"LC-TPC: Large Collaborative Projects"

Executive Summary

A Time Projection Chamber (TPC) has been chosen as the central tracking device for two of the current detector concepts at the International Linear Collider. The LC-TPC group is carrying out a comprehensive R&D program to develop the technology and prove the feasibility of a high-performance TPC required for this application. The new Micro-Pattern Gas Detector (MPGD) technologies, Gas Electron Multiplier(GEM) or Micromegas(MM), are attractive candidates for the gas-amplification because better precision and granularity may be achieved than in past TPCs. Extensive testing using GEM and MM is being pursued with the results being compared with each other and with the multi-wire proportional chamber (MWPC) technology used in TPCs up to the present. In addition, the proof-of-principle of CMOS readout techniques is being studied with both GEM and MM; if successful this will be a candidate for a final TPC. In addition to optimization of the gas-amplification, other issues including minimizing endplate material alignment and calibration most be understood before a TPC can meet the goals of the ILC. The R&D work is proceeding in three phases: 1) demonstration phase using small prototypes; 2) consolidation phase consisting of the building of a Large Prototype TPC with GEM and MM using both standard and CMOS readout techniques; 3) design phase which will profit from the experience gained in the first two phases. Presently (2005) phase 1) is under way and phase 2) is starting.

This project involves groups from institutions in all regions as listed below. To meet these goals the institutes listed on this research statement are working together, sharing information and experience in the process of developing a TPC for the linear collider, and of providing common infrastructure and tools to facilitate these studies. The distribution of efforts among these institutions is given in the text.

America Canada: Carleton, Montreal, Victoria. USA: Cornell, Indiana, LBNL, MIT, Purdue, Yale.

Asia China: Tsinghua. Japan: Chiba, Hiroshima, KEK, Kinki U Osaka, Saga, Kogakuin U Tokyo, Tokyo UAT, Tokyo ICEPP, NRICP Tokyo, Tsukuba. Philippines: Minadamo SU-IIT.

Europe France: LAL Orsay, IPN Orsay, CEA Saclay. Germany: RWTH Aachen, DESY Hamburg, Freiburg, Hamburg, Karlsruhe, MPI-Munich, Rostock. Netherlands: NIKHEF. Poland: UMM Krakow. Russia: BINP Novosibirsk, PNPI St.Petersburg. Sweden: Lund. Switzerland: CERN.

Goals and addressing the needs of the detector concepts

The goal of the LC-TPC group is to develop a TPC to serve as the tracking device of a detector meeting the demands of the ILC physics program. A detector at the International Linear Collider (ILC) will combine a tracking system of high precision with a calorimeter system of very high granularity. This detector will measure charged tracks with excellent accuracy, typically surpassing the precision of previously built detectors at LEP, the Tevatron, HERA or the LHC by a factor of 10. At the same time this detector must be optimized for the reconstruction of multi-jet final states stressing the jet energy resolution and the reconstruction of individual particles in jets. For the latter, the efficiency and reliability in reconstructing charged tracks are more important than precision. A TPC has been chosen as the central tracking device for two of the current detector concepts: the Global LC Detector concept (GLD) and the Large Detector Concept (LDC). These concepts each have a tracking system consisting of a large TPC combined with silicon detectors for vertexing, intermediate and external tracking. The GLD and LDC concepts differ mainly in their calorimetry. Arguments for a TPC as main tracker are:

Several issues must be addressed in developing a TPC to meet the requirements of the ILC physics program. TPCs have been used in a number of large collider experiments in the past and have performed well. However, these TPCs were read out using multi-wire proportional chambers (MWPCs). The thrust of our present R&D is to develop a TPC based on novel micro-pattern gas detectors (MPGDs), which promise better point and two-track resolution than possible with the MWPC readout and to be more robust in high backgrounds.

To obtain good momentum resolution and to surpress backgrounds near the vertex, the TPC must operate in a strong magnetic field. This magnetic field must be mapped and understood to O(10^-5) to minimize corrections for the distortion of drifting electrons.

There are two features of a TPC which must be compensated by proper design work as part of our R&D program. First, the readout endplanes and electronics present a significant amount of material to the interaction products in the forward direction. The goal is to keep this below 30% X_0. Second, the 50 microsecond memory time of the the readout (due to the TPC drift length) integrates over background and signal events from 160 ILC bunch crossings at 500 GeV. The latter is being compensated by designing for the finest possible granularity: the sensitive volume is envisaged to consist of at least 1.5 x 10^6 pads and 10^3 time buckets per pad, giving more 1.5 x 10^9 3D-electronic readout voxels (two orders of magnitude better than at LEP). In the case that CMOS techniques are ripe, the granularity could be one to four orders of magnitude larger, depending on the design. The occupancy of the TPC predicted by present simulations is about 0.3% due to backgrounds from beam-beam effects and gamma-gamma interactions based. The TPC will be designed to cope with a factor ~50 higher backgrounds

Results to date

Systems under study at the moment are Micromegas meshes (MM) and Gas Electron Multiplier (GEM) foils. Both operate in a gaseous atmosphere and are based on the avalanche amplification of the primary produced electrons. The gas amplification occurs in the large electric fields in the MPGD microscopic structures with sizes of the order of 50 micrometers. MPGDs lend themselves naturally to the intra-train un-gated operation at the ILC, because, with proper voltage settings, they display a significant suppression of the number of back-drifting ions.

Small test TPC have been operated using GEM and MM gas-amplification with results presented at the international and regional ILC workshops.


The TPC R&D work is taking place in three phases:

(1) Small prototying

Subgroups have been performing studies using small TPC prototypes, with sensitive pad sizes ~ 10-20 mm^2 and pad planes ~ 100 cm^2, in magnetic fields up to 5T, for a few years. These studies will continue for another year or so. During these studies much experience has been gained in the GEM and MM technologies. Most of the work has been done with cosmic rays using Star or Aleph electronics. At this time, serious test-beam studies have started. There are several plans for this phase listed below.

(2) Large prototype

The large prototype study, currently in the design stage, will continue for another four years. During this phase, the subgroups will consolidate to build a TPC prototype with a diameter of 80 cm to be operated in a B-field of 1T. We will use the large prototype will test the manufacture of large chambers with GEM and MM technologies and the feasibility of CMOS readout techniques. Envisaged is also the manufacture of prototype electronics better matched to these new technologies. This phase will gain experience for building a final TPC and will allow the final choice as to which technology is appropriate for the LC. Studies of using the large prototype will take advantage of a detector R&D facility to be built in Desy, which will be used by vertex, TPC and calorimeter groups. Other plans during this phase are listed below.

Distribution of responsibilities for the components of the large prototype is being organized at present (2005).

(3) Design and construction phase.

Based on the experience gained, the the TPC for an ILC experiment will be designed, built and commissioned. This will take another four years, so that altogether the final TPC will be ready for installation in the ILC detector by 2015.

For more details of the R&D program see LC Note LC-TPC-2001 at http ://www-flc.desy.de/lcnotes/ .

Critical Items and funding

Timely construction of the EUDET test facility at DESY is a critical item for the large prototype phase of this project. Beyond that, all groups are in need of increased funding for all phases. This is particularly true of the large prototype phase. It is planned that EUDET will provide the field cage as well as the magnet and other infrastructure. However, other critical, costly components, such as the endplates and and read-out modules must be provided by the contributing institutions.

Please address the following questions in your statement.

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Topic revision: 22 Dec 2005, DanPeterson
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