The large size straw drift chambers of the COMPASS experiment

https://doi.org/10.1016/j.nima.2005.10.026Get rights and content

Abstract

Straw drift chambers are used for the Large Area Tracking (LAT) of the Common Muon and Proton Apparatus for Structure and Spectroscopy (COMPASS) at CERN. An active area of 130 m2 in total is covered by 12 440 straw tubes, which are arranged in 15 double layers. The design has been optimized with respect to spatial resolution, rate capability, low material budget and compactness of the detectors. Mechanical and electrical design considerations of the chambers are discussed as well as new production techniques. The mechanical precision of the chambers has been determined using a CCD X-ray scanning apparatus. Results about the performance during data taking in COMPASS are described.

Introduction

The Common Muon and Proton Apparatus for Structure and Spectroscopy (COMPASS) [1] is a large aperture, high rate spectrometer, set up at the CERN Super Proton Synchotron SPS to study the spin structure of nucleons using a polarized muon beam, interacting in a polarized target. In particular, the process of photon gluon fusion into a charm-anticharm quark pair, which fragments to D+D¯ mesons, is used to measure the contribution of gluons to the nucleon spin. Moreover, hadron beams are used to study the production of charmed baryons, of “exotic” hadrons (hybrids and glueballs) and to measure the polarizability of hadrons.

The setup of COMPASS, as it was in 2004, is shown in Fig. 1. The detection of particles over a large acceptance and a large momentum range requires the use of a two-stage spectrometer. The 15 double layers of large area straw drift chambers, which are described here, are used for tracking and momentum determination of charged particles produced at large scattering angles (15–200 mrad). The chambers are grouped together in five modules. Each module contains three double layers with vertical, horizontal and inclined straw tubes and measures one space point. The inclined double layers are rotated by 10° with respect to the vertical ones. The chambers with vertical and inclined straws are of the same type (called type X), while the chambers with horizontal straws have a slightly different geometry (type Y). The exact dimensions of both types are given in Table 1.

In the following, the detailed dimensions refer to the type X chambers with vertical wires, which measure horizontal coordinates. A schematic view of a double layer is shown in Fig. 2. Each chamber consists of two layers of thin-film drift tubes (straws) of a length of 3202 mm which are mounted into an Al-frame. The area, covered by each double layer, is about 9 m2. The straws of one layer are glued together to one plane. Every plane is divided into three sections. The central part (section B, see Fig. 2), being closer to the beam axis, is exposed to higher rates. This part is made of 254 straws with 6.144 mm outer diameter while the outer two parts (section A and C) have 96 straws each with 9.654 mm outer diameter. The chosen diameters are a compromise between minimizing the number of channels and production cost while keeping the occupancy in each tube below 2% at maximum beam rates. The intensities, required at COMPASS, are 2×108 muons and up to 4×107 hadrons per 5.1 s spill for muon and hadron beams, respectively. A fast counting gas has to be used (Ar/CO2/CF4, 74:6:20).

The anode wires of the drift tubes are centered in the straws by two end-plugs and four small plastic pieces (spacers). The diameter of these gold-plated tungsten wires is 30 μm. The straws are supplied with the counting gas through the end-plugs and a gas-manifold, which is integrated into the Al-frame construction.

A thickness of only 40 mm along the beam direction was allowed for one double layer, so that three modules, containing 15 double layers in total, would fit in a volume with a length of less than 1 m between the first spectrometer magnet SM1 and the RICH detector of COMPASS. Thus, a large acceptance at a tolerable transverse size for the first stage of the spectrometer could be achieved by minimizing the thickness of the detectors.

The amount of material in the active part of the detector was optimized with respect to scattering and secondary interactions. The central part of the detector has a rectangular hole of about 20×10 cm2 for the beam.

The required spatial resolution per double layer is 200 μm at a detection efficiency larger than 99%. The internal mechanical precision of each double layer has been required to be (or to be known) better than 100 μm.

Section snippets

The straw tubes

Fig. 3 shows the structure of a straw tube. The tubes were produced by Lamina Dielectrics Ltd., Billingshurst, UK. The inner layer consists of a Carbon loaded Kapton 160 XC 370 foil from DUPONT, Wilmington, USA. It has a thickness of 40 μm±10% (data sheet DuPont) and a resistance of 370 Ω/square. This layer is glued onto a Kapton foil of a thickness of 12 μm and aluminized (500 Å) on one side; it has a resistance of about 1 Ω/square. Plastic foils have the advantage of low density and good

The straw chambers

The active part of each chamber consists of two layers of straws of a length of 3202 mm, which are glued together to a plane. A plane of this kind has a much higher mechanical stability compared to individual straws. This improves the ruggedness and the mechanical precision, which can be achieved. The load onto the frame, which would be needed to keep individual straws straight enough by tension, can be significantly reduced. The production technology, which is the basis for this design, will be

