LC-TPC R

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LC-TPC RD
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

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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

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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

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Principle of operation

• Very

Drift space
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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.
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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
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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
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Small-gap Wire TPC
MicroMEGAS TPC
0 -340 V - 640 V
0 2KV 0 - 300 V
55Fe
90Sr
wires
Cathode
grid
anode
Cathode
mesh
2mm 2mm 1cm
50 mm 1cm
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Magnetic field tests

• The positive ion feedback doesn t depend on
  magnetic field for the Wire chamber or for
  MicroMEGAS

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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

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STAR READOUT ELECTRONICS TEST BENCH
VME processor
Pulse generator
Optical link
Mother board
Front end cards
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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.