Experimental demonstration of the correction of coupled transverse dynamics aberration in an rf photoinjector

Abstract

The production of electron bunches with low transverse emittance approaches the thermal emittance of the photocathode as various aberrations are corrected. Recently, the coupled transverse dynamics aberration was theoretically identified as a significant source of emittance growth and a corrector magnet was proposed for its elimination [D.H. Dowell, F. Zhou, and J. Schmerge, PRAB 21, 010101 (2018)]. This aberration arises when the beam acquires an asymmetric distribution that is then rotated with respect to the transverse reference axis thus introducing a correlation in the vertical and horizontal planes. The asymmetry is introduced by a weak quadrupole field in the rf gun or emittance compensation solenoid and the rotation is caused by the solenoid. This Letter presents an experimental study of the coupled transverse dynamics aberration in an rf photoinjector and demonstrates its elimination by a quadrupole corrector consisting of a normal and a skew quadrupole. The experimental results agree well with theoretical predictions and numerical simulations. The study also demonstrates the emittance of a low charge beam can be preserved during transportation at its thermal value, which was 1.05 mm mrad/mm, for the cesium telluride photocathode and 248 nm UV laser used.

arXiv comment5 pages, 4 figures

References in corpus (5)

• Direct measurement of sub-10 fs relativistic electron beams with ultralow emittance
• Commissioning experience and beam physics measurements at the SwissFEL Injector Test Facility
• Exact Cancellation of Emittance Due to Coupled Transverse Dynamics in Solenoids and RF Couplers
• Spatial Control of Photoemitted Electron Beams using a Micro-Lens-Array Transverse-Shaping Technique
• Overestimation of thermal emittance in solenoid scans due to coupled transverse motion

Cited by in corpus (7)

• Transverse phase space characterisation in the CLARA FE accelerator test facility at Daresbury Laboratory
• Four-Dimensional Emittance Measurements of Ultrafast Electron Diffraction Optics Corrected Up to Sextupole Order
• Single shot cathode transverse momentum imaging in high brightness photoinjectors
• Rapid thermal emittance and quantum efficiency mapping of a cesium telluride cathode in an rf photoinjector using multiple laser beamlets
• Ampere-class Bright Field Emission Cathode Operated at 100 MV/m
• Eliminating uncertainty of thermal emittance measurement in solenoid scans due to rf and solenoid fields overlap
• Analysis of Skew Quadrupole Compensation in RF-Photoinjectors