IR FEL Monthly Report for May 1997

Navy IR Demo Contract WBS Elements

WBS 1 Project Management

May 1997 was the eleventh full month for the IR Demo project funded by the Navy.

Management

The IR FEL Demo project through the month of May 1997 has a total of $6,222K (less SRF and building) of performance scheduled. The work performed through the current period is $5,376K or 67% complete of 77% scheduled. The actual costs accrued through May totals $6,251k. This results in a schedule variance of -$845k (an decrease of $221k) and an increase in the negative cost variance to $875k (an increase of $99k).

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 precommissioning and 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.

Lots of high level activity occurred in Washington this week concerning potential FY98 funding for the FEL program. Senator Warner requested a briefing from ONR management on FEL R&D for Naval applications. A follow-up briefing will be held on Monday, June 2, with Adm. Baciocco (the chair of MTAC), and representatives from SURA and Jefferson Lab.

A teleconference was held during the month 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 listing agenda items concerning industry commitments to the FEL project and agreements for equipment consignments and loans to the User Facility

Jefferson Laboratory welcomed a number of important visitors to the Laboratory this month 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.

Important accomplishments for the month include the successful re-start of photogun measurements on the Injector Test Stand. Excellent progress was made on characterizing the performance of the gun at 350kV. The wiggler arrived at Jefferson Lab and after shipping problems was accepted from STI Optronics. Significant progress continued on the fabrication of the User Facility and the critical path electron beam transport components.

At the second Virginia Technology Summit, held in Richmond on May 21, the FEL Program was given high visibility in presentations by Senators Robb and Warner, the two gubernatorial candidates from Virginia, and from the group leader for a task force on high-performance manufacturing initiatives.

F. Dylla was invited to make a presentation at the Combustion Science Workshop held this week in Chantilly, VA sponsored by DOE-BES. Several attendees expressed interest in using the IR FEL for combustion research.

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.

Mike Kelley, DuPont, chairman of the LPC, visited the Lab on May 14 to discuss 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.

WBS 5.0 Instrumentation & Controls

Beam Instrumentation:

All 25 stripline BPMs have been delivered. These have been QA'd and passed through the CEBAF electron beam welder to correct for potential cracking on the electrical feedthru. Two of these were damaged during the repair process, these are being fixed in the CEBAF machine shop. The beam viewers are complete except for the wiggler flag assembly. These will be fitted with 1.5 micron aluminum foil and mounted in the accelerator enclosure as needed. The Happek interferometer is scheduled for testing at Vanderbilt in early July. The first of the two units is complete, the second is nearly done. The M56 bunch length cavities are in production. The electronics for these devices are essentially complete.

Safety Systems:

The personnel safety system installation is proceeding well. The cable pull was completed on schedule and the racks are installed and powered up. Most elements of the system will be complete for the July 1 cooldown of the quarter cryomodule. The Machine Protection System (MPS) design review is scheduled for June 26. The Argonne MPS boards are being fabricated.

Controls:

The HP server computers are being setup in the software groups offices. These will be moved to the new building in late June. Software efforts continue.

DC Power:

System documentation continues. The trim rack power supply cables are being fabricated in the service building.

Vacuum Controls:

The two vacuum control crate's designs are complete, fabrication and wiring will begin in June. The ion pump power supply control cards were delayed 2 weeks from a problem at the PC board vendor. These boards will be sent directly to the assembly house for stuffing.

WBS 6 Cryogenic Distribution

All major TL welding complete. All Vacuum Jackets are being pumped. I&C engineering and fabrication are both complete. Installation will be completed after 1/4 Cryomodule is in the FEL building. 4 of 5 U-tubes for CHL connection are complete. #5 is 75% complete. U-tube designs for the 1/4 Cryomodule in the FEL building were released. The shield return U-tube is 60% complete but on hold for TL installation. Working final connections of gas lines at Flex can. Gas lines in tunnel are complete. We are on schelule for July 1 cooldown. Detail plans still need to be made.

WBS 7 Beam Transport

All remaining dipole magnets were able to start fabrication during the month while some parts are already complete on some styles. A first trial assembly of magnets where a Everson Electric attempted to glue Mu metal and brass to pole pieces was not successful. A plan is in place to prototype this assembly to achieve success.

