The CLIC positron production scheme

The CLIC (Compact Linear Collider) positron source is based on the conventional scheme, using a metal converter target and an Adiabatic Matching Device (AMD) composed of a Flux Concentrator (FC) and a constant magnetic field along the positron Pre-Injector linac. The positrons are accelerated with L-band RF structures. Beam dynamics simulations are described for the positron production in the target and capture section in the AMD. The distribution of the energy deposition in the target is studied with the EGS4 code. The dependence of the positron yield on several parameters is studied and optimised using both EGS4 and analytical calculations. Following this optimisation, a new set of design parameters is proposed and particle tracking simulations are performed to estimate the overall performance

Numerical Simulation of Permanent Magnet Method for Measuring Critical Current Density in Superconducting Film: Dominant Experimental Conditions for Crack Detection

AbstractThe scanning permanent magnet method for measuring the critical current density in a high-temperature superconduct- ing (HTS) film has been reproduced numerically. For this purpose, a numerical code has been developed for analyzing the time evolution of a shielding current density in an HTS film with a crack. The results of computations show that the attractive force Fr and repulsive one Fa are observed near the endpoints of the crack when the symmetry axis of the magnet approaches the crack. In addition, the both forces, Fr and Fa, have the maximum value only when the magnet is located above the crack. This means that the crack size and position can be estimated by using the scanning method

Development of an intense positron source using a crystal--amorphous hybrid target for linear colliders

In a conventional positron source driven by a few GeV electron beam, a high amount of heat is loaded into a positron converter target to generate intense positrons required by linear colliders, and which would eventually damage the converter target. A hybrid target, composed of a single crystal target as a radiator of intense gamma--rays, and an amorphous converter target placed downstream of the crystal, was proposed as a scheme which could overcome the problem.This paper describes the development of an intense positron source with the hybrid target. A series of experiments on positron generation with the hybrid target has been carried out with a 8--GeV electron beam at the KEKB linac. We observed that positron yield from the hybrid target increased when the incident electron beam was aligned to the crystal axis and exceeded the one from the conventional target with the converter target of the same thickness, when its thickness is less than about 2 radiation length. The measurements in the temperature rise of the amorphous converter target was successfully carried out by use of thermocouples. These results lead to establishment to the evaluation of the hybrid target as an intense positron source.Comment: 17pages, 10figure