PS Booster Research Articles

Uncontrolled Longitudinal Emittance Blow-Up during rf Manipulations in the CERN PS

The CERN Proton Synchrotron (PS) determines the basic bunch spacing for the Large Hadron Collider (LHC) by means of rf manipulations. Several rf systems in a frequency range from 2.8 MHz to 200 MHz are available for beam acceleration and manipulations. Each of the six bunches injected from the PS Booster is split in several steps into 12 bunches spaced by 25 ns, yielding a batch of 72 bunches at transfer to the Super Proton Synchrotron (SPS). In the framework of the LHC Injector Upgrade (LIU) project the bunch intensity must be doubled. However, with most of the planned upgrades already in place this intensity has not yet been achieved due to collective effects. One of them is uncontrolled longitudinal emittance blowup during the bunch splittings. In this contribution, measurements of the blow-up during the splitting process are presented and compared with particle simulations using the present PS impedance model. Beam-based measurements of the impedances of the rf cavities have been performed. They revealed that to reproduce the instability an additional impedance source is required in the PS impedance model.

Design of the New Proton Synchrotron Booster Absorber Scraper (PSBAS) in the Framework of the Large Hadron Collider Injection Upgrade (LIU) Project

The Large Hadron Collider (LHC) Injector Upgrade (LIU)Project at CERN calls for increasing beam intensity for the LHC accelerator chain. Some machine components will not survive the new beam characteristics and need to be rebuilt for the new challenging scenario. This is particularly true for beam intercepting devices (BIDs) such as dumps, collimators, and absorber/scrapers, which are directly exposed to beam impacts. In this context, this work summarizes conceptual design studies on the new Proton Synchrotron Booster (PSB) Absorber/Scraper (PSBAS), a device aimed at cleaning the beam halo at the very early stage of the PSB acceleration. This paper outlines the steps performed to fulfil the component design requirements. It discusses thermo-mechanical effects as a consequence of the beam-matter collisions, simulated with the FLUKA Monte Carlo code and ANSYS finite element software; and the impedance minimization study performed to prevent beam instabilities and to reduce RF-heating on the device.

Distributed Optical Fiber Radiation Sensing in the Proton Synchrotron Booster at CERN

In this paper, we report on the development and first deployment of a distributed optical fiber radiation sensor (DOFRS) for the online monitoring of radiation levels in the high-energy accelerator facilities of CERN. The DOFRS is composed of two basic parts: a set of suitably chosen radiation sensitive optical fibers (OFs), to be installed in the machine tunnel, and an optical time domain reflectometer (OTDR), to be installed in a radiation-free area. We carried out a calibration of the radiation response of a P-doped multimode OF under 60Co $\gamma $ -rays and in the mixed-field radiation environment of the CHARM facility at CERN. By performing OTDR measurements, we are able to probe the radiation-induced attenuation in the OF along its length and calculate the deposited radiation dose with a spatial resolution of 1 m. In this paper, we describe the main features associated with DOFRS implementation in the proton synchrotron booster (PSB) at CERN. We also report the first results obtained from the monitoring of PSB radiation levels since its recommissioning in April 2017. The performances and advantages of the DOFRS system are discussed.

Quadrupole Design for the 2 GeV Upgrade of the CERN PS-Booster

The CERN large hadron collider (LHC) Injectors Upgrade seeks to reliably deliver the beams required for the High-Luminosity LHC (HL-LHC). As part of this, the proton synchrotron booster (PSB) will be upgraded from 1.4 to 2 GeV and will accelerate higher intensity beams. Along the transfer lines between the PSB and the proton synchrotron there are several dc-operated quadrupole magnets that are unable to produce the gradients required for the 2 GeV HL-LHC beams. To minimize power consumption, these will be replaced by laminated quadrupole magnets, operated in pulse to pulse modulation mode. The field homogeneity requirements imposed on these magnets is very tight, requiring a homogeneity of $5\times 10^{-4}$ on the integrated gradient. Such strict requirements presented several issues for the design, especially when considering the space constraints that naturally apply when upgrading a pre-existing accelerator. The design of these quadrupole magnets is summarized here.

