The two RICH detectors will have separate gas systems, because different
radiator gases are needed for the different momentum ranges to be covered
by the two detectors.
The RICH1 detector will be operated with C F as radiator gas.
As this gas is used in the Forward RICH of DELPHI and will be used in
the RICH of HERA-B, experiences and knowledge gained there can be
relied upon. For instance, the recirculation gas system can be modelled
Forward RICH (see Fig.5 in ).
An estimation of the cost for the different items (condenser unit, evaporator vessel, purifiers, compressor, differential pressure gauge and actuators, valves and pipes) leads to 100 kCHF. In addition, a monitoring system for H O and O concentrations, for UV-light transmission and for gas composition will be needed ( 75 kCHF).
As radiator for RICH2 we now plan to use C F /N rather than C F / Ne as indicated in the proposal. With this choice we can use most of the existing gas system of the Omega RICH. Chromatic aberrations using nitrogen rather than neon increase somewhat. On the other hand the dispersion figure for C F we have used in our proposal and which was obtained by a first order extrapolation from refractive-index measurements of liquid C F  is contradicted by later measurements  so that the difference is probably not very large.
The Omega RICH gas system has been operated either
with pure N (WA89) or
with a C F /N mixture (WA94). Parts of this system need to be
upgraded in order to preserve its proper functioning and its reliability.
This applies in particular to
the gas compressor and to the control system. The system includes
monitoring devices for H O and O concentration, for UV
transmission, and for gas composition.
The cost for the upgrade is estimated to be
Bielefeld will take up responsibility for the gas system and provide funds (in part).