FUVITA - Instrument Description


1. Overview

Each of the two FUVITA telescopes consists of a telescope tube with optical baffle and telescope shutter, a sperical mirror of 20 cm diameter, the detector in the mirror focus at 1.4 m distance from the mirror (f=7), power supplies and the Control and Data Handling System (CDHS). The FOV is 1.2 degrees.
The only difference between both telescopes represent the mirror coatings, which is SiC in one case and Al/LiF in the other. These provide different bandpasses: with SiC the bandpass maximum is at 91 nm while for Al/LiF it is at 99 nm (when interstellar hydrogen absorption is taken into account). The bandpass width is about 9 nm in both cases.
The detector consists of a stack of 3 MCPs of 30 mm useful diameter which is preceded by a 200 nm thick Indium filter. This filter provides the long-wavelength cutoff in order to eliminate the interplanetary Lyman-alpha resonance scattering line. The short-wavelength cutoff below 91.2 nm is given in a natural way by the interstellar hydrogen absorption. Two-dimensional position encoding is accomplished by a 'Wedge -and -Strip' anode which intercepts the electron cloud emitted from the third MCP. The charge collected on each electrode of the anode is amplified by a charge-sensitive, shaping amplifier and subsequently digitized by 14-bit ADCs. The processor reads the ADCs and optionally computes the position for each event (including corrections if necessary). The data for each event (optionally as pulseheight values and time or as positions x,y, total pulseheight and time) are directly available on a serial MIL-standard bus. Or, the data are stored in the 32 Mbyte flash memory and transferred periodically to the FUVITA CDHS. In addition to the science data ‘housekeeping’ data on the status of the detector are recorded continuously and sent to the CDHS on request.
The power consumption of each detector alone is 6.5 W, the brutto power including power supplies and HV is 14 W.
The mass for each detector is 3.5 kg.


author : R. Henneck
last modification : 11/07/96