Fast-timing spectroscopy at ISOLDE

The advanced time-delayed (t) method has been used at ISOLDE since the relocation of the facility from the synchrocyclotron to the CERN proton synchrotron booster, a quarter of a century ago. The method was designed for precision measurements with low-intensity beams, achieving good efficiency and excellent time resolution with a compact setup. Over this time the technique has evolved to cope with the challenge of measuring lifetimes of complex level schemes of increasingly exotic nuclei populated in β decay. The ISOLDE facility provides unsurpassed opportunities to study many regions of the nuclide chart. The physics case encompasses topics of interest across the nuclide chart, including the evolution of shell structure around neutron shell and subshell closures such as N = 20, N = 40 and N = 50, shape coexistence, and octupole correlations in heavy nuclei. The recently commissioned ISOLDE decay station provides enhanced capabilities that will be fully exploited with the increased beam intensities available at the upcoming HIE-ISOLDE facility.

Controlled longitudinal emittance blow-up using band-limited phase noise in CERN PSB

Controlled longitudinal emittance blow-up (from 1 eVs to 1.4 eVs) for LHC beams in the CERN PS Booster is currently achievied using sinusoidal phase modulation of a dedicated high-harmonic RF system. In 2021, after the LHC injectors upgrade, 3 eVs should be extracted to the PS. Even if the current method may satisfy the new requirements, it relies on low-power level RF improvements. In this paper another method of blow-up was considered, that is the injection of band-limited phase noise in the main RF system (h=1), never tried in PSB but already used in CERN SPS and LHC, under different conditions (longer cycles). This technique, which lowers the peak line density and therefore the impact of intensity effects in the PSB and the PS, can also be complementary to the present method. The longitudinal space charge, dominant in the PSB, causes significant synchrotron frequency shifts with intensity, and its effect should be taken into account. Another complication arises from the interaction of the phase loop with the injected noise, since both act on the RF phase. All these elements were studied in simulations of the PSB cycle with the BLonD code, and the required blow-up was achieved.

Extending and refining the nuclear mass surface with ISOLTRAP

The Penning-trap mass spectrometer ISOLTRAP has received ISOLDE beams for the past 30 years! Following the move of ISOLDE to the proton-synchrotron booster site, ISOLTRAP has pioneered almost all of the techniques now associated with on-line ion trapping and manipulation for precision measurements of atomic masses. After an introduction on physics motivation, a brief history and description of the ISOLTRAP spectrometer is given, followed by an overview of the numerous developments and scientific results achieved since the previous ISOLDE Laboratory Portrait.

ISOLDE past, present and future

The idea of production of short-lived radioisotopes with the on-line technique has it roots in the early 1950s. In 1964 this became a reality when CERN approved an experiment at the 600 MeV proton synchro-cyclotron, the SC. The first experiments were performed in 1967 and since then the ISOLDE programme has gradually developed into a major undertaking. Since 1992 the ISOLDE Radioactive Beam Facility is linked to an external proton beam from the PS Booster. Today this 50 years old ‘lady’ is more vital than ever. With the successful start of HIE-ISOLDE in 2015 one may conclude that the facility is ready to face the next half century with the boost of the success and the necessary knowledge to face new challenges. In this introductory article we give an overview of the history and pick up a few examples along the nuclear chart as illustrations of the experimental achievements.

CERN Proton Synchrotron booster space charge simulations with a realistic model for alignment and field errorsn1

The CERN Proton Synchrotron booster (PSB) is one of the machines of the LHC injector chain which will be upgraded within the LHC Injectors Upgrade (LIU) project. The injection energy of the PSB will be increased to 160 MeV in order to mitigate direct space charge effects, considered to be the main performance limitation, aiming to double the brightness for the LHC beams. In order to better predict the gain to be expected, space charge simulations are being carried out. As a first step, benchmarking between simulations and measurements is needed. Efforts to establish a realistic modeling of field and alignment errors aim at extending the basic model of the machine toward a more realistic one. Simulations of beam dynamics with strong space charge and realistic errors are presented and analyzed in this paper.

