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Example illustrating a 3D reconstruction of TPC events .

TPC detector (Time Projection Chamber) : In high energy physics, a Time Projection Chamber (TPC) is a particle detector which provides a complete track information on charged particles traveling through a gas volume contained in the chamber. With a fast readout electronics it is possible to derive a 3D particle localization and tracking in a high-track-density environment. When a charged particle passes through the detector gas it  produces primary ionization along its track. Due to a homogeneous electric field along the z-direction, electrons from the ionization drift with a constant velocity to be collected at a segmented anode plate. So in a first step, the TPC records a 2D projection (XY) of the 3D particle track (XYZ). The missing z-coordinate, is determined by two parameters: the drift time and the drift velocity which it closely related to the gas properties. Furthermore, in high energy physics experiments a magnetic field is often applied along the length of the TPC, parallel to the electric field, in order to minimize the diffusion of the electrons coming from the ionization of the gas and also to provide an additional information on the particle momentum which can be determined from the bending of the 2D projected image of the track.

Objectives of our group

The goal of our group is the research and development of a novel technique in the folowing topics:

  • Development of Gas Mixing systems.
  • Development of TPC detectors and monitoring chambers.
  • Simulation tools for TPCs
Prototype of the field cage designed for a gas monitoring chamber for T2K.

Gas monitoring chamber: The gas monitoring chamber works using the same principle as the TPC in terms of gas ionization, electron drift under a static electrical field and electron gas amplification. However it is not dedicated to reconstruct tracks nor the identify particles. The maine task of this chamber is to monitor the properties of the gas that is fed to the gas large volume TPC. This monitoring chambers uses a simple field cage with a small sample gas volume flowing from the same gas line that feeds the large TPC detector. Two important parameters can be extracted from the monitoring chamber. The drift velocity and the gain of the gas amplification can be derived. These two parameters are then used as a calibration parameters for the large TPC detector. The drift velocity is used for the reconstruction of the z-component of the track. The second parameter is the gain which is used for calibrating the particle identification algorithms.

Dummy picture just for layout.

TPC readout : The TPC readout has to fulfill two main requirements. A fast electronics and a high detector granularity where both are combined to a high energy resolution for a better time and space resolution and hence for a better particle identification in a dense track-environment. Historically TPC detectors have used standard wire chambers and beside some limitations it was a full success. In the last decade, the R&D of TPC detectors were based on the use of Gas-Electron-Multipliers (GEM) which have been developed at CERN. GEMs are thin foil with both sides metalized and with many small etched holes. By applying a voltage difference to the metalized sides electrons drifting towards the GEM are amplified in the large electric field in the hole region. In the course of the development of Micro-Strip-Gas-Chambers for the CMS experiment GEM foils have been employed successfully at our group already. Also GEMs have been intensively studied for the ILC TPC detecor. For the near detector (ND-280) at the T2K experiment (japan), the TPC detector is foreseen to be Micromegas based. A Micromegas detector "MICRO MEsh GASeous detector" is one of the promising micropatterned gas detectors being considered for charge readout TPCs to be used for future large scale experiment like ILC. A MICROMEGAS has an amplification gap (50 to 100 μm). The amplification gap is made of a thin metallic mesh and many support pillars that separate the mesh from the anode readout strips. The detector can be operated in an intense radiation field and unavoidable discharges due to heavily ionizing particles do not easily damage the detector.

Systematic studies of gas properties

During several Bachelor- and Masterthesis, different properties of gases have been studied.

In combination with the Universal Gas Mixing System, a database was established to store the results and compare them with the corresponding simulation. You can find the database at:

http://web.physik.rwth-aachen.de/gasDB/

 

New fully automated gas mixing system.

Universal Gas Mixing System

During the past, a powerful gas mixing system has been developed. It is able to mix up to three different pure gases or gas mixtures with a precision of less than 0.1 Vol.-% independend of the gas type used. At the same time, it can supply chambers with a defined flow and pressure.

The whole system is computer controlled and can run without any manual interaction for weeks. The quality of the gas can be monitored by using a gas chromatograph and dedicated devices for monitoring the contamination by H2O and O2. For both contaminants optional modules exist, wich are able to remove them out of the gas flow. In addition to the control algorithms, alarms and interlocks are set to prevents the connected detector, which can also be a TPC, from operating under unsafe conditions.



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