347 research outputs found
Proton-beam emittance growth in SPS coasts
No full textProton-beam transverse emittance growth rates were measured during SPS coasts to assess the possibility of using the SPS as a testbed for the LHC prototype crab cavities. The SPS measurements in coasts were performed at different beam energies, for varying RF voltage, beam intensity, and chromaticity. Results from these measurements are presented with potential explanations for the observed emittance growth
Localization of transverse impedance sources in the SPS using headtail macroparticle simulations
No full textIn particle accelerators, the beam coupling impedance is one of the main contributors to instability phenomena that lead to particle losses and beam quality deterioration. For this reason these machines are continuously monitored and the global and local amount of impedance needs to be evaluated. In this work we present our studies on the local transverse impedance detection algorithm. The main assumptions behind the algorithm are described in order to understand limits in reconstructing the impedance location. The phase advance response matrix is analyzed in particular for the nominal gamma transition SPS lattice (Q26), studying the different response from 90, 180, 270 degree phase advance sections. The thin lenses scheme is also implemented and new analytical formulas for phase advance beating were derived. This enabled us to put reconstructing lenses everywhere in the lattice, and to study their positioning scheme. Limits in linear response are analyzed. This relates the upper and lower limits in reconstruction to the phase advance measurement accuracy and the linear response regime limit
Effects of cavity pre-detuning on RF power transients at injection into the LHC
No full textAt injection into the Large Hadron Collider (LHC), the radiofrequency (RF) system is perturbed by beam-induced voltage resultingin strong RF power transients and the instant detuning of thecavities. The automatic tuning system, however, needs time for themechanical compensation of the resonance frequency to takeplace. Acting back on the beam, the transients in RF power areexpected to limit the maximum injected intensity by generatingunacceptable beam loss. Reducing them is therefore essential toreach the target intensity during the High Luminosity (HL) LHCera. At LHC flat bottom, the cavities are operated using thehalf-detuning beam-loading compensation scheme. As implementedtoday, the tuner control algorithm starts acting only after theinjection of the first longer bunch train which causes the bunchesfor this injection to experience the largest power spikes. Thiscontribution presents an adapted detuning scheme for the RF cavitiesbefore injection. It was proposed as a path to decrease thetransients, hence increasing the available intensity margin for theavailable RF power. The expected gain is evaluated in particletracking simulations and measurements acquired during operation
LHC Crabs, Status
No full textThe status of LHC crab cavities is described, including overall planning & US roadmap, status of technology R&D, and status of simulations & experiments. Presented at 15th US-LARP collaboration meeting, SLAC, 1-3 November 2010
Assessment of thermal loads in the CERN SPS crab cavities cryomodule
No full textAs a part of the HL-LHC upgrade, a cryomodule is designed to host two crab cavities for a first test with protons in the SPS machine. The evaluation of the cryomodule heat loads is essential to dimension the cryogenic infrastructure of the system. The current design features two cryogenic circuits. The first circuit adopts superfluid helium at 2 K to maintain the cavities in the superconducting state. The second circuit, based on helium gas at a temperature between 50 K and 70 K, is connected to the thermal screen, also serving as heat intercept for all the interfaces between the cold mass and the external environment. An overview of the heat loads to both circuits, and the combined numerical and analytical estimations, is presented. The heat load of each element is detailed for the static and dynamic scenarios, with considerations on the design choices for the thermal optimization of the most critical components
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R-Square Impedances of Erl Ferrite Hom Absorber.
No full textAn R&D facility for an Energy Recovery Linac (ERL) intended as part of an electron-cooling project for RHIC is, being constructed at this laboratory. The center piece of the facility is a 5-cell 703.75 MHz super-conducting RF linac. Successful operation will depend on effective HOM damping. It is planned to achieve HOM damping exclusively with ferrite absorbers. The performance of a prototype absorber was measured by transforming it into a resonant cavity and alternatively by a conventional wire method. The results expressed as a surface or R-square impedance are presented in this paper
Validation of control loop modeling for power limitation studies with beams for HL-LHC
No full textFor HL-LHC intensities, transient beam loading after injection between the Super Proton Synchrotron (SPS) and the Large Hadron Collider (LHC) is expected to push the RF power in the LHC to the limit of the installed system. A detailed understanding of this process is necessary to minimize beam losses during LHC injection. Realistic models of the local SPS and LHC cavity control systems were implemented in the Beam Longitudinal Dynamics (BLonD) simulation suite to model bucket-by-bucket and turn-by-turn transient effects. We show the results of studies and detailed benchmarks of key observables such as bunch-by-bunch spacing, RF power at 2023 beam intensity and transfer functions against theory and measurements
HL-LHC RF Roadmap
No full textIn view of the HL-LHC parameters, the present and the future RF systems for the LHC are reviewed with a focus on technological aspects. This paper will describe the preparation and the test programof the SPS beam tests with crab cavities. Some aspects related to the integration of the crab cavity RF system in the LHC and the potential impact of the crab kissing scheme are addressed. The mode of operation for the 400 MHz accelerating RF system with HLLHC beam currents and the associated issues are briefly outlined with possible improvements to the ACS system. Finally, the use of a harmonic system both at 200MHz and 800MHz for bunch profilemanipulation and the associated technological challenges are described
R&D ERL: HOM Absorbers
No full textSeveral future accelerator projects at the Relativistic Heavy Ion Collider (RHIC) are based on Energy Recovery Linacs (ERL) with high-charge high-current electron beams. Their stable operation mandates effective higher-order-mode (HOM) damping. The development of HOM dampers for these projects is pursued actively at this laboratory. A strong HOM damping was experimentally demonstrated both at room- and at superconducting- (SC) temperatures in a prototype R&D five-cell niobium SRF cavity with ferrite dampers. A novel type of ferrite damper over a ceramic break for a R&D SRF electron gun also was developed. For future SRF linacs longer cryomodules comprising of multiple superconducting cavities with reasonably short transitions between them are planned. In such a configuration, the dampers, located closer to the cavities, will be at cryogenic temperatures; this will impose additional constraints and complications. Two room-temperature mock-up five-cell copper cavities were used to study various damper configurations. This paper presents results of simulations and measurements for several configurations
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