Management

September 1998 was the fourteenth month for the $3.7M IR Demo Upgrade and Commissioning project. Cost and schedule performance are described in the accompanying Performance Assessment report by Gordon Smith. This is the last detailed cost and schedule report for the project. Subsequent reports will track the only remaining open account, CA 321, the upgrade cryomodule system. Highlights for the month include: (1) completion of major maintenance on the photogun including repolishing of electrodes and replacement of pumping elements; (2) check-out of many hardware systems needed for the kilowatt demo and (3) sign-off of the Navy/DOE extension of the IR Demo contract to March 1999.

CA 221: Scaleable Optical Cavity

A major alignment check and readjustment of the wiggler viewers was performed to bring them back to the original tolerances set in April. All of the viewers were found to be within 100 microns or better horizontally but exhibited a vertical displacement of typically 600 microns. They were reset to within 100 microns vertically also. This brings them well within lasing tolerance. Subsequently we adjusted the wiggler position and have plans to readjust the downstream quadrupoles to bring them even more closely in line. The alignment of the optical cavity fiducials was reset. The purpose of these adjustments is to allow us to bring the performance of the FEL to its maximum value quickly with a minimum of tuning. The readjustment of the quads will be performed in October as will a final check of the wiggler position.

The Laser Safety System was installed in Lab 1 and an update of the specifications for that system agreed upon and given to the electronics group for fabrication. An internal review of the system and procedures is scheduled for mid-October. Nearly all hardware is complete for Lab 1. In addition, programming of the scanner system for the polymer demonstration has been tested and is nearly operational. Measurements of the high power 3 micron mirrors are underway at China Lake. A rewrite of the Laser Safety Operational Procedure is nearly complete incorporating all changes to the system since April. Finally, the drive laser system was cleaned and realigned to bring its power and stability performance back to what we had seen last December. We have experienced a gradual loss of about 20% in green power. Although several problems were uncovered and corrected there remains unknown the root cause of our drive laser power loss. We continue to pursue this investigation.

CA 321: Upgrade Cryomodule System

Cavities IA074, IA076, IA021, IA023 were RF tested at 2K under various cooldown conditions to identify if the excessive chemistry during the repair introduced enough hydrogen to reduce the Q-value if cooled down with cryomodule procedures. Results showed that IA021, IA023 cavities showed sloping Q value-vs-gradient curves. These two cavities were heat treated at 900 C for four hours in a vacuum furnace. IA021, IA023, IA006, IA004 were then tested with the same slow cooldown as above. This confirmed that IA021, IA023 were repaired and that IA006, IA004 did not suffer from this problem.

Preparation for assembly of the module is under way with IA074, IA076 tuned and aligned for final assembly steps. All peripheral components are completed for this pair and a mockup assembly was performed to test the new alignment scheme and finalize procedures. Mock fitup of a pair also occurred to finalize cryounit assembly procedures of the new dogleg couplers. Shields were fabricated for the magnetostrictive tuner tests. Teststand and vacuum hardware were cleaned and prepared for the final assembly of pairs.

CA 421: Commissioning Preparations

This account has been closed to further obligations since October.

CA 431: IR FEL Commissioning

At the beginning of the month, the photocathode gun was being reassembled after careful repolishing of the ball that supports the cathode. Following "standard" procedure, it was then vacuum-baked and high-voltage-processed, and the cathode was heat-cleaned and cesiated. Unfortunately the photoresponse of the cathode after cesiation was very poor, and field emission down the beamline showed up at around 300 kV. Another attempt at high-voltage processing, heat cleaning, and cesiation likewise failed. A diagnosis of the location of the field-emission site was then attempted with the aid of PARMELA simulations to guide the interpretation of observations of the field emission. The outcome was inconclusive. The best hypothesis is that the cathode itself field-emitted, but the rim of the hole in the ball in which the cathode is inserted field-emitted when the cathode was retracted due to an accentuated surface electric field. We decided to attempt helium-arc processing rather than go directly to opening the gun. The processing was done on 30 Sept. 98, with the outcome to be determined during the first week of October.

(Note: at press time for this report, after the cathode was removed, a crack was found near the outer edge of the GaAs wafer, which is the most likely source of field emission.

A refined Injector Checkout Procedure and an augmented High-Power Setup Procedure were written. A key feature of the latter is compression of a large energy spread after the wiggler into a small energy spread at the energy-recovery dump. The idea is to introduce quadratic nonlinearity by reinjecting a long bunch length into the cryomodule so as to take advantage of the RF curvature for momentum compaction. To do so reduces to a phase-matching procedure that cannot rely on the cryomodule gang phase because the gang phase has to be set for achieving a minimal bunch length at the wiggler for strong lasing. Instead, it centers primarily on adjusting the path length of the beam around the recirculation loop.

The simulation code PARMELA was generalized to include sextupole magnets, and by month's end a PARMELA deck for the entire FEL machine had been prepared. The purpose for developing the deck was to provide a tool for ascertaining more fully the character of the longitudinal phase space of the beam as it propagates through the machine, and thereby lend support to the aforementioned High-Power Setup Procedure. Simulations of the full machine are slated for October.

We also worked toward certifying the full Machine Protection System (MPS). By month's end, about 80-90% of the MPS was certified, with a residual four-item punch list awaiting resolution. Certification was slated to be completed during the first week of October.

FEL INSTALLATION

During the extended shutdown, many hardware and software updates were made, and they are enumerated in detail in the weekly reports. The principal hardware updates that bear on commissioning consisted of: configuring the viewers in the 180-degree dipole magnets so that they now work; installing two new viewers in the second recirculation arc; installing the beam scraper in the first recirculation arc; modifying various drive-laser subsystems for increased power and better stability of low-power RF; adjusting the 60 Hz raster magnets in the injector and energy-recovery dump lines (the raster currents will need to be reset prior to going cw); and upgrading the gun for increased pumping speed, faster baking, improved heating of the cesiator, and faster exchange of the conditioning and running resistors. Software updates accommodate the new hardware on the control screens and make the Analog Monitoring System functional.

Work on the FEL systems included installation of a low power pickoff on the FEL beam to allow for calibration of the optical transport losses. The optical collimator was cleaned, two nonfunctional picomotors were replaced, and the system was realigned and pumped down. The alignment of the optical cavity fiducials was reset. A major alignment check and readjustment of the wiggler viewers was done to bring them back to the original tolerances set in April. Finally, the wiggler itself was moved by 250 microns to bring it in line with the magnetic quadrupoles.

Significant progress on the Laser Safety System for the user labs occurred. Nearly all hardware is complete for Lab 1. The software for the overall system is complete, providing a one-look status of the safety conditions of all labs by way of the EPICS control system. At month's end, a review of the Laser Safety System had been tentatively scheduled for 16 Oct. 98.