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

cc: Division (M7), FEL Coordination Group

From: F. Dylla

Subject: IRFEL Weekly Report, May 5-9, 1997

Date: May 9, 1997

Management

Highlights for the week include the following: (1) the wiggler was shipped from STI Optronics and should arrive next week; (2) dipole magnet assembly continued according to our fast track plan; (3) a prototype mu-metal corrector magnet showed a very promising 1.5% total field error and (4) the ITS HV stack was operated at 420 kV.

A teleconference was held today (Friday) with the DOE Site Office (Wayne Skinner), Jefferson Lab Finance Dept. (Jim LeMaire), the Oak Ridge Field Office Finance Dept. and Gordon Smith to discuss the end of project billing procedure. The purpose of the conference was to work out procedures for ensuring that the construction project is fully billed to the Navy before the end of September.

We began preparations for two important FEL program meetings coming up next month. On June 9-10, MTAC will convene for its second meeting at Jefferson Lab. Agenda items were discussed with the SURA office prior to preparing a draft agenda for review by MTAC and the Navy HEL program office. We will take the opportunity during the June 25-26 LPC Workshop to hold a meeting of the Industrial Advisory Board (IAB). A letter was distributed to the IAB this week listing agenda items concerning industry commitments to the FEL project and agreements for equipment consignments and loans to the User Facility

Jefferson Laboratory was pleased to welcome a number of important visitors to the Laboratory this week who were given briefings and tours of the Lab's Facilities: Peter Rosen, Head of the High Energy and Nuclear Physics Program Office for DOE and Andrew Sessler, Director Emeritus of Lawrence Berkeley National Laboratory and president elect of the American Physical Society. In addition, meetings were held with Mark Pelaez, Vice President and Director of Engineering of NNS, and Dr. Ralph Romero, Engineering Manager of Solarex, Inc., about collaborations with the FEL program.

Proposals were received from Dan Henkel (HMT) and Shanti Nair (U. MA) for summer studies that would lead to formal proposals to be submitted to DOE-BES for laser-metal interactions.

As can be inferred from the documentation below, vigorous activity is planned for next week despite the fact that most of the principals will be away at the Particle Accelerator Conference in Vancouver.

Injector Test Stand

Regarding the photocathode gun:

We finished checkout of the entire beamline. We then operated the photocathode at 350 kV. Unfortunately, after 36 hours of operation, the cathode's quantum efficiency had degraded from its initial value of about 9% to a meager 0.05%. We hypothesized that this was due to the presence of field emission, and to reduce it we proceeded to do high-voltage processing to 420 kV. In the process, the high-voltage cable leading from the power supply to the gun arced at the gun-end of the cable. The cable was repaired Wednesday evening, 7 May 97. Afterward, the gun was processed to 420 kV (a new record!) with the repaired cable.

We then fabricated a cathode and operated the gun at 350 kV. The quantum efficiency, however, had degraded from about 5% to only 1.45% after only 2 hours of operation. There is also 150 nA of dark current at 350 kV, indicating major field emission after heat cleaning and cesiation of the cathode. Presently (as of 1400 9 May 97) we are processing the cathode without the laser to try and reduce this dark current.

The drive laser was operated continuously for ~ 50 hours in support of gun experiments. The remote control of the laser pulse selector was used extensively and worked well. Some tests of the divide-by-two electro-optical modulator were conducted with its new rf-matching circuit. Tests will continue next week.

Regarding cryounit commissioning and ceramic warm windows:

Qualification of the interlocks on the cryounit is underway to aid in preventing accidental window breakage like that which occurred during the earlier qualification tests.

Two completed ceramic-warm-window assemblies were tested in air up to 50 kW, during which they demonstrated good performance. However, during preparation for final qualification in the vacuum fixture, one of the warm windows cracked. This failure was not associated with rf operations and is not fully understood at this time.

Production of additional warm windows continues with four assemblies planned for completion during May. The first of these, scheduled for 15 May 97, will be qualified along with the existing ceramic warm window and installed on the cryounit. We also received this week four beryllium- oxide windows from Northrop-Grumman, as well as drawings for the window frames. Plans are to make the window assemblies and test them, an activity that will take about one month to complete.

These events make it difficult to achieve our 1 Jun 97 milestone for completion of off-line cryounit commissioning, though we are still trying. Our "hard" constraint is to have the cryounit installed and cooled down in the FEL Facility by 1 Jul 97, an event that is locked into the scheduled July shutdown of the nuclear-physics machine. At that time Lab resources will be available to commission the cryogenic system in the FEL Facility, and the cryounit will constitute a "load" for that system.

On a miscellaneous note, we received from Svetlana a new spare 50 kW klystron. Plans are to put it through in-house acceptance tests.

Accelerator Systems

Regarding the beam-transport system:

Progress on dipole magnets has been vigorous and steady. Everson Electric has pinned the parts for the first-article core of the optical-chicane dipole magnet. They have a gap that is uniform within 0.0002". The WBS manager visited Everson Electric Friday, 9 May 97, to discuss the possibility of contracting to them for the complete assembly (gluing the brass and mu-metal of all of the recirculation dipoles). Plans are to get a contract in place and the first article done next week. Magnet Enterprises International is planning to ship another five coils today for the optical-chicane dipoles. Next week we plan to inspect the first-article coils for the injection/extraction dipoles. Tooling for the coils for the reverse-bend and 180-degree dipoles is being fabricated.

Detail design of the rectangular Panofsky trim quadrupoles will start next week. Signing of the drawings for the sextupole core was delayed until today (9 May 97) because of a question about how tolerances should be established.

