The ATLAS detector is one of the general purpose detectors at the LHC. At the heart of the ATLAS detector is a system of silicon detectors. The Semiconductor Tracker (SCT) is a detector that the QMUL group has played a significant role in designing and building, in collaboration with a number of other institutes. The QMUL group is now working on a future upgrade of the ATLAS SCT.
From 1993 to 1996 the QM group worked on designing sensor structures so that the bias voltages of silicon sensors could be increased above the 100V mark (used by LEP detectors) to 500V. The work done by the group was used on sensors produced by Micron Semiconductors Ltd. Having developed sensor designs there is an important aspect of ensuring that heat generated in the sensor and readout electronics on a module can be removed from the detector effectively. In addition to designing detailed structures for the sensors, the group also followed a programme of thermal modelling of the sensors and as described in some of the following dealt with all aspects of cooling the SCT at some level. The figure below shows (top left) a detail of one of the sensor mask designs, (bottom left) a disc for the ATLAS SCT end cap, and (right) the SCT being inserted into the inner tracker.
The QMUL ATLAS SCT group was involved in many areas of the design, prototyping and construction of the sensor modules that ultimately form the heart of the ATLAS experiment at the CERN Large Hadron Collider. These activities include working on the silicon strip sensors themselves as described above, as well as the design and fabrication of the baseboards that support the silicon, and associated thermal modelling work. The figure below shows thermal simulation and measurements of (left) baseboards and (right) modules.
The figure below shows (left) a completed module showing the silicon strip sensor, readout ASICs, and bus cable within a module frame. In order to prevent the baseboard de-laminating, the QM group, in collaboration with CERN, developed procedures of punching patterns of holes in the pyrolytic graphite using using a laser (right). This baseboard is used as both a support, and as a thermal conduit for the ATLAS modules.
As each ATLAS SCT module is a valuable piece of precision instrumentation, it was necessary to design and fabricate a series of robust precision test boxes that could be used to handle modules in the laboratory and for test-beam experiments at CERN. QMUL had the responsibility for the design and construction of the test frames and shipping boxes for the ATLAS SCT modules. The figure above shows an ATLAS SCT sensor module in one of these test frames. Below one can see (top) transport boxes for batches of baseboards and individual units, and (bottom) a frame for a sensor module and a number of transport boxes for modules. During the module production phase, QM tested more than 400 modules (more than 13% of the sensors in the SCT) prior to having them mounted onto the SCT barrels.
Given the large number of sensor modules in the SCT, it is vital that one can extract the heat generated and transfer that away from any active volume of the detector. Following on from our role in the construction of the thermal baseboards for individual modules, the QM group constructed the heat exchanger for the SCT. Some images showing the detailed pipework required for this part of ATLAS are shown in the figure below.
The QMUL ATLAS SCT group participated in the following publications: