• H. Bluem, D. Holmes, T. Schultheiss
  AES, Medford, NY
• I. Ben-Zvi, A. Burrill, J. Kewisch, D. Pate, T. Rao, R.J. Todd, E. Wang, Q. Wu
  BNL, Upton, Long Island, New York

Funding: AES is funded under DOE SBIR contract #DE-FG02-06ER84450. BNL work is performed under DOE contract #DE-AC02-98CH10886.

The use of an RF electron gun with a magnetized cathode in place of a DC gun for ILC may reduce the requirements for emittance damping rings. Maintaining adequate lifetime of the necessary cathode material requires vacuum levels in the 10^-11 torr range. While vacuum levels around the 10^-9 torr range are common in a normal conducting RF gun, the cryogenic pumping of the cavity walls of a superconducting RF (SRF) gun may maintain vacuum in the range needed for GaAs cathode longevity. Advanced Energy Systems, Inc. is collaborating with Brookhaven National Laboratory to investigate the generation of polarized electron beams using a SRF photocathode gun. The team is developing an experiment to study the quantum lifetime of a GaAs cathode in a SRF cavity and investigate long term cavity performance while integrated with a cesiated GaAs cathode*. In addition to the experimental investigation, a design is being developed that is compatible with the production of high aspect ratio polarized electron beams. The mechanical and physics aspects of this design will be discussed.

*J. Kewisch, et. al., Presentation at PAC09.

• J. Kewisch, I. Ben-Zvi, A. Burrill, D. Pate, T. Rao, R.J. Todd, E. Wang, Q. Wu
  BNL, Upton, Long Island, New York
• H. Bluem, D. Holmes, T. Schultheiss
  AES, Medford, NY

Funding: Work supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. Department of Energy.

Gallium arsenide cathodes are used in electron guns for the production of polarized electrons. In order to have a sufficient quantum efficiency lifetime of the cathode the vacuum in the gun must be 10^-11 torr or better, so that the cathode is not destroyed by ion back bombardment. All successful polarized guns are DC guns, because such vacuum levels can not be obtained in normal conducting RF guns. A superconductive RF gun may provide a sufficient vacuum level due to cryo-pumping of the cavity walls. We report on the progress of our experiment to test such a gun.

• J.J. Sredniawski, D. Holmes, T. Schultheiss
  AES, Medford, NY

Funding: Work supported by The Department of Energy under SBIR Contract DE-FG02-08ER85054

From past work we found that within the cost of the String Assembly that dominates the overall cost of the cryomodules for ILC, the greatest cost elements are the helium vessel with the 2 phase pipe assembly, the niobium material, and the SRF cavity fabrication*. The cost of niobium is dependant upon market supply and demand and is essentially out of our control. We have carried out an aggressive study to reduce the cost of cavity fabrication in a high production environment**, which leaves the helium vessel for further investigation. It is recognized that significant cost savings may be realized if the helium vessel could be constructed of stainless steel instead of titanium material as is currently planned. To facilitate this change (AES) has designed a niobium to stainless steel transition assembly that will interface the helium vessel to the SRF Cavity at each end. Details of the design and analysis of the low cost helium vessel assembly are discussed along with potential cost reductions for the ILC high production run.

*E. Bonnema, J. Sredniawski,"ILC RF Unit Industrial Cost Study Methodology & Results"
**A. Favale, J. Sredniawski, M. Calderaro, E. Peterson,"ILC Cavity Fabrication Optimization for High Production"