Speaker
Description
The Micro-Pattern Gaseous Detectors (MPGD) are fast radiation detectors capable of operating in high luminosity environment, and offer high gain and good position resolution. Operation of gas detectors is in general often limited by secondary effects, originating from avalanche-induced photons and ions. For example, Ion Back-Flow (IBF), the issue being studied in the present work, can make a detector incapable in high flux scenarios. Gas amplification results in a large number of electron-ion pairs. The ions drift opposite to the direction of electrons in presence of high electric field. The accumulation of these secondary positive ions often leads to significant space charge in high rate experiments, which distorts the electric field locally. Hence, it is important to study the IBF characteristics of detectors proposed to be used in many accelerator based experiments.
Micromegas(MICRO-MEsh GAseous Structure) is one of the successful MPGDs being used(or proposed to be used) for charged particle tracking in high rate environments in many high energy physics experiments. It is a parallel plate detector consisting of a very thin metallic micromesh which separates the low field drift region( ∼ 200V /cm) from the high field, ( ∼ 50kV /cm) amplification region. The amplification gap between micromesh and the read-out plate(anode) is very small, of the order of ∼ 100μm. The drift gap between drift mesh and the micromesh is usually much larger than the amplification gap to ensure sufficient primary ionization. The gas amplification occurs in the amplification region resulting as many number of electron-ion pairs. These positive ions produced by the avalanches
being massive are not affected much by the diffusion and follow the drift field lines. Most of the positive ions are collected at the micromesh giving rise to mesh current and only a small fraction of them drifts back to drift mesh resulting drift current. This IBF depends on the field ratio, detector geometry, gas mixture etc.
During the present study, IBF has been experimentally estimated as the ratio between drift current(I c ) to the total current which includes, the mesh current(I m ) and drift currrent measured, IBF = I c /(I c +I m ). The present work involves the measurement of IBF using two drift meshes in the experimental set up. Several Ar-based gas mixtures, in particular, Argon + Isobutane (95:5), T2K gas composed of Argon + Isobutane + CF 4 (95:3:2) and Argon + CO 2 (80:20), have been used for the characterization of a bulk Micromegas detector and measurement of IBF. We will present the effect of various experimental parameters on IBF and discuss optimization of the related experimental setup.
References:[1] P. Colas, I. Giomataris, V. Lepeltier, ION BACKFLOW IN THE MICROMEGAS TPC FOR THE FUTURE LINEAR COLLIDER, Nuclear Instrumments and Methods in Physics Research A 535 (2004) 226-230, arXiv:physics/0412057 .
[2] P. Bhattacharya, D. Sankar Bhattacharya, S. Mukhopadhyay, S. Bhattacharya, N. Majumdar, S. Sarkar, P. Colas and D. Attie, INVESTIGATION OF ION BACKFLOW IN BULK MICROMEGAS DETECTORS, 2015 JINST 10 P09017 IOP Publising, arXiv:1605.02896v1 .
| Presentation type | Oral |
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