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LC-TPC R&D

LC-TPC R&D. M. Ronan LBNL Berkeley and many others not mentionned from LBNL Berkeley, LAL Orsay, DAPNIA Saclay, IPN Orsay and LBNL Berkeley, CERN, Karlsruhe, MPI Munich. GEM, MicroMEGAS and MWPC techniques Preliminary studies drift velocities, positive ion feedback , aging, ...

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LC-TPC R&D

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  1. LC-TPC R&D M. Ronan LBNL Berkeley and many others not mentionned from LBNL Berkeley, LAL Orsay, DAPNIA Saclay, IPN Orsay and LBNL Berkeley, CERN, Karlsruhe, MPI Munich • GEM, MicroMEGAS and MWPC techniques • Preliminary studies • drift velocities, positive ion feedback , aging, ... • Fe55, Sr90 and cosmic ray measurements • Mini-TPC construction and magnetic field test program M. Ronan LC-TPC R&D

  2. Gas Electron Multiplier (GEM) • High (100 mm) pitch small pad response function • No ExB effects better resolution • Direct electron signal no losses • Efficient ion collection no gating grid ?? • Easy to build dead zones potentially small • Robust to aging insensitive to LC backgrounds • Multi-stage structures large gains (103-104) • Low mass construction no wire frames M. Ronan LC-TPC R&D

  3. MicroMEGAS readout structures • High (50 mm) pitch small pad response function • No ExB effects better resolution • Direct electron signal no losses • Funnel effect very efficient ion collection • Electron amplification independent of the gap to first order promising dE/dx • Easy to build dead zones potentially small • Robust to aging insensitive to LC backgrounds • Good electro-mechanical stability large gains (103-104) • Low mass construction no wire frames M. Ronan LC-TPC R&D

  4. Principle of operation • Very Drift space M. Ronan LC-TPC R&D

  5. Gain Stability The gain variation is flat (maximal) as a function of the gap around a few 10mm Thus a MicroMEGAS TPC has a good potential for dE/dx measurements. M. Ronan LC-TPC R&D

  6. Positive ion feed-back - funnel effect Due to diffusion, when S2 small wrt avalanche cloud size, the positive ions are unlikely to follow the field lines back into the drift space. • Very S1 Ideal feedback = Eamplification / Edrift = S2 / S1 Ions return to the grid: related space charge effects are suppressed S2 M. Ronan LC-TPC R&D

  7. Gas studies Drift properties: to obtain a high drift velocity plateau at low E-field, an Ar-dominated carrier is required Hydrogen should be avoided because of neutron background Use of CF4 as a quencher improves sT M. Ronan LC-TPC R&D

  8. Small-gap Wire TPC MicroMEGAS TPC 0 -340 V - 640 V 0 +2KV 0 - 300 V 55Fe 90Sr wires grid Cathode anode mesh Cathode 2mm 2mm 1cm 50 mm 1cm M. Ronan LC-TPC R&D

  9. Magnetic field tests • The positive ion feedback doesn ’t depend on magnetic field for the Wire chamber or for MicroMEGAS M. Ronan LC-TPC R&D

  10. Large Mini-TPC Test Chamber • Saclay 2 Tesla superconducting (MRI) magnet • STAR Front-End (FEE) electronics Analog waveform sampling at 10-40 MHz, 1024 channels with amplifier-shape, SCA, 10 bit ADC, 512 time slices deep, low noise • Modular VME data acquisition running VxWorks Stand-alone and MIDAS online systems, VB Pad Monitor, Java histogramming package • Removable detector endplate plan to test MicroMEGAS, asymmetric Wire chamber, options for spreading signal M. Ronan LC-TPC R&D

  11. M. Ronan LC-TPC R&D

  12. STAR READOUT ELECTRONICS TEST BENCH VME processor Pulse generator Optical link Mother board Front end cards M. Ronan LC-TPC R&D

  13. M. Ronan LC-TPC R&D

  14. CONCLUSION • Amplification, drift velocities, diffusion, aging, positive ion feedback, ... are being studied for GEM, MicroMEGAS and MWPC TPC ’s operating with different gases and readout technologies. • New results for a GEM TPC running on cosmic rays without a magnetic field. • First operation of a MicroMEGAS TPC in a magnetic field. • Strong multi-institution collaborations building GEM, MicroMEGAS and asymmetric Wire chamber Mini-TPCs for cosmic ray tests in high magnetic fields. M. Ronan LC-TPC R&D

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