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

cc: Division (M7), FEL Coordination Group

From: F. Dylla

Subject: IR Demo Project Weekly Report, September 8-11, 1998

Date: September 11, 1998

Management

This week was devoted principally to installation and maintenance activities. Highlights for the week include: (1) reassembly of the photocathode gun after polishing the cathode ball and anode plate, (2) start-up of the vacuum bake of the gun; and (3) fabrication of two new viewer assemblies to be installed in the second recirculation arc for facilitating commissioning with energy recovery.

On Thursday, 11 Sep 98, we held an internal review of the Machine Protection System (MPS) to establish the status of the MPS inputs, MPS hardware, and associated documentation. Check-out of the full MPS will be done next week as part of our operations start-up activities.

Meetings were held this week to identify the remaining work necessary for completion of the Laser Safety System (LSS) and for identifying the procedures needed for use of the FEL light by FEL experimenters. These are the last remaining items to be closed out from the FEL Accelerator Readiness Review held in May.

FEL Installation/Maintenance Activities

The following tasks were completed this week ("*" denotes higher-priority tasks):

* Flush drive-laser transport line with dry nitrogen.

* Install 60 Hz raster interlock PCBs for injector and energy-recovery dumps.

* Replace Video Mux with updated version.

* Remove itserve and upgrade felsrv 2 to HP-UX 10.20.

* Complete installation of beam scraper.

Align scraper after installation.

Install additional layer of water jugs on top of straight-ahead dump.

* Perform pump-down tests of 2F06A.

Remove, repair, and reinstall beam-position monitor (BPM) 4F06.

* Increase size of view ports for 5F01 and 5F04.

* Check alignment of quadrupole magnets and wiggler in 2F region.

* Reconnect BPMs 0G01, 2F02, and 4F06.

* Reconnect trim magnets 0G01, 2F02, and 4F06.

FEL Commissioning Activities

According to progress on refurbishing the gun, we should be able to pull beam off the gun on Friday, 18 Sep 98, although that could conceivably slip to the following Monday. The gun is being set up today (Friday, 11 Sep 98) for vacuum baking over the weekend. High-voltage processing of the gun is scheduled for next week, as are hot system checks. Beam operations are slated to begin in earnest on 21 Sep 98.

A draft, augmented procedure for lasing cw with energy recovery was prepared this week, extrapolating from our accomplishments last month. The general idea, by necessity, is to concentrate on obtaining low-loss recirculated beam while containing it within the energy-recovery dump line. Most likely the difficulties we need to overcome are:

- poor dispersion profile in the back leg that, in turn, generates poor longitudinal match during energy recovery;

- possibly poor transverse match of the recirculated beam into the cryomodule (chromatic aberrations may lead to mismatch when the beam is far off momentum);

- insufficient configuration control (that arose due to the time pressure created by the upcoming FEL Conference, a situation that will not be present when we turn back on).

Using a simulation he wrote, D. Douglas found how to compress a large energy spread after the wiggler into a small energy spread at the energy-recovery dump. The idea is to introduce quadratic nonlinearity, i.e., nonzero T_566, 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 that the beam follows through the recirculation loop.

Once the basic setup for strong lasing is established (starting in pulsed mode, of course), nothing prior to the wiggler can be touched. The available knobs for energy recovery are then:

- trim quadrupoles for M_56 adjustments,

- sextupoles for T_566 adjustments prior to reinjection into the cryomodule, - trim dipole string for path length adjustments,

- reinjection (5F) quadrupoles for transversely matching the recirculated beam into the cryomodule,

- extraction dipole string (FELEXT) for centering the waste beam in the dump.

All adjustments will need to be in small increments from the basic setup because the beam properties in the dump line are sensitive to all of these knobs.

B. Yunn is beginning an effort to extend the PARMELA deck to include the entire beamline past the wiggler for simulations of the beam dynamics with energy recovery. The code needs to be generalized to include sextupoles, and Yunn believes he can do so.

C. Bohn, R. Li, and B. Yunn put together a plan for running simulations of the first recirculation arc that include coherent synchrotron radiation. The plan is designed to support the parametric studies that can be done experimentally. Probably one complete simulation can be done this month, and due to lack of computational funds the remaining simulations must be postponed to October, when computational funds will be reinstated for next fiscal year.