Superconducting Spoke Cavities Research Articles

Suppression of multipacting growth in a superconducting spoke resonator by the use of higher order modes

Abstract Multipacting is a vacuum discharge phenomenon that constrains the performance of accelerator structures and various microwave devices significantly. The different ways to mitigate multipacting discharge have been a central research goal in Accelerator Physics & Technologies for a prolonged period. In this work, both Monte-Carlo and particle-in-cell (PIC) simulations show that the multipactor avalanche can be mitigated, by the use of Higher Order Modes (HOMs). The intuition behind the approach of using HOMs to suppress multipacting has been explained first. Then, the multipacting suppression has been demonstrated in a simple 1-D metallic gap, when it is exposed to a second carrier frequency in addition to fundamental rf mode, with the help of a Monte-Carlo simulation code. Finally, a detailed PIC simulation has been carried out using CST Microwave studio, to investigate the effect of various HOMs on the multipactor growth in a superconducting spoke cavity. It is observed that a slight excitation of some particular modes can drastically diminish the multipactor growth. Simulation has been done first without any HOMs, to calculate the growth rate and also to spot the discharge location. Next, among various HOMs (more specifically, quadrupole modes), only those have been selected, whose magnetic field locations coincide with the multipacting prone zone of the cavity. In a simulation study, the presence of these preselected quadrupole modes has been found to exhibit a substantial suppression effect on the multipacting growth of the cavity.

Modeling of Superconducting Spoke Cavity with its Control Loops Systems for the MYRRHA Linac Project

Modeling of Superconducting Spoke Cavity with its Control Loops Systems for the MYRRHA Linac Project

RF design of a compact 648 MHz single spoke cavity at CSNS

In order to increase CSNS beam power from 100 to 500 kW, the linac injection energy needs to be increased from 80 to 300 MeV. The combined layout of superconducting spoke cavities and elliptical cavities will be adopted to accelerate H− beam to 300 MeV. In this paper, a compact single spoke cavity with Φ50-mm beam aperture was proposed, with the RF performance of the spoke cavity optimized to Ep/Eacc value. The simulation got optimum results of Epeak/Eacc = 4.97 and Bpeak/Eacc = 8.42 mT/(MV/m), and the max is 1.52 at Eacc = 7.74 MV/m. A 648 MHz βg = 0.4 single spoke cavity with beam aperture Φ50 mm was proposed in the paper. This compact cavity may be a very promising option for CSNS linac upgrading. In addition to the optimization of the RF parameters, the multipacting behavior of the cavity is also studied, and cavity shape is optimized to reduce value.

The superconducting magnet for ADS injection-I

The cryomodule I for ADS Injection-I had been designed, fabricated and online tested. The CM1 contains seven superconducting magnets, seven superconducting spoke cavities and seven beam position monitors. The superconducting magnet, which is a kind of multifunction magnet in a 170mm length axial space, contains a solenoid for beam focusing and two correctors for orbit correction. The design goals for the magnets are to meet the required integral field strength and to reduce the leakage field of less than 2 G at the nearby superconducting spoke cavities. The 2.1K, 31 mbar cryogenic system, where the magnets and spoke cavities shared with, force the magnet must select a kind of conduction cooled current leads. The first one of the batch magnets was tested in a vertical Dewar in HIT in July, 2014. The measurement results met the design requirements. Online operation of CM1 in September, 2015 showed that seven magnets can work at 230A under 4.2K and 2.1K respectively. This paper will present the magnet and current lead design, field measurement and the installation progress.

The ESS Spoke cryomodule and its test valve box

The European Spallation Source project aims at being the most powerful neutron source feeding multidisplinary researches. Based on superconducting radiofrequency technologies, the linear accelerator will operate for the first time a 56 meter long section of niobium double Spoke cavities. Paired in 13 cryomodules, each cavity will generate an accelerating pulsed field of 9MV/m. A prototype cryomodule housing two superconducting Spoke cavities and their RF power couplers is now being fabricated and assembled. It provides the cryogenic environment for their operation in a 2K saturated superfluid helium bath: a 50 K thermal shield, a cold magnetic shield, and integrates all the interfaces necessary to be operational within the linac machine. This prototype will be tested in 2016 at IPNO site and then at Uppsala university FREIA facilities. A valve box was designed to take into account the specific features of this prototype cryomodule and of both test sites. This valve box is also considered as a prototype of the cryogenic distribution of the linac Spoke section. This element will then be used for the tests of the series cryomodules.

