Management

July 1998 was the twelfth 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. Highlights for the month include: (1) generation of 311 watts of cw 5 micron FEL light (a new world's record for FELs); (2) demonstration of electron beam recirculation and energy recovery while lasing at low power. All hardware components and operational modes of the machine have now been exercised.

A draft extension of the contract for the period October 1, 1998 to March 30, 1999 was forwarded to the DOE Site Office and Navy Program Office during July for comments. The extension would allow us time to continue processing of SRF cavities for the second FEL module and delay final assembly of the module until we have reached the point of diminished returns on cavity performance. Since the second module is not needed for a period of at least a year, the delayed assembly would yield a higher performance module. This module would continue to serve as a useful testbed of processes for the CEBAF Energy Upgrade and as a hot spare for both the CEBAF accelerator and the FEL linac.

CA 221: Scaleable Optical Cavity

This month we tested the high power outcoupling mirror for 5 microns with 90% reflectivity. This outcoupler was used for the new 311 watt cw power record that was obtained during FEL commissioning. John Foley, an expert in optics modelling and design from Mississippi State, joined the FEL team in July for a 6-month sabbatical visit. Dr. Foley began his task of modelling our present design for scaleable optical cavities for the Demo FEL and consideration of potential alternative designs that might have performance and/or reliability improvements.

CA 321: Upgrade Cryomodule System

We received final three cryogenic shields for the upgrade cryomodule; completed all remaining HOM load braze assemblies and installed four ceramics to support first cavity pair assembly. HOM loads will have final RF characterization completed.

CA 421: Commissioning Preparations

This account has been closed to further obligations since October.

CA 521: IR FEL COMMISSIONING

Several commissioning tasks were done during the first week of the month. These included, for example: checking the magnetostrictive tuner for one of the cryounit cavities; running the cryomodule cavities at their peak gradients; doing lasing studies with both cw and pulsed beam; and replacing the outcoupling mirror in the optical cavity with a 90% reflective mirror to deliver higher power (the original mirror was 98% reflective, as inferred from the laser pulse profile, and in particular the short fall time at the end of the laser pulse).

On 9 July 98 we lost the photocathode due to arcing and vacuum activity near 350 kV. Recesiation did not help; therefore, we decided to replace the cathode. Mid-month activities centered on restoring the gun, including changing out the photocathode wafer. The ultimate result was that, despite successful high-voltage processing to near 500 kV, we had difficulty holding off voltage beyond 335 kV after cesiation. Consequently we operated the gun at 330 kV, lower than its nominal operating voltage of 350 kV.

Despite the difficulties with the gun, by month's end we had achieved three notable accomplishments: (1) recirculating pulsed beam all the way around the recirculation loop while recovering energy from the macropulses (which means beam was taken through the entire machine), (2) lasing with this beam while maintaining energy recovery from the macropulses and keeping the beam squarely on the viewer in the energy-recovery dump, and (3) lasing into the straight-ahead dump to achieve 311 W cw.

FEL INSTALLATION

Installation highlights in July included:

Completing installation of all eight sextupole magnets and air-core corrector magnets in the recirculation arcs, adding neutron shielding to the straight-ahead dump, wrapping mu-metal where possible through the recirculation loop to screen the Earth's magnetic field, installing beam-loss monitors along the recirculation loop, and hooking up most of the back-leg diagnostics.

Installation and alignment of the optical cassette can to the polymer roller assembly in Lab 1 and putting the transport line to Lab 1 under vacuum; completion of the electrical hookup to the large roller assembly and near completion of the electrical hookup to the web roller; verification of the ability to operate two labs at once by inserting a 50% mirror in Lab 1 and showing that a surrogate HeNe laser beam in Lab 3 was unaffected except in intensity.

Replacing the outcoupling mirror in the optical cavity with a 90% reflective mirror.