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Micromegas TPC and wire TPC First measurements in a magnetic field

Micromegas TPC and wire TPC First measurements in a magnetic field. P. Colas 1 , Y. Giomataris 1 , J. Jeanjean 2 , V. Lepeltier 2 , J. Martin 1 , A. Olivier 1 1) DAPNIA Saclay 2) LAL Orsay.

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Micromegas TPC and wire TPC First measurements in a magnetic field

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  1. Micromegas TPC and wire TPCFirst measurements in a magnetic field P. Colas1, Y. Giomataris1, J. Jeanjean2, V. Lepeltier2, J. Martin1, A. Olivier1 1) DAPNIA Saclay 2) LAL Orsay • A small-gap wire chamber TPC and a Micromegas TPC (both 1cm drift) have been put in 1-2 Tesla magnetic field • Feedback has been measured and progress on simulation has been made. P. Colas - Micromegas and wire TPCs

  2. Experiment • We ran end of June with a small-gap TPC and a micromegas TPC • The primary ionization was provided by • an 55Fe source (25 MBq, gain typically 100,000) for the wire chamber • a 90Sr source (1 GBq, gain a few 100) for the micromegas • The currents from the supplies are monitored, allowing to measure the feedback. • Mainly the results from micromegas are shown here. • The results from the wire chamber are: no significant effect of the magnetic field, though simulation predicts an increase of 50% on the feedback from 0 to 2 T. To be understood. P. Colas - Micromegas and wire TPCs

  3. SETUP P. Colas - Micromegas and wire TPCs

  4. detector Ar:CH4 90:10 2T Magnet High voltage and monitoring P. Colas - Micromegas and wire TPCs

  5. Small-gap wire TPC Micromegas TPC 0 +2KV 0 - 300 V 0 -340 V - 640 V 55Fe 90Sr wires grid Cathode anode mesh Cathode 2mm 2mm 1cm 50 mm 1cm P. Colas - Micromegas and wire TPCs

  6. Feedback : theory and simulation • We (Jerôme Martin) carried out simulations with 2D geometry to: • Understand the feedback • look at the effect of the magnetic field : predicts 50% increase in the wire chamber, and no effect in micromegas • Ideally, the feedback is given by the inverse field ratio E(drift)/E(amplif) • It is less good (i.e. larger) if the dispersion in the avalanche is small with respect to the hole pitch • The two important quantities are s : the dispersion after 50 microns and • l, the pitch. The hole size does not matter when the field ratio is high P. Colas - Micromegas and wire TPCs

  7. Theoretical ion feedback Hypothesis on the avalanche Gaussian diffusion Periodical structure Avalanche Resolution l 2*sigma P. Colas - Micromegas and wire TPCs

  8. Theoretical ion feedback Calculations Sum of gaussian diffusions 2D 3D P. Colas - Micromegas and wire TPCs

  9. 500 lpi (sigma/l=0.25) 1000 lpi (sigma/l=0.5) 1500 lpi (sigma/l=0.75) Theoretical ion feedback Results P. Colas - Micromegas and wire TPCs

  10. Theoretical ion feedback P. Colas - Micromegas and wire TPCs

  11. P. Colas - Micromegas and wire TPCs

  12. P. Colas - Micromegas and wire TPCs

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