MEMORANDUM

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

cc: Division (M7), FEL Coordination Group

From: F. Dylla

Subject: IRFEL Weekly Report, April 14-April 18, 1997

Date: April 18, 1997

Management

We conducted a 2-day project review for the Navy High Energy Laser Office on Monday and Tuesday (April 14-15). The first day focussed on the status of Instrumentation and Controls (I&C), RF window testing for the SRF systems, and the Injector Test Stand. On Tuesday the remaining WBS elements were reviewed by touring FEL hardware that is currently being tested in the Test Lab and Optics Trailer or installed in the FEL Building.

On April 15-17, Jefferson Lab hosted a workshop sponsored by the DOD Laser Systems Safety Working groups. J. Cook presented an overview of the Navy HEL program and G. Neil presented a summary of the Jefferson Lab FEL program.

The spring meeting of the SURA Board of Trustees was held in Washington on April 16-17. F. Dylla preseted a status report on the FEL program and met with representatives from the Vanderbilt and Duke FEL Laboratories on matters of potential and continuing collaboration.

The cost and schedule summary data for the month of March was prepared for the monthly report and for presentation at the April 15 Navy project review.

Injector Test Stand

Having completed bake-out of the photocathode gun, we prepared the gun and its beamline for operation, including reinstalling the diagnostic hardware in the beamline that had been removed for the bake. Then, after reinstalling the sulphur hexafluoride tank and reactivating the nonevaporable getters in the gun, we began high-voltage (HV) processing of the new ceramic stack and coated cathode-support tube. As of now (noon, 18 Apr 97) the voltage has reached 340 kV after about 8 hours of processing, a better result than obtained in previous HV processing. The processing procedure is iterative and takes time because turning up the voltage entails burning through breakdown barriers as they are successively reached.

We operated the photocathode drive laser was operated in support of diagnostics development. It operated normally. We will receive the new variable-speed electro-optical modulator tomorrow (19 Apr 97).

High-power radiofrequency (rf) testing of the cryounit successfully began. Performance of the subject cavity was reverified up to its quench limit. Its performance is slightly improved from earlier tests, probably due to a slight difference in ambient static magnetic field, and the tests indicate cavity performance remains consistent with its projected 9 MV/m operation. Up to 18 kW rf was introduced into the waveguide with no performance degradation of the waveguide. Today (18 Apr 97) we are switching to the second cavity which is configured with a polyethylene warm window for 8 kW operation.

Regarding ceramic warm windows, we processed one of the bad ceradyne ceramics by air- firing it for 30 hours to oxidize fully its bulk material. Tests of the fired ceramic in the ring- resonator test assembly indicated greatly reduced dielectric losses, signifying full recovery of its dielectric performance. This is a very encouraging result.







Accelerator Systems

Regarding the beam-transport system:

Fabrication of the optical-chicane dipole magnets continued unabated. Our WBS manager, G. Biallas, is visiting Everson Electric today (18 Apr 97) to discuss the fine points of the first-article core. This vendor has completed rough machining and heat treatment. Magnet Enterprises International completed the first-article coil on 14 Apr 97 and have wound sets of pancakes for four more of the 16 required coils.

During a site visit on 14 Apr 97, G. Biallas also discussed details concerning manufacture of the 180-degree dipole coils and reverse-bend dipoles with Magnet Enterprises International. They had generated drawings for the tooling for potting the reverse-bend coils. Process Equipment Company received the steel for these magnets' cores and were programming the burning tables to create the blanks.

The coil contract for the injection-chicane dipoles was awarded to Magnet Enterprises International, and winding details were discussed with them. A local vendor, Master Machine, won the contract for the cores.

Magnet measurements were done to determine the scaling of the fringe field of the square Panofsky-style design for the trim quadrupoles. Magnet measurements of a prototype Haimson coil were also done. The Haimson coils have a 7% multipole content while we need 1 %. Therefore they are out of the running for our air-core correctors. We have identified two alternatives thus far. We can make the coils with cosine-theta distributions and flat ends for good field cut-off, and we have a line on some that were made in the 1980's at Livermore Lab. At a minimum, these are needed at the entrances and exits of the 180-degree dipoles because they have to be able to run AC. We can also try to use mu-metal (which saturates at 8 kG, while we need only 100 G fields for 42 MeV) to make window-frame magnet cores. We have started to work on one of these in our Machine Shop.

The drawings of the sextupole coils were readied for signature while their core drawings are in process.

The written procedure to weld the injection X-chamber is being composed, and the fixturing is being prepared. Girders for the back leg are nearly complete, while their QG-style quadrupoles are being qualified on the Magnetic Test Stand.

Multipole measurements on the ten QB-style quadrupoles surplused from CEBAF continue.

In the vacuum area, detailing of the chambers for the optical-chicane dipoles is at 30%. The design of the reverse-bend chambers started at Northrop-Grumman. The vacuum-pump order was placed. Design of the chambers for the 180 degree dipoles neared completion.

The first rotating-coil-probe system for nulling the dipoles at the switch points was received.

