R. Arnold SLAC 24 June 2002 Real Photon Collaboration Conceptual Design Review Beam Monitoring Instruments

Spent Electron Detectors Dump Collimator Toroids Wire Array Cherenkov -- “thin” detector Ion chamber -- “thin detector” Secondary Emission Quantameter -- “thick” detector Electron beam instruments in BSY Photon beam instruments in ESA

Photon Beamline in SLAC BSY Dump magnets Sweep magnet C37 Collimator Electron dump e- and  beam from diamond  beam to ESA Beam monitors go here

Photon Beamline for E160 ESA BSY Q27 Q28 GoniometerDump Toroid Wire Array Sweep Ion chambers C37Collimator D3LASS Dipole Detectors Compton Polarimeter Ion Ch. Dump BendTarget SEQ

Spent Electron Detectors Purpose is to measure electrons that have radiated Measure energy spectrum mirror image of photons Continuously monitor flux for every beam pulse Monitor beam quality and diamond condition Parasitic to the photon beam, non interfering Detailed spectral shapes are used to compare to calculations of photon flux and polarization Design number of channels and resolution to match expected spectral shapes Goals and Requirements

SED Design Features Detectors are segmented ion chambers Located outside and under vac chmb in B33, B34 Cover electron energy ~1 to ~38 GeV Position vac chmb to optimize SED performance Segmentation matched to expected spectral features Radiation hard construction (metal and ceramic) Readout into CAEN ADC’s Design optimized by GEANT simulations Similar to one used in 1970’s SLAC photon beam

Typical Spent Electron Spectra For various energies of beam and coherent gamma peak Spent Electron Energy (GeV) Beam / Gamma = 45 / 15 GeV45 / 25 GeV 48 / 35 GeV48 / 45 GeV

GEANT Simulation B33 x scale compressedB34 Cu bar SED Ion chamber B33 normal scale SED Ion chamber

Position of vac chambers is important GEANT results with chambers and Cu bars parallel to magnet axis gap spike shadow Cu bars Cu bar in gap

Gap in Cu bar causes problems

Preferred Design Cu bars parallel to each other fill the gap with short bars B33 Magnet vac chamber Small ion chamber under bellows Cu bar

SED Ion Chamber Construction Al plates Al channel with lid Macor (ceramic) 8 cm long segments HV and signal path Sealed Al Box with N gas flow through All radiation hard materials

SED installation under B33 vac chamber ion chamber

SED Assembly Side View B33 B34 Small ion chamber Region below 1 GeV not covered

Resolution Study 5 GeV Response to mono energetic peaksRadiative tail -- no coherent peaks z position in SED ion chamber -- 8 cm bins

SED Response vrs X X (cm) in Ion Chamber SED Ion chamber SED Position and X response B33 cut view

Input electron spectra SED response Beam / Gamma = 45 / 15 GeV 45 / 25 GeV

Input electron spectra SED response Beam / Gamma = 48 / 35 GeV 48 / 45 GeV

A line Torroid Assembly 4 inch aperture 20 kW supported in air

Existing dump line torroid components Ferrite to be reused Make new coils and supports for torroid in air 4.9 inch aperture

Dump Line Wire Array Parameters Similar to E158 Wire Array -- uses SEM from wires Measure electron beam integrated over every pulse Monitor beam spot, energy, position continuously 48 x 48 wires, in CuBe, in spacing Under tension to prevent sagging from expansion Radiation hard all metal and ceramic construction In separate vac tank Readout via twisted pair to CAEN ADC’s in CHA

Dump Line Wire Array Conceptual design

Typical Performance of E158 Wire Array

E160 End Station A Plan Start with E158 Layout D2 Collimator D3 Dipole New for E160 LASS DipoleDetectors Compton Polarimeter Ion Ch. SEQ

Thin/Thick detector method for diamond alignment Thin = cherenkov and ion chamber -- measures number of gammas Thick = SEQ -- measures energy of gammas Data from SLAC beam in ‘70s

Secondary Emission Quantameter Total Absorption shower detector Measures total energy of one beam pulse Uses secondary emission from Cu plates Non saturating (no gas) Power capacity to 10 kW Water cooled

SEQ Al foil + 1/2” Cu plates inch High Power Total Absorption Secondary Emission Quantameter Built in ‘70’s for SLAC photon beams

E158 detector cart -- support stand for SEQ, Cherenkov and Ion chamber

Cherenkov, Ion Chamber, SEQ