Public Abstract

DE-SC0021426: Superconducting RF electron gun

Award Status: Active

Institution: Research Foundation for the State University of New York d/b/a RFSUNY - Stony Brook University, Stony Brook, NY
UEI: M746VC6XMNH9
DUNS: 804878247

Most Recent Award Date: 11/08/2024
Number of Support Periods: 2
PM: Farkhondeh, Manouchehr

Current Budget Period: 11/01/2021 - 10/31/2026
Current Project Period: 11/01/2020 - 10/31/2026
PI: Litvinenko, Vladimir

Supplement Budget Period: N/A

Public Abstract

High-current low-emittance CW electron beams are of great importance for existing and future DOE facilities, medical, industrial and homeland security applications, and beyond. Such beams are indispensable for nuclear and high-energy physics fixed target and collider experiments, cooling high energy hadron beams, generating CW beams of monoenergetic X-rays (in FELs) and γ-rays (in Compton sources), high-power EUV beams for manufacturing the next generation of microchips, border cargo inspection, to mention just a few. Polarization of electrons in these beams provides extra value by opening a new set of observables and frequently improving the data quality by boosting signal to background ratio. The CW super-conducting radiofrequency (SRF) electron gun is one of the most advanced, but also one of the most challenging, technologies promising to deliver such beams. While SRF technology is paving the way for the future accelerators, the compatibility of advanced SRF technology with complex photocathodes remains on the forefront of the modern accelerator science, and many important questions remain unanswered. SRF cavities that operate at cryogenic temperatures naturally work as a powerful cryo-pump to provide the ultra-high vacuum environment for photocathodes by freezing harmful gas species. Still, multiple effects can affect efficiency and even survival of high quantum efficiency and polarized photocathodes. The necessity to keep the photocathodes at room temperature while being surrounded by cryogenic temperature creates additional complexity for SRF gun design and operation. Complex and volatile chemical compounds used for photocathodes could contaminate surfaces of the SRF cavity. Such high QE compounds could create centers for cold electron emission which degrades performance of the SRF gun. Such a circumstance would require development of the in-situ processing techniques for restoring the SRF cavity performance. We propose to upgrade the unique and fully functional CW SRF facility installed at RHIC facility (BNL) by adding high-current and polarized beam capabilities. Our 1.25 MeV SRF gun has demonstrated sustained CW operation generating electron bunches with record-low transverse emittances and record-high bunch charges. The cathodes survive many months of continuous operation. Nevertheless, the average beam current, determined by the needs of the project, is limited to about 100 microamperes. We propose to extend the capabilities of this system to high average current of 100 milliampere in two steps: increasing the current 30-fold at each step. The goal of this R&D is to demonstrate reliable long-term operation of the high-current low-emittance CW SRF guns. We also propose to test polarized GaAs photocathodes in the ultra-high vacuum environment of the SRF gun. The upgrades include the cathode preparation and UHV cathode transfer system, and a polarimeter to measure polarization of the generated electron beam. Finally, we propose to optimize in-situ processing, including both He treatment and plasma processing, for restoring and improving performance of our gun’s quarter-wave SRF cavity. Our proposed research will significantly advance state-of-the art accelerator capabilities relevant to existing and next-generation nuclear physics facilities and it will address areas of special interest: (1) Transformative accelerator R&D in next generation ion and electron sources, and (2) Transformative accelerator R&D in SRF technology for restoring cryomodule performance at SRF-based accelerator facilities. One example is R&D to establish practical and reproducible in-situ plasma processing techniques. A collaboration of experts in the SRF technology and high brightness electron guns – both unpolarized and polarized - from Stony Brook (SBU)), Brookhaven National Laboratory (BNL), FERMI National Accelerator Laboratory (FNAL) and Thomas Jefferson National Accelerator Facility (TJNAF) is uniquely able to address the DOE need for novel CW sources of polarized and unpolarized electron beams. Each of the collaborating institutions brings unique skills critical for the overall success of the proposed research program. Finally, the use of an existing and operational $20M SRF facility at BNL makes this proposal very cost effective.

High-current low-emittance CW electron beams are of great importance for existing and future DOE facilities, medical, industrial and homeland security applications, and beyond. Such beams are indispensable for nuclear and high-energy physics fixed target and collider experiments, cooling high energy hadron beams, generating CW beams of monoenergetic X-rays (in FELs) and γ-rays (in Compton sources), high-power EUV beams for manufacturing the next generation of microchips, border cargo inspection, to mention just a few. Polarization of electrons in these beams provides extra value by opening a new set of observables and frequently improving the data quality by boosting signal to background ratio.

The CW super-conducting radiofrequency (SRF) electron gun is one of the most advanced, but also one of the most challenging, technologies promising to deliver such beams. While SRF technology is paving the way for the future accelerators, the compatibility of advanced SRF technology with complex photocathodes remains on the forefront of the modern accelerator science, and many important questions remain unanswered.

SRF cavities that operate at cryogenic temperatures naturally work as a powerful cryo-pump to provide the ultra-high vacuum environment for photocathodes by freezing harmful gas species. Still, multiple effects can affect efficiency and even survival of high quantum efficiency and polarized photocathodes. The necessity to keep the photocathodes at room temperature while being surrounded by cryogenic temperature creates additional complexity for SRF gun design and operation. Complex and volatile chemical compounds used for photocathodes could contaminate surfaces of the SRF cavity. Such high QE compounds could create centers for cold electron emission which degrades performance of the SRF gun. Such a circumstance would require development of the in-situ processing techniques for restoring the SRF cavity performance.

We propose to upgrade the unique and fully functional CW SRF facility installed at RHIC facility (BNL) by adding high-current and polarized beam capabilities. Our 1.25 MeV SRF gun has demonstrated sustained CW operation generating electron bunches with record-low transverse emittances and record-high bunch charges. The cathodes survive many months of continuous operation. Nevertheless, the average beam current, determined by the needs of the project, is limited to about 100 microamperes. We propose to extend the capabilities of this system to high average current of 100 milliampere in two steps: increasing the current 30-fold at each step. The goal of this R&D is to demonstrate reliable long-term operation of the high-current low-emittance CW SRF guns. We also propose to test polarized GaAs photocathodes in the ultra-high vacuum environment of the SRF gun. The upgrades include the cathode preparation and UHV cathode transfer system, and a polarimeter to measure polarization of the generated electron beam.

Finally, we propose to optimize in-situ processing, including both He treatment and plasma processing, for restoring and improving performance of our gun’s quarter-wave SRF cavity.

Our proposed research will significantly advance state-of-the art accelerator capabilities relevant to existing and next-generation nuclear physics facilities and it will address areas of special interest: (1) Transformative accelerator R&D in next generation ion and electron sources, and (2) Transformative accelerator R&D in SRF technology for restoring cryomodule performance at SRF-based accelerator facilities. One example is R&D to establish practical and reproducible in-situ plasma processing techniques. A collaboration of experts in the SRF technology and high brightness electron guns – both unpolarized and polarized - from Stony Brook (SBU)), Brookhaven National Laboratory (BNL), FERMI National Accelerator Laboratory (FNAL) and Thomas Jefferson National Accelerator Facility (TJNAF) is uniquely able to address the DOE need for novel CW sources of polarized and unpolarized electron beams. Each of the collaborating institutions brings unique skills critical for the overall success of the proposed research program. Finally, the use of an existing and operational $20M SRF facility at BNL makes this proposal very cost effective.