GDS: Gas-Filled

Detectors and Systems

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The aim of the present network activity is to assemble and coordinate a large group of research collaborations that are in the process of developing new capabilities with gas-filled detection and active-target systems in the field of nuclear physics. Gas-filled time-projection chambers and active-target detection systems have found profitable applications in nuclear physics due to their high efficiency and ability to detect low-energy particles. Examples include the CENBG TPC, designed for studying 2-proton radioactivity and the active targets IKAR at GSI, MAYA at GANIL, and TACTIC at York/TRIUMF that are used for scattering and reaction studies over a wide range of energies. While these detectors have each been extremely successful, recent advances in high-density front-end electronics now permit very large numbers of channels to be read and processed. Smaller pixel sizes, higher data rate throughput, the ability to change gains and thresholds on a channel-by-channel basis, and software-level fully numeric triggering are some of the main advantages that next-generation detectors will have over previous ones. Between 2010 and 2013, new detector projects including MINOS, ACTAR TPC, and SpecMAT have all been funded through competitive grants awarded by the European Research Council (ERC) and together represent a total EU investment of nearly 4.4M€. These projects highlight the potential for these types of detection systems in nuclear physics and imply that the demand for a networking activity between these collaborations, and several others interested in using these technologies, is both essential and timely.

Artistic view of ACTAR TPC with some ancillary detectors.

This network activity will encompass all applications of gas-filled detectors and systems in the nuclear-physics community such as position-sensitive beam tracking and monitoring detectors, continuous-flow gas targets, high-rate gas counters, and gas-filled magnets and spectrometers. It aims to coordinate solutions towards several of the long- standing challenges that must be overcome before gas-filled detector systems can achieve their full potential. High- intensity beams in excess of 10⁶ ion/s, large energy losses associated with heavy-ion beams, and large dynamic ranges are some examples. Requirements for new types of gases and mixtures will be coordinated including conceptual designs for integrated gas chambers and ultra-pure gas-handling and recycling systems for rare and expensive gases (such as ³He). Organisation of the needs for auxiliary detectors, such as scintillating materials and semi-conductor devices, that need to be operated inside the gas volume or within large magnetic fields will be studied. The GDS network will exchange information through dedicated workshops and topical meetings between physicists and engineers already working on these projects across Europe. It will assist and promote collaborations and personnel working on similar projects and will encourage the support and training of highly qualified personnel in this rapidly evolving field.

Coordinator: Thomas Roger (GANIL)

Deputy coordinator: Fabiana GRAMEGNA (INFN)

Involved partners:
GANIL (Coordinator: Thomas Roger), INFN LNL (Coordinator: Fabiana GRAMEGNA), CNRS (Coordinator: Freddy Flavigny), KU Leuven (Coordinators: Tommaso Marchi, Riccardo Raabe), CEA SPhN (Coordinators: Alain Gillibert, Emmanuel Pollacco), USC GENP (Coordinator: Héctor Alvarez Pol)

• Task 1: Management/GDS Coordination (GANIL)

  The main objectives of this task are to harmonise the various activities described in the tasks of the GDS network, assist with the dissemination of information and knowledge gained to the broader community, and suggest ways to combine the existing resources of the various collaborations in order to maximise the efficiency and potential of these projects. This task will provide the platform for these activities through the organisation of workshops between all of the EU communities working on GDS projects.

• Task 2: GDS in strong and non-uniform magnetic fields (CEA, KU Leuven)

  To reach particle identification and energy resolution over an extended dynamic range several detector projects require magnetic fields. However, access to magnets with uniform strong fields of 2-5 Tesla and with “volumes” that can house an active target or time projection chamber with their auxiliary detector arrays is non-existent in Europe. The role of this task is to combine the available knowledge and expertise to develop new ideas and capabilities for future ones through the deployment of non uniform electric and magnetic fields within the active volume.

• Task 3: Novel detection systems for high-intensity and heavy-ion beams (USC, GANIL)

  The large number of ionisation electrons produced from unreacted high-intensity (>10⁶ ions/s) or heavy-ion beams (i.e., Ni, Sn, Pb, U) creates significant space charge that degrades the homogeneity of the drift electric field in gas- filled detection systems. Experiments suffer from poorer resolution, or in some cases, cannot be performed at all. New solutions to operate an active-target detection system at the highest possible beam intensities, exploring different possibilities and investigating new detection capabilities for auxiliary detection systems will be coordinated in this task.

• Task 4: Rare-gas target handling and recycling systems (CNRS, CEA)

  This task aims to propose solutions towards the realisation of a gas-handling system for rare-gaseous targets for use in rare-isotope beam experiments. Among the most important is ³He as it provides several unique probes such as one- proton transfer (³He,d) reactions or charge-exchange (³He,t) reactions. Rare gases are essential for certain types of experiments but the cost of obtaining such gases in useable quantities is often a major deterrent. It is therefore imperative to recirculate a limited volume of gas, while retaining its quality for long-term operation. This task will collect the available data on what handling and recycling systems are already in existence, assess their main limitations, and propose how they could be improved. Data on the operational characteristics of new gas mixtures will also be collected in this task.

• Task 5: Auxiliary detectors (INFN, KU Leuven)

  Depending on the physics goals of each experiment, different types of auxiliary detectors such as neutron and γ-ray detectors must be coupled to GDS to complement the identification and track reconstruction in the gas volume. Silicon detectors, inorganic and organic scintillators need to be used in various compact geometries around the gas volume (or even operating inside it) and in the vicinity of strong magnetic fields. Despite the obvious improvements in overall sensitivity, the actual realisation of coupling a GDS to an array of auxiliary detectors is far from trivial. This task will be devoted to sharing the available information on new types of detector materials and their operational characteristics as it pertains to the joint use of different types of auxiliary detectors with the next generation GDS.