MEMORANDUM

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

cc: Division (M7), FEL Coordination Group

From: F. Dylla

Subject: IRFEL Weekly Report, April 7-April 11, 1997

Date: April 11, 1997

Management

We prepared for the Navy Program Office's site visit scheduled for Monday and Tuesday of next week. Plans are to hold in-depth discussions concerning IRFEL instrumentation and control, warm windows, and follow-on injector work, as well as tour relevant areas in the Test Lab and the FEL Facility.

We met with the DOE site office to propose the Accelerator Readiness Review (ARR) process that was outlined in last week's report. The essence of the proposal was to track ARR activities and hold a single formal ARR early in 1998. DOE's initial response was generally favorable, but the precise date of the formal ARR is presently undecided. DOE asked for a few days to consider our proposal in depth, and we are expecting their feedback sometime next week.

G. Neil presented a talk on the Jefferson Lab FEL Program at the Duke University FEL Laboratory on 3 April 1997. Duke expressed strong interest in the Program because of their experience in both the IR and UV wavelength bands. The visit gave us an opportunity to study their electron transport system (which is interesting because it is compact and has a 10% energy acceptance) and their optical cavity alignment system (which provides < 100 nrad of alignment stability).

Injector Test Stand

The bake of the gun and beamline was completed, and the insulating materials were stripped in preparation for reassembly of the beamline hardware. In total, the gun reconfiguration and bake were completed on schedule. In addition, test plans for "Transverse Emittance", "Cathode-Life Tests", and "Emittance Measurements off the Cathode Centerline" were completed using Jefferson Lab 's standard form.

We tested the EPICS control system developed for the photocathode gun's high-voltage power supply. This is part of preparing for remote operation of the system from the Machine Control Center during the May runs.

We had a glitch with the instrumentation of the temperature diodes in the cryounit. The cause turned out to be a wiring error which was easily fixed. The cryounit is now ready for high-power radio frequency (rf) testing, and we are anticipating the start of these tests this evening (11 Apr 97).

Regarding the drive laser, we tested KD*P crystals for thermal blooming. The vendor (Conoptics) uses these crystals in fabricating our variable-speed electro-optical (EO) modulators. At somewhat higher power inputs than we anticipate (6.15W at the crystal), we found no evidence of thermal blooming. We anticipate receiving a new EO modulator next week. The laser itself was operated this week in support of diagnostics development and performed normally.

Accelerator Systems

Regarding the beam-transport system:

Fabrication of the optical-chicane dipole magnets continued. A visit to the contractor is scheduled for 14 Apr 97 to view the first article. We have resolved how to install the mu-metal bought by Everson Electric to meet the field-flatness specification between the coils. We are also supplying them brass from a supplier that is within our thickness tolerance.

We sent the remaining copper to Magnet Enterprises International to build coils for the 180- degree and reverse-bend dipoles. The core-fabrication contract was won by Process Equipment Company, the same firm that machined all the cores for the CEBAF arcs. At week's end the steel is in transit to them.

We received bids for fabricating the injection-chicane dipoles and are evaluating them. Preparation of the drawing package for the sextupole magnets started. To accelerate delivery we will sign the coil drawings and get them out for bid while we finish the core and assembly drawings.

We have decided to change gears and pursue a brute-force, easy-to-measure, square Panofsky- style design for the trim quadrupoles. Despite trying for months, we still have no reliable way to measure the rectangular style. We will soon measure an existing 4-inch-aperture QJ quad to obtain a scaling value for the fringe field and ascertain whether field clamps will be necessary.

We are still working on choosing a geometry for the air-core corrector magnets. We need 1% total multipole content, but the original CEBAF air cores carry 3% multipoles. We will soon measure a set of Haimson coils to give us another data point. Haimsons are relatively easy to fabricate. If

necessary, we will ask Northrop-Grumman to do three-dimensional magnet calculations to verify expeditiously the design choice. They have indicated the necessary manpower is available.

We are preparing to weld the X-chamber that connects the injection line to the recirculation loop using a written fabrication procedure. The contract was awarded to make the parts for the Y- chamber that connects the energy-recovery dump to the recirculation loop. Design continued on the remaining stands, brackets, and girders needed in the injection line and dump, with special emphasis on the layout of the bolt pattern. Contracts are in place for the stands and girders needed for first light, as well as for back-leg girders. An incentive contract on the girders will shorten

delivery to match availability of the QG quadrupoles that are now going through acceptance testing on the Magnet Test Stand.

Multipole measurements on the ten QB quadrupoles surplused from CEBAF started this week in preparation for mounting them to the rails on the optical tables. The QGs are also being measured, with no rejects thus far.

Detailing of the vacuum chambers for the optical-chicane dipoles is scheduled but not yet done. Lack of progress here is not presently causing undue problems. The design concept for the reverse-bend vacuum chambers is complete and was sent for detailing to Northrop-Grumman. The final bid for vacuum pumps is due today. Design of the vacuum chambers for the 180-degree dipoles was delayed for a week but is starting up with sign-off expected next week.

