Field Shaping Electrodes Research Articles

AXEL: High-pressure Xe gas TPC for BG-free [formula omitted] decay search

AXEL is a high-pressure xenon gas time projection chamber for neutrinoless double-beta decay (0ν2β) search. The AXEL has a unique readout system called ELCC which has a cellular structure and photosensors to detect electroluminescence light produced by ionization electrons. We demonstrated the performance of the ELCC with a small prototype detector (AXEL-HP10L). The obtained energy resolution corresponds to 0.82−1.74% (FWHM) at the 0ν2β Q-value. We are constructing a new prototype (AXEL-HP180L) in order to study the energy resolution at the Q-value of 0ν2β with a new design of ELCC with unit structure, newly developed electronics board, field-shaping electrodes, and Cockcroft–Walton-type high voltage power supply. For a future 1-ton scale large AXEL detector, we are developing new background-reduction techniques; topology identification with machine learning, positive-ion detection, and active-shield options.

Novel field cage design for the PandaX III double beta decay experiment

PandaX III is a High Pressure gaseous xenon Time Projection Chamber for Double Beta Decay detection. It will be installed deep underground in the JinPing Laboratory in Szechuan province, China. During its first phase the detector will operate with 200 kg of enriched 136Xe. The detector consists of a mesh cathode in the center of a cylindrical vessel and Micro-Bulk Micro-Megas at both ends to read out the drifting charges. The active volume is surrounded by an array of electrodes to shape the homogeneous drift field, the so called field cage. Gaseous xenon, however, is a poor dielectric. It would require in excess of 10 cm to safely stand off the HV between these electrodes and the grounded detector walls. Nearly a quarter of our available xenon would be wasted in this dead space. In a new design the electric field outside the field shaping is totally contained in a cylinder 1.6 m diameter and 2 m long. For manufacturing two 50 mm thick Acrylic plates are bend into half cylinders and bonded together. The outside surface of the cylinder is covered with a copper mesh as ground plane. The gap between field cage and detector vessel can be now reduced to 1 mm, and this gap is field free. The amount of wasted xenon is reduced by a factor 100. The field shaping electrodes and the resistive divider network are mounted on 5 mm thick Acrylic panels suspended on the inside of the field cage. This design is realized with low radioactivity materials.

A field-shaping multi-well avalanche detector for direct conversion amorphous selenium

Purpose: A practical detector structure is proposed to achieve stable avalanche multiplication gain in direct-conversion amorphous selenium radiation detectors. Methods: The detector structure is referred to as a field-shaping multi-well avalanche detector. Stable avalanche multiplication gain is achieved by eliminating field hot spots using high-density avalanche wells with insulated walls and field-shaping inside each well. Results: The authors demonstrate the impact of high-density insulated wells and field-shaping to eliminate the formation of both field hot spots in the avalanche region and high fields at the metal–semiconductor interface. Results show a semi-Gaussian field distribution inside each well using the field-shaping electrodes, and the electric field at the metal–semiconductor interface can be one order-of-magnitude lower than the peak value where avalanche occurs. Conclusions: This is the first attempt to design a practical direct-conversion amorphous selenium detector with avalanche gain.

A practical design of a cylindrical tissue-equivalent proportional counter for microdosimetry.

A 12 mm tissue-equivalent proportional counter (TEPC) was designed, constructed and successfully tested. This detector achieves features common to others TEPCs, but it does not use field shaping electrodes and it is able to work at higher bias voltages which makes it capable of measuring the whole range of energy deposition events for gamma rays. The following approach was used to design the detector: first of all the use of a cylindrical shape detector featured as simple as possible but keeping its performance as well, the next point is to avoid the use of field shaping tubes and the last one is to make the preamplifier small and as close as possible to the detector. Its construction is based on a cylindrical proportional counter with A-150 tissue-equivalent material as cathode, TE-methane gas as a proportional gas and a 20 microns diameter wire as anode.

Ionization beam-profile monitor at HIMAC

A prototype non-destructive beam-profile monitor employing tandem-type MCPs has been designed and tested at HIMAC. The monitor can measure the vertical beam profile of a circulating ion beam in the synchrotron. In a series of tests, however, it was found that the monitor had a defect in the accuracy of the measured profiles. It was caused by an electric field distortion in the work area. The electric field was improved so as to create a uniform equipotential distribution with the aid of a 3D-field simulation code. The field-shaping electrodes were replaced to longer ones, and the applied voltages of each electrode were changed to the optimum values. The monitor has been successfully used for studies of electron cooling as well as monitoring the beam under normal-mode operation in the HIMAC synchrotron.

Three-dimensional position sensing and field shaping in orthogonal-strip germanium gamma-ray detectors

We have fabricated a prototype orthogonal-strip germanium detector for gamma-ray imaging studies. With this detector we demonstrate that a gamma-ray interaction event in the detector can be located in three dimensions. In particular, we determine the interaction depth from the difference in time in the arrival of the holes at an electrode on one side of the detector and the arrival of the electrons at an electrode on the opposing detector surface. This depth of interaction sensing should lead to improved image resolution. A separate issue with such a detector is the loss of energy resolution and efficiency resulting from incomplete charge collection for interaction events taking place in the gap regions between the detector electrodes. We also demonstrate with our prototype detector that this problem can be substantially reduced by using field-shaping electrodes. A bias applied between the charge-sensing electrodes and the field-shaping electrodes improves the charge collection to the charge-sensing electrodes and consequently the detector performance.