Fabrication of the mu-metal prototype corrector magnet was completed, and the magnet was tested. Field errors totaled about 1.5% (mostly quadrupole), even though the prototype comprised a very crude core. A design with inherently better tolerances will have be used if this option is chosen, but the result is very encouraging. Hysteresis and saturation effects were not measured, so we cannot yet declare victory.

Regarding the air-core-corrector option, we evaluated a simple modification of the mounting position in our existing design and verified that we could not do any better than 3% error. Evaluating the addition of a second coil set is planned as the next step. First analysis of the Lawrence Livermore Lab coil parameters indicated that we would need 12-layer coils to achieve our required field, as opposed to their 2-layer coils.

Welding the X-chamber that connects the injection line to the recirculation loop is planned to start next Wednesday (14 May 97) after the welders do a 60-inch test piece. The test piece will enable evaluation of the ability to keep twist at an acceptable level, or the remove it by selected weld-bead placement.

We started detail design of the scraper and insertable dumps.

Regarding cryomodule fabrication:

Assemblies of cryounits #1 and #3 are progressing on schedule. Cryounit #1 is now in the final stage of assembly. Reassembly of cavity pair #2 was completed, and it is being readied for retesting in the Vertical Test Assembly. Retest had been planned for next week, but it in fact might be completed today (9 May 97). On the whole, the schedule for cavity-pair assembly remains tight but manageable.

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

The radiation monitors for the Personnel Safety System arrived. They are being tested and "broken in". Plans are to install them with the safety racks next week.

The network servers arrived and are being set up. Most of the remaining racks will be put in their places in the FEL Facility next week, given that the floor in their area is being tiled today (9 May 97).

The deficient welds of the beam position monitors have successfully been repaired. The weld problem arose at the vendor from insufficient heat when tacking the vacuum-feedthrough tips to the large plates of the electrode. We repaired them in-house using our electron-beam welder.

Web documentation of the I&C system continues with vigor.

FEL Systems

Wiggler

STI Optronics shipped the wiggler on 6 May 97, and it should arrive in Newport News on 13 May 97. Measurement results and other deliverables were received this week and are being checked.

Our Machine Shop is going to try hydrostatic pressing of tubing for the wiggler vacuum chamber using a 100-ton press. Hydrostatic rolling produced a good cross section, but the tube straightness was out of specification. If pressing does not work, the tube will be welded using the electron-beam welder and annealed at high temperature to eliminate the ferromagnetic domains in the material.

All components necessary for the wiggler girder assembly are in house. The girder should be assembled by 16 May 97. Drawings for the wiggler support were approved for construction.

Optics

Optical hardware for the mirror cans was sent to the vendor this week. Fabrication of the Brewster window pick-off is also on schedule. One of the optical tables that will support an optical cavity assembly was moved to the accelerator vault in the FEL Facility. Some of the stand hardware for the optical tables also arrived this week. Design of the collimator is nearing completion.

Brazing tests on calcium fluoride substrates (provided gratis by Optovac) are in progress. On 9 May 97 we informally hosted Albert Ogloza (of NAWC China Lake), one of the staff responsible for measuring the absorption in our infrared-mirror coatings.

Commissioning/Operations

Considerable progress has been made toward identifying a suitable start-up scenario for high- current operation of the FEL. The accelerated and decelerated currents are within 1.5 degrees of being out of phase with each other, and this helps greatly to keep rf transients tractable. There are several start-up scenarios that appear viable, but perhaps the best option combines a gradual ramp-up of the bunch frequency with a gradual ramp-up of the charge per bunch. This aids in keeping rf transients quiescent in the injector, which turns out to be the major concern.

A task list and schedule was drafted to generate the remainder of the commissioning plans prior to 1 Oct 97. First-light commissioning plans are already done. What remains is to develop the plans to get full-power operation following first light.

Facility

The first optical table for the accelerator vault was received, and the second is due in two weeks. First delivery of stands for the wiggler and the optical tables occurred, accounting for about half of them. Approximately 20 optical-table, magnet, and wiggler stands were bolted in downstairs along the first-light line. They will be grouted next week.

We finished hooking the dump skid to the low-contamination water (LCW) pipes. Upstairs, Jefferson Lab crews began installing the LCW pipes on the walls after installing and painting the unistrut holders. Preparations are continuing for LCW hookup to the South Linac over Memorial Day.

More painting in the gallery area was completed, enough to allow us to clean the area this weekend, begin putting more racks in their final position, and begin hooking things up. A pit was dug, a pad was poured, and the sleeves for the cryogenic lines were placed and welded to the lower-level feedthroughs. The other end was poured into a concrete wall mount. A landing pad was constructed, attached to the outside of the Facility's loading door, and load tested. It will make delivery of large items to the upstairs easier. Drywall of the upstairs injector area is half finished. Electricians continued installing conduit and the last two transformers. A large amount of plumbing continued toward finishing up some areas for HVAC and for the bathrooms. More parts for the elevator were received. The tile is in the clean room, and the floor of the control room is ready for carpeting Monday. The control racks will go in the control room today (9 May 97). Two labs are now fully painted, and two chemical hoods were installed. Outside, some of the top edging and window finishing continued, as did store-front work.

We set up for the cable pull from the Machine Control Center. A termination box was mounted on the side of the building, and holes were punched into the communications room. We are still shooting to have communications on the net by 1 Jun 97.

Design began in earnest for the drive laser's optical transport system. Design is nearly completed for the high-voltage-power-supply ancillary components. The tank is to be placed in position by 16 May 97. Clean Air Technology requested an extension of the delivery date for the clean room to 9 Jun 97 due to a delay in the delivery of the air-handler unit for the room. The drawings have been checked and approved with the exception of a clarification on the electrical circuits.