1. Active Collimator Test in Hall B Richard Jones, University of Connecticut, for the GlueX collaboration GlueX Collaboration Meeting September 18-20 2008, Storrs

2. GlueX Collaboration Meeting, September 18-20, 2008, Storrs 2 Outline design and simulation position stability specification prototype construction test setup in Hall B alcove results with Hall B photon beam recommendations

3. GlueX Collaboration Meeting, September 18-20, 2008, Storrs 3 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

4. GlueX Collaboration Meeting, September 18-20, 2008, Storrs 4 12 cm5 cm beam Active collimator simulation

5. GlueX Collaboration Meeting, September 18-20, 2008, Storrs 5 x (mm) y (mm) current asymmetry vs. beam offset 20% 40% 60% Active collimator simulation

6. GlueX Collaboration Meeting, September 18-20, 2008, Storrs 6 inner ring of pin-cushion plates outer ring of pin-cushion plates beam centered at 0,0 10 -4 radiator I e = 1  A Detector response Monte Carlo

7. GlueX Collaboration Meeting, September 18-20, 2008, Storrs 7 using inner ring only for fine-centering ±200  m of motion of beam centroid on photon detector corresponds to ±5% change in the left/right current balance in the inner ring Position sensitivity Monte Carlo

8. GlueX Collaboration Meeting, September 18-20, 2008, Storrs 8 Position sensitivity intensity inside aperturepolarization inside aperture

9. GlueX Collaboration Meeting, September 18-20, 2008, Storrs 9 Prototype construction Pin cushions fabricated using EDM machine in FSU Physics shop pure tungsten too brittle machinable tungsten OK finding the right material is crucial

10. GlueX Collaboration Meeting, September 18-20, 2008, Storrs 10 Prototype construction partitioned anode (Al) insulating cathode holder (CaB6)

11. GlueX Collaboration Meeting, September 18-20, 2008, Storrs 11 Prototype construction

12. GlueX Collaboration Meeting, September 18-20, 2008, Storrs 12 Installed in Hall B alcove direction of scans Notice: cable on one side hangs into the beam. Only one channel pair can be read out at a time

13. GlueX Collaboration Meeting, September 18-20, 2008, Storrs 13 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

14. GlueX Collaboration Meeting, September 18-20, 2008, Storrs 14 Results with Hall B photon beam +x inner channel –x inner channel empirical fit Note the abundance of beam trips during this scan – duration ~50 min.

15. GlueX Collaboration Meeting, September 18-20, 2008, Storrs 15 Results with Hall B photon beam fit the blue, overlay on green fit the green, overlay on blue

16. GlueX Collaboration Meeting, September 18-20, 2008, Storrs 16 Results with Hall B photon beam inner wedges, raw data outer wedges, raw data inner cable outer

17. GlueX Collaboration Meeting, September 18-20, 2008, Storrs 17 Recommendations New beam test without narrow upstream collimator to enable a more quantitative test of simulations. New beam test without narrow upstream collimator to enable a more quantitative test of simulations. Instrument all four wedges along one axis and demonstrate ability to reproduce beam position. Instrument all four wedges along one axis and demonstrate ability to reproduce beam position. Record currents at frequency 1KHz and measure 60Hz beam motion, and higher harmonics. Record currents at frequency 1KHz and measure 60Hz beam motion, and higher harmonics.