The sextupole cores are about to be contracted while the trim quad design package is in checking. The fabrication of the long Panofsky-style quadrupoles for the recirculation dump was awarded to New England Electric Co.

The remaining quads went through and passed magnetic tests.

Engineering concentrated the correctors for 43 locations. The specification is 1% harmonic content while the standard design used for the CEBAF, with 3% harmonics is not good enough. Prototyping a design based on mu metal as a core material yielded acceptable harmonic content but still had the disadvantage for operations of exhibiting hysteresis. At month's end, discussions indicated the most difficult high aspect ratio correctors in the arcs and the phasing dipoles may be able utilize the mu metal design even though hysteresis is present. This will have to be accepted by the commissioning group before adoption.

Additional analysis indicated that reducing the maximum required field integral on the remaining correctors (air core) by 44% is a prudent change to the requirement. We will start the TOSCA magnetic modeling once we have chosen a direction. At the same time, a vendor is putting together a preliminary proposal to produce most of the air core correctors.

In the vacuum system, parts for the vacuum chambers for the optical chicane are out for bid and the chamber for the 180 degree dipoles was signed off. Northrop Grumman completed details for the first of six return bed chambers.

We made good progress on the assembly drawings for the optical chicane and

first-light beam line and on design of the insertable dumps.

Stands for the Optical Chicane and the injector were installed in the enclosure.

WBS 8 RF Systems

Final testing and calibration of the Chopper cavity was completed. The Quarter cryomodule

heaters were tested and placed under CTF control. A new spare 50 KW klystron was received

last month with a loose input cable. The vendor has been contacted for instructions on how they

want it repaired. The first spare unit was returned. The 1427 MHz Drive Amplifier, Distribution

cables, connectors for the FEL Master Oscillator system are on order and due to arrive in June. The Cathode Power Supply, High Powered Amplifier, and 2 sets of Low Level RF racks were moved to their final position in the FEL building.

The high voltage power supply gas-filled transmission line elbow components are out for bid. The gun power supply high voltage tank was installed in its final location. The legs were cut by a couple of inches to align the output flange with the beam centerline. Hipotronics has been working hard on fabrication and final assembly of the klystron power supply during the month of May, but it still looks like the delivery date will slip about two to three weeks. (mid to late June) We are working with Sanford Jones at Pollydata, Inc., to develop the Magnetostrictive tuner system. Sanford will submit a proposal early June. We plan to make a rudimentary test on the cold cryounit during June if possible. The third (spare) 50 KW RF circulator is on site, and will be run for acceptance test during June if possible.

WBS 9.2 Injector Move

Design of all components in the injector except the optical transport line was completed in May. The layout design for the transport design was completed and details begun. The laser clean room was delivered and partially installed. The completion of the clean room was delayed by two weeks due to delays from the subcontractors to Clean Air Technology. The flooring and air handling unit were delayed by at least two weeks. The plan is now to install Jefferson Lab equipment in parallel with clean room completion so that the overall schedule slip is lessened. The high voltage power supply tank was installed but needed to be modified before it could be moved into its final location. The modifications were completed by month's end. The design for the crane rails for the gun and cryounit were completed and all the parts ordered. The rail will be ready for the cryounit move on June 16.

WBS 9.4 Wiggler

The wiggler was delivered from STI Optronics on May 12. All the vertical shock indicators in the box were tripped. We believe that the wiggler crate slid off its palate and fell several inches. Measurements of the wiggler indicated no shift in the relative position of the wiggler jaws and discussions with STI Optronics did not lead us to believe that any damage could be done to the wiggler. We therefore accepted delivery of the wiggler. It is now ready for installation on the wiggler girder. The machine shop was successful in producing wiggler vacuum chamber tubing of very uniform cross section and flatness. This will be used to test the welding techniques before final assembly. All drawings for the wiggler vacuum chamber and its support as well as the wiggler girder assembly drawing were signed off. The parts for the wiggler vacuum chamber support were ordered. The are due in mid June.

WBS 9.6 Optics

FEL

We received the hardware for mounting the upstairs optical transport pipe. The stands for the optical tables supporting the cavity assemblies and collimator arrived and were grouted in and one of the tables was moved downstairs in anticipation of installation. The mirror cans and diagnostic pickoffs will arrive in early June. We can then make real progress to finish installation of the optical transport. The stepper motor chassis and optical hardware were built and turned over to the software engineer for testing. This is proceeding well. The last fabrication process on the optical cavity assemblies was completed. The optical collimator design was completed, signed off, and is being fabricated at a local machine shop. We received 5 micron mirrors from Rocky Mountain Instruments, one set was shipped to China Lake for testing, the other two sets were returned, as they did not meet specs.

