Design of Injection and Extraction Systems with Optimisation of Lattice and Layout for the CERN PS2 Synchrotron

The CERN Proton Synchrotron PS2 is one of the foreseen accelerators for the LHC injector upgrade. This upgrade aims first at increasing the instantaneous luminosity of LHC and second at providing a reliable beam for the CERN accelerator complex. From this aspect, the main characteristics of the PS2 are high reliability for high intensity beams. The goal of this thesis was the design of the machine’s lattice and injection/extraction systems meeting the constraints coming mainly from the LHC beam type but also from beam requirements of experiments at PS2 and the SPS. In the design, the given energy range together with filling schemes for different beam types and RF cogging were first used to define the circumference of the machine. Estimates on the space requirements of injection/extraction systems were made in order to divide the total machine length between arc and long straight section. Existing tunnels for transfer lines together with the minimisation of the total transfer line length favoured a race track shape machine. The energy range of PS2 does not allow to omit transition crossing by injecting above or extracting below transition. Two significantly different lattice types were therefore designed, one with a real value of gamma transition and another with negative momentum compaction (NMC) with imaginary value of gamma transition and thereby no transition crossing. In case of the real gamma transition lattice, diff erent cell structures were studied according to their bending power and optics behaviour. A FODO cell with 90˚ horizontal phase advance met the constraints best and was chosen to build a closed lattice. This lattice was optimised to use as few quadrupole families as possible with a missing magnet scheme chosen to suppress the dispersion in the long straight section. Concerning transition crossing, longitudinal space charge and impedance from the existing PS were scaled to the PS2 to estimate the necessary parameters of a gamma transition jump. A first- and second-order jump scheme were designed and their influence on the bare optics analysed. The second lattice design approach was the NMC. Here, the dispersion function is forced to oscillate between negative and positive values and by placing dipoles mainly in areas of negative dispersion the value of gamma transition can be made imaginary. This lattice suffers from complexity in hardware and operation but it has the big advantage of avoiding transition. The decision for a 40 MHz RF system which does not impinge on the choice of gamma transition simplified designing an NMC lattice that meets the aperture constraints. Concluding the lattice choice, the NMC is presently the PS2 baseline because it avoids the complexities of transition crossing and the inevitable beam loss, which for a high intensity machine is a prime concern. The second part of this thesis concerns the desig n of beam transfer systems. Different beam types necessitate two injection and three extraction systems. On the basis of the constraints from these systems a concept for the whole long straight section was chosen. The structure was decided to be a central split triplet with two FODO cells attached on each side. This allows to place the challenging H- injection in one drift and accomodate the other systems in the FODO cells. Constraints of the different systems were determined and accordingly the optics was optimised. A resulting concept is given for the injection/extraction straight which is interchangeable between the two lattice options

Beam Losses and Collimation Considerations for PS2

The high intensity beams with different emittances foreseen to be delivered by the PS2, an upgraded version of the actual CERN Proton Synchrotron, require strict control of beam losses in order to protect the machine components and enable their hands-on maintenance. Beam loss simulations based on dedicated numerical tools are undertaken for a variety of PS2 beams and for different loss mechanisms, along the whole accelerating cycle. In this respect, a first iteration of the collimation system is presented

Laser Stripping for the PS2 Charge-Exchange Injection System

Laser stripping for an H- injection system into the proposed PS2 accelerator could provide an attractive alternative to the use of a conventional stripping foil. In this paper possible concepts for a 4 GeV laser stripping system are outlined and compared, using either laser or magnetic initial stripping steps and a resonant excitation of the intermediate H0 atom, followed by a final magnetic stripping. Issues of laser power, overall efficiency and emittance growth are discussed

Collimation Considerations For PS2

A main concern in high intensity rings is the evaluation of uncontrolled losses and their minimization using collimation systems. A two-stage system is foreseen for the PS2. The fundamental design strategy for the collimation design is presented, including machine apertures and collimator materials. The dependence of the collimator system efficiency on the primary scraper length and the impact parameter of the particle is evaluated for different collimator locations. Beam loss maps are finally produced displaying the detailed power load deposited around the ring

4 GeV H- Charge Exchange Injection into the PS2

The proposed PS2 will accelerate protons from 4 to 50 GeV. The required beam intensity and brightness can only be achieved with a multi-turn H- charge exchange injection system, where the small emittance injected beam is used to paint the transverse phase space of the PS2 machine. This paper describes the constraints and conceptual design of the H- injection system and its incorporation into the present PS2 lattice. The requirements for the special injection system elements are described, in particular the injection chicane and painting magnet systems and the change exchange foil. Some key performance aspects are investigated, including the stripping efficiency, expected emittance growth and beam loss arising from the simulated number of multiple foil traversals, together with estimates of foil heating

Gamma Transition Jump for PS2

The PS2, which is proposed as a replacement for the existing ~50-year old PS accelerator, is presently considered to be a normal conducting synchrotron with an injection kinetic energy of 4 GeV and a maximum energy of 50 GeV. One of the possible lattices (FODO option) foresees crossing of transition energy near 10 GeV. Since the phase-slip-factor $\eta$ becomes very small near transition energy, many intensity dependent effects can take place in both longitudinal and transverse planes. The aim of the present paper is on the one hand to scale the gamma transition jump, used since 1973 in the PS, to the projected PS2 and on the other hand based on these results the analysis of the implementation and feasibility of a gamma transition jump scheme in a conventional FODO lattice

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Peer Reviewe

PS2 Injection, Extraction and Beam Transfer Concepts

The replacement of CERN's existing 26 GeV Proton Synchrotron (PS) machine with a separated-function synchrotron PS2 has been identified as an important part of the possible future upgrade programme of the CERN accelerator complex. The PS2 will require a number of new beam transfer systems associated with injection, extraction, beam dumping and transfer. The different requirements are briefly presented, together with an overview of the conceptual design of these systems, based on the initial PS2 parameter set. The required equipment sub-system performance is derived and discussed. Possible limitations are analysed and the impact on the overall design and parameter set is discussed

Fast Injection into the PS2

The conceptual considerations of a fast injection system for protons and ions in the proposed PS2 accelerator are presented. Initial design parameters of the injection septum and kicker systems are derived, taking into account rise and fall times, apertures and machine optics. The requirements for an injection dump used for failures are described. Possible limitations and technical issues are outlined

Beam Loss Control for the Unstripped Ions from the PS2 Charge Exchange Injection

Control of beam losses is an important aspect of the H-injection system for the PS2, a proposed replacement of the CPS in the CERN injector complex. H- ions may pass the foil unstripped or be partially stripped to excited H0 states which may be stripped in the subsequent strong-field chicane magnet. Depending on the choice of the magnetic field, atoms in the ground and first excited states can be extracted and dumped. The conceptual design of the waste beam handling is presented, including local collimation and the dump line, both of which must take into account the divergence of the beam from stripping in fringe fields. Beam load estimates and activation related requirements of the local collimators and dump are briefly discussed