MEMORANDUM

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

cc: Division (M7), FEL Coordination Group

From: F. Dylla

Subject: IRFEL Weekly Report December 16-20, 1996

Date: December 20, 1996

Management

The first meeting of SURA's Marine Technical Advisory Committee was held on Dec. 17-18. The committee was given presentations on the status of the Navy's High Energy Laser Program, the Jefferson Lab's 1 kW Demo and the MW FEL Workshop. An initial report from the committee is expected next month.

A meeting was held on Dec. 19 with R. Marianelli (DOE-BB), and D. Lehman (DOE Construction Project Office) to review the preliminary agenda and list of potential reviewers for the Feb. 24-25 DOE-BES review of the Jefferson Lab FEL program.

The top level design drawing for the IR FEL was frozen as of Dec. 20. All subsequent changes will be subject to a change control process.

Injector Test Stand

Regarding upgrading the photocathode gun:

The College of William and Mary retested one of the electrodes having the FM Technologies coating to assess its field-emission characteristics after baking at 650 C. The test was successful in that no field emission was seen. The new stalk was completed and sent to FM Technologies for coating. Unfortunately, it had just left our premises when the vendor called with the news that their coating chamber could not accept the tube with its welded-on flange. At week's end we are bringing back the tube and preparing to remove the flange. Contractual arrangements for the coating are still not finalized. The vendor is now estimating mid-to-late January delivery of the coated stalk.

Concerning other ITS-related progress:

Installation activities remained on schedule except for the above final assembly of gun. We upgraded the harp in the light box with one of the new stainless steel frames to make it more structurally resilient to baking. Work continues on upgrades to the photocathode drive laser and its optical transport system.

Accelerator Systems

Today (Friday, 20 December) we froze the top-level machine drawing, established a Lattice Review Committee, and formally instituted a change-control process. The lattice is designed to provide a high-brightness electron beam for lasing and high acceptance for energy recovery in keeping with the goals of the IRFEL Program. These goals are to generate first light (requiring nominally 38 MeV, 1.1 mA cw electron beam without energy recovery), followed by high-power operation (requiring nominally 42 MeV, 5 mA cw electron beam with energy recovery), and during commissioning, to investigate effects of space charge and coherent synchrotron radiation on the electron-beam dynamics. A second cryomodule can be added to boost the beam energy to 75 MeV without affecting the design or placement of the second recirculation arc. Details at the subsystem level are generally fluid, i.e., not yet frozen, but any changes at the subsystem level that affect the lattice are now subject to review by the Lattice Review Committee.

Further tests of the prototype dipole magnet have shown that the use of high-µ pole-surface material coupled with a Purcell gap is sufficient to meet the specifications on the uniformity of the transverse field profile. However, we have not yet closed the dipole magnet review because we felt it important to consider edge effects on the field and explore a geometry that will provide a sharp cutoff. The magnet has been reconfigured for this, and measurements of its edge fields are on the verge of beginning. We project that, once this data is available, we can close the review, and we anticipate doing so during the first week of January. In the meantime, Northrop Grumman has completed the design of the optical-chicane dipoles to the 99% level. Upon closing the review, we will expedite their procurement.

Development of ceramic warm windows continues to be pursued vigorously. We tested one window, but it failed at 50 kW, 50% duty cycle. In preparation for manufacture of more windows, massive stainless-steel flanges that are already in house have been inspected and cleaned. They are ready for copper plating, and will be ready for final assembly sometime today (Friday, 20 December). Testing of windows should resume on 23 December. A detailed test schedule was developed and implemented that leads to installation on the injector cryounit of the best two qualified windows by 15 January 1997.

The higher-order-mode (HOM) stainless-steel subassemblies were qualified, and final assembly started at the vendor. Braze tooling for the HOM assemblies were designed and manufactured. We are making additional glassy carbon tiles for HOM production.

Considerable progress ensued concerning the development of the beam-position monitors (BPMs). Experiments with the prototype stripline BPM indicated that the location of the troublesome 1455 MHz resonance could be adjusted by shortening the electrodes. Doing so significantly enhances the ease and accuracy of calibration. Thus, to affirm this finding, we decided to design and fabricate a second prototype with shorter electrodes. This prototype is projected to be available for testing by mid-January, after which it will be available for commissioning with 10 MeV beam in the Injector Test Stand. In addition, a schedule was drafted for all of the families of BPMs needed for the IRFEL, and it was coordinated with the beam- transport schedule. We could not close out the BPM Review this week, so we set a date for the closeout meeting at 9 January 1997.

The bunch-length monitor under development at the University of Georgia is proceeding well. They are building two units, one of which will be evaluated at 10 MeV in the Injector Test Stand. The stepper-motor-controller printed circuit boards are complete, and chassis construction is progressing. The University of Georgia will also provide manpower to write the required software to enable the measurement to be a single step operation. A graduate student spent a few days with us this week as part of planning for these tasks.

FEL Systems

Wiggler

We are still negotiating with Northrop-Grumman over the contract for the vacuum chamber and vacuum chamber support. The detailed drawings for the wiggler supports should be complete next week.

Optics

Meetings were held with the TJNAF Machine Shop to prioritize tasks and assign responsibilities for fabricating parts for the optical cavity. We are awaiting estimates from one more vendor for turning mirrors for the optical transport before we begin placing orders. Work is underway on detailing drawings for the optical transport system, specifically the beam diagnostics pick-off.

Operations/Commissioning

A detailed draft of the goals and plans for the 350 keV experiment was prepared. For the goals, we consider that we must: (1) achieve "nominal" beam parameters for FEL operation, (2) achieve stable operation at 350 kV, and (3) develop a procedure to reproduce beam conditions using only diagnostics that will be in the FEL injector. We also consider that we should: (1) attempt operation at >350 kV, (2) perform beam-parameter studies to understand the physics of the gun, and (3) make emittance measurements versus solenoid settings. If done properly, the parametric studies would satisfy all other goals except operation at voltages >350 kV. Given that the "musts" are achieved, the breadth and depth of our experimental program will ultimately be weighed against schedule considerations.

Facility

We received a budgetary quote from Clean Air Technology for the FEL Facility's clean room. This is the vendor we had used for the ITS clean room. The quote is about 20% higher than for the previous work, but this is not surprising considering the amount of demand in the market today. Design of the high-voltage power supply for the gun should be completed next week.

Preparations continued for the foundation of the services building throughout the week. Above the facility filling was nearing completion of the interfloor area. Most of the volume of fill had been placed and nearly all of the penetrations had been set and prealigned. The foundation work continued in the lobby/loading dock area. The retaining wall was completed near the ramp door. Rebar was placed in preparation for pouring the retaining wall near the loading dock. Inside the facility the electricians began laying in the conduit for the building power and lighting. Jefferson lab personnel initiated the survey effort for the as built drawings. The u-channel was begun to be hung on the wall for services piping. Drawings of the cable trays were in signoff.