To: J. Cook, D. Helms, W. Skinner

cc: Division (M7), FEL Coordination Group

From: F. Dylla

Subject: IR Demo Project Weekly Report, March 16-20, 1998

Date: March 20, 1998

FEL Management

The highlight for this week was a very successful effort of linac commissioning which started with the recommissioning of the photogun and ended with delivery of the required CW beam (2 microamps at 38 MeV) to process the polarized deuterium targets for Nuclear Physics. Commissioning activities were suspended as scheduled on Thursday to allow the polarized target irradiation hardware to be installed in front of the tune-up dump. These experiments will last for approximately a week and then commissioning will re-commence after removal of the irradiation hardware.

On Wednesday, March 18th the FEL project technical and monthly report for February 1998 was completed and forwarded to the DOE and Navy Program Offices.

One of our local universities, Norfolk State, was recently notified that NSU's Materials Research Laboratory was on a short list for a multiple-year NSF CREST grant. On Wednesday NSF sent a visiting review team to NSU. F. Dylla was asked to review NSU's proposed and on-going collaborations with the FEL User Facility and the ARC. The review appeared to go well and a successful grant will strengthen our NSU proposed experiments with the FEL.

This week, two additional candidates for William and Mary's proposed new professorship in atomic, molecular and optical physics came through for discussions and interviews with the FEL staff. All four candidates would make excellent additions to this discipline in the local university community.

Installation Activities

The installation of the 180 dipole and vacuum chamber on the west arc was completed after minor modifications to increase the viewer visibility. The vacuum chamber for the 180 dipole was installed for fit-up measurements prior to final assembly on a future machine maintenance day.

The present configuration of the Machine Protection System (MPS) was checked out and is operational for first light beam characteristics (1.1mA).

Particulate contamination was observed within the optical transport system. The piping and mirror cans were removed during the polarized target installation period for cleaning. We hope to re-install the system next week during the two day period scheduled for removal of the irradiation hardware. The source of the contamination was not identified.

Commissioning

With this week's successful commissioning of the injector and linac with cw electron beam up to about 8 µA, we are ready to begin GEN target irradiation and will start ASAP this afternoon. M. Seely led a discussion of the associated procedure and technical details. Some highlights are:

- The FEL operator, not the Physics Division participant, will have final say in the respective shift activities. We all expect collegial communications, but the attendees felt it important to establish unambiguously the "crew chief".

- Per Physics Division request a couple of weeks ago, GEN target irradiation will be controlled from the FEL Control Room rather than the MCC due to the use of some specialized diagnostic equipment and cabling for the equipment.

- Warm target will require 8-10 hours of 2 µA irradiation, and cold targets will require 5-6 hours of 2 µA irradiation.

- A ceramic viewer with a hole, along with a monitoring camera, will be installed to monitor beam position on the target. CTR may be sufficient to look at the whole beam profile (we'll see tonight). The ceramic will tolerate up to 80 µA current.

- Target irradiation does not require precise delivery of dosage. A factor-of-two measurement of electron-beam current is more than sufficient. We will therefore use the BCM cavity on the linac as the principal current monitor. It was tested this week with beam and "calibrated" against the picoammeters on the straight-ahead dump.

- The cold dewar will be located at the downstairs elevator foyer until it is needed in the beamline. The dewar needs to be topped off about every 8 hours. When the dewar is moved into the vault, we will not have both access doors closed with the dewar and a person inside (for ODH safety). Rather, one door will remain open in the process, which is eminently doable since at least two people will be involved.

- An approximately uniform beam (at the 10% level) is needed across the target. We will therefore leave the raster magnet on during irradiation, per our original plan.

- Everyone is looking forward to the upcoming activity. The discussion was very good.

L. Merminga followed with a presentation of beam-breakup (BBU) modeling results given the latest measurements of higher-order modes in the cryomodule. The simulations were for two passes with energy recovery. The threshold current is calculated to be about 25-30 mA. Accordingly, we might be able to tune the HOMs in such a way as to "make" BBU for observation and experiments. During nominal operation with 5 mA beam, BBU should not be a problem. D. Douglas indicated it may be possible to run with three passes and amplify the BBU by another factor of order two, so there are interesting possibilities for experiments. Ultimately, the interest is ascertaining what is a sufficient safety margin with regard to BBU when one designs higher-current machines.