To: J. Cook, D. Helms, W. Skinner

cc: Division (M7), FEL Coordination Group

From: F. Dylla

Subject: IR Demo Project Weekly Report, January 26-30, 1998

Date: January 30, 1998

Management

Agenda topics for the Feb. 17-18th Navy program meeting were generated and agreed upon. The meeting will include status report on the installed FEL hardware; a review of the commissioning results to date and the commissioning plans for the remainder of the year; a status report on the upgrade activities and a discussion of the possible outyear upgrade options.

Discussions continued with BNL on potential collaborative activities with regard to FEL development and applications. An MOU which covers these activities was signed by the respective light source managers.

On Jan. 28th, F. Dylla attended the biannual meeting of the AIP Corporate Associates Advisory Committee. Contacts were renewed with research directors at Lucent, IBM Research, Xerox, and Ford Research. All requested status reports on the research proposals which are currently being prepared for the IR Demo.

On Jan. 30th, Don Swenson from Linac Systems visited the laboratory to discuss the company's current effort to develop hardware for RF energy recovery which is being performed under a SBIR contract to DOE.

Installation Activities

This week the injector gun was HV processed, heat treated, and a cathode was made and tested. A leak in the SF6 system was also found and fixed.

Two 8 kW klystrons for the FEL cryomodule satisfactorily passed their tests this week. They will be installed Monday. Testing will continue to find a spare unit.

To make the injector more robust, the RF software was modified and tested. Additional tests will be done next week when the RF system is operated.

The CAMAC RF buffer cards were modified to allow better contact with their mating connectors.

The collimator next to the optical cavity was repositioned this week. The mounting of the first pellicle was modified and is being installed today.

The first set of data for the DY, 180° bend magnet was completed and is in review. The vacuum chambers for both DY magnets are ready for cleaning and installation later this month.

Installation is in progress for the piping to provide LCW cooling for the trim magnet resistors.

Equipment for the MPS is in-house and is being assembled for installation early next week.

Commissioning Activities

The FEL cryounit and cryomodule are being cooled to 4K today. Cooldown to 2K is anticipated to occur during day shift Monday, 2 Feb. 98. Checkout of SRF and RF in both the cryounit and cryomodule will follow, and it appears that there is sufficient time to complete both before 0800, 5 Feb. 98, at which time plans are to resume FEL commissioning with electron beam. Meantime, we have made steady progress in refurbishing the gun. High-voltage processing and heat treatment were completed this week, and cathode preparation commenced this morning.

The GEN target chamber is scheduled to be installed on 17 Feb. 98, at which time the FEL will be used to irradiate targets for polarization in support of the nuclear physics program. Commissioning goals for the preceding time, 5-17 Feb. 98, are:

- MUST: Develop "save/restore" machine settings for GEN runs; verify them just prior to 17 Feb. 98 shutdown.

- SHOULD: Obtain first-light beam quality in injector (~6 mm-mr @ 60 pC bunch charge).

- LIKE: Commission injector with first-light current (1.1 mA).

The shift schedule for the next three months was completed and distributed to affected Jefferson Laboratory staff.

Installation and configuration of the Machine Protection System (MPS) is progressing. We project that enough of the MPS will be complete, prior to resumption of beam operations, to permit running 1.1mA current in the injector before shutdown for GEN target installation, and we want to keep that option open per the aforementioned goals. Discussions about MPS set points for the currents in the dump-line magnets have been ongoing, and a formal meeting was held this week to decide on strategies and inputs.

Over the past few months, Rui Li has made great progress in simulating the beam dynamics attending coherent synchrotron radiation (CSR). She has written a two-dimensional self-consistent code that incorporates gaussian macroparticles and has been benchmarking it. First, she successfully benchmarked it against analytic theory for a rigid-line bunch propagating through a simple 90-degree dipole magnet. Next, she compared the code's predictions to those of DESY, which lacks self-consistency but should be accurate when CSR is only a perturbative effect. To do so, she invoked a model problem posed by Paul Emma at SLAC which involves a single dipole. Predictions for CSR-induced energy spread were in agreement for this problem, which is one where the DESY code can be validly applied. Rui also modeled the first optical chicane in the FEL, obtaining 2.4% emittance growth for 120 pC bunches. Interestingly, this compares with 3% emittance growth predicted analytically from the rigid-line bunch model accounting for transients (one obtains roughly 10% growth if the steady-state CSR field is used, which we had inferred to be an upper bound). The reason for agreement is that the simulation indicates the line bunch serves as a fair approximation to the actual bunch configuration throughout the chicane. This will not be true, however, in the first recirculation arc of the FEL where the bunch dynamics is quite violent. Rui will be simulating that arc in the near future.

Presently, the basic difficulty with the macroparticle code is that it takes a long time to run, several hours of Cray II CPU time for the aforementioned examples, principally due to the necessary incorporation of causality. Rui has been optimizing the code to reduce run time, and she continues to do so.