ITS

The photocathode drive laser was operated ~ 407 hrs. in support of gun experiments. The longest continuously operating period was ~ 100 hrs. We now use two variable-speed EO modulators, built using AR coated crystals, rather than index-matching fluid. The bias on these modulators may be changed from the Control Room, in order to optimize the net extinction ratio. There is also remote control of the macropulse and micropulse frequency, this was thoroughly exercised and worked well. The divide-by-two EO modulator continues to be problematic; progress will be slow until gun experiments conclude in June.

Injector, SRF, Facility, and Other Activities Outside Navy IR Demo Contract

INJECTOR TEST STAND

Regarding the photocathode gun, the month began with a plethora of technical difficulties, but it ended with a gun that was operating well at 350 kV cathode stand-off voltage. Early on, the photocathode efficiency would degrade rapidly to a uselessly low value. We hypothesized that this was due to the presence of field emission, and to reduce it we ultimately opened the gun and reinserted the cathode-anode spacer to lower the electric field at the cathode (but not the operating voltage, which remained at 350 kV). In conjunction, we made a novel modification to the gimballed mount of the gun which allowed disassembly without affecting the beamline valve, thus preserving the beamline vacuum and thereby saving considerable time.

After reassembly and baking, the gun performed very well at 350 kV. However, we remain unsure about the cause of the earlier cathode degradation. Cursory examination of the degraded cathode under a microscope revealed that it was "frosted" (the arsenic was vaporized out of its surface), a condition that could lead to field-emission sites. This was probably caused by heat cleaning at too high temperature when we were attempting to heal the field-emission sites by cleaning near 700 C. Consequently, we retained our standard baking temperature of 580 C when preparing the reconfigured gun for operation with beam.

The initial cathode degradation in the reconfigured gun was not bad, from 7.2% to 4.3% in the first 24 hours of operation. The dark current (field emission) was measured at 1.3 nA at 350 kV cathode voltage; however, measurements indicate the emission current doubles in magnitude for every 10 kV increase in cathode voltage, as is consistent with the Fowler-Nordheim equation. We measured bunch lengths at bunch charges of 1, 10, 60, and 135 pC at 350 kV. We also measured transverse emittance at 1, 30, 60, 100, 135 and 150 pC/bunch. However, we observed some beam scraping during the transverse measurements and subsequently verified the light box as the location using Geiger-Muller tube detectors. By month's end, we had begun an investigation to determine ways to reduce the scraping.

Further high-power radiofrequency (RF) testing of the cryounit remained on hold pending development of suitable warm ceramic windows. Qualification of the interlocks on the cryounit was completed to aid in preventing accidental window breakage like that which occurred during last month's unsuccessful 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; its cause is not fully understood.

Meanwhile, construction of the FEL Facility has been proceeding rapidly, and its cryogenic system will be ready for commissioning 1 July 1997. The injector cryounit needs to be installed there by that time to constitute a load for the cryogenic system. In view of the short time remaining, we reformulated our plans for warm-window development. For the immediate need, we successfully tested and qualified two ceramic warm windows to 10 kW in the resonant ring and vacuum-test fixture. This will enable running the injector with 1.1 mA average current and thereby support all planned commissioning activities and beam-physics experiments through achievement of first light. The windows are to be installed in the cryounit on 2 June 1997. A short cold test of the cryounit will follow to characterize window/waveguide performance.

Work will continue on production of 50 kW ceramic warm windows for installation in the cryounit sometime after its move to the FEL Facility. The short-term plan is to produce six 50 kW windows based on the existing design, which has performed satisfactorily under "normal" operating conditions; recent failures are attributed to off-normal operations that led to run-away conditions, depositing extreme amounts of RF power into the windows. Two medium-term programs are ongoing to provide alternative solutions for RF warm windows, the BeO Northrop Grumman windows, and redesign of Jefferson Lab windows. Regarding the former, ceramics are in-house, flanges are in production, and final assemblies are due to be completed by the end of June. Regarding the latter, the JLab design uses a thin wall, water cooled, copper waveguide support for the ceramic braze joint. Ceramics have been ordered from Wesco and will be ground locally. Prototype assemblies are expected in August 1997.

