| Irfu-10-282
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| Micromegas for charge readout of double phase Liquid Argon TPCs
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| A. Delbart, M. Zito et al. |
| The 128 μm bulk-micromegas detector is a mature semi-industrial technology well suited for high quality and large scale production of large active area MPGDs as illustrated by its use in the Time Projection Chambers (TPCs) of the ND280 near detector of the T2K experiment. The cooling of a 128 μm bulk-micromegas detector down to 77 K proves its robustness at low temperatures and that is therefore a natural candidate for charge readout in Giant Liquid Argon TPCs.
We propose the use of bulk-micromegas technology as charge readout in the vapour phase of
a double phase Liquid Argon TPC. We have made a series of gain measurements with bulk
and micro-bulk micromegas at room temperature up to 4.5 bars to predict the behaviour and
performances of micromegas in the double-phase Liquid Argon TPC conditions at 87 K. Gas
gains of up to 500 were measured in pure Argon at room temperature and 3.5 bars with a 50 μm
standard micro-bulk. But the large diffusion of electrons in pure argon demands the operation
of the detector with sufficiently low drift over amplification field ratios in order to fully transfer primary electrons in the amplification gap. Gain simulations are in good agreement with these measurements and a gain of 100 in a 128 μm bulk-micromegas is expected in pure Argon at
87 K. Such a large effective gain should be sufficient for charge readout of double-phase liquid Argon TPCs.
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