Negative ion drift velocity and longitudinal diffusion in mixtures of carbon disulfide and methane

Abstract

Negative ion drift velocity and longitudinal diffusion has been measured for gas mixtures of carbon disulfide (CS2) and methane (CH4)' Measurements were made as a function of total pressure, CS 2 partial pressure and electric field. Constant mobility and thermal-limit longitudinal diffusion is observed for all gas mixtures tested. Gas gain for some of the mixtures is also included.

A review of the discovery reach of directional Dark Matter detection

“…The choice of the target medium is thus critical. CS 2 offers the possibility to drift negative ions, which enables very long drift distances with minimal diffusion and hence large volumes [51][52][53][54][55][56][57]. Directional electron-drift TPCs are using CF 4 , for the spin content of 19 F that enables a sensitivity to spin dependent interaction [58], and for the properties of this gas: electron drift velocity, diffusion and its scintillation output, which can be used for optical readout [22,59].…”

“…The key feature of the DRIFT detector is the fact that negative ions (CS − 2 ) are used to transport the ionization signal to the readout plane composed of Multi-Wire Proportional Counters (MWPC) [57]. It opens the possibility to develop TPCs with very long drift distances with minimal diffusion and hence large volumes [53][54][55][56][57]. The gas mixture currently used is 73% CS 2 + 25% CF 4 + 2% O 2 at a pressure of 55 mbar.…”

High precision measurements of carbon disulfide negative ion mobility and diffusion

“…Ideally, in a negative ion TPC (NITPC), electrons would be rapidly captured by molecules with moderate electron affinity at the site of ionization, transported with minimum diffusion in 3 dimensions to the readout plane where they would be stripped and then undergo normal electron avalanche to produce gas gain at the readout plane. A number of authors have found molecules approaching this ideal 1,3,4,5,6 . For the past decade the Directional Recoil Identification From Tracks (DRIFT) collaboration 7 has utilized carbon disulfide, CS 2 , for negative ion transport in a low pressure NITPC to search for dark matter.…”

A review on the discovery reach of Dark Matter directional detection

“…The choice of the target medium is thus critical. CS 2 offers the possibility to drift negative ions, which enables very long drift distances with minimal diffusion and hence large volumes [51][52][53][54][55][56][57]. Directional electron-drift TPCs are using CF 4 , for the spin content of 19 F that enables a sensitivity to spin dependent interaction [58], and for the properties of this gas: electron drift velocity, diffusion and its scintillation output, which can be used for optical readout [22,59].…”

“…The key feature of the DRIFT detector is the fact that negative ions (CS − 2 ) are used to transport the ionization signal to the readout plane composed of Multi-Wire Proportional Counters (MWPC) [57]. It opens the possibility to develop TPCs with very long drift distances with minimal diffusion and hence large volumes [53][54][55][56][57]. The gas mixture currently used is 73% CS 2 + 25% CF 4 + 2% O 2 at a pressure of 55 mbar.…”