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Description
Summary
The ALICE Detector Data Link (DDL) is a high-speed, duplex, point-to-point optical
link designed to interface the readout electronics of all the ALICE detectors to
the DAQ computers in a standard way. The DDL consists of the Source Interface Unit
(SIU), an optical cable up to 300 meters, and the Destination Interface Unit (DIU).
The DDL provides enough bandwidth to transfer data from the detectors at 200 MB/s.
The SIU will be attached to the Front-end Electronics, hence it will be exposed to
the radiation caused by the interacting particles. According to the latest
simulations, the highest radiation level for the SIU card is expected at the inner
radius of the TPC detector, where the total ionizing dose is 1.3 krad and the 1 MeV
equivalent neutron fluence is 1.47 × 10^11 neutrons/cm2 for 10 years of operation.
The hardware consists of three main, and several auxiliary components. The full-
duplex optical transceiver makes the conversion between the optical serial data and
the high-speed differential electrical data. The electrical transceiver performs
data conversion serial-to-parallel and parallel-to-serial. The DDL protocol and
additional logic functions are implemented in a programmable logic device (FPGA).
The components of the SIU card have been extensively tested. The results show that
the TID effects have little impact on the components used. The single event effects
(SEE), however, can provoke two different types of error. High-energy particles may
change the content of the registers or the user memory therefore increases the
single-bit-error rate. According to the measurements, this error rate increase is
negligible compared to the bit-error rate always present during optical
transmission. In addition, the particles may as well alter the content of the
configuration memory cells of the SRAM-based FPGA device used on the prototype
cards. This type of error may cause functional interrupt at a rate, which is only
marginally acceptable.
We developed a new version of the SIU card using alternative logic device, namely
the ACTEL ProASIC+ device family based on flash memory technology. We carried out
two series of tests to investigate the configuration loss in radiations
environment. The first series of measurements was carried out in TSL, (Uppsala,
Sweden) using protons at energy of 150 MeV and 180 MeV. The 2nd series of
measurements was done at ATOMKI (Debrecen, Hungary) using thick target p+Be
neutrons with spectrum extending up to En=14 MeV. The methods and results of the
measurements are shown in this paper.
