Beam dynamics and commissioning of low and medium energy H- beam at Linac4

The First step of the CERN Large Hadron Collider injectors upgrade (LIU) project is Linac4. It accelerates H- ions to 160 MeV in an 80 m long accelerator housed in a tunnel 12 m underground, presently under construction. It will replace the present 50 MeV proton Linac2 as injector of the proton accelerator complex to increase the LHC luminosity. It consists of a 45 keV RF volume source, a twosolenoid Low Energy Beam Transport (LEBT), a 352.2 MHz Radio Frequency Quadrupole (RFQ) accelerating the beam to 3 MeV, a Medium Energy Beam Transport (MEBT) line. The MEBT houses a fast chopper to selectively remove unwanted micro-bunches in the 352 MHz sequence and avoid losses at capture in the CERN PSB (1 MHz). After chopping, the beam acceleration continues by a 50 MeV Drift Tube Linac (DTL), a 100 MeV Cell-Coupled Drift Tube Linac and a Pi-Mode Structure bringing the beam to the final energy of 160 MeV. Linac4 has been commissioned with a temporary source up to 12 MeV. The beam commissioning stages of Linac4 in LEBT, MEBT and one phase of the first DTL tank at 12 MeV is presented in this thesis. The simulation codes that had been used were Travel, Delta and Trace3D. After an introduction on the CERN accelerator complex and Linac4, the physics of a charged particle beam in a linear accelerator as well as the fundamentals of beam diagnostics related to the work of this thesis are summarized for completeness. The Linac4 beam commissioning results are summarized in Chapters 4, 7 and 8. In these chapters the numerical simulations that predict the beam characteristics and machine parameters are described. The measurement techniques and results are explained. Then the results of the measurements have been compared with the expectation from simulations and a beam dynamics pattern has been acquired. The end-to-end simulation process with the purpose of matching the beam to the accelerating structure, RFQ, DTL, CCDTL and PIMS, is reported in Chapter 6. During commissioning the LEBT solenoids and the MEBT elements (Quadrupole magnets and buncher cavities) were set to the theoretical values for matching the beam to the RFQ and the first DTL tank, respectively. In the experiment, the Linac4 beam was matched to the related structures as expected from simulations data. The MEBT beam commissioning was performed in two stages. During the five months period between January and June 2013 the MEBT beam was commissioned at a temporary location. At this phase of the measurement the beam transmission and transverse beam profile have been taken at several locations along the accelerator with the help of the permanent diagnostic tools in the line and a temporary diagnostics bench and the functionality of the elements validated. The MEBT chopper dynamic was tested and it was confirmed that it is possible to maximize the transmission of the main beam and remove the chopped beam simultaneously. After Linac4 installation at its final location the LEBT and MEBT beam commissioning was repeated during the period between November 2013 and March 2014. This commissioning confirmed the 3 MeV Test Stand results and covered more aspects of the 3 MeV commissioning strategy in the longitudinal plane as well as the transverse planes. The beam misalignment was diagnosed and treated. It was confirmed that when the MEBT chopper is chopping the beam, the emittance of the main beam didn’t change either in orientation or in size. With the slit-and-grid emittance measurements data the permanent beam diagnostic devices of the MEBT were cross calibrated and in addition, an empirical beam distribution was prepared for further simulations through the next stages of acceleration. The buncher cavities were calibrated and before moving the temporary diagnostic bench, the MEBT settings for matching the beam to the DTL tank1 were obtained. The DTL tank1 was installed in July 2014 and the first phase of 12 MeV commissioning was performed till mid-August. The MEBT elements were set to match the beam to the DTL and accelerate it. The 3 MeV MEBT beam was passed through the DTL as the simulation code predicted. During the first phase of DTL commissioning the accelerated beam was partly characterized. The upcoming phases of the DTL commissioning in October 2014 will be longer and will fully characterize the Linac4 12 MeV beam

Linac4 Transverse and Longitudinal Emittance Reconstruction in the Presence of Space Charge

Linac4 is a pulsed, normal-conducting 160 Mev H^{−} linear accelerator presently under construction at CERN. It will replace the present 50 MeV Linac2 as injector of the proton accelerator complex as part of a project to increase the LHC luminosity. The 3 MeV front end, composed of a 45 keV ion source, a Low Energy Beam transport (LEBT), a 352 MHz Radio Frequency Quadrupole (RFQ) at 3 MeV and Medium Energy Beam Transport (MEBT) housing a beam chopper, and the first Drift Tube Linac (DTL) tank at 12 MeV have been commissioned during the first half of 2014. The transverse and longitudinal emittance reconstruction technique in the presence of space charge, that will be used for the next commissioning stages and permanently during the Linac operation, was successfully tested and validated. The reconstruction method and the results obtained at 3 and 12 MeV are presented in this paper

Transverse Beam Profile Measurements in the Linac4 Medium Energy Beam Transport

Linac4 is a 160 MeV H^{−} linear accelerator presently under construction at CERN. It will replace the present 50 MeV proton Linac2 as injector of the proton accelerator complex as part of a project to increase the LHC luminosity. The Linac4 front-end, composed of a 45 keV ion source, a Low Energy Beam Transport (LEBT), a 352.2 MHz Radio Frequency Quadrupole (RFQ) which accelerates the beam to 3 MeV and a Medium Energy Beam Transport (MEBT) housing a beam chopper, has been commissioned in the Linac4 tunnel. The MEBT is composed of three buncher cavities and 11 quadrupole magnets to match the beam from the RFQ to the next accelerating structure (DTL) and it includes two wire scanners for beam profile measurement. In this paper we present the results of the profile measurements and we compare them with emittance measurements taken with a temporary slit-and-grid emittance measurement device located after the MEBT line

Longitudinal Beam Profile Measurements in Linac4 Commissioning

Linac4, the future 160 MeV H^{−} injector to the CERN Proton Synchrotron Booster, is presently under construction at CERN as a central step of the planned upgrade of the LHC injectors. The Linac front-end, composed of a 45 keV ion source, a Low Energy Beam Transport (LEBT), a 352.2 MHz Radio Frequency Quadrupole (RFQ) and a Medium Energy Beam Transport (MEBT) housing a beam chopper, has been installed and commissioned. Precise measurements of the longitudinalμbunch profiles of ion beams were possible with the help of a Bunch Shape Monitor (BSM) developed at INR Moscow. These were crucial for the successful commissioning of the three RF buncher cavities mounted along the MEBT and well complemented with higher precision the information provided in parallel by spectrometer measurements