200 MW S-band traveling wave resonant ring development at IHEP

The resonant-ring is a traveling wave circuit, which is used to produce high peak power with comparatively smaller stored energy. The application to be considered is its use as a high power simulator mainly for testing the klystron ceramic output window, as well as for high power microwave transmission devices. This paper describes the principle of a resonant ring and introduces the structure and property of the newly constructed traveling wave resonant ring at IHEP. Our goal is to produce a 200 MW class resonant ring at 2.856 GHz with a pulse length of 2μs and repetition rate of 25 Hz. The installation, commissioning and testing of the ring have been completed and a peak power of 200 MW at 3 μs has been achieved. The conditioning results show that all the parameters of the resonant ring reach the design goals.     

200 MW S-band traveling wave resonant ring development at IHEP

The resonant-ring is a traveling wave circuit, which is used to produce high peak power with comparatively smaller stored energy. The application to be considered is its use as a high power simulator mainly for testing the klystron ceramic output window, as well as for high power microwave transmission devices. This paper describes the principle of a resonant ring and introduces the structure and property of the newly constructed traveling wave resonant ring at IHEP. Our goal is to produce a 200 MW class resonant ring at 2.856 GHz with a pulse length of 2 μs and repetition rate of 25 Hz. The installation, commissioning and testing of the ring have been completed and a peak power of 200 MW at 3 μs has been achieved. The conditioning results show that all the parameters of the resonant ring reach the design goals.     

Study of multipacting effect in sub-harmonic buncher of SSRF linac

During the design process, multipacting effect has been taken into consideration using a 2D simulation code MultiPac and all of the corners are rounded to suppress the multipacting effect in the pill-box cavity. However, unexpected multipacting effect prevents the increase of the input power when the magnetic field of focusing coils is added after adequate conditioning and a novel method is adopted to suppress it by introducing extra coils to counteract the field. This paper focuses on the simulation of multipacting effect in different magnetic field configurations. The experimental observations and simulation results of multipacting effect are presented and details of the multipacting process are also analyzed.     

Study of multipacting effect in sub-harmonic buncher of SSRF linac

During the design process, multipacting effect has been taken into consideration using a 2D simulation code MultiPac and all of the corners are rounded to suppress the multipacting effect in the pill-box cavity. However, unexpected multipacting effect prevents the increase of the input power when the magnetic field of focusing coils is added after adequate conditioning and a novel method is adopted to suppress it by introducing extra coils to counteract the field. This paper focuses on the simulation of multipacting effect in different magnetic field configurations. The experimental observations and simulation results of multipacting effect are presented and details of the multipacting process are also analyzed.     

RF thermal and new cold part design studies on a TTF-Ⅲ input coupler for Project-X

An RF power coupler is one of the key components in a superconducting (SC) linac. It provides RF power to the SC cavity and interconnects different temperature layers (1.8 K, 4.2 K, 70 K and 300 K). The TTF-Ⅲ coupler is one of the most promising candidates for the High Energy (HE) linac of Project X, but it cannot meet the average power requirements because of the relatively high temperature rise on the warm inner conductor, so some design modifications will be required. In this paper, we describe our simulation studies on the copper coating thickness on the warm inner conductor with RRR values of 10 and 100. Our purpose is to rebalance the dynamic and static loads, and finally lower the temperature rise along the warm inner conductor. In addition, to get stronger coupling, better power handling and less multipacting probability, one new cold part design was proposed using a 60 mm coaxial line; the corresponding multipacting simulation studies have also been investigated.     

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.     

