Heat deposition by transient beam passage in spoilers

Future electron-positron linear colliders must produce bunches of tiny emittance grouped in short bunch trains in order to provide adequately large luminosities. A collimation system must be installed between the end of the main linac and the optical elements of the final focus to protect the detectors from errant beams. With ordinary values of the betatron functions, the transverse beam size is of a few microns. With such sizes, the local deposition of heat of even a single bunch train is so high that no material can survive such an event.The problem is solved by increasing the beam sizes at the location of the collimators. But the use of large betatron functions is costly and can induce strong optical errors. It is therefore important to compute precisely safe beam sizes which allow the survival of the collimators, in order to limit their increase to the minimum needed. The deposition of heat occurs both by ionisation along the path of the particles which traverse the material and by ohmic image current heating at the surface of the collimator, for that fraction of the beam which flies outside the collimator.With small bunches, heat diffusion is substantial even with short bunch trains and helps to reduce the excursion of temperature. The rise of temperature is computed by solving analytically the time-dependent heat equation in two spatial dimensions near an interface with vacuum. Numerical results are given for the CLIC study

Fast Neutron Detectors Based On Micromegas Technology

After a short description of the Micromegas principle, a new concept of neutron detectors based on this technique is presented. The report is illustrated by an overall picture of the possible use of these detectors in different domain such as: nuclear physics, inertial fusion and industrial application. A particular description will be devoted to the compact detector named "PiccoloMicromegas". This detector, able to measure neutron flux in a broad range of energy of neutron (from thermal to several MeV), is developed for the measurements of neutrons flux in-core of the future generations of the nuclear reactors (fast and possibly Accelerator Driven System (ADS))

A new low intensity beam profiler for SPIRAL2

WEPF14International audienceIn the framework of SPIRAL 2 ion beams, several beam profile monitors are presently being developed at GANIL. One of them is a low-intensity beam-profile monitor that works as a secondary electron detector. This Emission-Foil Monitor (EFM) will be used in the radioactive beam lines of SPIRAL2 and in the experimental rooms of this new facility. The ions produce secondary electrons when they are stopped in an aluminium emissive foil. The electrons are then accelerated using an electric field and guided using a magnetic field to a double-stage microchannel plate (MCP). A 2D pixellated pad plane placed below the MCP is used to collect the signals. The magnetic field created by permanent magnets in a closed magnetic circuit configuration permits the beam-profile reconstruction to be achieved with a good resolution. The EFM can visualize beam-profile intensities between only a few pps to as much as 109 pps and with energies as low as several keV. This profiler has been under development since 2009 and is currently manufactured. Recent results of this monitor are presented in this article

MAD Version 9

The program MAD is widely used for accelerator design and beam dynamics studies. For many years, its input language has been the nearest thing to a world-wide standard for describing accelerator structures. The new Version 9 is a complete rewrite using a systematic object-oriented methodology based on the CLASSIC classes [2] for accelerator physics. It provides many improvements over the previous MAD Version 8. These include: (i) support for multiple beam-lines simultaneously, facilitating, for example, matching constraints that couple the two rings of a two-ring collider, (ii) much improved Lie-algebraic map calculations, (iii) a uniform method and format for exchanging many kinds of structured data with other programs, (iv) an improved and more consistent input language. In addition, we report on a parallel 3D Poisson field solver for space charge calculations in high intensity particle beams. Applied to the PSI injector cyclotron, this shows the general nature of MAD Version 9 as a state-of- the-art problem-solving environment. We describe the current status of the program and how to get it, outline future plans and illustrate some of the new features

Overview of the CLIC Collimation design

The collimation system of the Compact Linear Collider (CLIC) should simultaneously fulfill three different functions. It must (1) provide adequate halo collimation to render the detector background acceptable, (2) ensure collimator survival and machine protection against mis-steered beams, and (3) not significantly amplify incoming trajectory fluctuations via the collimator wake fields. We describe the present layout of CLIC post-linac collimation and characterize its potential performance

Experimental investigation of ground-state properties of 7H with transfer reactions

