Abstract
Micromegas detectors are an optimum technological choice for the detection of low energy x-rays. The low background techniques applied to these detectors yielded remarkable background reductions over the years, being the CAST experiment beneficiary of these developments. In this document we report on the latest upgrades towards further background reductions and better understanding of the detectors' response. The upgrades encompass the readout electronics, a new detector design and the implementation of a more efficient cosmic muon veto system. Background levels below 10−6keV-1cm-2s-1 have been obtained at sea level for the first time, demonstrating the feasibility of the expectations posed by IAXO, the next generation axion helioscope. Some results obtained with a set of measurements conducted in the x-ray beam of the CAST Detector Laboratory will be also presented and discussed.
Highlights
CAST-Micromegas electronics upgradeThe readout electronics of the CAST-Micromegas detectors have been upgraded for the 2013 data taking campaign
Level Background levelVETO OFF VETO ON Raw spectrum Energy VETO OFF VETO ON Energy(keV)final background energy spectra before and after the application of the veto cut are represented for the 2013 sunset CAST-M18 data [20]
The background level is for the first time below ∼ 10−6 keV−1cm−2s−1, a milestone in the CAST-Micromegas ultra-low background program and a step forward to the levels required by IAXO
Summary
The readout electronics of the CAST-Micromegas detectors have been upgraded for the 2013 data taking campaign The former Gassiplex-based electronics [14] have been replaced by the AFTER chip based electronics developed for the readout of the large T2K time projection chambers [15, 16]. The rejection power with AFTER-based readout electronics is higher than with former Gassiplex readout electronics as a consequence of the improvement in S/N ratio of the strip signals with respect to the mesh pulse (the only source of temporal information with Gassiplex electronics) This fact allows to efficiently extend the cluster analysis to the temporal direction. This is due to the better performance of CAST-M18 with respect to CAST-M10, which it is a much older detector with some strips not electronically instrumented for being in shortcut with the mesh
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