Beam Position Stabilization Using an Active Collimator

in Hall D at Jefferson Lab

Richard Jones,University of Connecticut,for the GlueX collaboration

American Physical SocietyDiv. of Nuclear Physics MeetingOctober 23-26 2008, Oakland, CA.

APS DNP Meeting, October 23-26, 2008, Oakland, CA2

Tungsten pin-cushion detector

– used on SLAC coherent bremsstrahlung beam line since 1970’s

– SLAC team developed the technology through several iterations

– reference: Miller and Walz, NIM 117 (1974) 33-37

active device

primary collimator (tungsten)

Active collimator design

APS DNP Meeting, October 23-26, 2008, Oakland, CA3 12 cm 5 cm

beam

Active collimator design

APS DNP Meeting, October 23-26, 2008, Oakland, CA4

x (mm)

y (m

m)

current asymmetry vs. beam offset

20%

40%

60%

Active collimator simulation

APS DNP Meeting, October 23-26, 2008, Oakland, CA5

inner ring ofpin-cushion plates

outer ring ofpin-cushion plates

10-4 radiatorIe = 1A

Simulated detector response

Monte CarloMonte Carlo

APS DNP Meeting, October 23-26, 2008, Oakland, CA6

using inner ring only for fine-centering

±200 m of motionof beam centroid onphoton detector

corresponds to

±5% change in theleft/right currentbalance in the innerring

Position sensitivity

Monte CarloMonte Carlo

APS DNP Meeting, October 23-26, 2008, Oakland, CA7

Position sensitivity

intensity inside aperture polarization inside aperture

APS DNP Meeting, October 23-26, 2008, Oakland, CA8

Prototype construction

Pin cushions fabricated Pin cushions fabricated using EDM machine in using EDM machine in FSU Physics shopFSU Physics shop

• pure tungsten too brittle

• machinable tungsten OK

• finding the right material is crucial

APS DNP Meeting, October 23-26, 2008, Oakland, CA9

Prototype construction

partitioned anode (Al) insulating cathode holder (CaB6)

APS DNP Meeting, October 23-26, 2008, Oakland, CA10

Prototype construction

APS DNP Meeting, October 23-26, 2008, Oakland, CA11

Installed in Hall B alcove

direction of scans

Notice: cableon one sidehangs into the beam.

Only oneOnly onechannel pairchannel paircan be readcan be readout at a timeout at a time

APS DNP Meeting, October 23-26, 2008, Oakland, CA12

Results with Hall B photon beam

beam energy 5.053 GeV radiator 50 microns thick (3 10-4 rad.len.) beam current 9.0 nA (1% of max Hall D flux) radiator-collimator distance ~65 m beam collimated upstream of CLAS to

0.43 m/E – beam transverse size truncated

APS DNP Meeting, October 23-26, 2008, Oakland, CA13

Results with Hall B photon beam

inner wedges, raw data outer wedges, raw data

innercableouter

curr

ent

(arb

. un

its)

curr

ent

(arb

. un

its)

APS DNP Meeting, October 23-26, 2008, Oakland, CA14

Results with Hall B photon beam

fit the blue, overlay on green fit the green, overlay on blue

curr

ent

(arb

. un

its)

curr

ent

(arb

. un

its)

APS DNP Meeting, October 23-26, 2008, Oakland, CA15

Future plans

New beam test without narrow upstream collimator New beam test without narrow upstream collimator to enable a more quantitative test of simulations.to enable a more quantitative test of simulations.

Instrument all four wedges along one axis and Instrument all four wedges along one axis and demonstrate ability to reproduce beam position.demonstrate ability to reproduce beam position.

Record currents at frequency 1KHz and measure Record currents at frequency 1KHz and measure 60Hz beam motion, and higher harmonics.60Hz beam motion, and higher harmonics.