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.