PSPICE controlled-source models of analogous circuit for Langevin type piezoelectric transducer

The design and construction of wide-band and high efficiency acoustical projector has long been considered an art beyond the capabilities of many smaller groups. Langevin type piezoelectric transducers have been the most candidate of sonar array system applied in underwater communication. The transducers are fabricated, by bolting head mass and tail mass on both ends of stacked piezoelectric ceramic, to satisfy the multiple, conflicting design for high power transmitting capability. The aim of this research is to study the characteristics of Langevin type piezoelectric transducer that depend on different metal loading. First, the Mason equivalent circuit is used to model the segmented piezoelectric ceramic, then, the impedance network of tail and head masses is deduced by the Newton's theory. To obtain the optimal solution to a specific design formulation, PSPICE controlled-source programming techniques can be applied. A valid example of the application of PSPICE models for Langevin type transducer analysis is presented and the simulation results are in good agreement with the experimental measurements.     

Development of a 500 MHz high power RF test stand

A flexible high power RF test stand has been designed and constructed at IHEP to test a variety of 500 MHz superconducting RF components for the upgrade project of the Beijing Electron Positron Collider (BEPCⅡ), such as the input coupler, the higher order modes (HOMs) absorber and so on. A high power input coupler has been conditioned and tested with the RF power up to 250 kW in continuous wave (CW), traveling wave (TW) mode and 150 kW CW in standing wave (SW) mode. A prototype of the HOMs absorber has been tested to absorb power of 4.4 kW. An introduction of the test stand design, construction and high power tests is presented in this paper.     

Design Consideration of 650-MHz Circular Electron-Positron Collider Klystron and Simulation of Its Beam Tester

We present the first phase RD for the 800 kW cw, 650 MHz klystron for the future circular electron-positron collider(CEPC) project in China. The CEPC requires 192 klystrons and it is desired to be designed in the Institute of High Energy Physics,CAS, and manufactured domestically. Therefore,we present the manufacturing schedule of this project; the three-stage development from the beam test tube to the klystron having a high efficiency structure. Design of the beam test tube that comprises electron gun and collector is presented. First, gun simulation having a modulating anode is performed using DGUN software. The uniform beam trajectories with a beam perveance of 0.64 μA/V~(3/2) are simulated. We employ a Ba-dispenser cathode of radius 35 mm with φ10 hole at the center and obtain a current density on cathode less than 0.45 A/cm~2. The beam trajectories are also simulated over beam test tube of length about 2 m with a magnetic field of 213 Gauss. Thermal analysis of the collector is performed using the ANSIS-CFX code and hence the cooling structure is determined. Mechanical design is almost carried out and it is in manufacturing stage.     

Mode control in a high gain relativistic klystron amplifier with 3 GW output power

Higher mode excitation is very serious in the relativistic klystron amplifier, especially for the high gain relativistic amplifier working at tens of kilo-amperes. The mechanism of higher mode excitation is explored in the FIC simulation and it is shown that insufficient separation of adjacent cavities is the main cause of higher mode excitation. So RF lossy material mounted on the drift tube wall is adopted to suppress higher mode excitation. A high gain S-band relativistic klystron amplifier is designed for the beam current of 13 kA and the voltage of 1 MV. PIC simulation shows that the output power is 3.2 GW when the input power is only 2.8 kW.     

Mode control in a high gain relativistic klystron amplifier with3 GW output power

Higher mode excitation is very serious in the relativistic klystron amplifier, especially for the high gain relativistic amplifier working at tens of kilo-amperes. The mechanism of higher mode excitation is explored in the PIC simulation and it is shown that insufficient separation of adjacent cavities is the main cause of higher mode excitation. So RF lossy material mounted on the drift tube wall is adopted to suppress higher mode excitation. A high gain S-band relativistic klystron amplifier is designed for the beam current of 13 kA and the voltage of 1 MV. PIC simulation shows that the output power is 3.2 GW when the input power is only 2.8 kW.     

Study on the HOMs coupler design of spoke cavity

The superconducting spoke cavity has been proposed to accelerate the proton in the low energy section of high power proton linac for an Accelerator Driven Sub-critical System (ADS). Considering that the High Order Modes (HOMs) in the superconducting cavity have far reaching influence on power dissipation and beam stability, the analysis of HOMs of the spoke cavity is needed. In this paper, we put emphasis on the analysis of HOMs of the spoke cavity and the HOMs coupler design.     

