The tracking of particles in future particle physics experiments require large detectors working at high counting rates, with good spatial and time resolution.

Micro Pattern Gaseous Detectors, like the GEM (Gas Electron Multiplier, developed by F. Sauli), and the Micromegas (MicroMesh Gaseous detector, developed by I. Giomataris), emerge as very promising tools.

Compared to MultiWire Proportionnal Chambers (MWPC), these detectors have improved capabilities in term of localization, counting rate and granularity for charge particle tracking at high-luminosity colliders.

The RDD department participated to TPC prototypes tests in a magnetic field with a particle beam in collaboration with the LAL (Laboratoire de l’Accélérateur Linéaire, France ), the CEA-Dapnia Saclay (France) and the KEK laboratory ( Tsukuba , Japan) . This activity takes place in the R&D efforts for the ILC (International Linear Collider).

Experimental characterizations of a TPC with a Micromegas were performed with cosmic rays in different argon based gas mixtures with different quenchers (Isobutane, Methane, CF₄, CO₂ …) at different magnetic field values (up to 2 T), provided by the Saclay Magnet.

The traditional methods for the experimental studies of MPGDs have some drawbacks. A radioactive source, like ⁵⁵Fe, does not provide an event-by-event localized interaction point in gas, nor a time-reference. Charged particles provided by an accelerator beam or cosmic rays, which are at the minimum ionization, yield only a few tens of primary electrons per centimeter in the gas, thus limiting spatial and energy resolutions to a limited range of number of primary electrons.

A test-bench, developed at the RDD department of IPN Orsay, allows the production of a point-like electron source by focusing a 337nm wavelength laser on a thin metallic nickel-chromium layer deposited on a quartz lamina. The number of primary electrons can be adjusted from one to several thousands by varying the laser light intensity and the focusing.

The experimental set-up consists in:
- an optical tuning and focusing system made with several lenses.
- A MPGD detector, mounted on three 1 µm precision motors for moving in the three directions of space.
- Electronics readout and data acquisition system. The data are analyzed offline with the ROOT package.

Measurements on spatial and energy resolutions were performed with a Micromegas detector (3mm drift gap, 125µm amplification gap,  44x44mm² active surface). The anode is made of 128 gold strips of 338µm pitch. The gas mixture was Ne 90% Isobutane 10%. The number of primary electrons was between 60 and 2000 and the gain adjusted in consequence from 2.10⁴ down to 10³. The source size is estimated to less than 100 µm. A spatial resolution of 5 µm was obtained with 2000 primary electrons. The gain variance is estimated below 0.2.  See the article by T. Zerguerras et al. for more details.

The Detector Department of IPN Orsay participates to the R&D activities on the ACtive TARget detector (ACTAR), in collaboration with GANIL and CEA/IRFU. This detector uses the gas both as a target and detection medium for low-energy ions, produced by nuclear reactions induced by a SPIRAL-like beam. A first prototype was built and mounted on the laser test-bench of the Detector Department that was modified in order to take the new mechanical constraints into account. It uses a 160-µm thick amplification gap Micromegas, with a 1.6-mm drift zone. Tests in a Ne 95% Isobutane 5% mixture at atmospheric pressure were performed with a 337-nm wavelength laser to measure the Single-Electron Response (SER), that characterizes the gas gain fluctuations of the detector, and the Fano factor associated to the interaction processes of the laser with the drift foil. Further details on test methods and results can be found in the related Paper.

Since May 2010, the Detector Department of IPN Orsay joined the RD51 collaboration that gathers 73 Universities and Research Laboratories from 25 countries worldwide. The main objective of RD51 is to advance technological development and application of Micropattern Gaseous Detectors not only in Particle and Nuclear Physics but also in Medical Imagery and for the industry. The main research topics are the physics characterization of MPGDs, their applications, the development of simulation and analysis software tools, the studies with beam-tests and the development of new production methods. The Detector Department of IPN Orsay is particularly involved in the two first activities quoted.