Negative Ion Time Projection Chamber operation with SF6 at nearly atmospheric pressure

E Baracchini,F Renga,G Cavoto,S Tomassini,G Mazzitelli,F Murtas

doi:10.1088/1748-0221/13/04/p04022

Abstract

We present the measurement of negative ion drift velocities and mobilities for innovative particle tracking detectors using gas mixtures based on SF6. This gas has recently received attention in the context of directional Dark Matter searches, thanks to its high Fluorine content, reduced diffusion and multiple species of charge carriers, which allow for full detector fiducialization. Our measurements, performed with a 5 cm drift distance Negative Ion Time Projection Chamber, show the possibility of negative ion operation in pure SF6 between 75 and 150 Torr with triple thin GEM amplification, confirming the attractive potentialities of this gas. Above all, our results with the mixture He:CF4:SF6 360:240:10 Torr demonstrate for the first time the feasibility of SF6− negative ion drift and gas gain in He at nearly atmospheric pressure, opening very interesting prospects for the next generation of directional Dark Matter detectors.

Highlights

- The novel properties of SF6 for directional dark matter experiments N.S
: We present the measurement of negative ion drift velocities and mobilities for innovative particle tracking detectors using gas mixtures based on SF6
In this paper we studied the drift velocities and mobilities of SF−6 ions in various gas mixtures

Summary

Motivations

With its high Fluorine content, the choice of SF6 has a clear advantage over CS2:CF4 mixtures for both SI and SD searches The low He atomic number can extend the experiment sensitivity down to few GeV WIMP masses, and its low density may allow to reach nearly atmospheric pressure operation while still maintaining tracks from low energy nuclear recoils long enough to be measured. Three-dimensional tracking has been recently shown with a 7 Liter active volume prototype with 20 cm drift distance, triple thin GEM amplification and light readout through a CMOS camera and a PMT [10], obtaining a ∼ 100 μm tracking resolution on minimum ionising particles The advantage of this technique is that, with the proper large aperture and suitable focal length lens, large areas can be imaged with high tracking precision at reduced costs and number of channels. The possibility to compare with and extend to lower E/N values the measurements presented in [6], since this information is important for large volume and long drift distance detectors

The NITPC detector

The Beam Test Facility and the Experimental Setup

Drift velocity and mobility measurements

Findings

Conclusions