度响应有重要影响。依据相似准则,通过试验模型的数据,预测了实际大尺寸的飞机结构的入水冲击响应,研究结果对入水结构的设计具有一定的参考价值。

国产45MW速调管实验研究

对45 MW实验速调管的电子枪、谐振腔和聚焦磁场结构设计进行了优化研究与测试分析,并对实验管进行了高功率测试分析,以检验设计方案的可行性与合理性。在300 kV高压下,输出脉冲功率达45 MW,其重复频率12.5 Hz,脉宽为2μs,效率约42%,增益约49 dB。速调管电子枪导流系数约为2.05μp,与电子枪的理论设计基本吻合。从输出功率与电压的关系来看,速调管谐振腔与聚焦磁场的设计与优化可满足国产45 MW速调管的需要。

直线感应加速腔横向阻抗的测量

采用束流模拟法测量强流直线感应加速器加速腔横向阻抗，给出了加速腔的测量结果。采用了时域变换法提高不匹配情况下测量精度的方法，对引起测量误差的原因进行了分析。这有助于深入理解强流加速腔内的物理过程，改进加速腔设计，提高直线感应加速器整机性能。

腔体结构参数对毛细管放电型脉冲等离子体推力器放电特性的影响

毛细管放电型脉冲等离子体推力器在微纳卫星在轨机动应用中具备良好的发展前景.本文系统研究了单次放电能量5 J条件下,不同毛细管腔体尺寸参数对推力器能量沉积特性、烧蚀特性、输出推力参数和等离子体羽流参数的影响规律.实验结果表明,增大毛细管腔体内径会显著降低放电电流密度,减小沉积能量和等效功率;增大腔体长度有助于提升能量传递效率.腔体结构尺寸变化影响单位面积沉积能量和管壁温度,进而改变烧蚀特性.当毛细管内径从1 mm增加至3 mm时烧蚀质量显著下降,随着腔体内径的进一步增大,等效烧蚀质量近似不变;烧蚀质量随毛细管长度的增加持续增大,但单位面积烧蚀质量不断下降.推力器元冲量取决于烧蚀质量与其等效速度,烧蚀特性的差异进一步影响腔体内等离子体密度和等效压强,影响等离子体电热加速过程.毛细管腔体内径和长度的不断增加,使得加速过程滞后于放电和烧蚀过程,作用于加速过程的电弧沉积能量比例降低,降低推力器等离子体喷射速度,元冲量减小,比冲降低,总体效率下降.结合总体效率传递模型分析,毛细管内径对推力器效率的影响主要体现在能量传递效率方面,毛细管长度变化主要影响等离子体电热加速效率,优化推力器总体效率需要从能量沉积效率和加速效率两方面入手.

直线感应加速器输运过程模拟

对直线感应加速器中电子束的输运过程进行数值模拟研究,采用了时域有限差分与粒子模拟相结合的方法。在对直线感应加速器建模的过程中,成功地使用了非均匀网格模型,实现了对加速腔精细结构的建模。并在加速间隙处加入了加速场。通过3个步骤实现了直线感应加速器加速腔中聚束磁场的模拟,最后将聚束场与加速段结合起来模拟电子束的输运过程,并对结果加以分析,验证了方法的正确性。

超导在加速器中的应用概况

文中简要回顾了世界上已建造的大型超导加速器 ,重点介绍未来的超导加速器方案 ,对超导新材料在加速器中的应用研究以及我国超导在加速器中的应用研究情况作了简要介绍。