J. Kadyk

Wire chamber aging

Abstract An overview of wire chamber aging is presented. A history of wire aging studies and the manifestations of wire aging are reviewed. Fundamental chemical principles relating to wire chamber operation are presented, and the dependences of wire aging on certain wire chamber operating parameters are discussed. Aging results from experimental detectors and laboratory experiments are summarized. Techniques for analysis of wire deposits and compositions of such deposits are discussed. Some effects of wire material and gas additives on wire aging are interpreted in chemical terms. A chemical model of wire aging is developed, and similarities of wire chamber plasmas to low-pressure rf-discharge plasmas are suggested. Procedures recommended for reducing wire aging effects are summarized.

TEST OF A LARGE SCALE PROTOTYPE OF THE DIRC, A CHERENKOV IMAGING DETECTOR BASED ON TOTAL INTERNAL REFLECTION FOR BABAR AT PEP-II

Abstract The principles of the DiRC ring imaging Cherenkov technique are briefly explained and its choice for the B a B ar detector particle identification system is motivated. A large scale prototype of the DIRC for the B a B ar experiment is then described. Details of the design of this prototype and its test in a hadronic particle beam at the CERN-PS are presented, and results from various prototype and test configurations are given. For example, after correcting for geometrical acceptance and estimated collection effects, the number of photoelectrons was measured to be 146 ± 1.8 ± 9 cm −1 , for a track angle of 20° at zero photon transmission distance. The effective attenuation loss was measured to be 4.1 ± 0.7% per meter of bar length, and the observed single photon resolution was 10.0 ± 0.2 mrad. This performance is consistent with what was expected from earlier tests and Monte Carlo simulations, and will be fully adequate for the physics demands of the B a B ar experiment.

The Directional Dark Matter Detector (D3)

Gas-filled Time Projection Chambers (TPCs) with Gas Electron Multipliers (GEMs) and pixels appear suitable for direction-sensitive WIMP dark matter searches. We present the background and motivation for our work on this technology, past and ongoing prototype work, and a development path towards an affordable, 1-m 3 -scale directional dark matter detector, D 3 . Such a detector may be particularly suitable for low-mass WIMP searches, and perhaps sufficiently sensitive to clearly determine whether the signals seen by DAMA, CoGeNT, and CRESST-II are due to low-mass WIMPs or background.

A high resolution wire scanner for micron-size profile measurements at the SLC

Abstract Fine conductive fibers have been used to measure transverse beam dimensions of a few microns at the Stanford Linear Collider (SLC). The beam profile is obtained by scanning a fiber across the beam in steps as small as 1 μm, and recording the secondary emission signal at each step, using a charge sensitive amplifier. We first outline the mechanical construction and the analogue electronics of the wire scanner. We then describe its performance in test beams and in actual operation. The article closes with a brief discussion of performance limitations of such a beam profile monitor.

Microgap gas chamber studies

Hydrogenated amorphous silicon carbide (a-Si:C:H) has been used as an insulating support pedestal for the anode strip in microgap gas chambers (MGCs) in an attempt to make a thicker high quality insulating layer. MGCs having 2.3 or 4.6 /spl mu/m thick a-Si:C:H and 2.0 /spl mu/m thick SiO/sub 2/ insulating layers have been built and tested. In this paper, the results of gas gains, strip damage by discharges, and preliminary aging studies are presented.

Studies of electron avalanche behavior in liquid argon

Electron avalanching in liquid argon is being studied as a function of voltage, pressure, radiation intensity, and the concentrations of certain additives, especially xenon. The avalanches produced in an intense electric field at the tip of a tungsten needle are initiated by ionization from a moveable americium (/sup 241/Am) gamma ray source. Photons from xenon excimers are detected as photomultiplier signals in coincidence with the current pulse from the needle. In pure liquid argon the avalanche behavior is erratic, but the addition of even a small amount of xenon (/spl les/100 ppm) stabilizes the performance. Similar attempts with neon (30%) as an additive to argon have been unsuccessful. Tests with higher energy gamma rays (/sup 57/Co) yield spectra and other performance characteristics quite similar to those using the /sup 241/Am source. Two types of signal pulses are commonly observed: a set of pulses that are sensitive to ambient pressure, and a set of somewhat smaller pulses that are not pressure dependent.

Microstrip gas chambers fabrication based on amorphous silicon and its carbon alloy

Thin (/spl sim/1000 /spl Aring/) semiconducting films of hydrogenated amorphous silicon (a-Si:H) and its carbon alloy (a-SiC:H) were applied to microstrip gas chambers in order to control gain instabilities due to charges in or on the substrate. The surface resistivity has been successfully controlled in the range of 10/sup 12/-10/sup 16/ /spl Omega///spl square/ by changing the relative amount of the carbon content and boron doping level. The light sensitivity, which is defined as the ratio of light-to-dark conductivity, was reduced to nearly unity by doping. Gas gains of /spl sim/2000 and energy resolution of 20% FWHM were achieved and the gain remained constant over a week of operation. Upon prolonged irradiation, the detector overcoated with a-SiC:H aged more slowly by approximately an order of magnitude than the one without surface coating. a-Si:C:H film is an attractive alternative to ion-implanted or semiconducting glass due to the wide range of resistivities possible, and the feasibility of making deposits over a large area at low cost.

GEM: performance and aging tests

Performance and aging tests have been done to characterize gas electron multipliers (GEMs), including further design improvements such as a thicker GEM and a closed GEM. Since the effective GEM gain is typically smaller than the absolute GEM gain, due to trapping of avalanche electrons at the bottom GEM electrode, we performed field simulations and measurements for better understanding, and discuss methods to eliminate this effect. Other performance parameters of the GEMs are also presented, including absolute GEM gain, short-term and long-term gain stabilities.

A columnar cesium iodide (CsI) drift plane layer for gas avalanche microdetectors

A new method is proposed to improve the spatial and time resolutions, and the detection efficiency with respect to the angle of the incident particles, for gas avalanche micro detectors. The new technique uses a thin (/spl sim/200 /spl mu/m) columnar CsI layer at the drift plane that acts as an efficient source of electrons produced by secondary emission due to the incident particles, and as an electron multiplier. In this paper, we present the measurements of the electron multiplication factor and detection efficiency of this layer, using a /sup 90/Sr /spl beta/-source.

GEM-type detectors using LIGA and etchable glass technologies

Gas electron multipliers (GEMS) have been made by a deep X-ray lithography technique (LIGA process) using synchrotron radiation on polymethylmethacrylate (PMMA) and by ultraviolet (UV) processes using a UV etchable glass. The gain, stability, and rate capability for these detectors are described. The LIGA detectors described consist of PMMA sheets of various thicknesses, 125-350 /spl mu/m, and have 150/spl times/150 /spl mu/m/sup 2/ holes spaced with a pitch of 300 /spl mu/m. Thin copper electrodes are plated on the top and bottom surfaces using a Damascene method, followed by electroless plating of the copper onto a palladium-tin-base layer. For various thicknesses of PMMA, measurements have been made of absolute gain versus voltage, time stability of gain, and rate capability. The operating gas mixture was usually Ar/CO/sub 2/ (70/30) gas, but some tests were also done using P10 gas. We also made GEM-like detectors using the UV etchable glass called Foturan, patterned by exposure to UV light and subsequent etching. A few measurements using these detectors will be reported, including avalanche gain and time stability.