DETECTOR DEVELOPMENT FOR THE ATLAS SCT UPGRADE PROGRAMME
The ATLAS detector is one of the general purpose detectors at the LHC. At the end of the life of the LHC experiment, the accelerator will be upgraded to the sLHC and run at a higher luminosity (more data per unit time) than the existing one. In this harsh environment many of the components of the existing ATLAS experiment will not be able to operate. One of these will be the silicon central tracking (SCT) detector. In anticipation of the sLHC, many scientists are starting to design a new set of detectors. The QMUL group has a role in the design and construction of the upgraded SCT, and collaborates with a number of other institutes on this programme of R&D.
The current activities concerning the construction of a replacement ATLAS SCT revolve around the development of "staves" with 10 silicon sensors attached to each side of a rigid support plank. The QMUL group is actively working on a wide range of aspects of the ATLAS SCT upgrade programme from understanding the correct choice of materials to use in constructing staves, precision engineering and prototyping, through to end use test beam work at CERN. All areas of this R&D programme require close collaboration between physicists, engineers, and the experts in our departmental workshops. Some highlights of this work are discussed below.
Material modelling and tests (mechanical and thermal)
The QMUL group plays an important role in performing both mechanical and thermal tests of samples of material or composite structures for the ATLAS upgrade programme. In addition to physically performing tests, we are involved in a number of thermal and mechanical Finite Element Analysis studies. The image below (top-left to bottom right) show our 3 point bend test jig, TIM tower for thermal measurements, and mechanical and thermal FEA simulations.
SCT tracker support structures
The stave support structure is an integral part of the tracker upgrade project, which aims to provide a rigid cooled structure, instrumented with a number of silicon sensors. The QM group has produced a number of precision engineered components used in the assembly of full sized and mini stave objects for mechanical testing. These include prototype ribs (with thin walls) for an early support structure prototype shown (top-left) in the figure below, along with support ribs for the current stave prototypes (top-right) with a number of jigs used during construction. We are also actively studying possible stave core material options including that of a corrugated CFRP core structure, such as that shown (bottom). We are preparing samples so that a full size stave using a corrugated core can be built in the near future.
Stave testing and transport boxes
Now that the UK community is starting to produce full sized and mini staves, we need to develop a set of test frames and facilities as well as transport boxes that will give us the ability to inspect the prototypes and transport them from one institute to another safely. We are involved in many aspects of this programme from the design and construction of a dedicated environmental chamber for stave thermal cycling studies, to design and construction of stave transport boxes. One can see the design for the environmental chamber below.
CERN test beam work
It is expected that the sLHC tracking systems will be exposed to a fluence of particles of the order of 1x1015 neq / cm2 (about 10 times larger than the LHC). One important aspect of any detector R&D for such a device is to establish that all components of the detector will survive such conditions. This means not only the silicon sensors we rely upon to detect particles, but all support materials including the glue used to assemble the detector.
The QMUL group plays a key role in the construction of test beam facilities and samples, through to manning shifts on irradiation test beams at CERN. The group has constructed several irradiation test boxes that will eventually be used to irradiate samples of silicon to the expected fluence of the sLHC as a part of this ongoing programme of material validations. The following image shows one of these test boxes in a test-beam at CERN, where the inset shows sensors that were mounted onto the lid of the box prior to irradiation in the test-beam.
As the project evolves we anticipate testing irradiated silicon sensors in our clean room. A similar role of testing new silicon sensors was performed by the QMUL group for the original ATLAS experiment.
A critical part of any project involves book keeping: who makes what components, tracking parts, tracking tests, and so on. The QMUL group played a lead role in setting up, and maintains the UK ATLAS SCT upgrade database.
The QMUL ATLAS SCT upgrade group have participated in the following publications:
- G. Beck et al., "Analytic model of thermal runaway in Silicon Detectors", Nucl. Instr. Meth. in Physics Research, A 618 (2010), pp. 131-138.
Please contact Dr. A. J. Bevan for more information.
Bi-weekly local SCT upgrade meetings are held on Mondays between 10 and 11am in room 410B.