Speaker
Description
Summary
The use of programmable logic devices such as FPGAs is a very attractive
solution for High Energy Physics applications. They can typically be repro-
grammed in the field giving the often needed flexibility to develop and update
already deployed instrumentation. However, a major caveat of SRAM based
FPGAs are their susceptibility to radiation. The configuration of the FPGA is
stored in SRAM memory and single event upsets in this configuration memory
may lead to a malfunction of the FPGA design. In the main tracking detector
of ALICE, the Time Projection Chamber, a total of 216 Readout Control Units
(RCUs) are used to readout the data from detector with FPGAs directly in the
datapath. For Run 1, these FPGAs were SRAM based, and a dedicated re-
configuration solution was implemented to continuously detect and correct any
SEUs in the configuration memory of these FPGAs. During the first LHC run-
ning period this reconfiguration solution has detected and corrected thousands
of single event upsets and a summary of these measurements will be presented.
Following the increase in energy for Run 2, it was decided that a new Readout
Control Unit, the RCU2, was needed to avoid a significant loss of efficiency of
the Readout Electronics. To increase the radiation tolerance, a Flash based
FPGA, the Microsemi SmartFusion2, is used. The flash technology offers an
immunity to SEUs. While this is good for the detector operation, it implied
that a new type of radiation monitor was desirable. This radiation monitor
(RadMon) is based on the idea of the LHC Radmon, featuring 4 8 Mb Cypress
SRAM memories and a flash based controller FPGA. The Radmon loops over
all addresses for all SRAMs and writes a known pattern. This is then read
back and SEUs are counted by comparing against the expected pattern. The
patterns written to the SRAMS are inverted between each cycle. There are
individual SEU counters per SRAM IC, and these are polled using a custom
device driver in the Linux system installed on the embedded microController
in the SmartFusion2. By minor modifications to the existing Detector Control
System framework, this information is available online in the control room. Due
to an increased numbers of bits and a higher SEU cross section for the memories,
the new solution will provide an order of magnitude higher sensitivity compared
to the FPGA based solution.
The RCU2 have been through several irradiation campaigns and there have
been targeted beamtime to test the functionality of the RadMon. The paper
will show the results from these irradiation campaigns as well as discussing the
main differences between the solution in Run 1 and the RadMon solution to be
used in Run 2. These solutions both provide valuable information about the
radiation environment in the ALICE TPC.
