Abstract
Field emission is one of the most serious issues in the degradation of superconducting cavity performance. However, surveying field emission sources during the cavity performance test (called the ``vertical test'') and cryomodule operation is difficult. Therefore, to precisely investigate electron emissions from the field emission source, we developed a diagnostic system for the energy recovery linac 1.3 GHz nine-cell superconducting cavity for both vertical tests and the cryomodule operation. The developed system is comprised of two types of sensors: a carbon sensor and a Si $p$-$i$-$n$ diode, that measure the temperature rise and the radiation produced by electron emissions, respectively. Rotating the sensor array around the cavity axis in the vertical test provides detailed information on the entire cavity surface. The precise x-ray mapping profile measured by the system in the vertical test enables identification of the local emission source. This paper describes how the field emission source is identified in the vertical test from the standpoint of not only experimental results obtained with the newly developed rotating mapping system but also the detailed approach based on precise simulations. In addition, field emission studies with the optimized instrumentation have been extended to cryomodule tests, both standalone and in the beam line. These developments allow us to monitor changes in the cavity field emission signatures introduced by cryomodule assembly and beam operation.
Highlights
IntroductionProduction of a high gradient field and high-current beam operation is a key requirement for particle acceleration
TO FIELD EMISSION STUDIESProduction of a high gradient field and high-current beam operation is a key requirement for particle acceleration
We described field emission studies conducted in the vertical tests and during cryomodule operation with the KEK-ERL model-2 cavities for the compact ERL (cERL)
Summary
Production of a high gradient field and high-current beam operation is a key requirement for particle acceleration. A superconducting cavity is one of the most promising technologies for accelerating particles owing to the advantage of near-zero electrical resistance of the accelerating cavity surface compared with a normal conducting cavity. In high-energy physics, the linear collider is based on superconducting accelerators with a high gradient accelerating field [1]. Free-electron lasers such as EURO-XFEL [2] and LCLS-II [3] and light sources based on the energy recovery. Linac (ERL) [4] have been designed and constructed as next-generation light sources with superconducting cavities. An ERL-based light source requires reliable high-current beam operation with a high gradient field generated by a superconducting cavity
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