Speaker
Description
Summary
New advances on RPCs (Resistive Plate Chambers) show that only since a few
years ago it is possible to use RPCs for precise time of flight measurements at
normal conditions of pressure and temperature with inexpensive materials.
These detectors are becoming widely used because their excellent TOF
capabilities and reduced cost, facing in some applications the well assessed
technology of plastic scintillators. The RPC detectors that will be installed in the
low angle region of HADES (High Acceptance DiElecton Spectrometer) are used
for both, particle identification and triggering. 1024 double-sided readout
detectors will be distributed in an active area of about 7 squared-meters,
distributed in 6 sectors, covering a polar angle between 18 and 85 deg. with
2pi azimuthal acceptance.
The electronic systems involved in the RPC system are: the Front-End that
digitizes the signals from the RPC cells, the Readout that label and pack the
digital signals from the Front-End and the power supply and slow-control
system. All of them are based on custom-made boards.
The Front-End electronics of the HADES RPC consists of two different boards.
The Daughterboard provides the specific signal processing for timing and
charge measurement. This digital conversion converts the fast analog RPC
signals into time-window signals where the rising edge provides information
about the timing and the width codifies the charge. The digitized signals are
converted to LVDS and transmitted through the Motherboard which also
provides stable supply voltages and programmable threshold DACs for the
discriminators.
A general-purpose trigger and readout board with on-board DAQ functionality is
currently being developed. Its primary application was to be a 128-channel
Time to Digital Converter (TDC) electronics based on the HPTDC (achieving 40
ps resolution) to read out the HADES RPC detector, but the new version has
been designed in a way to be detector independent and thus may serve for
any high speed data acquisition by using a flexible add-on board concept.
Custom power supply boards provide the required voltages to the Front-End
electronics: +5V, -5V and +3.3V. This power supply boards are based on
commercial switching DC/DC modules that have been conveniently filtered
(common and differential modes) to obtain clean power supply voltages. This
supply boards will also contain sensing capabilities to implement the low
voltage monitoring system, based on Linux computers-on-chip that runs Epics
in a distributed system over the Ethernet.
HADES is currently installed at GSI Darmstadt (Germany), and has as main goal
the detection of electron pairs produced in relativistic pion-nucleus and nucleus-
nucleus collisions, with high invariant-mass resolution and high acceptance, to
obtain information about the modification of the properties of vector mesons in
nuclear matter, both normal and hot and compressed. HADES consists of
several sub-detectors providing triggering, and particle identification and
discrimination capabilities. Among these sub-detectors the RPC detectors
covers the TOF system at low angles, where the particle rate where particle
rates reach their maxima, whereas plastic scintillator rods read by photo-
multiplier tubes are set up for large angles. The new RPC detector will increase
the granularity and time resolution to levels that will allow extending the range
of possible collisions in HADES from C-C to Au-Au.
