Minutes of the Orion Technical Meeting: Oct. 9, 2000

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Location: Room 144D (Beige Room),

Admin. and Engin. Bldg., SLAC

Present: Clay Corvin, Johnny Ng, Robert Noble, Dennis Palmer,

Robert Siemann, Dieter Walz

Minutes recorded by: Robert Noble

1. Meeting time:

Due to schedule conflicts, the time of the Orion Technical

Meeting will be changed to one hour earlier. Future meetings

will be on MONDAYS, 9 AM in the BEIGE ROOM (Room 144D) in

the A&E Building (Bldg. 41) at SLAC.

2. Agenda Items Discussed:

- D. Palmer briefly reported on the initial use of the

newly-received PC version of TRANSPORT (AccelSoft PBO Lab

2.0, Gilespi Assoc.; accelsoft@ghga.com). A trial design

of a transport line from the NLCTA injector at the 50 MeV

point (after the chicane), through the shielding wall

at a 20 degree angle, and into the proposed Orion low-energy

experimental hall was performed with a simplified input file.

A triplet of quads are placed on either side of the wall

so only a hole accomodating a beampipe with flange needs

to be bored. Improved calculations are in progress using

more accurate beamline component descriptions and input

beam parameters.

- In preparation for J. Rosenzweig's visit to SLAC on Oct.

12 to discuss the Orion photoinjector design, R. Noble

summarized the current design parameters for the proposed

S-band Photoinjector. The assumption is that the Orion source

will be based on the well-known BNL/SLAC/UCLA design of which

several units have been built. Although an X-band photoinjector

would be a natural source for the 11.4 GHz NLCTA accelerator,

little experience exists in such a source, and the risk to the

planned two-year Orion construction schedule would be high.

Lower frequencies than S-band simply make it increasingly

difficult to obtain a short enough bunch for the X-band

accelerator. The suggestion was made that the design bunch

length should be reduced from 10 psec to 2.5 psec to facilitate

this injection. The issue was raised that simultaneously

obtaining a 1 nC bunch charge, 7.5E-7 m-rad normalized rms

emittance and 2.5 psec bunch length may be too optimistic.

Although it has a low quantum efficiency, a copper cathode

is the default choice due to its long-life and robustness.

A consistent set of design parameters that can likely be

achieved consistent with the perceived user needs will be the

goal of the October 12 meeting. These choices will impact the

parameters for the laser and rf systems.

- A new scheme for the RF photoinjector source placement at the

NLCTA front-end was discussed. Because the present long-pulse,

electron gun at NLCTA will be needed for some experiments

in the Orion program, runtime will be shared between the

new RF gun and the NLCTA gun. Given the limited overhead height

and limited aisle space, it was suggested that only one source

be operating into the accelerator and the other be stored

on its own support cart offline (for repair or modification).

The sources would be interchangeable with either one able to

be attached to the same front-end beampipe flange. The two

sources and their carts can be located on a narrow-gauge track

("The Orion Express") to facilitate the interchange. D. Walz

will sketch out a rough design for this concept.

- A new scheme for the extraction beamlines needed at the high-

energy (300 MeV) end of NLCTA to send beam to the Orion

high-energy hall was discussed. The spectrometer magnet at the

end of the NLCTA beamline is presently followed by two

beampipes terminating in the iron beam absorber. For Orion,

it was suggested that two holes be bored through the absorber

at these entry points. The angled-beamline would be used for

normal beam extraction to the high-energy hall. The straight-

ahead hole would be plugged with iron but be removable if a

future experimental program required this beam port. With the

straigh-ahead hole plugged, the beam absorber with spectrometer

magnet locked off becomes a safety device allowing personnel

to work in the high energy hall when the low-energy part of

NLCTA and any rf systems are operating.

3. Added Notes:

Although not part of this meeting, it should be noted that

later in the day a discussion was held between R. Siemann,

R. Noble, D. Walz, Marc Ross and Chris Adophsen regarding Orion

RF Gun placement and space issues at End Station B where NLCTA

is located. The above-mentioned concept for having inter-

changeable electron sources was agreed to be a reasonable

working plan for the Orion Technical Design Study. This

would always allow returning to the original NLCTA source

arrangement. In addition, NLC cavity testing will need

high-quality, single bunches (anticipated for a few hours

per week), and the new Orion RF source can easily provide

this service as part of its operating schedule.

Regarding space at End Station B, the floor area north of the

NLCTA enclosure will be partially occupied for at least the

next three years by the racks, power supplies, modulators

and klystrons for the so-called NLC "8-Pack" rf-station test.

The Orion program has a need for a 20 foot by 40 foot area

in that neighborhood for the Photoinjector's Laser Room as

well as a small triangular region next to the NLCTA north wall

where the Low-Energy beamline connects to the Orion Low Energy

Hall. Participants agreed to remain in contact as the "8-Pack"

layout is drafted so potential space conflicts can be resolved

early on. Also, coordination of the utility (water and power)

modifications at End Station B needed for the "8-Pack" test

and the Orion facility is needed in order to avoid conflicts

and maximize the benefit of these improvements to the Lab.

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