Regarding cryomodule fabrication:

Assembly of the first cryounit for the cryomodule continues unimpaired and on schedule. Its helium vessel will be buttoned up and leak checked today (18 Apr 97).

The second cavity pair was reprocessed this week, and it is now in the Vertical Test Assembly awaiting retest.

Performance problems reported last week with regard to the third cavity pair were traced to the power coupler. After correcting the problem, we retested the pair successfully; it sustained >10 MV/m without field emission. This pair is presently awaiting final leak check prior to accepting it for installation in its cryounit.

Regarding electron-beam instrumentation and controls (I&C):

The requisition was signed for support stands for the beam-viewer cameras. They each attach to the view ports and support both the charge-coupled-device camera and the deflecting mirror.

The video multiplexers arrived, and the layout for the video distribution is being finalized. At issue is which signals are to be viewed simultaneously.

The electronics filter banks and cable sets for the beam-position monitors were ordered.

We set up a new "gateway" for I&C (and others) www information: http://www.jlab.org/accel/fel/documentation/evans/fel-bear.html. This gateway is found in section 5.11.2 of Jefferson Lab's FEL Documentation Page.

FEL Systems

Wiggler

Design work continues on the injector elements including the high voltage power supply elbow, the gas handling system for the HVPS, and the crane rail system in the injector area. Design work was begun on the drive laser optical transport line.

Final drawings for the wiggler vacuum chamber and its support were received. The machine shop has received the components it needs to carry out hydrostatic pressing of the vacuum tubing for the chamber. The final assembly drawings for the wiggler girder are being checked. Almost all components needed for assembly are in house. The wiggler has been assembled and shimmed for the 12 mm gap at STI Optronics. The rms phase error is less than 3 degrees, compared to the specification of 5 degrees. This is the most critical parameter of the design. The inital trajectory offset is on the order of 100 microns at 42 MeV and the trajectory wander is less than 100 microns peak to peak. This is excellent performance. The performance at 12 mm exceeds all the specifications for the weak field gap. Measurements of the weak field gap of around 15 mm are in progress at week's end. The performance should be better than at the strong field gap.

Optics

The custom 5-way crosses and flanges for the optical-cavity assemblies have been faced off and cleaned for welding, which is planned for next week. Development of the collimator continues to progress. The optical-transport pipe in the FEL Facility's accelerator enclosure has been welded, and it is awaiting delivery and installation of the mirror cans. The Plexiglas used as laser shielding around the mirror heat-sinking test stand is now installed.

Operations/Commissioning

A series of electron-beam simulations from photocathode to wiggler was done to explore the implications of adjusting the charge per bunch without changing the machine settings. The results were generally favorable in that, for example, machine settings were found that reflect a relative insensitivity of electron-beam properties in going from first-light beam (60 pC per bunch) to full- power beam (135 pC per bunch). A simulation of zero-current-beam propagation with these machine settings pointed to some concerns about beam degradation in this case. The concerns are pragmatic because ghost pulses will be present, and they will behave as a zero-current beam. As a consequence, some preliminary tracking studies through the entire machine were done with this beam, and these tracking studies suggest that no significant beam loss arises.



Facility

Another week of rapid progress on the Facility has come to pass. Exterior panels were placed around the second floor, with the exception of a small area near the injector where extra panels are needed. Store-front work continues, with the cover on the loading dock nearly complete. The framing in the lab areas was completed early in the week, less some minor rework which will be required. The framers then moved into the second-floor lobby area and framed the bathrooms. Drywalling was completed in the control room and optical-control room. The walls were sealed and painted. The control-room window trim was cleaned and painted. Drywall hanging began in several other key areas where its installation holds up attachment of key components to the wall, including by some electrical circuit panels, the ladder to the roof, etc. A roof drain was moved to permit repositioning of the HVAC unit by the control room. The water chiller for the HVAC was placed and welded in to the piping in the equipment room. The electrical transformer was turned on. Power was sent to both the upstairs and downstairs switchgear, and the "real" lights were turned on downstairs and partially upstairs. We now have main power downstairs. Some modifications were made to the placement of circuit breakers for the HVAC to get a large switchbox out of the aisleway. Downstairs the welding and leak checking of the cryogenic lines is proceeding well, and installation of stands for the injector and injector dump has begun. Many additional stands were marked out on the floor for bolt placement.

We decided this week to purchase the optical bench needed for the Facility clean room. This keeps us from having to wait until the ITS is shut down to move its optical bench. The cost of moving was nearly one-third the cost of a new one, and the schedule is helped substantially by the purchase.

We are pushing to get most of the cables pulled and penetrations plugged by 1 Jul 97 and thereby eliminate the need for oxygen-deficiency-hazard monitoring of the second floor. Dry nitrogen was added to the services to be provided in the second-floor labs. We decided to add a small platform outside the second-floor door to aid installation of crane-delivered materials before the berm is complete. We set a target date of 23 May 97 for interconnecting the Facility's low- contamination-water systems with those of the nuclear-physics machine.