MEMORANDUM

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

cc: Division (M7), FEL Coordination Group

From: F. Dylla

Subject: IRFEL Weekly Report, May 12-16, 1997

Date: May 16, 1997

Management

The Office of the Secretary of Defense released $6M of Fiscal 1997 funding to the Office of Naval Research to support the Navy High Energy Laser (HEL) Program. Follow-up discussions are underway between the Navy HEL Program Office, Jefferson Lab, and the DOE Site Office concerning the allocation of the funding. A revised Navy-DOE memorandum of Agreement supporting release of the new funds to Jefferson Lab is in preparation. A portion of the Fiscal 97 funds would be used for commissioning the baseline IR FEL Demo and to begin the design and fabrication of an upgrade of the IR Demo. A revised proposal for the upgrade reflecting the use of both Fiscal 97 and potential Fiscal 98 DOD was prepared and forwarded to the Navy HEL Program office.

A draft agenda for the June 9-10 Maritime Technical Advisory Committee (MTAC) meeting was prepared. The agenda was reviewed by the SURA president and forwarded to the MTAC chairman for his comments.

Mike Kelley, chairman of the LPC, visited the Lab on May 14 to discuss preparations for the upcoming June 25-26 LPC meeting and draft agreements to cover the loan and consignment of LPC supplied equipment for the FEL User Facility.

A total of 14 papers related to the FEL project were presented by members of the Accelerator Division at this week's Particle Accelerator Conference in Vancouver, Canada.

Technical highlights for the week included the arrival of the wiggler from STI Optronics on Monday and operation of the gun at 420 kV for significant periods of time. However, there may be problems due to potential mishandling of the wiggler by the shipping agent. Details are given below. With regard to operation of the gun, even though the high voltage stack could successfully withstand 420 kV, we found that the GaAs photocathode could not be properly conditioned and had to be removed and replaced by week's end. Again, details are given below. Significant progress was made in the continued fabrication of the User Facility and the critical path electron beam transport components.

Injector Test Stand

The week's activities on the injector test stand can be characterized as exhausting, frustrating but in the end instructive. At the end of last week the photogun was suffering from high field emission from localized spots on the GaAs photocathode. Successive attempts from last Friday to this Wednesday to eliminate the field emission dark current by HV conditioning and reforming the cathode surface by the standard cathode heating/recesiation process failed. By holding the cathode at high voltage the dark current would decrease with time constants of several hours but the quantum efficiency fell with a similar time constant so that by the time the dark current was suppressed the field emission activity had poisoned the photoemission characteristics of the cathode. There appeared to be a fundamental reason for appearance of field emission sites on the cathode. On Wednesday evening we decided to vent the gun HV assembly to remove and replace the cathode. At the same time we would reintroduce the cathode/anode spacer which lowers the cathode field in case this change which was introduced in the new HV assembly also affected the field emission characteristics of the cathode. On Thursday a novel modification was made to the gimballed mount of the photogun which allowed the assembly to be rotated for disassembly without affecting the beamline valve, thus preserving the beamline vacuum and two weeks of schedule. By the end of the day on Friday, the photogun was reassembled and under vacuum with a new hydrogen cleaned, photocathode and the assembly was being prepared for bakeout. We expect to re-start gun operations on May 27th.

Upon initial examination of the GaAs photocathode we noticed a series of pits that could be resolved by eye on the GaAs surface. These pits could be field emission sites and should not be present. The cause of these pits is unknown at this time until we do a more careful microscopic examination of the GaAs surface.

On the positive side for the weeks events with the ITS: significant HV conditioning of the new stack assembly occurred because of the campaign to reduce the dark current. On Monday evening the stack assembly was held at 420 kV for more than 12 hrs. In addition, the laser was operated continuously for 91 hours in support of anticipated gun experiments, and for software upgrades. We now have remote control of the DC bias for all EO modulators, and control of the rf level for the divide-by-two EO modulator. We conducted additional tests of the divide-by-two EO modulator and found that our rf amplifier has insufficient output to create full modulation. We will continue tests once we find an rf amplifier with higher output.

Regarding warm window fabrication activities for the ITS cryounit tests:

A replacement for the warm window assembly that failed during the mild bakeout tests last week is still in fabrication at our electron beam welder. This window uses a low loss alumina from Japan. Four additional ceramics (from one of standard supplier-Ceradyne) were sent for air firing which has been shown to substantially reduce the rf losses. These materials will be back next week for rf testing.

