Technical Design Report Super Fragment Separator

DRAFT
experiment the EXL community has already come up with detailed requests to the NUSTAR DAQ
group. The EXL front-end electronics which includes the ADC will have its own Time stamp &
slow control facilities. The slow control facilities will allow a level of hard and software debugging.
The slow control will allow the modification of e.g. the sub-trigger, choice of pre-amplifiers and
amplifiers, the shaping, the gain, discriminators, sampling, ADC functions, calibration and test
sequences, cable redundancy, high voltage, and bias settings. The structure required to manage the
above should, is requested from the NUSTAR DAQ system. Apart from the control aspects, also
the data collection chain from the digitized data has to be implemented, where the expected data
rates for both experiments are approaching the 100 MBytes/sec limit.
Controls: We foresee two kinds of data from the experiments: event-wise data that is taken with
the physics and control triggers and what we call slow control data, like scaler readouts, beam
profiles and so on. These data are of interest for the distributed slow control system throughout the
NUSTAR facility and the accelerator. For this example, profile data may be taken to generate a
feedback loop in order to perform automatic beam steering, whereas scaler data can provide information
on the sanity of the particular setups. Of particular interest are fast control loops based on
digital signal processing techniques, that can be already implemented in FPGA based front-end
readout cards, coupled to slow control processes via e.g. a on board processor. The available
processing power allows for an optimization of already single detector channels on-line so that the
setup time can be drastically reduced. Such systems are currently tested for pile-up rejection and
correction, pulse shape discrimination and intelligent adaptive triggering.
2.4.A1.1 Time and trigger distribution systems
As can be seen from the above discussion one of the main infrastructures delivered by the
NUSTAR DAQ framework will be a hierarchical time distribution system. Existing architectures
for large scale time and trigger distribution systems are given e.g. by the TTC for LHC experiments
[88], or the TCS [89,90] build for the COMPASS experiment, both at CERN. The Accelerator
Division is currently working on a next generation timing system [91]. A Prototype system is
available since mid 2007 and is being built by Work µ-wave GmbH. The activity was originally
prompted by the requirement of the PHELIX experiment to synchronize a laser shot with the arriving
pulse to a precision of 100 ps, thus the internal name "BuTiS" for 'Bunchphase Timing
System'. This scope has of course widened, the objective is now to provide the timing reference for
all FAIR accelerator components, and if there is interest, also the experiments. The currently
available prototype system provides an absolute precision of 100 ps for the timestamps across the
whole GSI site, and a timing jitter of well below 10 ps. The system is used as campus reference for
standard frequencies (currently under evaluation are 200 MHz and 10 MHz) and standard time
(UTC) which can be derived from a GPS based reference or a labelling of certain pulses via accelerator
controls. In addition, auxiliary information channels are foreseen which will provide for
example triggers for specific accelerator events.
Local time-stamps: A campus wide synchronisation method allows for common timestamps
between different experiments. The common clock is not enough on its own for full synchronisation
- one needs to be able to correlate particular clock edges with particular values of the timestamp
counters in order to start from the same timestamp value everywhere. Existing local time
distribution systems like e.g. the GSI TITRIS [92] modular, which is similar to the CENTRUM
built by GANIL [93] and also the proposed AGATA GTS [94], have to be adapted to allow for the
157