RF characters study of a pick-up parallel-setting HOM coupler

A pick-up parallel-setting high order mode coupler(pps-HOM coupler)has been fabricated at Peking University.It has been tested on a coaxial transmission line and a 2-cell TESLA-shape copper cavity.The test result of the 2-cell TESLA cavity shows that the coupler can cut off the fundamental mode TM010 and absorb HOMs electively.As its RF properties are insensitive to the probe dip length,there is no need to adjust the probe repeatedly during practical operation.     

RF characters study of a pick-up parallel-setting HOM coupler

A pick-up parallel-setting high order mode coupler （pps-HOM coupler） has been fabricated at Peking University. It has been tested on a coaxial transmission line and a 2-cell TESLA-shape copper cavity. The test result of the 2-cell TESLA cavity shows that the coupler can cut off the fundamental mode TM010 and absorb HOMs electively. As its RF properties are insensitive to the probe dip length, there is no need to adjust the probe repeatedly during practical operation.     

A coaxial HOM coupler for a superconducting RF cavity and its low-power measurement results

A resonant buildup of beam-induced fields in a superconducting radio frequency(RF)cavity may make a beam unstable or a superconducting RF cavity quench. Higher-order mode(HOM)couplers are used for damping higher-order modes to avoid such a resonant buildup. A coaxial HOM coupler based on the TTF (TESLA Test Facility)HOM coupler has been designed for the superconducting RF cavities at the Proton Engineering Frontier Project(PEFP)in order to overcome notch frequency shift and feed-through tip melting issues. In order to confirm the HOM coupler design and finalize its structural dimensions, two prototype HOM couplers have been fabricated and tested. Low-power testing and measurement of the HOM couplers has shown that the HOM coupler has good filter properties and can fully meet the damping requirements of the PEFP low-beta superconducting RF linac.     

A coaxial HOM coupler for a superconducting RF cavity and its low-power measurement results

A resonant buildup of beam-induced fields in a superconducting radio frequency (RF) cavity may make a beam unstable or a superconducting RF cavity quench. Higher-order mode (HOM) couplers are used for damping higher-order modes to avoid such a resonant buildup. A coaxial HOM coupler based on the TTF (TESLA Test Facility) HOM coupler has been designed for the superconducting RF cavities at the Proton Engineering Frontier Project (PEFP) in order to overcome notch frequency shift and feed-through tip melting issues. In order to confirm the HOM coupler design and finalize its structural dimensions, two prototype HOM couplers have been fabricated and tested. Low-power testing and measurement of the HOM couplers has shown that the HOM coupler has good filter properties and can fully meet the damping requirements of the PEFP low-beta superconducting RF linac.     

Stop band characteristics of a TESLA cavity coaxial-type HOM coupler

A TTF-type coaxial higher order modes (HOM) coupler has been used in a TESLA 9 cell cavity. It is impossible to measure the stop band characteristics of the HOM coupler with the cavity. A measurement device for the coaxial transmission line type for the HOM coupler has been designed at Peking University. Experimentally it was shown that the average voltage standing wave ratio of the coaxial transmission line is smaller than 1.08. The experimental results of the stop band characteristics of the TTF-type HOM coupler have been fitted for the simulation. This paper describes the design of the measurement device and discusses the experimental and simulation results of stop band characteristics of the HOM coupler.     

Stop band characteristics of a TESLA cavity coaxial-type HOM coupler

A TTF-type coaxial higher order modes (HOM) coupler has been used in a TESLA 9 cell cavity. It is impossible to measure the stop band characteristics of the HOM coupler with the cavity. A measurement device for the coaxial transmission line type for the HOM coupler has been designed at Peking University. Experimentally it was shown that the average voltage standing wave ratio of the coaxial transmission line is smaller than 1.08. The experimental results of the stop band characteristics of the TTF-type HOM coupler have been fitted for the simulation. This paper describes the design of the measurement device and discusses the experimental and simulation results of stop band characteristics of the HOM coupler.     

Physical design study of the CEPC booster

A physical design study of the Circular Electron-Positron Collider(CEPC) booster is reported. The booster provides 120 GeV electron and positron beams for the CEPC collider with top-up injection. The booster is mounted above the collider in the same tunnel. To save cost, the energy of the linac injector for the booster is chosen as 6 GeV, corresponding to a magnetic field of 30.7 Gs. In this paper, the booster lattice is described and optimization of the cell length is discussed. A novel scheme of bypass near the detector of the collider is designed.The extremely low magnetic field caused by low injection energy is studied, and a new ideal of wiggling bands is proposed to mitigate the low-field problem. Beam transfer and injection from the linac to the booster are considered.     

