Experimental results of the laserwire emittance scanner for LINAC4 at CERN

Within the framework of the LHC Injector Upgrade (LIU), the new LINAC4 is currently being commissioned to replace the existing LINAC2 proton source at CERN. After the expected completion at the end of 2016, the LINAC4 will accelerate H- ions to 160 MeV. To measure the transverse emittance of the H- beam, a method based on photo-detachment is proposed. This system will operate using a pulsed laser with light delivered via an optical fibre and subsequently focused through a thin slice of the H- beam. The laser photons have sufficient energy to detach the outer electron and create H0/e- pairs. In a downstream dipole, the created H0 particles are separated from the unstripped H- ions and their distribution is measured with a dedicated detector. By scanning the focused laser across the H- beam, the transverse emittance of the H- beam can be reconstructed. This paper will first discuss the concept, design and simulations of the laserComment: Presented at the International Conference on Laser Applications at Accelerators, LA3NET 2015; Submitted to Nucl. Instr. and Meth. in Phys. Res. section

A Project for Teaching Science in Sub-Saharan Africa

Teaching has been a major concern during my career at CERN and it was my wish to end my career as a lecturer at a university in the developing world. CERN has collaborations with institutes in many countries around the globe, except countries in Sub-Saharan Africa. … and since I have friends in Ghana, why not at the University of Cape Coast (UCC)? With several months of SLS leave before my retirement I left for Ghana in September for a 4 months, 1 semester teaching assignment at the School of Agriculture and Natural Sciences in the Department of Computer Science and Information Technology. Having worked in the Beam Instrumentation group at CERN, reading out sensors did not have too many secrets for me and together with my colleagues at UCC we decided of a course on Embedded Systems where small Internet enabled devices read different types of sensors (temperature, humidity, light intensity …) or control devices like leds, relays, motors etc. In addition I had a group of students working on a simple obstacle avoiding robot or a robot whose movement can be controlled via BlueTooth. The course consisted of formal lecture with a big component of hands-on exercises. This presentation will explain the hardware choices made, show the documentation system and give an overview over the lecture material for the embedded systems course with some anecdotes of my stay thrown in. An outlook of future collaboration with UCC is also given. &nbsp;&nbsp;</p

Performance of Linac-4 instrumentation during commissioning

Linac-4 is CERN’s new H⁻ Linac, which will replace the aging Linac-2 proton machine. Linac-4 is being built and commissioned in stages. While the machine is permanently equipped with the standard beam instrumentation necessary to ensure smooth operation, three dedicated measurement benches have also been designed to commission the source and LEBT at 45 keV, the MEBT and its chopper at 3 MeV as well as the first DTL tank at 12 MeV and finally the full DTL at 50 MeV and CCDTL at 100 MeV. The beam after the PIMS structures at the Linac’s full energy of 160 MeV will be sent to a beam dump and commissioned with permanently installed instruments. Installation and commissioning of the machine up to the CCDTL is now complete. This contribution will present the results from the various commissioning stages, showing the performance of the various diagnostic devices used and comparing the data obtained to simulations

Commissioning of the CERN LINAC4 Wire Scanner, Wire Grid and Slit-Grid Monitors at 3 and 12 MeV

The CERN LINAC4 has been commissioned up to 12 MeV. The H^{−} beam transverse profile distributions were measured by both wire grids and wire scanners. A slit-grid system located on a temporary diagnostics bench was used to characterize the transverse emittance during the two different stages of commissioning: at the exit of the RFQ (3 MeV) and DTL1 (12 MeV). The wire signal is a balance between the negative charge deposited by the stripped electrons from the H^{−} and the charge lost due to secondary emission. Optimal settings were found for the repelling plates used to suppress secondary emission, which were confirmed by electromagnetic simulations. In addition, suppression of the secondary emission due to the beam space charge was observed. The benefit of changing the wire scanner geometry in order to minimize the cross-talk between horizontal and vertical wires and the observation of thermionic emission on carbon wires are also discussed

Beam Instrumentation Performance during Commissioning of CERN's Linac-4 to 50 MeV and 100 MeV