The properties of nuclei with extreme neutron–to–proton ratios, far from those naturally occurring on Earth, are key to understand nuclear forces and how nucleons hold together to form nuclei. 7H, with six neutrons and a single proton, is the nuclear system with the most unbalanced neutron–to–proton ratio known so far. However, its sheer existence and properties are still a challenge for experimental efforts and theoretical models. Here we report experimental evidences on the formation of 7H as a resonance, detected with independent observables, and the first measurement of the structure of its ground state. The resonance is found at ∼0.7 MeV above the 3H+4n mass, with a narrow width of ∼0.2 MeV and a spin and parity. These data are consistent with a 7H as a 3H core surrounded by an extended four-neutron halo, with a unique four-neutron decay and a relatively long half-life thanks to neutron pairing; a prime example of new phenomena occurring in what would be the most pure-neutron nuclear matter we can access in the laboratory.Spanish Ministerio de Economía y Competitividad under contracts FPA2009–14604–C02–01 and FPA2012–39404–C02–01

Micromegas detector developments for MIMAC

The aim of the MIMAC project is to detect non-baryonic Dark Matter with a directional TPC. The recent Micromegas efforts towards building a large size detector will be described, in particular the characterization measurements of a prototype detector of 10 $\times$ 10 cm$^2$ with a 2 dimensional readout plane. Track reconstruction with alpha particles will be shown.Comment: 8 pages, 7 figures Proceedings of the 3rd International conference on Directional Detection of Dark Matter (CYGNUS 2011), Aussois, France, 8-10 June 2011; corrections on author affiliation

Performance of the improved larger acceptance spectrometer: VAMOS++

International audienceMeasurements and ion optic calculations showed that the large momentum acceptance of the VAMOS spectrometer at GANIL could be further increased from $\sim$ 11% to $\sim$ 30% by suitably enlarging the dimensions of the detectors used at the focal plane. Such a new detection system built for the focal plane of VAMOS is described. It consists of larger area detectors (1000 mm × 150 mm) namely, a Multi-Wire Parallel Plate Avalanche Counter (MWPPAC), two drift chambers, a segmented ionization chamber and an array of Si detectors. Compared to the earlier existing system (VAMOS), we show that the new system (VAMOS++) has a dispersion-independent momentum acceptance . Additionally a start detector (MWPPAC) has been introduced near the target to further improve the mass resolution to $\sim$ 1/220. The performance of the VAMOS++ spectrometer is demonstrated using measurements of residues formed in the collisions of 129Xe at 967 MeV on 197Au

Tests of Micro-Pattern Gaseous Detectors for Active Target Time Projection Chambers in nuclear physics

Active target detection systems, where the gas used as the detection medium is also a target for nuclear reactions, have been used for a wide variety of nuclear physics applications since the eighties. Improvements in Micro-Pattern Gaseous Detectors (MPGDs) and in micro-electronics achieved in the last decade permit the development of a new generation of active targets with higher granularity pad planes that allow spatial and time information to be determined with unprecedented accuracy. A novel active target and time projection chamber (ACTAR TPC), that will be used to study reactions and decays of exotic nuclei at facilities such as SPIRAL2, is presently under development and will be based on MPGD technology. Several MPGDs (Micromegas and Thick GEM) coupled to a 2×2 mm2 pixelated pad plane have been tested and their performances have been determined with different gases over a wide range of pressures. Of particular interest for nuclear physics experiments are the angular and energy resolutions. The angular resolution has been determined to be better than 1° FWHM for short traces of about 4 cm in length and the energy resolution deduced from the particle range was found to be better than 5% for 5.5 MeV α particles. These performances have been compared to Geant4 simulations. These experimental results validate the use of these detectors for several applications in nuclear physics

Neutron imaging with a Micromegas detector

The micropattern gaseous detector Micromegas has been developed for several years in Saclay and presents good performance for neutron detection. A prototype for neutron imaging has been designed and new results obtained in thermal neutron beams are presented. Based on previous results demonstrating a good 1D spatial resolution, a tomographic image of a multiwire cable has been performed using a 1D Micromegas prototype. The number of pillars supporting the micromesh is too large and leads to local losses of efficiency that distort the tomographic reconstruction. Nevertheless, this first tomographic image achieved with this kind of detector is very encouraging. The next worthwhile development for neutron imaging is to achieve a bi-dimensional detector, which is presented in the second part of this study. The purpose of measurements was to investigate various operational parameters to optimize the spatial resolution. Through these measurements the optimum spatial resolution has been found to be around 160 microns (standard deviation) using Micromegas operating in double amplification mode. Several 2D imaging tests have been carried out. Some of these results have revealed fabrication defects that occurred during the manufacture of Micromegas and that are limiting the full potential of the present neutron imaging system.Comment: 6 pages, 10 figures, presented at IEEE 2004 conference in Roma, Ital