Physics design of a 10 MeV injector test stand for an accelerator-driven subcritical system

The 10 MeV accelerator-driven subcritical system (ADS) Injector I test stand at Institute of High Energy Physics (IHEP) is a testing facility dedicated to demonstrate one of the two injector design schemes [Injector Scheme-I, which works at 325 MHz], for the ADS project in China. The injector is composed of two parts, the linac part and the beam dump line. The former is designed on the basis of 325 MHz four-vane type copper structure radio frequency quadrupole and superconducting (SC) spoke cavities with beta = 0.12. The latter is designed to transport the beamcoming out of the SC section of the linac to the beam dump, where the beam transverse profile is fairly enlarged and unformed to simplify the beam target design. The SC section consists of two cryomodules with 14 beta = 0.12 Spoke cavities, 14 solenoid and 14 BPMs in total. The first challenge in the physics design comes from the necessary space required for the cryomodule separation where the periodical lattice is destroyed at a relatively lower energy of similar to 5 MeV. Another challenge is the beam dump line design, as it will be the first beam dump line being built by using a step field magnet for the transverse beam expansion and uniformity in the world. This paper gives an overview of the physics design study together with the design principles and machine construction considerations. The results of an optimized design, fabrication status and end to end simulations including machine errors are presented.

Design and test of a superconducting magnet in a linear accelerator for an Accelerator Driven Subcritical System

A batch superconducting solenoid magnet for the ADS proton linear accelerator has been designed, fabricated, and tested in a vertical dewar in Sept. 2013. A total of ten superconducting magnets will be installed into two separate cryomodules. Each cryomodule contains six superconducting spoke RF cavities for beam acceleration and five solenoid magnets for beam focusing.The multifunction superconducting magnet contains a solenoid for beam focusing and two correctors for orbit correction. The design current for the solenoid magnet is 182A. A quench performance test shows that the operating current of the solenoid magnet can reach above 300A after natural quenching on three occasions during current ramping (260A, 268A, 308A). The integrated field strength and leakage field at the nearby superconducting spoke cavities all meet the design requirements. The vertical test checked the reliability of the test dewar and the quench detection system. This paper presents the physical and mechanical design of the batch magnets, the quench detection technique, field measurements, and a discussion of the residual field resulting from persistent current effects.

Error analysis and lattice improvement for the C-ADS Injector- I

The injector Scheme- I (or Injector- I) of the C-ADS linac is a 10 mA 10 MeV proton linac working in CW mode. It is mainly comprised of a 3.2 MeV room-temperature 4-vane RFQ and twelve superconducting single-spoke cavities housed in a long cryostat. Error analysis including alignment and field errors, and static and dynamic ones for the injector are presented. Based on detailed numerical simulations, an orbit correction scheme has been designed, which shows that with correction the rms residual orbit errors can be controlled within 0.3 mm and a beam loss rate of 1.7×10−6 is obtained. To reduce the beam loss rate further, an improved lattice design for the superconducting spoke cavity section has been studied.

Superconducting Spoke Cavities for High-Velocity Applications

Center for Accelerator Science, Department of Physics, Old Dominion University, Norfolk, Virginia 23529, USA,and Accelerator Division, Thomas Jefferson National Accelerator Facility, Newport News, Virginia 23606, USA(Received 12 July 2013; published 3 October 2013)To date, superconducting spoke cavities have been designed, developed, and tested for particlevelocities up to

Physical design of superconducting magnet for ADS injection I

A superconducting solenoid prototype magnet for Accelerator Driven Subcritical System (ADS) Injection I has been designed and fabricated, which has also been tested in a liquid Helium state inside a vertical Dewar in the Haerbin institute of Technology in November 2012. The design current was 210 A, when the test current reached 400 A no quench occurred so the solenoid magnet was forced to quench by the embedded heaters. The integral field strength, leakage field at the nearby upstream and downstream superconducting spoke cavities all meet the design requirements. At the same time, it also checked the reliability of the vertical test Dewar and the quenched detection system. The superconducting prototype magnet has accumulated valuable experiences for the coming batch magnets production and cryogenic test.

