M. Luethi

Experimental study of electric breakdowns in liquid argon at centimeter scale

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 40 kV/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).

A method to suppress dielectric breakdowns in liquid argon ionization detectors for cathode to ground distances of several millimeters

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.

Measurement of the drift field in the ARGONTUBE LAr TPC with 266 nm pulsed laser beams

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.

Multi-channel front-end board for SiPM readout

We describe a novel high-speed front-end electronic board (FEB) for interfacing an array of 32 Silicon Photo-multipliers (SiPM) with a computer. The FEB provides individually adjustable bias for the SiPMs, and performs low-noise analog signal amplification, conditioning and digitization. It provides event timing information accurate to 1.3 ns RMS. The signal-to-noise ratio of 12 is attained for the first photo-electron peak. The back-end data interface is realized on the basis of 100 Mbps Ethernet. The design allows daisy-chaining of up to 256 units into one network interface, thus enabling compact and efficient readout schemes for multi-channel scintillating detectors, using SiPMs as photo-sensors.

Performance of cryogenic charge readout electronics with the ARGONTUBE LAr TPC

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.

On the electric breakdown in liquid argon at centimeter scale

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).