Accelerator Systems

Regarding Fabrication of the Magnets

The sextupole coils contract was awarded to MEI, of Oakland, CA. The long Panofsky magnet (QI) drawing package is complete and ready for review. The QG quadrupole magnets were released for installation (dated 5/9/97). The DU/DV dipole magnets are in the final machining stage at Master Machine. The DG dipole (air core prototype) was awarded to Syntronic Inc. The first article core for the optical chicane (DW) dipoles is ready for inspection at Everson Electric. The coils for the DW dipoles are all complete and shipped to Jefferson Lab.

Regarding Fabrication of the Vacuum System

The optical chicane chamber fabrication drawings are complete. The vendor bid process was initiated. The wiggler adjacent vacuum tube fabrication drawings have been signed off and the assembly drawing awaits final sign off by the WBS manager. The Backleg girder assembly drawings are all signed off and girder assembly is in process. East and West return bend chamber detail drawings have started.

Regarding Fabrication of the Cavity Pairs and Cryounits for the Cryomodule

Cavity Pair #1: Instrumentation wiring completed this week. This is the last work needed for the unit and it will be pushed over early next week to cryomodule assembly. Cavity Pair #2: Installation of spacer flanges on Thursday, next insertion into helium vessel next week. Cavity Pair #3: Vertical testing this week complete with helium processing. Excellent performance was achieved on this pair. The top cavity reached gradients greater than 17 MV/m. The bottom cavity initially had heavy field emission but was helium processed to a useable gradient of 11-12 MV/m. Next week final alignment check and turnover to cryounit assembly. Cavity Pair #4: Start of vertical test late this week. Will continue with helium processing next week and possible turnover to cryounit assembly.

Regarding Fabrication of Instrumentation and Controls

Two motor control (OMS) chassis have been built up and one in progress. FEL Control Room Racks have been organized and placed in the FEL Building. Fabrication continues on the Vacuum System crates and the ion pump power supply printed circuit board.

Regarding Fabrication of Cryogenic Systems

The warm gas lines and sleeve transfer lines were inserted into the facility penetration sleeves. We started connections of gas lines in the tunnel to gas lines in sleeves and also started sub-assemblies for gas lines around the expansion can. We completed hydrostatic pressure test of the 5" bayonet gate valve.

FEL Systems

Wiggler

The wiggler was received for STI Optronics on Monday, 5/12/97. Unfortunately all shock sensors indicated a vertical drop of > 5 G's had occurred at some point in shipment. There was no obvious physical damage to the crate or the wiggler and it is probable that no damage was done. Our intent at this time is to perform some careful physical measurements to the system and determine if our values agree with those taken at STI. We will also perform some level of magnetic field testing although it is impractical for us to perform the same level of measurement that STI has already done. We will decide the next step based on the results of those tests. The rest of the wiggler associated components are being assembled on the wiggler optical bench.

Optics

Drawings for the collimator were signed and sent to Procurement. We are now starting work on miscellaneous stands for the mirror cans, and the mirror cassettes in the User Labs. The bellows assemblies are being brazed to the cooled mirror holders, essentially the last machining step to complete the optical cavity assemblies. Tests continue on the software to control and monitor the gimbal mount's position. Brazing tests to mount calcium fluoride substrates into the mirror holders are in progress.

Commissioning/Operations

The commissioning meetings this week were canceled due to the Particle Accelerator Conference in Vancouver.

Facility

Work continued at a high pace this week. Electricians were pulling cables to all the switch boxes and hooking up the motors in the HVAC units. Drywall continued in the bathroom areas which are now about 40% complete. Assembly of the stairwell skylight structure began. The last pieces of the storefront are being assembled and attached. A room was constructed for the elevator hydraulics and drywall and sprinklers were installed. Railing was added in the stairwell. Sprinklers were tested in most parts of the upstairs. Drywall was put in and taped in the area where the clean room will be installed. Touchup painting is going on in several labs and the injector area. Floor cleaning and minor leveling was performed in the control room in preparation for carpet. Control system racks were moved into the control room. Safety system racks were brought into the building as were the communication racks and set in place in the communications room. Fiber and communication lines were pulled into the building from the main machine control center and crews began hooking those into the racks. Cryogenic lines were lowered into the sleeves. Dirt is finally being mounded up around the building with building grounds and sealing blankets being installed next to the concrete.

In preparation for the injector move into the FEL User Facility, the gun high voltage tank was lowered into the injector pit, surveyed, and bolted into position. Design detailing on the clean room was almost complete with finalization of the electrical wiring plan. Arrangements were made for the contractor to arrive on site and receive Jefferson Lab safety training courses on 5/27/97. Unloading of the clean room into the User facility is scheduled for 5/28/97. It will take about 10 days to install.