HD Review March 30, 2011 Franz Klein

Transcription

1 HD Review March 30, 2011 Franz Klein

2 !! Circularly & linearly polarized photon beam on longitudinally polarized target Circularly polar. photon via helicity transfer from 92 calendar days Linearly polar. photons via longitudinally polar. electrons coherent bremsstrahlung from 116 calendar days an oriented thin diamond

3 Linac E e Hall B P e P! days 1)! (2) Y C 42 2)! (3) Y C 50 3)! (3) N L 16 4)! (4) N L 32 5)! (5) N L 68 Spring 2011: circularly polar. beam (setting 1): measure double-spin asymmetry for " production Additional electron beam test: 2 days in May 11 (low current < 0.5 na) max. 2 weeks in Dec 11 or May 12 (I beam < 10 na)

4 for circularly polarized photon beam:!! beam current up to 60 na (photon beam produced on 10-4 r.l. radiator)!! instability of beam current < 5%!! accuracy of beam energy 5x10-4 (instability of E beam < 10-4 )!! beam divergence at 2C24A: < 100 µrad!! beam spot size at tagger harp: # x, # y < 150 µm!! beam position instabilities at 2C21A and 2C24A: < ±100 µm!! max. electron beam polarization (direct reporting)!! beam charge asymmetry < 5x10-4!! beam halo at tagger harp (shoulder/peak) ~10-4!! bleed-through from other halls < 10-3!! under no circumstances must the beam spot position on the tagger dump be adjusted by changing the tagger magnet current!! machine fast shutdown interlocked with tagger magnet

5 for linearly polarized photon beam:!! beam current up to 20 na!! instability of beam current < 5%!! accuracy of beam energy 5x10-4 (instability of E beam < 10-4 )!! parallel beam: beam spot size at 2C21A and 2C24A: # x, # y < 150 µm!! difference in spot size at 2C21A and 2C24A: < 50 µm!! beam position instabilities at 2C21A and 2C24A: < ±100 µm!! beam halo at tagger harp (shoulder/peak) ~10-4!! bleed-through from other halls < 10-3!! all magnets between 2C21A and tagger must be off!! under no circumstances must the beam spot position on the tagger dump be adjusted by changing the tagger magnet current!! machine fast shutdown interlocked with tagger magnet

6 for electron beam tests:!! Spring 11: beam current below 0.5 na (CLAS start counter still in place, upstream beam line being changed from photon to electron setting)!! Dec 11 or May 12: beam current below 10 na (upstream beam line being changed and minitorus installed instead of start counter)!! tagger magnet de-energized (electron beam onto dump behind Faraday cup)!! use raster magnet to radiate the central part of HDice target uniformly!! beam spot size at 2C24A: # x, # y < 150 µm!! beam position instabilities at 2C21A and 2C24A: < ±150 µm!! beam halo at tagger harp (shoulder/peak) ~10-4!! bleed-through from other halls < 10-3

7 Hall-B instrumentation in standard photon running (except electron beam tests) Material in photon beam line:!! Kapton foil at exit of pair spectrometer!! He bag between pair spectrometer and cryostat (IBC)!! entrance window to IBC and radiation baffle (50 µm Al, 12.5 µm Al)!! 5.0-cm long solid HD (0.4 mol) with Al cooling wires (15% of target mass)!! 300 µm pctfe film for background monitoring!! four 50 µm Al radiation caps We expect negligible contribution to JLab s annual radiation budget from this experiment. Any handling or manipulation of beam line hardware must be reviewed and approved by the Radiation Control Department All irradiated targets must be surveyed by Radiation Control prior to extraction

8 !! standard photon beam and electron beam instrumentation using base equipment in Hall B!! Hall-B safety procedures well established!! documentation largely unchanged over ~12 years!! solely one non-base equipment: HDice target!! Potential hazards:!! Hydrogen (0.4 moles of HD): each cryostat has sufficient buffer volume that hydrogen can expand at room temperature in case of cryogenic cooling failure.!! Only a failure of upstream window could cause the gas to escape precaution: metal gate valve at upstream end of IBC, hydrogen sensor!! Overpressure: if IBC insulating vacuum fails, the 3He-4He coolant will boil and create a pressure up to 150 psi in some parts of the circuit precaution: extensive analysis and material testing

9 !! Shock wave from vacuum window failure: - precaution: upstream gate valve closed during service; in case that the valve has to be opened during service, hearing protection is required!! Magnetic fields: Storage Dewar has potentially high field, producing up to 870 G on contact with the outer wall of the cryostat precaution: area will be swept for loose metal objects & tape marking the 3ft zone (18 G) & warning signs. (Transfer Cryostat produces < 13 G on contact, therefore no significant hazard) In-Beam Cryostat has high field (<6 KG) immediately outside the target stick precaution: not accessible during in-beam operation, sweep for metal objects and warning signs during service!! Power supplies: several low-voltage (120 A at ±10 V) super-conducting magnet supplies, each equipped with a quench detection circuit. IBC has also a warm solenoid (100 G) around the target at all times. All leads out of power supplies are covered with insulating material.

10 !! RF connections: RF oscillators are used in NMR circuit at ~10 MHz, running at low powers no potential hazards are involved. RF cables are temperature stabilized, and the temperature is constantly monitored this would detect any fluid leak at the inlet connections; all coolant connections are also monitored during service periods.!! Access restrictions: whenever super-conducting solenoids are energized, a warning sign and warning beacon will be on. When Hall B is in Restricted Access, the region near the magnets will be roped off and additional warning signs posted. Magnets used with the HDice target: IBC: (1) 4 K solenoid coil, 1.0 T, 51 A max. (normally on); (2) 4 K saddle coil, 0.2 T, 68 A max. (intermittent use for spin rotation) (3) 4 K solenoid coil, 0.3 T, 17 A max. (target loading only) (4) 300 K solenoid, 0.01 T, 9 A (pol-insurance, normally on) TC: rare earth dipole, 0.1 T (permanent) SD: 4 K solenoid coil, 8 T (normally persistent, power supply off)

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13 !! standard Hall-B COO!! functional organization of the Hall-B team:

14 !! standard Hall-B COO!! HDice specific:!! Target Operation Sequence (target transfer and loading)!! Safety Considerations:!! qualified operator list for HDice In-Beam Cryostat (A. Sandorfi, X. Wei, M. Lowry, C. Bass, T. Kageya, A. D Angelo, D. Kashy for cryogenic buffer dewar and connection to ESR)!! cables and rope hazards must be removed when not in use and marked/guarded during service.!! all posted warning signs and placards must be observed.!! no contact to target scattering chamber when exposed.