Fermilab, Batavia, Illinois, USA
LANL, Los Alamos, New Mexico, USA
CEA/DSM/IRFU, France
We report the direct observations of the correlation of higher order modes (HOMs) generated by off-axis electron beam steering in TESLA-type SCRF cavities and sub-macropulse beam centroid shifts (with the concomitant effect on averaged beam size and emittance). The experiments were performed at the Fermilab Accelerator Science and Technology (FAST) facility using its unique configuration of a PC rf gun injecting beam into two separated 9-cell cavities in series with corrector magnets and beam position monitors (BPMs) located before, between, and after them. The ~100-kHz oscillations with up to 300-μm amplitudes at downstream locations were observed in a 3-MHz micropulse repetition rate beam with charges of 500 and 1000 pC/b, although the effects were much reduced at 100 pC/b. The studies were based on HOM detector circuitry targeting the first and second dipole passbands, rf BPM bunch-by-bunch data, and imaging cameras viewing multi-slit images for emittance assessments at 33 MeV. Initial calculations reproduced a key feature of the phenomena. In principle, these results may be scaled to cryomodule configurations of major accelerator facilities.
Fermilab, Batavia, Illinois, USA
Northern Illinois University, DeKalb, Illinois, USA
The FAST facility at Fermilab recently been commissioned has demonstrated the generation of electron beam within a wide range of parameter (energy, charge) suitable for accelerator-science and beam-physics experiments. This accelerator consists of a photo-electron gun, injector, ILC-type cryomodules, and multiple downstream beam-lines. It will mainly serve as injector for the upcoming Integrable Optical Test Accelerator (IOTA). At the same time we will also carry out a LINAC based intense gamma ray experiment based on the Inverse Compton scattering. It is essential to understand the beam emittance for both experiments. A number of techniques are used to characaterizing the beam emittance including slit based method and quad scan method. An on-line emittance measurement based on multi-slit method is developed so the emittance measured will be immediately available to support further beam optimization. In this report we will present the results from the emittance studies using this tool. We will also present the emittance measurement based on quads scan technique for the high energy beam line.