National Aeronautics and Space Administration

[VB10.02] The ISOMAX Magnet Spectrometer

T. Hams, H. Goebel, M. Bremerich, M. Hof, W. Menn, M. Simon (U. of Siegen), L.M. Barbier, E.R. Christian, S. Geier, S.K. Gupta, J.F. Krizmanic, J.W. Mitchell, J.F. Ormes, R.E. Streitmatter (NASA/GSFC), A.J. Davis, G.A. DeNolfo, R.A. Mewaldt, S.M. Schindler (Caltech)

Central to the ISOMAX balloon-borne cosmic ray instrument is a precision magnetic spectrometer system, using advanced drift-chamber (DC) tracking and a large, high-field, superconducting magnet. The DC system has 24 layers (16 bending, 8 non-bending) of hexagonal drift cells in three chambers and a lever arm of 1.4 m. Pure CO₂ gas is used. For relativistic Z=1 particles, the spatial resolution is about 70 mu and is expected to improve for higher charges. The magnet is a split-pair design with 80 cm diameter coils and a vertical warm bore with 61 cm x 63 cm cross-section. It has been operated to a central field of 1.04 T (80% of its full design field) and a field of 0.8 T was employed in the August, 1998, flight of ISOMAX. The design of the DC system and its Z dynamic range will be presented as well as a discussion of its spatial resolution and efficiency for different incident particle Z. The general performance of the magnet and the maximum detectable rigidity (MDR) of the spectrometer for different Z will also be discussed. The full ISOMAX instrument and details of the other detector systems are presented elsewhere at this meeting. ISOMAX was supported by NASA: RTOP 353-87-02 (GSFC) and grant NAGW-1919 (Caltech), and in Germany by the DFG and the BMFT.