We present a study on the dependence of electric breakdown discharge properties on electrode geometry and the breakdown field in liquid argon near its boiling point. The measurements were performed ...with a spherical cathode and a planar anode at distances ranging from 0.1 mm to 10.0 mm. A detailed study of the time evolution of the breakdown volt-ampere characteristics was performed for the first time. It revealed a slow streamer development phase in the discharge. The results of a spectroscopic study of the visible light emission of the breakdowns complement the measurements. The light emission from the initial phase of the discharge is attributed to electro-luminescence of liquid argon following a current of drifting electrons. These results contribute to set benchmarks for breakdown-safe design of ionization detectors, such as Liquid Argon Time Projection Chambers (LAr TPC).
The Liquid Argon Time Projection Chamber (LArTPC) is a prime type of detector for future large-mass neutrino observatories and proton decay searches. In this paper we present the design and ...operation, as well as experimental results from ARGONTUBE, a LArTPC being operated at the AEC-LHEP, University of Bern. The main goal of this detector is to prove the feasibility of charge drift over very long distances in liquid argon. Many other aspects of the LArTPC technology are also investigated, such as a voltage multiplier to generate high voltage in liquid argon (Greinacher circuit), a cryogenic purification system and the application of multi-photon ionization of liquid argon by a UV laser. For the first time, tracks induced by cosmic muons and UV laser beam pulses have been observed and studied at drift distances of up to 5 m, the longest reached to date.
In this paper we present results on measurements of the dielectric strength of liquid argon near its boiling point and cathode-anode distances in the range of 0.1 mm to 40 mm with spherical cathode ...and plane anode. We show that at such distances the applied electric field at which breakdowns occur is as low as 40kV/cm. Flash-overs across the ribbed dielectric of the high voltage feed-through are observed for a length of 300 mm starting from a voltage of 55 kV. These results contribute to set reference for the breakdown-free design of ionization detectors, such as Liquid Argon Time Projection Chambers (LAr TPC).
The Liquid Argon Time Projection Chamber (LAr TPC) technique is a promising technology for future neutrino detectors. At LHEP of the University of Bern (Switzerland), an R&D program towards large ...detectors are on-going. The main goal is to show the feasibility of long drift paths over many meters. Therefore, a liquid Argon TPC with 5 m of drift distance was constructed. Many other aspects of the liquid Argon TPC technology are also investigated, such as a new device to generate high voltage in liquid Argon (Greinacher circuit), a recirculation filtering system and the multi-photon ionization of liquid Argon with a UV laser. Two detectors are built: a medium size prototype for specific detector technology studies, and ARGONTUBE, a 5 m long device.
Purpose: The precise localization of the prostate is critical for dose-escalated conformal radiotherapy. This study identifies and characterizes a potential cause of inaccurate prostatic ...localization—respiratory-induced movement.
Methods and Materials: Prostate movement during respiration was measured fluoroscopically using implanted gold fiducial markers. Twenty sequential patients with CT
1-T
3 N
0 M
0 prostate carcinoma were evaluated prone, immobilized in customized thermoplastic shells. A second 20 patients were evaluated both prone (with and without their thermoplastic shells) and supine (without their shells).
Results: When the patients were immobilized prone in thermoplastic shells, the prostate moved synchronously with respiration. In the study the prostate was displaced a mean distance of 3.3 ± 1.8 (SD) mm (range, 1–10.2 mm), with 23% (9/40) of the displacements being 4 mm or greater. The respiratory-associated prostate movement decreased significantly when the thermoplastic shells were removed.
Conclusion: Significant prostate movement can be induced by respiration when patients are immobilized in thermoplastic shells. This movement presumably is related to transmitted intraabdominal pressure within the confined space of the shells. Careful attention to the details of immobilization and to the possibility of respiratory-induced prostate movements is important when employing small field margins in prostatic radiotherapy.
We report on the design, construction, and operation of a PID temperature controlled and vacuum tight camera casing. The camera casing contains a commercial digital camera and a lighting system. The ...design of the camera casing and its components are discussed in detail. Pictures taken by this cryo-camera while immersed in argon vapour and liquid nitrogen are presented. The cryo-camera can provide a live view inside cryogenic set-ups and allows to record video.
ARGONTUBE is a liquid argon time projection chamber (LAr TPC) with a drift field generated in-situ by a Greinacher voltage multiplier circuit. We present results on the measurement of the drift-field ...distribution inside ARGONTUBE using straight ionization tracks generated by an intense UV laser beam. Our analysis is based on a simplified model of the charging of a multi-stage Greinacher circuit to describe the voltages on the field cage rings.
ARGONTUBE is a liquid argon time projection chamber (TPC) with an electron drift length of up to 5 m equipped with cryogenic charge-sensitive preamplifiers. In this work, we present results on its ...performance, including a comparison of the new cryogenic charge-sensitive preamplifiers with the previously used room-temperature-operated charge preamplifiers.
We present a method to reach electric field intensity as high as 400 kV/cm in liquid argon for cathode-ground distances of several millimeters. This can be achieved by suppressing field emission from ...the cathode, overcoming limitations that we reported earlier.
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