Measuring the performance of the coaxial HOM coupler on a 2-cell TESLA-shape copper cavity

Coaxial High Order Mode （HOM） couplers have been fabricated at Peking University and their RF performance has been measured on a test device consisting of a coaxial transmission line and a 2-cell TESLA-shape copper cavity. The test results on the 2-cell TESLA-shape copper cavity with HOM couplers indicate that the coupler can cut off the fundamental mode TM010 and absorb HOMs effectively after a careful adjustment. The optimal angle of the HOM coupler with the beam tube is found. The initial test results of HOM couplers are presented in this paper.     

Measuring the performance of the coaxial HOM coupler on a 2-cell TESLA-shape copper cavity

Coaxial High Order Mode (HOM) couplers have been fabricated at Peking University and their RF performance has been measured on a test device consisting of a coaxial transmission line and a 2-cellTESLA-shape copper cavity. The test results on the 2-cell TESLA-shape copper cavity with HOM couplers indicate that the coupler can cut off the fundamental mode TM010 and absorb HOMs effectively after a careful adjustment. The optimal angle of the HOM coupler with the beam tube is found. The initial test results of HOM couplers are presented in this paper.     

用于PKU-FEL注入器的腔式BPM的设计

设计了用于PKU-FEL注入器的腔式位置诊断装置。该BPM腔采用的偶极模TM110模的频率与PKU-FEL主加速器的基模频率一致,都是1.3 GHz;通过在圆形腔上镶入两个完全一致的矩形腔解决了腔式BPM的Cross-Talk问题。 根据PKU-FEL的设计要求,所设计的BPM腔的最小位置响应约10 mm,动态范围大于30 mm,时间响应小于束团间距。还估算了该BPM腔引起的束团功率损耗。结果表明,BPM腔引起的束团功率损耗是可以忽略的。     

用于PKU-FEL注入器的腔式BPM的设计

 设计了用于PKU-FEL注入器的腔式位置诊断装置。该BPM腔采用的偶极模TM₁₁₀模的频率与PKU-FEL主加速器的基模频率一致,都是1.3 GHz;通过在圆形腔上镶入两个完全一致的矩形腔解决了腔式BPM的Cross-Talk问题。 根据PKU-FEL的设计要求,所设计的BPM腔的最小位置响应约10 mm,动态范围大于30 mm,时间响应小于束团间距。还估算了该BPM腔引起的束团功率损耗。结果表明,BPM腔引起的束团功率损耗是可以忽略的。     

Physics design of collimators to reduce lost particle background at the CEPC

At the CEPC (Circular Electron Positron Collider), which is proposed by the Chinese high energy physics community, the dominant background comes from radiative Bhabha scattering and the beamstrahlung effect according to preliminary research. Therefore, it is necessary to incorporate a collimator system to intercept particles that may be lost near the interaction region (IR). In this paper, we introduce some limitations in choosing the position and width of the collimators. A certain parameter range is determined which is confined by the β function and the width of the collimators. A suitable choice of the half width is made by exploring this parameter range. A simulation of the particle loss rate in the IR and the hit density in the vertex detector with and without the collimators shows that the set of parameters of the collimators we designed is appropriate and effective.     

Prospects for chargino pair production at the CEPC

The proposed Circular Electron Positron Collider(CEPC)with a center-of-mass energy√s=240GeV will primarily serve as a Higgs factory.Additionally,it will offer good opportunities to search for new physics phenomena at low energies,which can be challenging with hadron colliders;however,these discoveries are highly motivated by theoretical models developed to explain,e.g.,the relic abundance of dark matter.This paper presents sensitivity studies for chargino pair production by considering scenarios for both a Bino-like and a Higgsino-like neutralino as the lightest supersymmetric particle and using a full Monte Carlo(MC)simulation.By assuming systematic uncertainties at the level of 5%,the CEPC has the ability to discover chargino pair production up to the kinematic limit of for√s/2 both scenarios.The results have a minor dependence on the reconstruction model and detector geometry.These results can also be considered as a reference and benchmark for similar searches at other proposed electron-positron colliders,such as the Future Circular Collider ee(FCC-ee)or the International Linear Collider(ILC),given the similar nature of the facilities,detectors,center-of-mass energies,and target luminosities.     

被动型氢脉泽微波腔优化仿真设计

利用电磁场微波理论, 对简化近似后的被动型氢脉泽微波腔模型建立了微波腔频率谐振方程、无载Q值以及填充因子的解析表达式. 通过计算找到了无载Q值与填充因子乘积最大时的微波腔尺寸. 实验表明, 新设计的微波腔的各项性能完全满足被动氢脉泽的使用要求. 该腔体的无载Q值达到9800, 填充因子值达到1.2, 并且该微波腔的原子填充区域是已有文献报道中体积最大的.     

Study and design of RF coupler for Chinese ADS HWR superconducting cavity

An RF power coupler is a key component of the superconducting accelerating system in Chinese ADS proton linac injector I, which is used to transmit 15 kW RF power from the power source to the superconducting HWR cavity. According to the requirement of working frequency, power level, transmission capability and cooling condition, the physics design of coupler has been finished, which includes RF structure optimization, thermal simulation, thermal stress analysis and so on. Based on this design, the prototype of HWR coupler has been fabricated, and it has successfully passed the high power test.     