Track chambers based on proportional drift tubes with wire field shaping electrodes

The characteristics of track chambers based on round 60 mm diameter drift tubes with four wire field shaping electrodes, using a 88% Ar + 12% CO 2 gas mixture at atmospheric pressure, are described. These track chambers are planned to be used at the Serpukhov accelerator.

Studies of drift tubes with field shaping electrodes

The design of the drift tubes with flat and with wire field shaping electrodes is described. The physical characteristics of the tubes are studied in the beam of Serpukhov accelerator. The optical measurements of wires displacements are made for a long (7.4 m) drift tube with wire field shaping. The comparison of two drift tube options is presented.

Studies of drift tubes with field shaping electrodes

Studies of drift tubes with field shaping electrodes

Influence of external grounded screens on the electric field structure in a drift chamber

The structure of electric fields in a drift chamber is considered both taking into account the influence of adjacent components and the presence of dielectric walls. It is shown that additional field shaping electrodes can preserve the uniformity of the electric field in the detector and protect it from the distortion by an external grounded screen. This design allows the first drift cell to end as close as 5 mm from the outer surface of the grounded screen. It was incorporated in the FTC detector in the L3 experiment at CERN.

Cosmic ray tests of SDC prototype muon drift tubes

Preliminary results are presented from cosmic ray tests of the SDC muon detector prototype module. The module consists of 30 drift cells. Each drift cell is a 9m long, 73mm inner diameter aluminum tube with simple field shaping electrodes. The anode wire is gold plated tungsten. The construction of the module makes use of the drift tubes as structural elements. The resolution and efficiency are approximately 200μm and 99%, respectively.

The optimization of the electrostatic field inside the ZEUS forward drift chambers: calculations and measurements

The electrostatic field inside small drift cells shows in general edge effects which are not negligible. These are usually corrected by field-shaping wires or strips. The operating voltages of the field-shaping electrodes have to be adjusted to maximize the field homogeneity. We present the underlying ideas of such an optimization procedure for the cells of the ZEUS forward drift chambers. Using the finite difference code PROFI, the optimization can be performed automatically by a multiple solution of the Poisson equation. An experimental verification of the optimal voltages was carried out by measuring the gas amplification at the six sense wires. Modifications of the drift cell geometry were necessary for calibration measurements with a laser beam. This caused additional distortions of the electrostatic field. Their influence was calculated using the MAFIA code, which allows to include open boundary conditions.

Analytic solution of the potential and electric field of a jet type drift chamber

Starting from the known two-dimensional potential of a multiwire proportional chamber, the analytic expressions of the potential and the electric field are derived for a jet type drift chamber with a central wire plane of alternating sense and potential wires. The design goal of any jet chamber, namely the periodicity of the electric drift field, is imposed as a boundary condition at the beginning. In this way, the formulae are short and can be easily evaluated. In particular, expressions are given for the mean potential of the central wire plane, the drift field and the wire surface fields. Moreover, wire cathodes frequently used in jet chambers are described by analytic expressions. For a given drift field the difference of the potential as compared to a continuous metal cathode is presented. These results allowed to construct a two-dimensional computer simulation of the full OPAL jet chamber with no explicit periodicity but all its boundaries. Using field shaping electrodes a geometrically short yet quite satisfactory termination of a sense wire plane is demonstrated. Finally an example is presented, which is calculated in detail.

Large area drift tube chambers for a muon detector at the [formula omitted

The large area muon detector for the UA1-experiment at the CERN pp-collider consists of simple and robust 4 m × 6 drift chamber modules, which are constructed of extruded aluminium profiles. Electrical field calculations show that a saturated drift velocity can be achieved up to a drift length of 7 cm with only three additional field shaping electrodes and an optimized tube profile. The field calculations as well as results about the spatial resolution of such a drift tube are presented. The coordinate along the wire can be determined from the time difference of the pulses at both ends of the tube.

The development of a new drift chamber with a new gas mixture

A drift chamber of 1 cm spacing incorporating parallel foils which act as field-shaping electrodes was successfully operated producing a linear space-to-drift-time ratio that will enable the determination of positions of charged-particle tracks directly from timing spectra. The results indicate that spatial resolutions of 100–150 μm can be obtained from a single chamber filled with an argon-methane-acetylene gas mixture at atmospheric pressure. A simplified construction which liminates field-shaping wires, and uniform equipotential lines in the chamber which results in uniform electron drift velocities, are the main advantages of this new design.

A Proportional Counter for Space and High Altitude Dosimetry Applications

Recent studies investigating the energy deposited by ionizing radiation in microscopic absorption sites have led to a program at Battelle-Northwest to develop a portable tissue equivalent proportional counter for use in mixed radiation fields. In the previous investigations, a 10 cm diameter spherical counter was used. This counter is very sensitive to mechanical shock due largely to a spiral grid surrounding the anode. The grid is necessary to produce uniform gas multiplication regardless of the location of ionizing events within the cavity. The wall thickness is sufficient to assure charged particle equilibrium when using the counter for gamma-rays or neutrons. The present development program is based on a much simpler and more rugged proportional counter. This device is 5 cm in diamter and uses a single 0.001 inch diameter stainless steel wire as the anode without a spiral grid. Uniform gas multiplication is obtained by field shaping electrodes near the end of the wires. The small counter is more stable and much less susceptible to mechanical shock. To simulate spherical absorption sites on the order of 1? diameter, the counters must be operated at pressures of a few mm Hg of tissue-equivalent gas. This special gas is composed of nitrogen, methane, and carbon dioxide in percentages of 3.2%, 64.4% and 32.4%, respectively. With a gas pressure equivalent to a 2 micron absorption site, the count rate is 2,000 to 3,000 counts per millirad when exposed to 0.75 MeV monoenergetic neutrons.