ATC-GE-XX-0000 / Rev. No.: 1
/ Template for R&D proposals
for ATLAS upgrades
TGC upgrade for SLHC
ATLAS Upgrade Document No: / Institute Document No. / Created: 08/01/2008 / Page: 1 of 2
Modified: 08/01/2008 / Rev. No.: 1.00
Abstract
An R&D program is proposed to increase the large area rate capabilities of the TGC detectors, while including in every gas-gap tracking capabilities in two dimensions, combined with trigger capabilities in a way that will permit to remove false combinations.
Contact Person: G. Mikenberg ()
Prepared by:
G. Mikenberg (Weizmann Institute) / Checked by:
ATLAS High Luminosity Upgrade Steering Group / Approved by:
Distribution List
ATLAS High Luminosity Steering Group
ATLAS Project Document No: / Page: 1 of 7
1Introduction
It is expected that the SLHC upgrades will not increase the expected rates in the MUON region with respect to the High Luminosity regime of the LHC, by more than a factor of 20, since otherwise this would require a very large replacement of the MUON Spectrometer instrumentation, and in particular of the two types of Trigger Detectors. Such an increase in rate is compatible with the local rate capabilities of the TGC detectors, which have been operated in test beams with rates exceeding 100KHz/cm**2, given a safety factor of more than 5. The most affected regions in the ATLAS MUON Spectrometer at the SLHC are, in terms of a large rate increase, the so-called “Small Wheels” and the innermost layer of the so-called “Big Wheels”. While the increase in the photon and MIP rates can be tackled by a high rate capability of a detector, a few MeV neutrons will give very high signals in most of the gas detectors using C components. This is partly solved for the Big-Wheels by introducing a moderator wall behind the End-Cap Toroid, however, this is not possible in front of the End-Cap Toroid, due to the lack of space. It is therefore at a premium to try to combine the functionalities of the present TGC, in the JD disk with those of the tracking chambers in the Small-Wheel, to gain some space for such a moderator. Furthermore, with the high collision rates expected at the SLHC, the possibility of 2 MUON-like tracks hitting the same set of chamber volumes could become important (in particular for the 50ns SLHC option), which leads to ambiguities which can be overcome by having 3 measured coordinates in each chamber volume (one of these coordinate being wide enough to be used for trigger purposes).
The present proposal is intended to develop a set of prototypes based on the TGC technology developed for the OPAL experiment that should satisfy the above requirements. This is intended to be done in the following ways:
i)The requirement of high surface (not local) rate capability can be achieved by placing the strip readout as close as possible to the graphite layer (100 microns), which would allow to reduce the surface resistivity to 10-20KOhm/square, while keeping the same tranparency of the graphite cathodes (see Fig. 1). This low surface resistivity will allow keep the operating voltage almost constant through the full surface of the chamber (see Fig. 5), while keeping the local rate capabilities achieved in the past (see Fig. 4).
Fig. 1: Arrangement of the OPAL TGC. The internal dimensions are diferent for the present proposal, with an anode-to-cathode distance of 1.4mm and a anode-to-anode distance of 1.8mm. There should also be a readout for the wires.
ii)The need of 3 independent measurements in each gas gap is automatically achieved by using the two cathode planes (one for precision measurements and one for pads that are used for trigger purposes), while the wires are grouped together to measure the azimuthal coordinates.
iii)The main unknown, where additional R&D is required, is the expected position resolution which is needed to optimize the strip granularity, their capacitance and the needed electronics for the precision measurements. A first test has been performed using 2 small 10X10 cm**2 TGC detectors exposed to a 10GeV/c pion beam in PS-T9 test beam, to give credibility to the present proposal. Each detector was equiped with identical strip readouts on each of its cathodes (to evaluate the influence of the strip widths and corresponding electronics looking at the same avalanche) and had groups of 1.5 and 2mm pitch strips, which could be combined. Both chambers were equiped with the same type of front end electronics used in the ATLAS TGC, but equiped also with analog readout. The set-up is shown in Figs. 2-3. Since the proper material was not available to contruct detectors with a distance between the graphite cathode and the strip readout of 100 microns, the detectors were construccted with a distance of 500 microns and a graphite surface resistivity of 70KOhm/square. This lead to a lower transparency of the graphite, however the signals were large enough to be able to obtain a good charge centroid, using the charge collected in each strip. The resulting resolutions, obtained by measuring the difference of the centroids in two coupled TGC detectors, devided by Sqrt(2) are very encouraging, as shown in Fig. 6. It can be seen that position resolutions ranging between 60 to 150 microns have been obtained up to the largest incident angle of MUON’s in the so-called Small-Wheel region. The worsening of the resolution as a function of angle is expected in this type of wire-chamber detectors, due to the elongation of the avalanche along the wire, however the results achieved satisfy the needs for the SLHC upgrade. The resolution at large incident angles can probably be further improve by reducing the gap between the graphite cathode and the anode wires. Such a change in the internal chamber geometry is also part of the proposed R&D.