Fabrication of the high power input coupler for BEPCⅡ superconducting cavities

The BEPCII storage ring adopts two 500 MHz superconducting cavities (SCC). Each one is equipped with a 500 MHz input power coupler. The coupler is to feed 150 kW power in continuous wave (CW) mode with both standing and traveling wave modes. Due to high power feeding and high frequency of the coupler, its fabrication is a big challenge. The fabrication started with two key components,the window and the antenna. Up to now, two sets including windows and antennas have been made by IHEP. And a 270 kW RF power in CW has passed through the coupler during the high power test. The fabrication details are presented in this paper.     

A STUDY OF HIGH POWER MICROWAVE AIR BREAKDOWN

This paper presents the results of research on microwave breakdown in air, it includes the experimental study and the theoretical analysis. The experimental study has been done in a waveguide with a frequency of 9.37GHz, the peak power up to 200kW, pulse width from 0.3 to 2.0μs. The repetition rate of microwave source is from single pulse to 970 pulse per second. The process of the breakdown of repetition pulse has also been recorded for a burst of ten pulses. A theoretical model for breakdown threshold is presented also. The theoretical are in good agreement with the experimental ones.     

A new compact structure for a high intensity low-energy heavy-ion accelerator

A new compact accelerating structure named Hybrid RFQ is proposed to accelerate a high-intensity low-energy heavy ion beam in HISCL （High Intensive heavy ion SuperConducting Linear accelerator）, which is an injector of HIAF （Heavy Ion Advanced Research Facility）. It is combined by an alternative series of acceleration gaps and RFQ sections. The proposed structure has a high accelerating ability compared with a conventional RFQ and is more compact than traditional DTLs. A Hybrid RFQ is designed to accelerate 238U34＋ from 0.38 MeV/u to 1.33 MeV/u. The operation frequency is described to be 81.25 MHz at CW （continuous wave） mode. The design beam current is 1.0 mA. The results of beam dynamics and RF simulation of the Hybrid RFQ show that the structure has a good performance at the energy range for ion acceleration. The emittance growth is less than 5% in both directions and the RF power is less than 150 kW. In this paper, the results of beam dynamics and RF simulation of the Hybrid RFQ are presented.     

RF power coupling for the CSNS DTL

The China Spallation Neutron Source (CSNS) drift tube linac (DTL) consists of four tanks and each tank is fed by a 2.5 MW klystron. Accurate predication of RF coupling between the RF cavity and ports is very important for DTL RF coupler design. An iris-type coupler is chosen to couple the RF power to the DTL accelerating cavity. The physical design of the DTL coupler and the calculations of RF coupling between the cavity and coupler are carried out. The results from the numerical simulations are in excellent agreement with the analytical results.     

End-to-end simulation of the C-ADS Injector Ⅱ with a 3-D field map

The InjectorⅡ, one of the two parallel injectors of the high-current superconducting proton driver linac for the China Accelerator-Driven System (C-ADS) project, is being designed and constructed by the Institute of Modern Physics. At present, the design work for the injector is almost finished. End-to-end simulation has been carried out using the TRACK multiparticle simulation code to check the match between each acceleration section and the performance of the injector as a whole. Moreover, multiparticle simulations with all kinds of errors and misalignments have been performed to define the requirements of each device. The simulation results indicate that the lattice design is robust. In this paper, the results of end-to-end simulation and error simulation with a 3-D field map are presented.     

The design of a five-cell high-current superconducting cavity

Energy recovery linacs are promising for achieving high average current with superior beam quality. The key component for accelerating such high-current beams is the superconducting radio-frequency cavity. The design of a 1.3 GHz five-cell high-current superconducting cavity has been carried out under cooperation between Peking University and the Argonne National Laboratory. The radio-frequency properties, damping of the higher order modes, multipacting and mechanical features of this cavity have been discussed and the final design is presented.