Uncoupled thermoelasticity solutions applied on beam dumps

In particle accelerators the process of beam absorption is vital. At CERN particle beams are accelerated at energies of the order of TeV. In the event of a system failure or following collisions, the beam needs to be safely absorbed by dedicated protecting blocks. The thermal shock caused by the rapid energy deposition within the absorbing block causes thermal stresses that may rise above critical levels. The present paper provides a convenient expression of such stresses under hypotheses described hereafter. The temperature field caused by the beam energy deposition is assumed to be Gaussian. Such a field models a non-diffusive heat deposition. These effects are described as thermoelastic as long as the stresses remain below the proportional limit and can be analytically modeled by the coupled equations of thermoelasticity. The analytical solution to the uncoupled thermoelastic problem in an infinite domain is presented herein and matched with a finite unit radius sphere. The assumption of zero diffusion as well as the validity of the match with a finite geometry is quantified such that the obtained solutions can be rigorously applied to real problems. Furthermore, truncated series solutions, which are not novel, are used for comparison purposes. All quantities are nondimensional and the problem reduces to a dependence of five dimensionless parameters. The equations of elasticity are presented in the potential formulation where the shear potential is assumed to be nil due to the source being a gradient and the absence of boundaries. Nevertheless equivalent three-dimensional stresses are computed using the compressive potential and optimized using standard analytical optimization methods. An alternative algorithm for finding the critical points of the three-dimensional stress function is presented. Finally, a case study concerning the proton synchrotron booster dump is presented where the aforementioned analytical solutions are used and the preceding assumptions verified.

Direct Drive and Eddy Current Septa Magnet Designs for CERN's PSB Extraction at 2 GeV

In the framework of the LIU project, new septa magnets have been designed between CERN's PS booster (PSB) extraction and PS injection. The upgraded devices are to deal with the increased beam energy from 1.4 to 2 GeV at extraction of the PSB. The direct drive recombination septa in the PSB transfer line to the PS and the eddy current PS injection septum together with a bumper at injection have been investigated using finite-element software. For the recombination magnets, an increase in magnet length is sufficient to obtain the required deflection; however, for the PS injection elements, a more novel solution is necessary to also achieve increased robustness to extend the expected lifetime of the pulsed device. The injection septum will share the same vacuum vessel with an injection bumper, and both magnets will be located adjacent to each other. The new PS injection magnet will be the first septum operated at CERN based on eddy current technology. The magnetic modeling of the devices, the comparison of the performance of the present 1.4-GeV devices with the predictions for the upgraded 2-GeV devices, and the solutions retained to achieve the field requirements are described in this paper.

Systematic studies on the effect of linear lattice optics for space-charge limited beams

The HL-LHC (High Luminosity LHC) project aims to an increase of the luminosity of the LHC by a factor of 10. In order to realize this ambitious goal, the LHC itself has to undergo a major upgrade accompanied by an extensive upgrade of the complete injector complex referred to as LHC injector upgrade (LIU). In the framework of the LIU project, a new rapid cycling synchrotron (RCS) as an alternative to the energy upgrade of the existing PS Booster has been proposed. Motivated by the optics studies conducted for this RCS, the more general question of the influence of the linear optics on the machine performance has been raised. In this paper, we want to investigate this question by comparing different lattices with the final aim of identifying lattice characteristics advantageous under strong space-charge effects.

Chromaticity Effects for Space Charge Dominated Beams in the CERN PS Booster

Chromaticity Effects for Space Charge Dominated Beams in the CERN PS Booster

The stripping foil test stand in the Linac4 transfer line

The 160 MeV H− beam from the Linac4 (L4) linear accelerator at CERN will be injected into the proton synchrotron booster (PSB) with a new H− charge-exchange injection system. It will include a stripping foil, to convert H− into protons by stripping off the electrons. To gain experience with these very fragile foils, prior to the installation in the PSB, and test different foil materials and thicknesses, lifetimes of the foils, the foil changing mechanism and interlocking functions, a stripping foil test stand will be installed in the L4 transfer line in 2015. This paper describes the mechanical design of the system and discusses the test possibilities and parameters.

Design, Manufacture and Test of a 1.3 T/10 Hz Dipole Model for Rapid Cycling Synchrotrons

The construction of a compact rapid cycling synchrotron has recently been studied at CERN to replace the first stage of its accelerator complex, the proton synchrotron booster. Although currently there are no plans to build this machine, fast cycled accelerator magnets are of general interest for numerous reasons. This has led to the design, manufacture, and testing of a scaled model dipole as detailed in this paper to show the capability of producing and characterizing a magnet design based on high-silicon content grain-oriented steel able to operate up to 1.3 T at 10 Hz.

