Straw Tracking Detectors
List of detector developments and their specific properties:
Vacuum Straw Tube Tracker for the COSY-TOF Experiment
- 2704 straw tubes, each with 105 cm length, 10 mm diameter and 32 micron wall thickness (aluminized mylar)
- Stack of 13 planar double-layers with 3 different orientations
- Self-supporting layers, no mechanical frame for tube stretching
- Operated in the 25 m³ vacuum barrel of the COSY-TOF spectrometer
- Leakage of the detector on permeation level (= flow of gas molecules through 32 micron mylar film)
- Frontend electronics in vacuum (self-cooling)
- Status: Installed in 2009, since then several experiment beam times
- Experimental spatial resolution: 140 μm (sigma)
Central Straw Tube Tracker with Energy Readout for the PANDA Experiment
- 4636 straw tubes, each with 150 cm length, 10 mm diameter and 30 micron wall thickness (aluminized mylar)
- Barrel of 27 layers in radial direction, 19 axial and 8 stereo layers (± 3 deg)
- Hexagonal layout with 6 sectors of close-packed planar layers
- Self-supporting layers, no mechanical frame for tube stretching
- Energy-loss and drift time readout
- Spatial resolution: 150 μm (σrφ), 2–3 mm (σz)
- Specific energy-loss (dE/dx) resolution: 8±1 % (σ) (prototype measurements with proton beams)
- Status: in construction, Technical Design Report submitted
Straw Prototype Setups for High-Rate Beam Tests
- Various setups at the COSY accelerator for high-rate readout and aging tests
Straws are gas-filled cylindrical tubes with a conductive inner layer as cathode and an anode wire stretched along the cylinder axis. Charged particle tracks traversing a straw ionize the gas create about 100 electrons and ion pairs per cm gas. An electric field of a few kV between anode wire and cathode separates the electrons and ions. The electrons drift towards the anode with a characteristic drift velocity. Close to the wire the electrons are accelerated due to the strong electric field (E ~ 1/r) and a charge avalanche due to increasing ionizations by electron collisions with the gas molecules occurs. The avalanche generates a typical gas amplification of the primary charges of a factor of 104–105, which is high enough to create a sufficient charge signal (about 1-100 fC). The signal is further amplified and shaped by a dedicated electronic circuitry and readout via discriminators and time-readout boards and/or analog signal readout boards.
At IKP a novel techniques has been developed to reduce the material budget of the detector to an absolute minimum, which is important for a clean and background-free tracking of the charged particles. The technique of self-supporting straw layers by the gas over-pressure guaranties a wire tension of 108 kg and straw tube stretching of 2.7 tons (weight-equivalent), but at a detector weight of only 15kg for the 2700 straw tubes of the COSY-TOF straw detector. No dedicated (and heavy) mechanical frame structure for the wire and tube stretching is needed..
The thickness of the straw tube film wall is about 30 micron, which is the minimum possible. The COSY straw tube tracker is operated in the large (25 m³) evacuated time-of-flight barrel of the COSY-TOF spectrometer since about 3 years now. The leakage of the detector is on the permeation level, which is the minimum possible, and caused by the unavoidable molecular flow of the gas through the thin-walled (32 micron) mylar film..
For the PANDA Central Straw Tube Tracker (STT) an additional readout of the specific energy-loss (dE/dx) for a particle separation has been developed and tested with straw prototype setups and proton beams at the COSY accelerator. An energy resolution of about 8 % (sigma) has been measured. Considering the higher number of straw hits (layers) in the PANDA STT (27 layers instead of 16 for the prototype setups) an energy resolution of about 6 % could be achieved at PANDA.
More details about the PANDA-STT detector and a short summary of the COSY-STT (chap. 5.1 and 5.4) can be found in the recently submitted Technical Design Report (see link below).
Links:
http://arxiv.org/abs/1205.5441v2
Technical Design Report for the: PANDA Straw Tube Tracker (Eds. P. Gianotti, P. Wintz). PANDA Collaboration. (May 2012).
http://dx.doi.org/10.1063/1.1664352
A Large Tracking Detector In Vacuum Consisting Of Self-Supporting Straw Tubes (P. Wintz for the COSY-TOF Collaboration). AIP Conf. Proc. 698 (2004), pp. 789-792;
For further interest or specific questions please contact
Prof. J. Ritman
Director of the Nuclear Physics Institute of the Forschungzentrum Jülich and Full professor of the Ruhr-Univ.-Bochum
Phone +49 2461-61-3091
Email J.Ritman@fz-juelich.de
Dr. P. Wintz
Nuclear Physics Institute, Forschungzentrum Jülich GmbH
Phone +49 2461-61-4153
Email p.wintz@fz-juelich.de
