arXiv:physics/0406114v1 [physics.ins-det] 24 Jun 2004
Negative Ion Drift and Diffusion in a TPC
near 1 Bar
C. J. Martoff, R. Ayad, M. Katz-Hyman
Department of Physics, Temple University, Philadelphia, PA 19122, USA
G. Bonvicini, A. Schreiner
Department of Physics & Astronomy, Wayne State University Detroit, MI 48202,
Drift velocity and longitudinal diffusion measurements are reported for a Negative
Ion TPC (NITPC) operating with Helium + CS2 gas mixtures at total pressures
from 160 to 700 torr. Longitudinal diffusion at the thermal-limit was observed for
drift fields up to at least 700 V/cm in all gas mixtures tested. The results are
of particular interest in connection with mechanical simplification of Dark Matter
searches such as DRIFT, and for high energy physics experiments in which a low-Z,
low density, gaseous tracking detector with no appreciable Lorentz drift is needed
for operation in very high magnetic fields.
A TPC which drifts negative ions (in this paper, CS−
was invented to reduce diffusion in three dimensions to its thermal (lower) limit
without applying a magnetic field[1,2,3]. This provides the highest 3-D space-
point resolution attainable for long drifts, without the power requirements and
expense of a magnet.
2) rather than electrons,
Such characteristics are particularly important for the development of the
DRIFT series of direction-sensitive gaseous detectors searching for WIMP dark
matter . Three coordinates of good resolution on the recoil track are essential
for DRIFT, in order to measure the length and direction of tracks from low-
energy atom recoils produced by elastic scattering of massive WIMPs. The
standard solution of a TPC with magnetic field along the drift direction would
give good resolution in just two (transverse) coordinates. Furthermore the
Preprint submitted to Nuclear Instruments and Methods2 February 2008
0.03 0.035 0.04 0.045 0.05 0.055
0.06 0.065 0.07 0.075 0.08
Fig. 4. Typical Longitudinal Diffusion Data. Longitudinal diffusion for 80 mm drift,
measured as described in the text, for 500 torr He + 200 torr CS2 .
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http://www.lns.cornell.edu/public/LC/UCLC/projdesc/trk/WayneState Bonvicini 1022.pdf
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 Snowden-Ifft D P et al., Nucl. Instrum. Meth. A 498, (2003) 164.
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 Martoff C J et al, pp. 324 ff in Proc. 1stInt. Wkshp. on The Identification of
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 Model LS-1102-1, EG&G Optoelectronics, Salem, MA.
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