MEMORANDUM


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

cc: Division (M7), FEL Coordination Group

From: F. Dylla

Subject: IR Demo Project Weekly Report, December 1-5, 1997

Date: December 5, 1997

Management:

Highlights for the week include: confirmation of the acceleration capabilities of the injector quarter-unit to be 9.6 MeV/c; readiness for low current beam operation through the linac cryomodule until beam operations were suspended late Tuesday due to a valve failure; and good progress on preparing the remainder of the first light beamline for vacuum pumping.

Preparations were made for next week's visit by Congressional staffers from the Energy and Water Committee on Tuesday, Dec. 9, and by MTAC on Dec. 9-10.

Discussions continued with the management of NASA Langley Research Center concerning a joint presentation to the NASA Chief Technologist on Dec. 15th on a proposed NASA competition for research proposals to use the IR FEL.

Monthly progress reports that were completed last week for both the construction and upgrade projects for October 1997 were distributed to the Navy and DOE Program Offices on Monday, Dec. 1.

Installation Activities

The RF software was upgraded this week to fix several bugs. A newly installed code from a different application was consuming too much computer bandwidth. The RF code faulted itself for being too slow. The RF code is being tested again today with additional work set next week.

SRF commissioning is expected to be finished this evening with the cavity Q measurements. RF commissioning will be finished when the final coefficients are determined. (More details in the commissioning report below.)

All vacuum connections for the machine through the 1G, recirculation dump, have been made and pumped down. The vacuum chambers for the 2F, optical section, and 2G, straight ahead dump, are completed and installed. Pumpdown is planned for next week. LCW and instrument air connections have been made to all installed equipment. The shield stand for the 2G dump is installed.

The girders have been installed for both arcs. Mechanical fit-up for the 180° vacuum chambers is underway. Three DX magnets for the arcs have been installed.

The wiggler viewers have been checked several times using several methods and have been shown to be reproducibly aligned to within 100 microns of the axis defined by the first and last quadrupoles on the wiggler girder. Apertures have been set up on the optical benches for the optical cavity which define this aperture in the absence of accessibility to the quadrupole surfaces. The vacuum chambers around the wiggler were successfully installed and the viewer positions rechecked. Viewer assemblies were installed. It was found that one of the sets of lenses for these assemblies was the wrong focal length. It was possible to move components around to compensate for this and get an image of viewers one and two. The third awaits wiring of the power for the camera which should be done this weekend. The position of the resonator mirror mounts was measured and found to be within approximately one mm or less of the axis defined by the quadrupoles. This is 2% of the mirror aperture and is quite adequate.

Commissioning Activities

We ran tune-up beam to the injector dump at currents up to about 1µA, and measured momenta ranging up to 9.6 Mev/c to within ±10% accuracy, at which both cryounit cavities were operating on crest. Accordingly, momentum measurements were consistent with expectations given the cryounit cavity gradients established during SRF commissioning. The discrepancy in beam momentum versus SRF gradient that was reported two weeks earlier was traced to a 3 dB miscalibration, with the consequence that the gradients displayed on the screen in the control room are a factor of two off. The cause remains uncertain, but it is a simple matter to correct the control screen readouts. Cavity gradients reported from SRF commissioning of the cryounit were verified to be correct.

On 2 Dec. 97 we were preparing to put beam into the cryomodule, precisely on schedule. Upon being unlocked, the vacuum valve preceding the cryomodule stuck in the open position, leaving the cryomodule vulnerable to vacuum leaks in the upstream beamline. At this point beam operations were suspended. Concerted attempts to unstick the valve failed, and more intrusive techniques were rejected for fear of introducing a vacuum leak through the valve. The valve must be replaced, and there is a day-for-day slip in the commissioning schedule as we await replacement. Resumption of beam operations is projected for swing shift next Friday, 12 Dec. 97.

The "window of opportunity" presented by seizure of the valve is being used to measure the unloaded Qs of the cryounit cavities, an activity that began last night and will be completed tonight.

Plans for replacing the stuck valve are as follows: Two new valves are on order from VAT in Switzerland, and they are likely to be shipped today (but a small possibility exists that they would not be shipped until next Friday). Once we receive them, probably next Wednesday, we'll need to dismantle them, clean them, reassemble them, and put them through several cycles prior to installation, now projected for next Friday, 12 Dec. 97. Cryomodule warmup requires care and ideally should be done slowly, so plans are to begin warmup after finishing the unloaded Q measurements tonight. Cooldown will be rapid, projected to start the evening of 12 Dec. 97 and be complete to 2K 12-16 hours later, making the cryomodule ready to accept beam next Saturday.

A revised shift schedule was developed leading into Christmas. It provides for both running tune-up beam to the straight-ahead dump and generating 60 pC bunch charges (per first-light requirements) with which to check out emittance and bunch-length diagnostics.