WBS 3 - CRYOMODULE

ITS Operations

Two new ceramic warm windows were installed on the 1/4 cryomodule. These windows are rated at a reduced power level of 10 kW and will support first light operations. All cryomodule interlock systems underwent a complete ground up qualification in preparation for additional cryomodule operations. Both cavities were run without incident. Waveguide vacuum conditioning was required and was accomplished in 1-2 hours to reach the 10 kW power level. Waveguide vacuum and thermal performance was consistent with stable 50 kW operations.

Warm Windows

An additional warm window was qualified to 10 kW operational levels and installed with the existing window, qualified to 20 kW, on the 1/4 cryomodule in the ITS cave. These windows have been tested and will support first light operation. Work continues on producing warm windows for 50 kW operations. These efforts continue to focus on ceramic material performance and RF loss tolerant designs. Ceramic material from several vendors is being tested and characterized for window production. Additionally studies are ongoing to understand the effects of the firing processes required during window fabrication. At this time ceramic material has been identified with considerably lower rf losses that should lead to satisfactory windows. Two alternate designs being pursued with Northrop Grumman and personnel from SLAC are proceeding and look promising.

Cryomodule Production

Cavity pair assembly and vertical testing has been completed. All cavity pairs have been turned over to the cryounit assembly area. The second cryounit assembly is close to completion and turn over to the cryomodule assembly area. The remaining two cryounit assemblies are proceeding without issue. Cryomodule assembly has installed one beam pipe and is proceeding without issue. Cryomodule assembly schedule remains tight but still doable.

WBS 2 -- BEAM PHYSICS

The main consequence of the experimental finding in the ITS that there is scraping of the outer portions of high-charge bunches inside the light box is a reduction in the measured transverse emittance of these bunches. The outer parts of the beam are weighted heavily in the coordinate and velocity moments that comprise the transverse emittance. Consequently it is more difficult to compare the experimental results with scraping to numerical simulations wherein scraping is absent. In view of this development, we embarked on a series of numerical simulations to assess whether scraping can be significantly reduced or eliminated by varying the laser spot size at the photocathode. For instance, one would expect space charge to have less influence in a larger beam, so perhaps increasing the spot size will reduce scraping. At month's end, the investigation was in progress.

Simulations from cathode to wiggler were also done by including the cathode-anode spacer for lower electric field at the cathode, as is now the case in the ITS. The present status is that it has been easy to find settings that deliver the required beam at the wiggler, but the bunch lengths in the injection line are longer than desired given the performance specifications of the interferometric bunch-length diagnostics that will be installed there. These simulations are continuing in an effort to find solutions with acceptably short bunches in the injection line.

Considerable progress was 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.

The Particle Accelerator Conference was held 12-16 May 1997 in Vancouver, BC, Canada. Fourteen papers related to the FEL were presented by members of the Accelerator Division. Among these were two on the theory of coherent synchrotron radiation (CSR), and they were well received. We were able to discuss our plans for simulations with other CSR investigators, most notably those from DESY who have developed a simulation tool to characterize the buncher chicanes planned for the TESLA FEL. The DESY people have done excellent work and have been innovative in overcoming some of the inherent complexities. However, their code uses "particles" in the form of sheets in the vertical plane that move on orbits that are predefined by way of assigning them specific initial conditions. As they propagate, the sheets set up a model force that influences orbits of test particles. A disadvantage of this approach is that discreteness in the horizontal plane can generate artificially high numerical noise. Moreover, self-consistency is lost because there is no feedback from the evolving distribution of test particles to the force generated by the sheets. By contrast, we will use macroparticles in the bend plane, each with a Gaussian density profile to ensure continuity of the beam and thereby suppress numerical noise, and we will let them move self-consistently. We (in particular, Rui Li) are trying to develop an efficient algorithm for the force calculation, and discussions with the DESY people at PAC suggested a refinement in our approach that should lead to more efficient calculations. Once developed, we will be able to simulate the IRFEL lattice and make predictions to compare with results of the planned experiments. We also will be able to assess the efficacy of alternative lattice designs that have been proposed, e.g., by SLAC and Duke at the PAC, for canceling the CSR force.

