DOE Revue 913

Proposal Rating : 4/6

1.) Scientific and/or technical merit of the project

The proposal has substantial scientific merit. Increasing the gun high voltage is a clear step towards obtaining the objectives outlined in this proposal . The inverted gun geometry has been shown to at least allow a 3MV/m electric field gradient at the crystal surface when the gun voltage is 200 kV. It is important to note that such a gun routinely operated at 120 kV. The development of electrodes capable of 10MV/m is one possible mean to accomplish the proposals objectives. The proposal did not indicate what the potential was for the successful development of such electrodes.

The scientific and technical merit of this proposal has the following weakness:

The proposal indicates that the NEG pumps are currently pumping down to pressures of [math]10^{-12}[/math] Torr. The proposal identifies the limit of NEG pumps currently used in ultra high vacuum environments as a possible inhibitor to increasing the polarized electron current. The proposal did not indicate that cryo pumps can improve the vacuum. The typical cryo pump can easily go to [math]10^{-8}[/math] and vendors advertise [math]10^{-9}[/math] Torr. There are developments in the field which advertise [math]10^{-13}[/math] Torr cryo pumps just as there are some advertising [math]10^{-13}[/math] NEG pumps. The proposal would be improved by identifying a vacuum pumps which is proven to improve the vacuum by at least a factor of 10 over the current advertised limit of [math]10^{-12}[/math] Torr.

2.) Appropriateness of the proposed method or approach

The proposal seeks to increase available beam current at JLab through changes to the current electron gun and investment in low vacuum pumping technologies. Both of these approaches are focused on improving the vacuum quality within the vacuum chamber. An additional area of research involves a partnership with JLab's SRF Institute for the purpose of improving the smoothness of the niobium electrodes. This is also aimed at improving the vacuum by reducing a potential source of contamination, hydrogen ions. There is every indication that vacuum is a key limiting factor in progressing towards the goal of higher beam currents. The proposal did not provide an indication that this barrier has the potential to be overcome. It may also be prudent to indicate why it is unfeasible to add a second electron gun source that can inject electrons simultaneously with the current gun.

3.) Competency of Personnel

The PI has a well established track record including almost 10 years of experience in JLab's injector group. The PI has also been a Deputy for 5 years. The PI is more than competent to carry out the proposed work.

4.) Reasonableness and appropriateness of the Budget

It was difficult to assess the reasonableness of the materials and supplies costs. The budget materials and supplies section would benefit from an itemized list of supplies and their costs for items beyond $10,000. In particular it is unclear how much a cryo pump system capable of < [math]10^{-12}[/math] Torr would cost to implement.

5.) Relevance to DOE mission

The proposal will improve a well established DOE program at JLab. This is clearly a high priority in DOE's mission.

6.) Leadership within the scientific community.

Jefferson Lab has been a world leader in the development of polarized electron sources. The source produces mA level currents which accelerated to GeV energies for use by international collaborations in many nuclear physics experimental programs. The demands of the nuclear physics program drive the accelerator to perform well beyond its original design. The proposed development of a higher current source is the next progressive step towards meeting the high demands of the nuclear physics program.