Abstract
Multipacting (MP) in higher-order-mode (HOM) couplers of the International Linear Collider (ILC) baseline cavity and the Continuous Electron Beam Accelerator Facility (CEBAF) 12 GeV upgrade cavity is studied by using the ACE3P suites, developed by the Advanced Computations Department at SLAC. For the ILC cavity HOM coupler, the simulation results show that resonant trajectories exist in three zones, corresponding to an accelerating gradient range of $0.6--1.6\text{ }\text{ }\mathrm{MV}/\mathrm{m}$, $21--34\text{ }\text{ }\text{ }\mathrm{MV}/\mathrm{m}$, $32--35\text{ }\text{ }\mathrm{MV}/\mathrm{m}$ and $>40\text{ }\text{ }\mathrm{MV}/\mathrm{m}$, respectively. For the CEBAF 12 GeV upgrade cavity HOM coupler, resonant trajectories exist in one zone, corresponding to an accelerating gradient range of $6--13\text{ }\text{ }\mathrm{MV}/\mathrm{m}$. Potential implications of these MP barriers are discussed in the context of future high-energy pulsed as well as medium-energy continuous wave accelerators based on superconducting radio frequency cavities. Frequency scaling of MP's predicted in HOM couplers of the ILC, CEBAF upgrade, Spallation Neutron Source (SNS), and Free-Electron Laser in Hamburg (FLASH) third harmonic cavity is given and found to be in good agreement with the analytical result based on the parallel plate model.
Highlights
Multipacting (MP) is a phenomenon of resonant electron multiplication in which some specific inner surface areas of a radio frequency device are repeatedly bombarded by electrons that gain energy from the rf field contained in the device [1,2]
Frequency scaling of MP's predicted in HOM couplers of the International Linear Collider (ILC), Continuous Electron Beam Accelerator Facility (CEBAF) upgrade, Spallation Neutron Source (SNS), and Free-Electron Laser in Hamburg (FLASH) third harmonic cavity is given and found to be in good agreement with the analytical result based on the parallel plate model
Our simulation predicts a MP barrier in the gradient range of 6–13 MV=m in zone 1 of a CEBAF upgrade cavity
Summary
Multipacting (MP) is a phenomenon of resonant electron multiplication in which some specific inner surface areas of a radio frequency (rf) device are repeatedly bombarded by electrons that gain energy from the rf field contained in the device [1,2]. By adopting an elliptical profile in an axially symmetric cavity operated in the TM010 mode, “hard” MP's [5] in which electrons may gain energy of hundreds of electronvolts, can be fully avoided [6,7] This has allowed successful applications of elliptical SRF cavities for electron acceleration A commonly used HOM damper in a SRF cavity is a coaxial-type coupler, such as the one originally developed for the 1300 MHz Tera Electron Volt Energy Superconducting Linear Accelerator (TESLA) cavity [8]. The TESLA-style HOM coupler has been adopted in SRF cavities for the SNS, the energy doubling of CEBAF from 6 to 12 GeV, the European X-Ray Free Electron Laser (XFEL), and the proposed International Linear Collider (ILC). It is of great interest to compare the MP characteristics of the two
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