Linac-4, a 140 MeV H-linear accelerator is designed to replace the aging 50 MeV proton Linac. It will consist of an H-source and 45 keV LEBT, an RFQ and 3 MeV MEBT with a chopper, 3 drift tube linac (DTL) tanks accelerating the beam to 12, 30 and 50 Mev, cavity coupled structures (CCDTL) accelerating it to 100 MeV and a pi mode structure bringing it to its design energy of 160 MeV. This paper reports on the commissioning of the DTL and CCDTL with 2 dedicated temporary measurement lines, the first one adapted to the 12 MeV beam while the second one is dedicated to characterize the 50 MeV and the 100 MeV beams. The beam diagnostic devices used in these lines is described as well as results obtained

First Biennial African School on Fundamental Physics and its Applications

Discussion Session - Accelerator System Design (Part II) Tutors: C. Darve, J. Weisend II, Ph. Lebrun, A. Dabrowski, U. Raich Video Conference with the CERN Control Center. Experts in the field of Accelerator science will be available to answer the students questions. This session will link the CCC and SA (using Codec VC)

Progress in the Upgrade of the CERN PS Booster Recombination

The CERN PS Booster recombination lines (BT) will be upgraded following the extraction energy increase foreseen in 2018 and meant to reduce the direct space-charge tune shift in the PS injection for the future HL-LHC beams. Henceforth the main line elements, recombination septa, quadrupoles and dipoles must be scaled up to this energy. An increase in the beam rigidity by a factor 1.3 would require the same factor in the field integral of the septa, ∫Bdl, in order to bend the same angle and preserve the present recombination geometry, which is one of the main upgrade constraints. This paper describes the new optics, in particular in the new and longer septa. In addition we consider the upgrade of the so called BTM line that brings the beam to the external dump and where emittance measurements are taken thanks to three pairs of grids. The new proposed optics has also the advantage to simplify the design of the new dipoles. Here we study this new optics and the issues related to the emittance measurement at the new higher energy

Experimental Results of a Compact Laserwire System for Non-Invasive H⁻ Beam Profile Measurements at CERN's Linac4

A non-invasive laserwire system is being developed for quasi-continuous monitoring of the transverse profile and emittance of the final 160 MeV beam at CERN's LINAC4. As part of these developments, a compact laser-based profile monitor was recently tested during LINAC4 commissioning at beam energies of 50 MeV, 80 MeV and 10⁷ MeV. A laser with a tunable pulse width (1-300 ns) and ~200 W peak power in a surface hutch delivers light via a 75 m LMA transport fibre to the accelerator. Automated scanning optics deliver a free space <150 micron width laserwire to the interaction chamber, where a transverse slice of the hydrogen ion beam is neutralised via photo-detachment. The liberated electrons are deflected by a low field dipole and captured by a sCVD diamond detector, that can be scanned in synchronisation with the laserwire position. The laserwire profile of the LINAC4 beam has been measured at all commissioning energies and is found in very good agreement with interpolated profiles from conventional SEM-grid and wire scanner measurements, positioned up and downstream of the laserwire setup. Improvements based on these prototype tests for the design of the final system are presented

Design of a Laser-based Profile Monitor for LINAC4 Commissioning at 50 MeV and 100 MeV

A laser-based profile monitor has been designed for commissioning of CERN's LINAC4 accelerator at 50 MeV and 100 MeV, as part of the development of a non-destructive profile and emittance monitor foreseen for the final 160 MeV beam. The system is based on a low power laser which is scanned through the H⁻ beam. Electrons, which are photo-detached from the ions by the laser, are deflected by a steerer magnet and measured by a diamond detector. The custom designed diamond detector is tailored to minimize the disturbance due to the electromagnetic field of the passing main beam. The laser source will be installed in the LINAC4 Klystron gallery located 75 m away from the profile station and an optical fiber will transport the laser to the tunnel. The laser propagation for different pulse length and peak power values was characterized with laboratory tests with such a long fiber. In this paper we describe the overall design, focusing on key elements such as the fiber-based laser transport and the electron detection with the diamond detector