Fig. 2: picture of the test set-up during the T9 test beam Fig. 3 anodes and strip arrangement in test-beam chamber
Fig. 6: position resolution as a function of incident angle obtained for 2, 3 and 4 mm strips in the t9 test beam
The present proposal consists of the following steps:
i)Optimization of the precision measuremet strips: this is presently being done, through the construction of a series of small (10X10cm**2) that have identical strips on both cathodes looking at the same avalanche and comparing their position measurement for MIP’s from a Ru source. Various strip geometries, inter-space between strips and also floating strips between readout strips (as it is the case for the ATLAS-CSC detectors) are being tried. The front end electronics used are of the same type used in the present TGC electronics, but with analog signals. This process is expected to be completed in March 2008, to be performed mainly in Israel.
ii)Based on the outcome of the first step, a large size (128X128cm**2) doublet of TGC’s wil be constructed, that include rough pads for trigger, wire groups for the azimuthal readout and precision strips, based on the above optimization (to be performed in Israel). The detectors will be used in a test beam at the CERN SPS (H8) to be performed in August 2008. The front end electronics will again be based on the ATLAS-TGC’s, but with analog output (to be performed by the Japan-Israel TGC Colaboration). Depending on the availability of the GIF facility, a test might also take place in this facility in combination with other ATLAS detectors, to be able to measured the position resolution, using cosmic rays, in a high background environment.
iii)Taking into account the results obtained in ii), as well as results of signal modelling to be performed in parallel (in Argentina), the above mentioned doublets will be shipped to Japan, in order to developed new front-end electronics for the precision strip readout, in order to use in future prototypes (Japan, 2008-2009)
iv)In parallel to the construction of a full size prototype, new small detectors, with slightly different anode-to-cathode and anode-to-anode distance will be constructed to measure the possibility of improving the position resolution at large angles. This prototypes will also be tested in H8 (2008)
v)Following the design of the new prototypes of front-end electronics for the precision strip readout, as well as the results from the modified chamber geometry, a new full size, trapezoidal doublet of TGC will be constructed and tested (Israel, 2009). The prototype will be used in a test beam, to be performed either at CERN or in Japan (2009-2010).
vi)During 2010, the tools and infrastructure will be constructed to produce a detector of 8 layers, consistent with the replacement of the Small Wheels with such a TGC arrangement.
vii)In parallel, studies will be performed in Chile (Plasma group of PUC) on ion deposits on TGC wires under high irradiation (2009-2010).
2 Participating Institutions
Israeli TGC Collaboration (Technion, Tel Aviv University, Weizmann Institute)
Japan TGC Collaboration (……?????)
Argentinian ATLAS Cluster (Universidad of La Plata and Buenos Aires)
Chilean ATLAS Cluster (Pontifical Universidad de Chile and Universidad Federico Santa Maria)
3 Topic(s) and goal(s) of the R&D proposal
The various topics are described in detail in sessions i) to iv). The goal is to achieve a mass production device that can replace the trigger and tracking chamber in the MUON Small-Wheel region (as well as possibly in the inner-ring of the Big-Wheels), that can cope with a factor of 20 increase in rate, with the corresponding safety factors (5), as well allowing some extra space to implement and additional neutron filter.
4 Relation to existing efforts
The present effort constitutes a natural extension of the work performed by the Japan-Israel collaboration that has constructed the ATLAS MUON End-Cap trigger system. The addition of the groups from Argentina and Chile will permit these groups to get strongly involved in the hardware for the future ATLAS upgrades, while adding with their studies (ion deposits on wires) further knowledge for the present ATLAS operation.
5 Schedule
The schedule are presented as part of sessions i) to vii).
6 Resources
Presently approved funds for 2008:
25KEU (IL, Minerva)
10KUS$ (Special Fund from CONISEF, Argentina)
Expected funding, depending on present proposal approval:
For 2009, 2010
50KEU/year (IL)
Special requests in Argentina and Chile for similar amounts
Possible requests in Japan
Most of the manpower needs will be covered with the existing manpower for the maintenance of the ATLAS-TGC system.
References
[1] a backup document.