White Rabbit Newsletter, May 2017
CERN
Tsinghua University
We have adapted WR technology for a pre-clinical Positron Emission tomographic Instrument. The PET ring consists of 8 detector modules, each containing 6 LYSO arrays coupled to a 8*8 SiPM matrix. The signals from the SiPM are processed by a dedicated ASIC and then digitized and time-tagged with a commercial ADC and FPGA-based TDC respectively. Each module acts as a White Rabbit slave node to synchronize the time reference of the TDC. The extracted list mode data is also transmitted via the WR link. A standard WR switch collects the data from all 8 detector modules, but the firmware has been modified. The list mode data packages from each module are extracted while other packages enter the switching matrix as normal. The list mode data are then processed by dedicated timestamp coincidence logic. The outcomes are then re-packeted and send out via a separate port to a reconstruction PC. The scheme greatly simplifies the PET design by replacing traditional off ring electronics with a standard White Rabbit switch.
The design of dual-port Cute-WR mezzinine has been released. It can act as a slave with a redundant connection to improve the reliability or in daisy chain mode to support a cascade topology. We have verified the WR functionality on each port for both master/slave. The daisy chain for PTP transmission has been verified, and the routing of data frames is still under development. With the dual port mezzanine, we are also designing a portable calibration node which can play an important role in a WR auto-calibration procedure, WR array deployment and validating the synchronization accuracy, bringing the advantage of higher integration, more convenience and lower human workload (http://ieeexplore.ieee.org/document/7820218/).
A prototype array of 100 detector nodes are running in Tibet. For quite a long period, we suffered some instabilities, randomly losing nodes during power up and normal operation. The new released WRPC 4.0 has greatly improved the situation. The LHAASO project has been finally approved and more than 500 WRS and 7000 WR nodes will be deployed at an altitude of 4300m asl. At the end of 2018,a quarter of the full array is foreseen to operate.