Regarding other PAC highlights, our work on the multislit transverse-emittance diagnostic received considerable interest. That the team was able to build and commission this device with beam from the photocathode gun prior to the PAC is a noteworthy accomplishment. There is also considerable interest in the accelerator and FEL communities in developing x-ray sources by way of Thomson scattering from electron bunches, and several papers were presented at PAC on this subject. We (specifically Geoff Krafft) also presented a paper concerning production of short (picosecond), bright x-ray pulses that will occur as a by-product of lasing with the FEL, showing that the FEL competes well with other potential sources of short-pulse x-rays, and that upgrades of the machine will likewise generate even brighter x-ray beams.

WBS 4 -- IRFEL COMMISSIONING/OPERATION

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. We settled on an overall commissioning process in which a "commissioning planner" coordinates the activities of "principal investigators" and an "FEL experimental coordinator". The latter will interface with the "program deputy", who in turn directs the activities of the machine operators. Interfaces between these principals, FEL management, and Division management have been identified. Having settled on this overall commissioning process, we made a first cut at defining commissioning "teamlets" to turn on various IRFEL systems. This is one of the first steps in lining up necessary manpower, an effort that will evolve continually in the coming months.

Detailed plans were formulated for the content and manning of upcoming gun experiments in the ITS. The content is essentially unchanged from earlier plans that had been postponed due to the field-emission problems discussed in the Injector Test Stand section above. However, we are uncertain whether it would be prudent to spend the time necessary for executing all of those original plans, i.e., to characterize the longitudinal and transverse beam properties at bunch charges pertaining to "zero current", first light, and full-power operation, then to look at photocathode lifetime, performance at higher voltage, performance at other bunch charges, etc. Final decision on priorities awaits the outcome of the experiments in progress, as well as input from our Navy sponsor.

We made considerable progress establishing locations and types of weak-field corrector magnets based on the measured performance of various prototypes constructed to date. This activity is continuing, and our goal is to finish it very soon, pending the outcome of additional measurements in our Magnet Test Stand of existing prototypes that have been slightly modified for what hopefully will be improved field quality.

Facility

This month again showed rapid progress on the facility. The exterior siding was completed. By the end of the month the labs were ready for occupancy and drywall work was ready to begin downstairs and in the stairwell. Drywall work was completed in the injector area and the equipment room. Painting was completed in the gallery and labs. The stairwell and spire glass were installed. All HVAC units were connected to chilled water. HVAC return ducting was completed. Plumbing work was completed less the fixture installation. Tiling was 90% complete in the labs and gallery and started in the bathrooms. Electrical progress was also great.

Hookup of the HVAC units was underway at month's end. The wall outlets had been powered and tested. The cryogenic lines finished welding into the system after welding of the sleeves and installation of the transfer lines in the sleeves. 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. The LCW hookup to the South Linac occurred over Memorial Day. We performed 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. The communications rack was hooked up in the communication room. Safety systems finished box duct installation and began pulling cable and hooking in run/safe boxes, etc. The pressure vessel for the gun HVPS was set in placed, cut to the proper height and grouted in. RF staff placed racks in final position above the waveguide penetrations. The elevator installation was begun. The hydraulics were set in the room and plumbed in. The shaft was installed in the main hole. The optical tables for the accelerator vault were received. Delivery of stands for the wiggler and the optical tables occurred. Approximately 20 optical-table, magnet, and wiggler stands were bolted in downstairs along the first-light line. A landing pad was constructed, attached to the outside of the facility's loading door, and load tested. Dirt is finally dry enough to be mounded up around the building with building grounds and sealing blankets being installed next to the concrete. Design detailing on the clean room was completed with finalization of the electrical wiring plan. Despite having to co-exist around tilers, electricians, etc., the photo-injector clean room was delivered, assembled, and installed except for electrical hookup, and installation of the air handler. The facility is on track to be complete in early July and at the present time presents no significant limitations for the installation of FEL hardware.

Upcoming Meetings and Reviews

SURA Maritime Technical Advisory Committee, June 9-10, 1997

Laser Processing Consortium Meeting, June 25-26, 1997

International FEL Conference, Beijing, August 18-22, 1997

SURA Science and Technology Review, Sept. 16-17, 1997