MEMORANDUM

To: Distribution

From: F. Dylla

Subject: Monthly Report IR Demo FEL Upgrade and Commissioning Project, Nov. 1997

Date: December 18, 1997

Management

November 1997 was the fourth month for the $3.7M IR Demo FEL Upgrade and Commissioning project. Cost and schedule performance are described in the accompanying "Performance Assessment" report by Gordon Smith. A summary of the technical progress of the remaining three open cost accounts is given below.

CA 221: Scaleable Optical Cavity

A survey of existing coating capabilities as regards S and P wave losses at 54.7 degrees was completed. Owing to the unusual angle few companies are interested in quoting on the coating despite the relatively easy wavelength. Discussions continue with China Lake regarding providing a designed coating that will meet our requirements.

CA 321 Upgrade Cryomodule System

All eight cavities have been through at least one round of processing and testing. The achieved gradients for all of these cavities exceed 10 MV/m. Given that the cavity-pair assemblies are not needed for cryomodule assembly until later in the fiscal year, additional processing and testing will be done on the upgrade cryomodule cavities to push the maximum gradients. Components for the end-dish bellows assemblies have been machined. A majority of the HOM components and other small components needed for the cryomodule assembly have been received. Successful SRF commissioning of the IR Demo injector cryounit and linac cryomodule (as noted in the commissioning section below) have benchmarked the design changes we made to the standard CEBAF cryomodule design for use in the FEL cryomodule.

CA 421: Commissioning Preparation

This account was closed to further obligations last month (October). By January we expect the remaining cost obligations to be closed out including completion of the delivery of corrector magnets and components for the analog moniotoring system.



CA 521: IR FEL Commissioning

Commissioning activities focused principally on completing the injector, taking tuneup beam from the photocathode to the injection-line dump, and getting the cryomodule ready to accept beam. SRF and RF commissioning of the cryounit was completed. Nominal operating cavity gradients are 12 MV/m for the entrance cavity and 8.5 MV/m for the exit cavity, with unloaded Q at 5x10^9. By month's end we were routinely running beam through the injector and into its dump with average current ranging up to roughly 1 µA and with bunch charges of order 1 pC. Using the first dipole magnet, we measured the electron-beam momentum to be 7.5 MeV/c, to within ±10%, with the two cryounit cavities operating on crest. This value is lower than what was expected based on the nominal accelerating gradients of the cavities measured during the SRF commissioning process; however, we found the cause to be an incorrectly calibrated control- system screen that indicated artificially high cavity gradients. Electron-beam profiles on the viewers were consistent with simulation (PARMELA) results. (Note: After recalibrating the screens, we measured on the evening of 2 Dec. 97 the electron-beam momentum to be 9.6 MeV/c, to within ±10%, with the two cryounit cavities operating on crest, a value consistent with expectations.)

Both SRF and RF commissioning of the cryomodule was completed, resulting in a total available accelerating voltage of > 47 MV.

FEL INSTALLATION

Installation highlights in November included:

Completing all hardware installation from the photocathode to the energy-recovery dump in preparation for running beam not only through the injector, but also through the linac cryomodule (slated for early December).

Nearly completing hardware installation for the full straight-ahead machine. By month's end some vacuum chambers upstream and downstream of the wiggler still needed to be installed, as did one of the injection/extraction (DV) dipoles, raster magnets on the straight-ahead dump line, and shielding for this dump. We decided to install CEBAF-spare air-core corrector magnets as a temporary measure to enable running with tune-up beam as we await delivery of the "real" air- core correctors from the vendor.

The wiggler vacuum chamber was aligned and the electron beam viewers in the wiggler fiducialized with respect to the beam axis. Verifications of the physical stability were completed successfully. Secondary alignment apertures were established to permit alignment of the system without breaking electron beam vacuum. Clean hoods were constructed over the tables and the optical mounts and vacuum hardware placed in preliminary positions on their respective optical tables.

Making substantial progress toward installing the recirculation arcs. Three of the four DX arc dipole magnets were given their initial alignment as the first step of their installation. The first 180-degree arc dipole (DY) was installed in the east arc (minus its coil assembly) to allow vacuum chamber fit-up operations to proceed. The second 180-degree arc dipole (with a completed coil assembly) was installed in its magnetic measurement test stand which is now operational.

The fabrication of three high power (50 kW) warm window assemblies was completed in November. These windows will be installed in the injector cryounit in January during the CHL shut-down.