Initial observations of micropulse elongation of electron beams in a SCRF accelerator

TL;DR

This paper reports initial measurements of electron beam bunch lengths in a SCRF accelerator using a streak camera and OTR, revealing bunch lengths from 5 to 16 ps and a compressed sub-ps case, highlighting space charge effects.

Contribution

First implementation of a versatile bunch-length monitor at Fermilab's SCRF accelerator with initial observations of micropulse elongation and compression effects.

Findings

Measured electron bunch lengths from 5 to 16 ps.

Observed a compressed sub-ps micropulse case.

Demonstrated the use of streak camera and OTR for beam diagnostics.

Abstract

Commissioning at the SCRF accelerator at the Fermilab Accelerator Science and Technology (FAST) Facility has included the implementation of a versatile bunch-length monitor located after the 4-dipole chicane bunch compressor for electron beam energies of 20-50 MeV and integrated charges in excess of 10 nC. The team has initially used a Hamamatsu C5680 synchroscan streak camera to assess the effects of space charge on the electron beam bunch lengths. An Al-coated Si screen was used to generate optical transition radiation (OTR) resulting from the beam's interaction with the screen. The chicane bypass beamline allowed the measurements of the bunch length without the compression stage at the downstream beamline location using OTR and the streak camera. We have observed electron beam bunch lengths from 5 to 16 ps (sigma) for micropulse charges of 60 pC to 800 pC, respectively. We also report a compressed sub-ps micropulse case.