The power supplies for the injection/extraction dipoles are on order with delivery slated for 9 Aug 97. The first rotating-coil-probe system for use in nulling the dipoles at the switch points was ordered.

The straight-ahead dump design is nearing sign-off, and design work on the insertable dumps and the beam scraper is starting.

Regarding cryomodule fabrication:

Assembly of the first cryounit with the first cavity pair for the cryomodule continues to go well with no issues. The second cavity pair was disassembled for reprocessing. The third cavity pair is in testing in the Vertical Test Assembly. Initial data imply that this pair may also need to be reprocessed, but testing is continuing today (11 Apr 97).

The status of cryomodule fabrication is such that we are now tight on cavity-pair assembly, and this carries a possible impact of slipping installation of the cryomodule in the FEL Facility from mid-July to mid-August, an intermediate milestone. However, the assembly processes for the constituent cryounits and the cryomodule itself involves a number of steps that can be done in parallel as cavity pairs become available. Thus, there are various manpower-intensive means available by which to recover some schedule should it prove advisable to implement them.

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

Progress continues to be fast and furious. We began bolting into place the I&C racks in the FEL Facility, and we are in process of detailing all VME controls layouts for the FEL. The remaining X-terminals for the drive laser and user labs were ordered, and we are getting quotes on computer furniture for the laser control room. In addition, the remaining network hub for the FEL was ordered. Nomenclature for vacuum controls and magnet-power-supply channels were given to the Software Group for programming. All six control chassis for the beam viewers were completed.

Final weld-up of the stripline beam-position monitors (BPMs) began after very successful electropolishing. The Jefferson Lab staff member who designed these BPMs was present at the contractor facility to advise on the final weld-up. The contract is on track for its stipulated 60-day delivery.


FEL Systems

Wiggler

Assembly of the wiggler bench and fabrication of the vacuum-chamber tubes was started in our Machine Shop. The drawings for the vacuum chamber and its support were checked, and changes were given to the designer. We are now awaiting the final drawings for signature.

Optics

The output Brewster window and the custom 5-way crosses were received for the optical-cavity assemblies. The crosses are now at our Machine Shop for final machining and welding of flanges. Progress for the optical-transport system consisted of working with the designer to develop the collimator, and making further progress on the second-floor installation of the optical-transport pipe in the FEL Facility. Most of the Plexiglas used as laser shielding around the mirror-heat-sink test stand is now installed.

Operations/Commissioning

Follow-on simulations were done, in part to clarify the issues mentioned in last week's report. It turns out that, contrary to last week's report, the space-charge code, PARMELA, and the linear- optics code, DIMAD, do agree on transport through dipole magnets with space-charge turned off. A difference in the use of kinetic energy versus momentum between the codes caused the confusion. This week's refined PARMELA calculations for the machine setup at bunch charges of 60 and 135 pC give well-behaved emittances from gun to wiggler. The results indicate that going 7.5 degrees off crest in the injector cryounit improves the bunch-length and momentum-spread profiles. Sensitivity studies for cavity phase have not yet been done, but a 5 degree change resulted in only a 10% change in bunch length, implying that the sensitivity is sufficiently weak. We still need to check second-order lattice effects because they are not included in PARMELA. Plans also include doing 1 pC and 60 pC runs with a 135 pC setup to determine how easy it will be to ramp up the charge per bunch during commissioning.

A draft commissioning schedule was formulated for the IRFEL and is currently under discussion.

Facility

Work on the Facility continued rapidly through the week. Saturday work schedules for all subcontractors is the norm since the prime contractor is still under $1500/day penalties. Exterior siding is complete to the injector upstairs area (about 80% of the Facility). Work continued on the storefront. The main east window framing/mounting was installed. Interior studs were placed along the east-west wall bringing studding to > 60% complete. Studding was completed in the control room. Electrical and communication conduits were set, and mounting of dry wall began in those rooms. One main air-handler unit was hung; the second prepared for hanging. A PVC roof drain line will require minor relocation before final placement can occur. Temporary lighting was installed, and about 70% of the permanent lighting was hung. Installation of lighting conduits was initiated so hookup could begin. The main electrical switchgear was placed and connected on the second floor. The current plan is to connect both the first and second floor to main building power next Tuesday and commence circuit testing. Coring of the slab to permit mounting of safety rails in the equipment gallery was completed. Plans for utility services to the user labs were approved. Preliminary designs for hanging cable for the low-contamination-water system and the master oscillator are being drawn up. Modifications were made to the communications services planned for the user labs, nearly doubling the number of outlets. Locations of the communication cable trays were established. Welding continued on the optical-transport line downstairs. Rack assembly and installation continued upstairs. X-terminals, lan servers, and net communication were specified for the user labs.

Bolt layout for the injector area was passed to the alignment crew. The design of the coaxial line for the photocathode gun's high-voltage power supply is now complete pending review by the engineer in charge.