Design of Normal-Conducting Quadrupole Magnets for Linac4 at CERN

Linac4 is the first element of the Large Hadron Collider Injectors Upgrade Project and will replace the existing Linac2 as linear injector of protons for the CERN accelerators. A new transfer line will link Linac4 to the Proton Synchrotron Booster. Approximately a hundred normal-conducting electro-magnets are required for beam steering and focusing along the linac and the transfer line. This text concentrates on the design of the Linac4 quadrupole magnets. The design and the first magnetic measurements of the inter-tank quadrupole electro-magnets are discussed. In addition, the design and optimization of the transfer line quadrupole magnets are highlighted. The compatibility of the magnetic requirements and the power converter constraints for the latter magnet type is assessed.

Upgrade of the CERN Proton Synchrotron Booster Bending Magnets for 2 GeV Operation

Since its first operation in 1972 at an energy of 800 MeV, the CERN Proton Synchrotron Booster, which consists of four superimposed synchrotrons, has seen two upgrades: once to 1.0 GeV in 1988 and then to 1.4 GeV in 1999. During this time the main magnets of the machine have remained largely unchanged with small differences (1%) between the inner and outer gaps of the main bending magnet fields being compensated by trim power supplies. The future upgrade of the machine will demand to extract protons at an energy of 2.0 GeV and require almost double the original dipole field. At this field, due to saturation effects, the inner and outer gaps of the main dipole magnets will differ by up to 4%. This paper presents the design and implementation of a modification of the magnetic circuit strongly reducing these effects. We also discuss the results of experimental tests concerning the effects on field quality and eddy current transients, including the implications for the real-time magnetic field measurement system to control RF and power supplies.

Long-term residual radioactivity in an intermediate-energy proton linac

A new 160MeV H− linear accelerator (LINAC4) is being installed at CERN to replace the present 50MeV LINAC2 as proton injector of the PS Booster (PSB). During operation, the accelerator components will be activated by the beam itself and by the secondary radiation field. Detailed Monte Carlo simulations, for various beam energies and several decay times, were performed to predict the residual radioactivity in the main accelerator components and to estimate the residual dose rate inside the tunnel. The results of this study will facilitate future dismantling, handling and storage of the activated parts and consequently minimize the radiation dose to involved workers. The component activation was also compared with the exemption limits given in the current Swiss legislation and to the CERN design values, in order to make predictions for the future storage and disposal of radioactive waste. The airborne radioactivity induced by particles escaping the beam dump and the activation of the beam dump cooling water circuit were also quantified. The aim of this paper is to provide data of sufficiently general interest to be used for similar studies at other intermediate-energy proton accelerator facilities.

Design upgrade of the ISOLDE target unit for HIE-ISOLDE

The High Intensity and Energy HIE-ISOLDE project is a major upgrade of the existing ISOLDE and REX-ISOLDE facilities with the objective of increasing the energy and the intensity of the delivered radioactive ion beams (RIB) [1]. In order to accommodate the future increase of primary beam intensity delivered by the new LINAC4 H− driver to the Proton Synchrotron Booster (PSB) [2] and from this to ISOLDE, a major study is being carried out to upgrade the existing designs of the ISOLDE target and its supporting infrastructure. In particular, the extraction optics plays an important role in the initial beam transport and the quality of the beam supplied to the mass separators. Important factors include the emittance of the beam and the beam profile to avoid beam losses.A new double electrode extraction system has been developed for simplifying and improving the interface between the target unit and the frontend (target coupling table). Numerical and experimental studies have been performed in order to define the new extraction geometry, and the coupling table has been adapted to keep the compatibility. An alternative heating system is under study. An electron bombardment heating system is being developed as an option for avoiding the employment of big cross section cables. The results of these studies and the mechanical models developed are presented and discussed.

PAST AND PRESENT OPERATION OF THE CERN PS BOOSTER

This paper reviews 40 years of operation of the CERN Proton Synchrotron Booster, from the commissioning in the early 1970s until today's operation as injector for the Large Hadron Collider (LHC) and as one of the backbone accelerators for CERN's fixed-target physics program.