Coupler conditioning and high power testing of ADS Spoke cavity

Power couplers, used in China-ADS proton linac injector I, are required to transfer 6 kW RF power to the superconducting Spoke cavities. At present, first the two couplers of a coaxial design have been fabricated, which accomplished a high power test at IHEP. The test results indicated that couplers of this design are qualified to deliver 10 kW RF power in continuous travelling wave mode. This paper describes the coupler's room temperature test procedures and results and discusses the original high power test, which was terminated due to serious out-gassing and after some modifications. In the final test, the couplers smoothly exceeded the design power level.

Physics design for the C-ADS main linac based on two different injector design schemes

The China ADS (C-ADS) project proposes to build a 1000 MW Accelerator Driven sub-critical System around 2032. The accelerator will work in CW mode with 10 mA in beam current and 1.5 GeV in final beam energy. The linac is composed of two major sections: the injector section and the main linac section. There are two different schemes for the injector section. The Injector- I scheme is based on a 325 MHz RFQ and superconducting spoke cavities of the same RF frequency and the Injector- II scheme is based on a 162.5 MHz RFQ and superconducting HWR cavities of the same frequency. The main linac design will be different for different injector choices. The two different designs for the main linac have been studied according to the beam characteristics from the different injector schemes.

Proposal of Superconducting Spoke Cavity Development for Electron Accelerators

Proposal of Superconducting Spoke Cavity Development for Electron Accelerators

Superconducting spoke cavities for high-velocity applications

To date, superconducting spoke cavities have been designed, developed, and tested for particle velocities up to ${\ensuremath{\beta}}_{0}\ensuremath{\sim}0.6$, but there is a growing interest in possible applications of multispoke cavities for high-velocity applications. We have explored the design parameter space for low-frequency, high-velocity, double-spoke superconducting cavities in order to determine how each design parameter affects the electromagnetic properties, in particular the surface electromagnetic fields and the shunt impedance. We present detailed design for cavities operating at 325 and 352 MHz and optimized for ${\ensuremath{\beta}}_{0}=0.82$ and 1.

Design study on very low Beta spoke cavity for China-ADS

Very low Beta superconducting spoke cavity is one of the key challenges for the China-ADS project. In this paper, a new structure of 3βλ/2 spoke cavity is first studied in detail. Its RF and mechanical properties are simulated using CST-MWS and ANSYS, and compared with the traditional βλ/2 spoke structure.

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.

Study on the Lorentz detuning and tuning of β = 0.3, 352 MHz spoke cavity

The superconducting spoke cavity has been proposed to accelerate the proton in the low energy section of the high power proton linac for the Accelerator Driven Sub-critical System in China. In this paper, the basic geometric and RF parameters of a β = 0.3, 352 MHz spoke cavity are given, and the Lorenz detuning and tuning are presented.

Development of spoke cavities for the EURISOL and EUROTRANS projects

IPN Orsay is strongly involved within the EURISOL and EUROTRANS projects, especially collaborating to the overall design of their linac architecture. Since a few years, main part of the R&D work is dedicated to the development of superconducting spoke cavities and their associated components (RF coupler, tuning system horizontal cryomodule, etc.). Following the very promising results obtained with our first single-spoke prototype (2-gap, 352 MHz, beta 0.35), a new prototype has been designed and fabricated (2-gap, 352 MHz, beta 0.15) in order to be integrated in a future linac. The mechanical and RF tests, done on this prototype, are presented. Then, an overview of the latest beam dynamics calculations performed to design a linac using spoke cavities will be described.

High-energy ion linacs based on superconducting spoke cavities

The applicability of superconducting TEM-class spoke cavities to high-energy ion linacs is discussed, and detailed designs for two TEM-class, triple-spoke-loaded superconducting niobium resonant cavities are presented. The 345 MHz cavities have a velocity range of $0.4<\ensuremath{\beta}<0.75$ and a beam aperture of 4 cm. Spoke-loaded cavities offer several advantages compared with the higher-frequency elliptical-cell cavities that are currently being developed for this range of particle velocities. The proposed triple-spoke cavities can provide broader velocity acceptance, more accelerating voltage per cavity, reduced heat-load operation at 4.2 K, and increased longitudinal acceptance through the high-energy section. Application to the proposed U.S. rare-isotope accelerator driver linac is discussed in detail.