MEMORANDUM


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

cc: Division (M7), FEL Coordination Group

From: F. Dylla

Subject: IRFEL Weekly Report Sept. 23-27, 1996

Date: September 27, 1996


Management

On Sept. 24-26 we hosted a workshop on scaling FELs to the megawatt-power class for Northrop Grumman and the Navy High Energy Laser Office. Approximately 50 people attended the workshop which included representation from all the major laboratories in the US with FEL activities. Two classes of baseline machine concepts were examined: (1) a regenerative amplifier and (2) an oscillator with energy recovery. A list of high-level technical issues were identified for working groups to examine the necessary technology extrapolations and technical risks from existing demonstrations to high-power devices of interest to the Navy. Workshop summaries will be distributed to all attendees.

A successful review of the optical cavity design for the IRFEL Demo was held on Sept. 26.

Injector Test Stand

Injector commissioning activities included the following:

1) High frequencies were found to be present on the harp-position potentiometers. They are associated with the stepper-motor controls. New hardware, combined with modification of the software driver, is in development to eliminate current to the harp during the data-acquisition cycle.

2) The software to be used to take transverse emittance data in an automated fashion was successfully tested.

3) The photocathode's quantum efficiency remained relatively constant through the week at between 2.6 and 3.9%.

4) This week we ran beam up to 0.5 mA average current and 13 pC per microbunch. We found that the beamline's ion pumps had problems with ground currents, which were subsequently corrected.

Regarding development of the new HV stack:

1) Final processing of the ceramics for the new stack is finally at hand, about a week behind schedule, with two promised to be available Sept. 30. On Tuesday, 1 October, a representative from Jefferson Lab is slated to pick up the two ceramics from the supplier (WESCO) and take them to HiTemp for brazing. The kovar rings are in machining, and HiTemp is scheduled to start brazing next week.

2) The final ion-implantation samples are being delivered, and the ion-implantation rotisserie parts are undergoing small corrections.

3) Coating the electrodes to test the usability of the FM Technologies' coating for the cathode support tube is about a week behind schedule.

4 Polishing of the new cathode support tube is on time, reaching 600 grit and machining of the Mid Voltage Ring is nearly finished, per schedule.

Fabrication of the injector cryounit is essentially complete, and the cryounit will be installed in the SRF Test Cave on Tuesday, 1 October, where it will undergo acceptance tests.

Accelerator Systems

Testing of the prototype dipole magnet indicates that the field clamps at the magnet apertures didn't suppress fringe fields to within specified levels. Initial design of a saddle-coil configuration, with field clamps that are expected to solve the matter, took place this week. Formally, the dipole magnets are about one month behind schedule, but they are not on the critical path, and this schedule slip is not affecting the Sept. 97 milestone for hardware installation in the FEL Facility.

A detailed set of particle-tracking studies indicates, even under overly pessimistic circumstances, no need for an electron-beam scraper between the cryomodule and the wiggler. Indications are that a scraper placed in the first high-dispersion region of the first recirculation bend will add insurance for low (100-nA-level) beam loss during energy recovery. Additional analysis is slated to quantify this notion.

Designs of multislit apertures (for transverse emittance measurements of the 10 MeV electron beam) and their mountings were completed, as were the associated data-reduction algorithms. There are two designs, one for an unshielded aperture for the 10 MeV dump line to be used in running the injector after it is moved from the ITS to the FEL Facility, and one shielded aperture for the acceleration line preceding the cryomodule to be used in commissioning the FEL. An internal design review is scheduled for next week. If successful, the drawings will be detailed and the hardware will go into fabrication.

A procurement package for all of the shielded beam viewers required for the IRFEL was prepared, signed off, and forwarded to our Procurement Office.


FEL Systems

Wiggler

Final drawings from STI Optronics were delayed due to problems at the vendor's CAD subcontractor. We now expect to receive corrected copies of the final prints next week. This should allow us to approve the mechanical design and start design work on the vacuum chamber and support next week. There should be no impact on the schedule since design approval has been given and parts are being ordered.

Optics

Following approval of the resonator hardware at the Optics Review 9/26 (see management section) procurement of components was initiated with the purchase of optics blanks and vacuum components. A few minor drawing changes were initiated based on suggestions by the engineering review team which examined the drawings in parallel with the scientific staff review. Drawing signoff is expected next week to release components for fabrication. That will allow the component performance tests planned to proceed on schedule later this fall and early winter.

Operations/Commissioning

A list of all the current FEL beam diagnostics has been compiled and posted on the WWW in Section 5-1-7 of Jefferson Lab's FEL documentation. This list constitutes the baseline for the diagnostic suite and determines the associated development plan.

Facility

It was incorrectly reported last week that part of the ceiling had been poured. In fact the forms for the ceiling pour in the west third of the building were established. Those forms were extended this week to the western two thirds of the lower level. In addition walls were extended in the second third, and the pour for the lowest-level floor was completed. Wall forms have been placed in much of the east end. The overall building schedule is on track despite a very wet summer, and no significant problems are currently noted in the design or parts constructed.

Concerning plans for injector reinstallation: Held first installation planning meeting and identified a set of related action items. These include identifying cables needed, reviewing the cable tray layout, and identifying the options for moving or replacing the laser clean room.