Active Collimator Test in Hall B

Richard Jones,University of Connecticut,for the GlueX collaboration

GlueX Collaboration MeetingSeptember 18-20 2008, Storrs

GlueX Collaboration Meeting, September 18-20, 2008, Storrs2

Outline

design and simulation position stability specification prototype construction test setup in Hall B alcove results with Hall B photon beam recommendations

GlueX Collaboration Meeting, September 18-20, 2008, Storrs3

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

– SLAC experiment E-160 (ca. 2002, Bosted et.al.) latest users, built new ones

– performance is known

active device

primary collimator (tungsten)

Active collimator design

GlueX Collaboration Meeting, September 18-20, 2008, Storrs4 12 cm 5 cm

beam

Active collimator simulation

GlueX Collaboration Meeting, September 18-20, 2008, Storrs5

x (mm)

y (m

m)

current asymmetry vs. beam offset

20%

40%

60%

Active collimator simulation

GlueX Collaboration Meeting, September 18-20, 2008, Storrs6

inner ring ofpin-cushion plates

outer ring ofpin-cushion plates

beam centered at 0,0

10-4 radiatorIe = 1A

Detector response

Monte CarloMonte Carlo

GlueX Collaboration Meeting, September 18-20, 2008, Storrs7

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

GlueX Collaboration Meeting, September 18-20, 2008, Storrs8

Position sensitivity

intensity inside aperture polarization inside aperture

GlueX Collaboration Meeting, September 18-20, 2008, Storrs9

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

GlueX Collaboration Meeting, September 18-20, 2008, Storrs10

Prototype construction

partitioned anode (Al) insulating cathode holder (CaB6)

GlueX Collaboration Meeting, September 18-20, 2008, Storrs11

Prototype construction

GlueX Collaboration Meeting, September 18-20, 2008, Storrs12

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

GlueX Collaboration Meeting, September 18-20, 2008, Storrs13

Results with Hall B photon beam

beam energy 4.756 GeV radiator 1.8x10-3 rad.len. thick beam current 9.0 nA radiator-collimator distance ~40 m beam collimated upstream of CLAS,

so current, beam width truncated relative to Monte Carlo expectations

GlueX Collaboration Meeting, September 18-20, 2008, Storrs14

Results with Hall B photon beam

+x inner channel–x inner channelempirical fit

Note the abundance ofNote the abundance ofbeam trips during thisbeam trips during thisscan – duration ~50 min.scan – duration ~50 min.

GlueX Collaboration Meeting, September 18-20, 2008, Storrs15

Results with Hall B photon beam

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

GlueX Collaboration Meeting, September 18-20, 2008, Storrs16

Results with Hall B photon beam

inner wedges, raw data outer wedges, raw data

innercableouter

GlueX Collaboration Meeting, September 18-20, 2008, Storrs17

Recommendations

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.