F. Liello

Calibration of field inhomogeneities in a time projection chamber with laser rays

Abstract We present some results on the use of a set of laser beams to monitor and to measure the systematic displacements of the electron drift trajectories in a Time Projection Chamber of large (0.6 m 3 ) dimensions.

Detection of ultraviolet Cherenkov light from high energy cosmic ray atmospheric showers: a field test

Abstract We present the results of a test with a prototype apparatus aimed to detect the ultraviolet Cherenkov light in the wavelength range 2000–2300 A, emitted by high energy cosmic ray showers. The system consists of a gas proportional chamber, with TMAE vapour as the photosensitive element, placed on the focal plane of a 1.5 m diameter parabolic mirror. The test was done during the summer of 1989 with cosmic ray showers seen in coincidence with the EAS-TOP experiment, an extended atmospheric shower charged particle array now being exploited at Campo Imperatore, 1900 m above sea level, on top of the Gran Sasso underground Laboratory of INFN. The results were positive and show that a full scale ultraviolet Cherenkov experiment with good sensitivity, angular resolution and virtually no background from moonlight or even daylight can be envisaged.

ION TRAPPING PROPERTIES OF A SYNCHRONOUSLY GATED TIME PROJECTION CHAMBER

Abstract Studies have been made of the transmission of positive ions through the gating grid of a time projection chamber operated synchronously at a high rate. With a duty cycle of 25% (22 μs periodic wave form) it has been demonstrated that less than one positive ion in 7 × 10 −3 traverses the gating grid. This new gating technique can be used by a time projection chamber operating at the LEP e + e − collider.

TPC90, a test model for the ALEPH time projection chamber☆

Abstract A test model has been built to study the performance of prototypes for the ALEPH Time Projection Chamber. The device consists of a solenoid magnet providing a magnetic field up to 1.2 T inside a cylindric field cage of 75 cm diameter and 1.3 m length. It has been used to test two chambers of different design. We describe the setup and present results from measurements with these prototype chambers using laser beams and cosmic ray particles.

Influence of the magnetic field on the gating of a time projection chamber

A large cylindrical time projection chamber (TPC 90), 60 cm in diameter, a driftlength of 130 cm, as well as a smaller test-chamber of 30 × 30 × 15 cm3 have been used to investigate the effects of the magnetic field on the operation of a gated grid. The magnetic field is found to affect strongly the drifting electrons, but not for the positive ions. The results can be well explained by the specific configuration of the combined EandB fields near the gating grid wires and in the region of the proportional wires.

The CLUE experiment operating with 4 telescopes in La Palma

Abstract The CLUE experiment has started operation with four of the nine telescopes that are foreseen for its beginning. These telescopes are at present at Roque de Los Muchachos in the Canary Islands, in the same site as the HEGRA experiment. In winter 1997 we started taking data with the telescopes pointing directly at the moon. A description of the telescopes and the performance of the detector are given.

Status report on CLUE

Abstract The CLUE experiment uses a new cosmic ray detector array planned to operate for the next decade. It utilises a MWPC chambers sensitive to UV, to image Cherenkov radiation produced in cosmic ray showers. This approach is unique in that the instrument is insensitive to skylight backgrounds, has a threshold similar to that of visible Cherenkov experiments but a longer duty cycle. These features make possible a class of interesting cosmic ray physics experiments. The CLUE experiment has started operation with two of the ten telescopes that are foreseen for its beginning. These telescopes are at present at Roque de Los Muchachos in the Canary Islands, in the same site as the HEGRA experiment. A description of the telescopes is given and some data on the tests performed are presented.

Shower reconstruction in the CLUE experiment

Abstract The CLUE experiment studies primary cosmic rays (E≥2 TeV ) by detecting UV (190–230 nm) Cherenkov light produced by atmospheric showers. Since atmospheric absorption in the UV range is higher than in the visible range, CLUE cannot apply algorithms normally used in IACT 1 experiments to determine primary cosmic-ray direction. In this paper, we present a new method developed by CLUE. The algorithm performances were evaluated using simulated showers. Preliminary results of the source analysis using this new method are shown.

A method to measure the γ-ray content in VHE cosmic ray showers

Abstract An experimental technique is presented to determine the effectiveness of methods to tag photon initiated air showers and reject hadron initiated ones. The technique is based on the rate reduction in the Moon direction. With a photon energy threshold below or equal to 1 TeV, with an angular resolution of a few mrad and being insensitive to visible light, the proposed CLUE detector allows a wide and original physics program. In particular the direct measurement of the fraction of primary photons in the continuum of the cosmic ray flux is feasible with adequate statistics in a few months of data taking.

THE CLUE TRIGGER: A VME BASED TWO LEVEL TRIGGER FOR VHE EXPERIMENTS

Abstract We describe a trigger architecture developed for shower selection in the CLUE Cherenkov telescopes. The selection is made first in each telescope of the array looking at the low resolution images produced by fast electronics, than requiring temporal coincidence between units. Big effort has been put to simplify the programming of trigger configurations to help the user to switch easily between different observational and calibration requests.