Speaker
Description
The European Spallation Source, presently under construction at Lund (Sweden), will consist of a 537 m long linear proton accelerator delivering a 2 GeV proton beam with a 5MW power to a tungsten target, equipped with a highly optimised neutron moderator capable of providing a bi-spectral (thermal and cold) neutron beam to 42 beam ports, 22 of which are followed by a flight path leading to far away measuring stations.
A perfect knowledge of the proton beam is critical to maximize the number of protons on target and minimize beam losses. Transversal beam profile monitors are therefore essential for a good operation of the facility.
Due to the high power, all beam profilers to be used at nominal operating conditions will be of non-interceptive type. In the frame of the in-kind contribution agreement signed with ESS, CEA is going to deliver to the European Spallation Source five Non-invasive Profile Monitors (NPMs) to be installed in the Cold Linac section: one in the Spoke section, 3 in the Medium β section and one in the High β section. A single NPM has two units supporting profile measurements in both horizontal and vertical axis. Each unit is based on the detection of ions generated by the interaction of the proton beam with the vacuum residual gas and is called Ionisation Profile Monitor (IPM). It is composed by a cubic cell of 10 cm side and a read-out. A uniform electric field in one of the directions orthogonal to the beam propagation vector is set in each IPM to drive the ionisation charges towards the read-out. These transversal beam profile monitors will cover proton energies ranging between 90 MeV and 600 MeV and are conceived to deliver one profile/pulse at a residual gas pressure of 10^-9 mbar and with an uncertainty on the beam width of less than 10% of its dimension.
The high density of the proton bunches, typically 10^9 proton in a few mm^3 may lead to space charge effect distorting the profile measurements. Studies to contain the space charge effects have been performed. Two different read-outs (current reading from metallic strips and optical) were proposed and tested in two measurement campaigns at the IPHI accelerator at CEA Saclay. After careful analysis, the final choice fell on the read-out composed by a micro channel plate equipped with a phosphorous screen and followed by a camera. The detectors are now in construction at CEA.
A summary of all main steps of the project, with special focus on the space charge simulations and the experimental campaigns, will be presented.
