Management

January 1998 was the sixth 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. Summary of the technical progress of the remaining three open cost accounts is given below.

CA 221 Scaleable Optical Cavity

All work in this area is in connection with the commissioning of the FEL.

CA 321 Upgrade Cryomodule System

The procurement for the cryounit shields was placed and delivery is expected on schedule. Additional procurements are limited to warm window components, beam line valves (4), and HOM absorber ceramics. The modification of existing CEBAF components for FEL configuration is underway in the Jefferson Lab machine shop. Work continues on extending the performance of the cavities and will continue until performance meets anticipated fundamental limits or schedule constraints dictate.

During the Shutdown period the 1/4 and full cryomodules were warmed to room temperature. The 1/4 cryomodule was inspected for potential beam line obstructions. A valve was found partially closed and was opened. Additionally, new ceramic warm RF windows were installed on the 1/4 cryomodule.

CA 421 Commissioning Preparations

This account has been closed to further obligations since October. Remaining cost obligations (on corrector magnets and the Analog Monitoring System) should be closed out in January.

CA 521 IR FEL Commissioning

Jefferson Lab's liquid helium plant underwent a scheduled, thorough refurbishment during January. Consequently there was no commissioning of the FEL with electron beam. Instead, the month was devoted to preparing the machine for first light (see the Installation summary below) and understanding the data collected during the December run. Restart of commissioning with electron beam is scheduled for 5 Feb. 98. (Note added in proof on 19 Feb. 98: Restart turned out to be unsuccessful due to difficulties with the electron gun. The gun is being refurbished, and restart is presently envisioned to occur on 5 Mar 98.)

The photocathode gun was refurbished to repair a slow vacuum leak. It was successfully baked, processed with voltage up to 410 kV, and heat treated, and a cathode was made.

Considerable work went into installing and configuring the Machine Protection System in preparation for running 1.1 mA average current as is necessary for first light. This effort required an interplay between modeling the dump lines and electronic hardware configurations to establish set points and time scales for guarding against burn-through that would occur in the presence of hardware failures. At month's end most of the requisite hardware was either installed or ready for installation, and most of the set points had been established. The task was slated to be completed in mid-February.

As regards the anomalously large injector emittance associated with 60 pC bunches that had been measured in December, the cryounit was discovered to have an internal valve that was not completely open, subtending into the beam aperture a distance somewhere between 0.95 cm and 1.1 cm. During the December runs, this necessitated steering around the blockage, and presently it is thought that the concomitant beam "misalignment" was responsible for the observed distortion of the beam's transverse phase space. Simulations of an offset beam with PARMELA lent additional evidence to this conclusion.

The development of a self-consistent simulation of coherent synchrotron radiation (CSR) progressed to the point of modelling the first optical chicane in the FEL, resulting in a predicted CSR-induced emittance growth in this chicane that, with the planned bunch charges, would be too small to resolve with the quadrupole-viewer measurement technique. This result is favorable for lasing in that it suggests beam quality will be sufficiently preserved. Of course, we will measure emittances as we set up the machine. Modelling of the first recirculation arc is pending.

FEL INSTALLATION

Installation highlights in January included:

Two ceramic warm windows rated to 40 kW of RF power were installed in the cryounit.

At the beginning of the month it was found that two of the eight klystrons for the cryomodule could not reliably be powered to 8 kW, the value needed for first-light electron beam. They were replaced, and we now have the necessary bank of eight 8 kW klystrons.

The first set of data from the Magnet Test Stand for the first 180-degree (DY) dipole magnet was completed and is in review. The vacuum chambers for both 180-degree dipole magnets are ready for cleaning and installation. The repaired coils for the second DY magnet were received from the vendor, and in-house refurbishment of this magnet was started. The last DV magnet was installed and the alignment checked. The recirculation bends are now essentially complete minus the 180-degree magnets and chambers, the trim quadrupoles, and the sextupoles. The high-field-quality air-core correctors for the straight-ahead machine were received from the vendor, and they are in the Magnet Test Stand for characterization as a family. Upon restarting FEL commissioning in February we will continue to use the spare CEBAF air cores already installed, but we will replace them prior to attempting to achieve the high electron-beam quality needed for first light.

Engineers from Svetlana visited and personally tested the troublesome spare 50 kW klystron. It would only make 20 kW before failing and is therefore being returned to Svetlana per their instructions.

The alignment of the cryounit and its constituent cavities was checked and found to be accurate within about 1 mm, but an internal valve was discovered not to be fully open. This may solve the alignment problem that was found during commissioning in December (see detailed comments in the commissioning section above).

The straight-ahead dump line was reconfigured to accept the target chamber required for irradiating GEN targets in mid-February to support the nuclear-physics program.

Work continued in installing and setting up the optical systems for lasing. Tests of the alignment HeNe's suggested it would be advisable to modify the telescope mounts and the pellicle alignment registration. The drawings were modified and changes submitted to the shop. The software for the monochrometer was successfully operated. FEL spectra can now be directly read in EPICs.