Li, Zenghai | Engineering Papers

DOE OSTI2024

Higher Order Multipole Analysis of Beam Crabbing Mode at 197 MHz for Electron-Ion Collider

In the local crabbing scheme for Electron Ion Collider interaction region, beam rotation is initiated by one set of crab cavities at a high beta region with near 90 deg phase advance to the interaction point (IP), and ceased by an identical set of cavities on the symmetrically opposite side. The fundamental mode of all crab cavities is designed to apply a momentum kick to the particle bunches to complete this half cycle of rotation in the horizontal plane, meanwhile the electromagnetic (EM) field can be expanded into a series of harmonics. Despite the lowest dipole mode, higher harmonics cause instabilities during beam operation and loss of particles. We used SimTrack, which is the 6-d symplectic element-by-element tracking code developed at Brookhaven National Laboratory in 2015, to study the threshold of each higher-order harmonic multipolar mode with the criteria of maintaining a dynamic aperture of 6 σ or greater for the Hadron Storage Ring (HSR). In this paper, we showed the threshold for each higher harmonic multipole and their comparison with the multipole strength for the current crab cavity design.

43 PARTICLE ACCELERATORS↗

DOE OSTI2024

Improving Cathode Testing with a High-Gradient Cryogenic Normal Conducting RF Photogun

Future electron accelerator applications such as X-ray free electron lasers and colliders are dependent on significantly increasing beam brightness. With the observation that linac beam manipulation’s best preservation of max brightness is at the cathode, we are incentivized to create an environment where we can study how to achieve the highest possible photogun brightness. In order to do so, we intend to extract beams from high-brightness photocathodes with the highest achievable accelerating gradients we can manage in a klystron-powered radiofrequency (RF) photogun. We utilize here cryogenic normal conducting cavities to achieve ultra-high gradients via limitation of breakdown rates (BDR). The low temperatures should also reduce cathode emittance by reducing the mean transverse energy (MTE) of electrons near the photoemission threshold. To this end, we have designed and produced a new CrYogenic Brightness-Optimized Radiofrequency Gun (CYBORG) for use in a new beamline at UCLA. We will introduce the enabling RF and photoemission physics as a primer for the new regime of high field low temperature cathodes we intend to enter. We further report the current status of the beamline commissioning, including the cooling of the photogun to 100 K, and producing 0.5 MW of RF feed power, which corresponds to cathode accelerating fields in the range of 80–90 MV/m. We further plan iterative improvements to both to 77 K and 1 MW corresponding to our ultimate goal >120 MV/m. Our discussion will include future beamline tests and the consideration of the initial realization of an ultra-high-gradient photoinjector concept.

Lawler, Gerard Emile (ORCID:0000000160113435)↗