Computer simulation of electron-positron pair production by channeling radiation in amorphous converter (original) (raw)

A positron source using an axially oriented crystal associated to a granular amorphous converter

Chinese Physics C, 2012

A non conventional positron source using the intense γ radiation from an axially oriented monocrystal which materialize into e+e-pairs in a granular amorphous converter is described. The enhancement of photon radiation by multi-GeV electrons crossing a tungsten crystal along its <111> axis is reported. The resulting enhancement of pair production in an amorphous converter placed 2 meters downstream, is also reported. Sweeping off the charged particles from the crystal by a bending magnet upstream of the converter allows a significant reduction of the deposited energy density. Substituting a granular target made of small spheres to the usual compact one, makes easier the energy dissipation. The deposited energy and corresponding heating are analyzed and solutions for cooling are proposed. The configurations studied here for this kind of positron source allow its consideration for unpolarized positrons for the ILC.

Experimental Activities on High Intensity Positron Sources Using Channeling

2017

The positron source under investigation is using channeling radiation of multi-GeV electrons in a tungsten crystal. The radiated photons are impinging on the amorphous targets creating e+e− pairs. A dipole magnet between the crystalradiator and the amorphous-converter allows the charged particles to be swept off and only emitted photons to generate e+e− pairs in the converter. Granular targets of different thicknesses, made of small tungsten spheres, have been recently investigated as a target-converter. This paper is describing the experimental studies conducted at the KEKB linac with such device. After the description of the experimental set-up and beam parameters, the measurement methods and preliminary results are presented.

Investigations on a hybrid positron source with a granular converter

Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2015

Promising results obtained with crystal targets for positron production led to the elaboration of a hybrid source made of an axially oriented tungsten crystal, as a radiator, and an amorphous tungsten converter. If the converter is granular, made of small spheres, the heat dissipation is greatly enhanced and the thermal shocks reduced, allowing the consideration of such device for the future linear colliders. A positron source of this kind is investigated. Previous simulations have shown very promising results for the yield as for the energy deposition and the PEDD (Peak Energy Deposition Density). Here, we present detailed simulations made in this granular converter with emphasis on the energy deposition density, which is a critical parameter as learned from the breakdown of the SLC target. A test on the KEKB linac is foreseen; it will allow a determination of the energy deposited and the PEDD in the converter through temperature measurements. Four granular converters, made of W spheres of mm radius have been built at LAL-Orsay; they will be installed at KEK and compared to compact converters. A description of the experimental layout at KEK is provided. Applications to future linear colliders as CLIC and ILC are considered.

A Positron Source Using Channeling in Crystals for Linear Colliders

International Journal of Modern Physics A, 2010

An alternative way to the conventional positron source using intense electron beams, of some GeV, impinging on thick amorphous targets is presented. This source is using two successive targets: the first one is a tungsten crystal, which <111> axis is aligned with the beam direction, and the second is an amorphous target put at some distance from the crystal. The enhanced radiation due to electron channelling produces a large amount of photons which, consecutively, create high quantity of e +- e - pairs in the amorphous target. Between the two targets a sweeping magnet takes off all or part of the charged particles coming out from the crystal. An optimization procedure is carried out based on two important parameters: a) the distance between the two targets; b) the minimum energy above which the charged particles coming out from the crystal are allowed to hit the amorphous target. This optimization, which first step is presented here, aims to obtain the highest accepted yield (...

Crystal-based pair production for a lepton collider positron source

The European Physical Journal C

An intense positron sources is a demanding element in the design of future lepton colliders. A crystal-based hybrid positron source could be an alternative to a more conventional scheme based on the electron conversion into positron in a thick amorphous target. The conceptual idea of the hybrid source is to have two separate objects, a photon radiator and a photon-to-positron converter target. In such a scheme an electron beam crosses a thin axially oriented crystal with the emission of a channeling radiation, characterized by a considerably larger amount of photons if compared to Bremsstrahlung. The net result is an increase in the number of produced positrons at the converter target. In this paper we present the results of a beam test conducted at the DESY TB 21 with 5.6 GeV electron beam and a crystalline tungsten radiator. Experimental data clearly highlight an increased production of photons and they are critically compared with the outcomes of novel method to simulate the numb...

Positron Sources using Channeling: a promising device for Linear Colliders

2010

International audienceThe need of intense and bright positron sources for linear colliders has urged the researches on polarized and unpolarized positrons. For 20 years, continuous theoretical and experimental investigations on unpolarized positron sources using axially channelled electrons in aligned monocrystals have pointed to efficient solutions concerning not only the source intensity, but also the minimization of the deposited energy. Simulations using the channelling programme of V. Strakhovenko associated to GEANT4, provided a description of such sources composed of tungsten crystals as photon radiators and amorphous tungsten as converters, the so-called hybrid source; the incident electron energies are taken between 5 and 10 GeV. Here, some applications are shown for CLIC, for which this source is the baseline, and also for ILC. The simulations are also concerning the test at KEK of such hybrid source, with a sweeping magnet separating the crystal radiator and an amorphous ...

Experiment of positron generation using a crystal target at the KEK electron/positron linac

Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2001

We have performed an experiment of positron generation using a crystal target at an electron/positron linac at KEK. The target consists of a tungsten crystal to emit photons and an amorphous tungsten for pair creation, whose thicknesses are 0.5 and 2.0 radiation length, respectively. When the á1 1 1ñ crystal axis is oriented parallel to the 3 GeV incident electron beam, the positron yield is enhanced by 40% compared to values for the disoriented crystal. No eect of injecting intense ultra-short electron bunches on the crystalline structure is observed. The crystal orientation dependence of the positron yield as well as the enhancement factor can be explained by a simulation assuming a coherent bremsstrahlung process of the electron in the crystal. Ó

Experimental study of a crystal positron source

Physics Letters B, 2002

Tungsten crystals oriented on their 111 axis, were submitted to 6 and 10 GeV electron beams on the SPS-CERN transfer lines. The crystals, 4 and 8 mm thick, used alone or associated to 4 mm thick amorphous disk, were studied as positron sources. The emerging positrons were detected by a Drift Chamber partially immersed in a magnetic field, where their trajectories were reconstructed providing the energy spectrum and the angular distribution. Significant enhancements were observed for the crystal source when compared to the amorphous one of the same thickness. The gain was larger than 3 and 2 for the 4 mm and 8 mm targets, respectively. The presented results look very promising for e + e − linear colliders. 

Experimental Study of Positron Production from Monocrystalline Targets at the Kekb Injector Linac

2006

We report a series of positron-production experiments from an axially-oriented single-crystal target by 4- and 8GeV channeling electrons at the KEKB injector linac. The targets tested are tungsten crystals with different thicknesses (14.2 mm at maximum), and diamond crystals with two different thicknesses (7.25 mm at maximum). The axis for the tungsten crystals and that for the diamond crystals have been aligned to the electron beam by a precise goniometer. The positron-production efficiencies in the momentum range of less than 30 MeV/c were systematically investigated for each target by measuring the positron yield generated in the forward direction with a magnetic analyzer. The results show that the maximum positron-production efficiencies from the 9mm-thick tungsten crystal and from the 7.25-mm-thick diamond combined with amorphous tungsten are 17% and 12%, respectively, larger than that from amorphous tungsten at the momentum of 20 MeV/c. In a series of the experiments using the...