Ulysses - COSPIN-KET

The KET instrument

Flight spare model of the Kiel Electron Telescope
Figure 1: Flight spare model of the Kiel Electron Telescope: Sensor unit and the electronic box in the back. For comparison, a German five-mark coin, which is somewhat larger than a 2-Euro coin, is shown to demonstrate the size of the instrument. (original size)

The Kiel Electron Telescope (KET) is part of the Ulysses COsmic ray and Solar Particle INvestigation (COSPIN) experiment, which has been described in detail by Simpson et al. (1992). The KET is designed to measure electron, proton and alpha particle intensities in several energy windows ranging from a few MeV/n up to and above a few GeV/n. It has been calibrated by using a particle beam provided by an accelerator Sierks (1988). In space, particles of different species, incident directions and energies are observed nearly simultaneously. Such an environment cannot be simulated by an accelerator but can be simulated using an appropriate model. Results for protons and α-particles, and electrons have been described by Heber (1997), Rastoin et al. (1996), and in Clem et al. (2002).

Schematic sketch of the KET sensor system
Figure 2: Schematic sketch of the KET sensor system. D1 and D2 are 0.5 mm-thick semiconductor detectors, C1 is an aerogel Cerenkov-detector and A a plastic anticoincidence scintillator. C2 is a lead fluoride Cerenkov-detector and S2 a plastic scintillator. PM1 through PM4 are photomultipliers. (original size)

Functionally, the detector system consists of two parts: an entrance telescope and a calorimeter, surrounded by a guard counter.

The entrance telescope

is composed of a silica-aerogel Cerenkov detector C1 inserted between two semi-conductor detectors, D1 and D2. Together with the guard counter A, this combination defines the geometry, selects particles with velocity >0.938 and determines the particle charge.

The calorimeter

C2 consists of a 2.5 radiation length lead-fluoride (PbF2) crystal used as Cerenkov detector, in which electron showers develop. Finally, the scintillator S2 detects events not absobed in C2.