March 13, 2001



FROM: Dieter Walz

SUBJECT: Coherent Bremsstrahlung Beams to End Station A for Future Experiments E-159, E-160, and E-161

A meeting was held on 3/8/2001 with Peter Bosted, Roger Erickson, Ted Fieguth, and Dieter Walz attending. The purpose was to identify the tasks necessary to design, fabricate and install the facilities that will allow us to bring coherent Bremsstrahlung beams to ESA. The project consists of two major facilities, namely the magnetic transport system to dispose of the spent electron beams, and the goniometer facility and associated small aperture collimators to produce quasi-monochromatic coherent Bremstrahlung beams. The desired maximum electron beam energy is ~50 GeV. The A-bend transport system was upgraded a few years ago to handle such energies, but the four A-beam dump magnets are still limited to the original 25 GeV level. The specific solution to upgrade the dump line which I proposed to the collaborations to prepare the experimental proposals is identified as ID IIB on the solutions table dated 1/28/92, which is attached. Another solutions table dated 2/8/94 and its accompanying memo is also attached.

ID IIB proposes a reduction in the total angle of bend from 12° to approximately 8° and the addition of a 3rd coil to each magnet pole This new trajectory requires another beam dump to be mounted above the existing A-beam dump D-11 just ahead of the concrete buttress shielding the ESA alcove and the end station from D-11, see attached sketch. I have a suitable beam dump in storage which was used originally in the D-2/D-10 applications. It is 30 Xo long, adequate to attenuate a 50 GeV beam, and is rated at 60 kW. With sufficient flow rate, it can be pushed higher, to 80 kW and perhaps even 100 kW.

We agreed that for logistical and organizational reasons, it makes sense that the A-beam dump beam transport system upgrade should be undertaken by the Technical Division and the refurbishing and upgrading of the goniometer and associated collimation and g -beam monitoring system should be done by the Research Division. Roger Erickson suggested that a January 2003 date should be a goal for early commissioning.

The following specific topics were briefly discussed:

  1. Dump magnets and supports to be removed from the BSY at the earliest beam downtime that allows approximately 10 working days to accomplish the tasks. Magnets are 4.72 D120C with a 3-inch gap.
  2. A vacuum spool piece is required to continue delivery of electron beams to ESA in the interim. Spool piece to be designed and fabricated now so it is available if an early opportunity for magnet removal arises.
  3. Roger says next ROD day is tentatively March 21. Several of us will attempt to go to the BSY and look at magnet coils, vacuum chambers, future location of goniometer.
  4. Magnet coil design to be reviewed, decision to be made how many new coils including spares are needed (there are four new ones in the Warehouse). Coil fabrication to commence before removal of magnets from the BSY. Presently, coils are water-cooled copper conductor.
  5. The issue of a new soft bend (B< 500 G) to be placed ahead of the first dump dipole was brought up again. Peter will do an analysis to either strengthen the case or put it to rest.
  6. Magnet Power Supply - - old dump magnet supply is (was) rated at 1050A/660V/700 kW. Present condition unknown. Roger has talked to Martin Berndt about perhaps internally reconfiguring the SLC ARCS power supply, and also to Steve Lowe about dc cable routing for ~1000 A from Building 136 to the dump magnets. There are also 4 ea 567 kW power supplies in Building 108 which perhaps could be used. A new power supply might have eight months delivery time, costs unknown.
  7. The goniometer is to be refurbished with vacuum compatible stepper motors, cabling and micro-switches as needed. The special steering SEM to properly place the beam on the diamond targets is again required. Its whereabouts are unknown as of this date. The goniometer is to be installed at a location west of its historic location for most of the earlier experiments to gain an approximately 90 m lever arm to the end station.
  8. Dieter is looking into suitable diamond targets, 70-80m m thick. Several promising leads exist. Questions arouse about diamond target orientation. Robert Avakian (Erivan) recently asked whether additional rotational degrees of freedom could be provided. This needs further study.
  9. Ted talked about the control system to operate the goniometer. Much of the hardware was either cannibalized over the years or is obsolete. He will spearhead an investigation of what is needed. We also talked about software issues, who might be able to help us. Could/should one use Labview? It is not too early to start on the Control System
  10. We agreed to have our next meeting soon after the March 21 BSY visit.


Cc: Attendees 48 S. Mao 75 S. Williams

20 P. Anthony 48 S. Rokni