Tests of the chambers after their production

After the assembly work is finished, a quality control is performed for every chamber. The gas leakage under normal operation of a chamber is measured. The chamber is accepted, if the leakage rate stays below 5 l/h. This number has to be compared with the size of the active gas volumes (without taking into account the volumes of the gas manifolds), which is 126 l for a type X chamber and 104 l for a type Y. The leakage of the chambers is not limited by the diffusion of the gases through the straw

Summary and conclusion

The chosen production technology and chamber design allowed the construction of 2.8×3.2 m2 large tracking chambers with high accuracy, low mass and at a relatively low cost (they are among the largest detectors of their kind). The tracking accuracy is limited by the intrinsic straw drift tube and readout properties on one side and the mechanical precision of the straw tube planes on the other side. Firstly, we obtained a resolution of 220 μm per straw while the geometrical precision of wires

Acknowledgments

The authors express their gratitude to the Bundesministerium für Bildung und Forschung (BMBF) of Germany, which contributed the largest share, to the JINR and LPP Directorates, and also to their collaboration colleagues for their support and help in the organization of these works. The project was also supported by the Polish Ministry of Science and Information Society Technologies in the frame of two grants: 134/E-365/SPUB-M/CERN/P-03/DZ299/2000 and 134/E-365/SPB/CERN/P-03/DWM 62/2004-2006.

References (15)

  • J. Marzec

    Nucl. Instr. and Meth. A

    (2003)
  • W. Dünnweber

    Nucl. Instr. and Meth. A

    (2003)
  • B. Howell et al.

    Nucl. Instr. and Meth. A

    (1990)
  • COMPASS. CERN/SPSLC/96-14, SPSLC/P297,...
  • ATLAS ID TDR, v.2, CERN/LHCC/97-17,...
  • V.N. Bytchkov, et al., JINR, E-13-98-269, Dubna,...
  • V.N. Bytchkov, et al., JINR, E-13-98-209, Dubna,...
There are more references available in the full text version of this article.

Cited by (24)

  • Spatial resolution of thin-walled high-pressure drift tubes

    2011, Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment
    Citation Excerpt :

    The layers were staggered by one straw radius. The straws of the prototype were similar to the straws used for the COMPASS tracker and they were wound by two strips—an external strip of a 12 μm thick aluminized kapton HN50 film and an internal strip made of a 40 μm thick conducting kapton XC-160 film with graphite loading [4]. The anode wire is 30 μm gold plated tungsten.

  • A prototype coordinate detector based on granulated thin-walled drift tubes

    2011, Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment
    Citation Excerpt :

    The use of silicon pixel or strip detectors as well as of gas-filled micro-pattern gas detectors (such as GEM, micromegas and their varieties) in some cases is restricted by technological or budget problems. Coordinate detectors built on the basis of thin-walled drift tubes (straws) possess a number of advantages, such as a minimum material budget, good time-spatial parameters and the ability to work in high radiation environment, the flexibility of detector constructive solutions and their relatively low cost, which justifies their implementation in large experimental set-ups [1–4]. In order to eliminate their basic deficiency (low granularity of detecting elements, defined by the straw diameter and by the anode wire length), a new method for manufacturing straws with segmented anodes has been developed, which makes it possible to achieve a granularity as fine as 1 cm2 [5–7].

  • The GlueX central drift chamber: Design and performance

    2010, Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment
    Citation Excerpt :

    Clearly, an overall hermetic detector with adequate resolution is essential, and the CDC is a crucial subsystem. Straw tubes are a well-established technology [4–30] that has long been recognized as an alternative to multi-wire tracking chambers. Due to their cylindrical geometry, straw tubes can have very low mass, which reduces multiple scattering of charged particles.

  • Development of segmented straws for very high-rate capability coordinate detector

    2008, Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment
  • The COMPASS experiment at CERN

    2007, Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment
  • A new measurement of the Collins and Sivers asymmetries on a transversely polarised deuteron target

    2007, Nuclear Physics B
    Citation Excerpt :

    DSTs and miniDSTs are stored also centrally on tape, under CASTOR. The physics analysis is performed on the mini-DSTs, replicated in the different institutes, by means of PHAST, the COMPASS framework for the final data analysis [39]. Fig. 4 depicts the reconstruction and analysis system to which the data flow after they are stored centrally.

View all citing articles on Scopus
1

Present address: CERN, Dept. TS-LEA, 1211 Geneva 23, Switzerland.

2

Present address: Institut universitaire de radiophysique appliquée, Grand-Pré 1, 1007 Lausanne, Switzerland.

3

Present address: Uppsala University, Department of Radiation Sciences, Box 535, SE-75121 Uppsala, Sweden.

View full text