On the mechanism of Townsend avalanche for negative molecular ions

Time projection chambers drifting negative ions (NITPC) instead of electrons have several advantages. A NITPC can operate at very high reduced drift fields without diffusion runaway, and the readout digitization sampling rate requirement is considerably relaxed due to the low drift speed of negative...

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Bibliographic Details
Published in:Astroparticle physics 2010-05, Vol.33 (4), p.216-220
Main Authors: Dion, M.P., Martoff, C.J., Hosack, M.
Format: Article
Language:English
Subjects:
Avalanches
Carbon dioxide
Dark Matter
Diffusion
Drift
Gain
Low pressure
Molecular ions
Negative ion
Negative ion avalanche
Negative ions
Sampling
X-ray polarimeter
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Summary:Time projection chambers drifting negative ions (NITPC) instead of electrons have several advantages. A NITPC can operate at very high reduced drift fields without diffusion runaway, and the readout digitization sampling rate requirement is considerably relaxed due to the low drift speed of negative ions. The initiation of Townsend avalanches to allow gas gain in these devices has not been understood until now. It is shown here that the avalanche in low pressure CS 2 vapor is most likely initiated by collisional detachment of the electron from the negative molecular ion. In mixtures of nitromethane vapor with CO 2 the mechanism appears to be more complex.
ISSN:0927-6505
1873-2852
DOI:10.1016/j.astropartphys.2010.02.002