Study and design of RF coupler for Chinese ADS HWR superconducting cavity

An RF power coupler is a key component of the superconducting accelerating system in Chinese ADS proton linac injector I, which is used to transmit 15 kW RF power from the power source to the superconducting HWR cavity. According to the requirement of working frequency, power level, transmission capability and cooling condition, the physics design of coupler has been finished, which includes RF structure optimization, thermal simulation, thermal stress analysis and so on. Based on this design, the prototype of HWR coupler has been fabricated, and it has successfully passed the high power test.     

Design and high-power test of 800-kW UHF klystron for CEPC

To reduce the energy demand and operation cost for circular electron positron collider (CEPC), the high efficiency klystrons are being developed at Institute of High Energy Physics, Chinese Academy of Sciences. A 800-kW continuous wave (CW) klystron operating at frequency of 650-MHz has been designed. The results of beam-wave interaction simulation with several different codes are presented. The efficiency is optimized to be 65% with a second harmonic cavity in three-dimensional (3D) particle-in-cell code CST. The effect of cavity frequency error and mismatch load on efficiency of klystron have been investigated. The design and cold test of reentrant cavities are described, which meet the requirements of RF section design. So far, the manufacturing and high-power test of the first klystron prototype have been completed. When the gun operated at DC voltage of 80 kV and current of 15.4 A, the klystron peak power reached 804 kW with output efficiency of about 65.3% at 40% duty cycle. The 1-dB bandwidth is ±0.8 MHZ. Due to the crack of ceramic window, the CW power achieved about 700 kW. The high-power test results are in good agreement with 3D simulation.     

回旋速调管输入耦合器分析与设计

对Ka波段工作模式为TE01模和TE02模的两种回旋速调管的输入耦合器进行了详细研究,利用模式匹配理论和HFSS建模仿真计算了内圆柱腔和外同轴腔的尺寸;提出了一种与软件计算相结合的模式纯度计算方法,对内腔工作模式纯度、内外腔能量分数进行了计算。内腔侧面上的耦合缝的大小、角向位置都直接决定外同轴腔内的TEm11模向内圆柱腔的TE0n1模的耦合情况。针对耦合缝与输入波导成45°和0°分布两种情况,研究了耦合缝长、宽和角向偏移,以及内外腔频差对频率、Q值及内腔能量分数的影响。分别设计了Ka波段内腔工作模式为TE011、外腔为TE411和内腔TE021、外腔TE811的两种输入耦合器,并利用矢量网络分析仪对内腔工作模式为TE011的耦合器进行了冷高频测量,测得频率为34.257 GHz,与计算结果34.300 GHz仅相差43 MHz。     

The radio-frequency design of an iris-type coupler for the CPHS radio-frequency quadrupole

The Compact Pulsed Hadron Source (CPHS) project is a university-based proton accelerator platform (13 MeV, 16 kW, 50 mA peak current, 0.5 ms pulse width at 50 Hz) for multi-disciplinary neutron and proton applications. The CPHS linac consists of a 3 MeV radio-frequency quadrupole (RFQ) linac and a 13 MeV drift tube linac (DTL). Both the RFQ and DTL share a 325 MHz, 2.1 MW klystron source. A single iris-type radio-frequency (RF) coupler is used to feed 537 kW of RF power to the RFQ cavity. Three-dimensional electromagnetic models of the ridge-loaded tapered waveguide (RLWG) and the coupler-cavity system are presented, and the design process and results of the RLWG and iris plate are described in detail.     

回旋速调管输入耦合器分析与设计

 对Ka波段工作模式为TE₀₁模和TE₀₂模的两种回旋速调管的输入耦合器进行了详细研究,利用模式匹配理论和HFSS建模仿真计算了内圆柱腔和外同轴腔的尺寸;提出了一种与软件计算相结合的模式纯度计算方法,对内腔工作模式纯度、内外腔能量分数进行了计算。内腔侧面上的耦合缝的大小、角向位置都直接决定外同轴腔内的TE_m11模向内圆柱腔的TE_0n1模的耦合情况。针对耦合缝与输入波导成45°和0°分布两种情况,研究了耦合缝长、宽和角向偏移,以及内外腔频差对频率、Q值及内腔能量分数的影响。分别设计了Ka波段内腔工作模式为TE₀₁₁、外腔为TE₄₁₁和内腔TE₀₂₁、外腔TE₈₁₁的两种输入耦合器,并利用矢量网络分析仪对内腔工作模式为TE₀₁₁的耦合器进行了冷高频测量,测得频率为34.257 GHz,与计算结果34.300 GHz仅相差43 MHz。