Speaker
Description
Summary
A high performance and homogeneous calorimeter based on lead tungstate crystals is
an essential part of the CMS experiment.
The CMS electromagnetic barrel calorimeter is composed of scintillating crystals
grouped in 36 super-modules of 1700 crystals each. The scintillating light from a
crystal is detected by two avalanche photo-diodes (APDs).
The signal amplification and digitization, including the formation of Trigger Tower
sums on each group of 25 crystals, is performed inside the detector volume and
transported through high speed links (optical fibers) to the counting room. Lower
speed links are used to transport timing and control information to and from the
detector. This scheme requires a large quantity of radiation hard electronics
installed on the detector. The electronics must be highly reliable since it will not
be accessible during data taking.
The basic block of the electronics is a Trigger Tower made of 5x5 crystals. It
contains 1 Motherboard, 5 Very-Front-End (VFE) boards, 1 Front-End (FE) board,
1 Low Voltage Regulator (LVR) board and 2 Gigabit Optical Hybrid (GOH).
The Motherboard is connected to the avalanche photo-detectors by flexible kapton
ribbons and distributes the bias voltage to the APDs and the LV to the VFEs. The LVRB
contains three Detector Control Units to monitor input and output voltages and cards
temperature. The VFE consists of five identical readout channels, each one consisting
of a gain preamplifier (MGPA), a 12-bit 40MS/s 4-channels Analog to Digital Converter
and a buffer. It receives and distributes also the 40 MHz clock. The FE board
contains the trigger-primitives generation, the digital pipeline and the primary
event buffers together with the clock, control links and slow control for
configuration. The GOH boards house a data serializer, a laser driver chip (GOL)
and a laser diode with an attached fiber pigtail.
Each super-module contains about 552 PCBs (340 VFE, 68 FE, 68 LVRB, 68 MB and 8
token-ring link-boards), 138 Gigabit Optical Links, 17 LV distributors and 12
distributed fiber patch-panels. Each PCB element arrives fully qualified and labeled
with bar codes. A total amount of about 4.6 kW of heat has to be removed by the
cooling system in order to keep the crystal temperature within the specified
tolerance of +-0.1 K.
The installation and commissioning of the 37 (36 + 1 spare) barrel super-modules
shall be completed by early spring 2007.
To cope with the construction schedule we have prepared three completely independent
assembly stands. Each one consists of a support stand, a cooling unit, a HV and LV
system, a readout system for single trigger towers, a database and shared services as
the detector control system and the laser. Some extra stands with partial assembly
components are also available.
After a super-module arrives in the electronics integration area it is installed in
a frame and connected to services. Then the integration sequence proceed in steps, by
installing:
1. Motherboards.
2. Cooling system.
3. Trigger Tower electronics (VFE, FE, LVDB).
4. Token-rings including TRLB.
5. GOH, optical fibers and fiber patch-panels.
6. LV distribution, cables and patch panels.
7. Commissioning: one week operation and test of the completed super-module using
the standard CMS DAQ and control systems.
At each step the installed components and their locations are registered into a
database.
Installation sequence is optimized but still each phase covers the previously
installed items, so a full validation of each step is necessary. Extensive testing is
part of each installation step to evaluate the full functionality and performance. A
pulsed laser is available to test the full chain from crystal to optical fibers
outputs (from light-to-light). Internal test pulses are used to test and calibrate
the electronics.
The test strategy and procedure during the installation is described and results of
the system performance achieved are presented.
