Coupler induced transverse kick and emittance growth in single cell elliptical cavities of 10 MeV superconducting electron linac injector

• Published in: Journal of instrumentation Vol. 10; no. 3; p. T03001
• Main Authors: Dechoudhury, Siddhartha, Pandey, Hemendra Kumar, Dutta, Dipta Pratim, Naik, Vaishali, Chakrabarti, Alok, Chao, Yu-Chiu, Laxdal, Robert E.
• Format: Journal Article
• Language: English
• Published: 02.03.2015
• Subjects: Couplers; Electron beams; Emittance; Holes; Injectors; Mathematical analysis; Modules; Superconductivity
• ISSN: 1748-0221; 1748-0221
• DOI: 10.1088/1748-0221/10/03/T03001

A Capture Cryo Module (CCM) consisting of two single cell 1.3 GHz, [beta] = 1, niobium cavities is being developed for the superconducting electron linac injector at VECC. Electron beam of 100 keV and 2 mA from a thermionic gun will be accelerated in the CCM and thereafter in an Injector Cryo Module (ICM) to 10 MeV. Single cell cavities in the CCM are independently phased and a coaxial TTF-III coupler is chosen for rf power coupling into each cavity. The presence of the coupler perturbs the field symmetry of the cavity introducing local transverse kicks to the incoming electron beam in the coupler region. Numerical analysis taking into account the changing velocity profile as well as the off-axis field seen by the electron as it moves through the cavities has been carried out for estimating the kick. The variation of the kick with longitudinal position of electrons in the beam bunch introduces transverse emittance growth. This has been calculated using the field seen by the electron. The analytical calculations are compared with results from particle tracking with simulated 3D fields. It is found that coupler induced kick does not appreciably change the emittance values at 10 MeV.