Data Acquisition System of SND experiment

Paper: 401
Session: B (poster)
Presenter: Gaponenko, Igor, Budker Institute of Nuclear Physics, Novosibirsk
Keywords: control systems, data acquisition systems, trigger systems, large systems

Data Acquisition System of SND experiment

Dimova T.V.,Druzhinin V.P.,Dubrovin M.S.,Gaponenko I.A.,
Ivanchenko V.N.,Korol A.A.,Koshuba S.V.,Salnikov A.V.

Budker Institute of Nuclear Physics,
Lavrentyeva 11, 630090, Novosibirsk, Russia


Data Acquisition System created for the experiments with a non magnetic
Spherical Neutral Detector (SND) at the VEPP-2M collider at Budker Institute
of Nuclear Physics (BINP) in Novosibirsk is presented.
Electron-positron collider VEPP-2M is the world only machine in
a pre-phi-factory era, operating in the energy range 2E from 0.4 to 1.4 GeV,
covering the energies of resonance production of lightest quarkonia: rho,
omega, phi.
The maximum luminosity of the collider depends on its energy, and at the energy
of 2E=1000 MeV is equal to 3*10^30 cm^-2*sec^-1.
SND began data acquisition in the early 1995. The physical program of
the experiments requires to collect several tens of inverse picobarn during
two years of operation.

The readout part of the SND data acquisition system is based on the fast
bus-based electronics KLUKVA, developed in BINP specially for the purposes
of the detectors CMD-2, KEDR and SND.
The system has a three-lever trigger. The first two levels ( FLT & SLT ) are
implemented in hardware. They are tightly integrated with the timing and
control scheme of KLUKVA readout electronics.
The Third Level Trigger ( TLT ) is implemented as a special fast computer
code running on the main data acquisition computer.
This trigger checks and rejects events background before recording. In addition
TLT identifies collinear events of BhaBha scattering and two gamma annihilation.
These events are used to monitor collider luminosity.
The electronics of the other parts of the system is housed in CAMAC crates.

The software of the data acquisition system is implemented in a distributed
computing environment, including two VAXservers and two VAXstations running
under VAX/VMS operating system, SPARC and Pentium workstations running under
UNIX. The software is designed according to the functional-modular approach.
Some components were taken from the CERN/MODEL project, the others - were
specially developed for the SND DAQ system purposes.

DAQ system consists of two layers. The front-end part of the system, requiring
direct access to the detector electronics hardware is running on VAX-server,
the main DAQ computer. The detector data are read from readout electronics
into this computer via a specially designed interface module,
then they are checked by TLT, and, finally, written into the output disk file.
After the end of each run the new file is submitted to the remote
recording system. Some portion of the events is used by built-in DAQ system
processes to monitor the electronics and detector behavior. The remote
recording system serving for the experimental data archiving and as interface
to the OFFLINE data processing system is running on the VAX/VMS
cluster consisting of two workstations.
The back-end software is implemented at the UNIX workstations. This code
implements the run control, online monitoring, and DAQ system parametrization.

The current version of the data acquisition system allows to process the
detector events with a maximum rate up to 40 Hz.
During the first years of experiments with SND there were acquired
about 5 inverse picobarn of experimental data.
In the nearest future the system will be upgraded in order to cope with
planned substantial increase of the VEPP-2M luminosity.