SLAC, Menlo Park, California
UMAN, Manchester
The CLIC linear collider aims at accelerating multiple bunches of electrons and positrons and colliding them at a center of mass energy of 3 TeV. These bunches are accelerated through X-band linacs operating at an accelerating frequency of 12 GHz. Each beam readily excites wake-fields in the accelerating cavities of each linac. The transverse components of the wake-fields, if left unchecked, can dilute the beam emittance. The present CLIC design relies on heavy damping of these wake-fields in order to ameliorate the effects of the wake-fields on the beam emittance. Here we present initial results on simulations of the long-range wakefields in these structures and on beam dynamics simulations. In particular, detailed simulations are performed, on emittance dilution due to beams initially injected with realistic offsets from the electrical centre of the cavities and due to statistical misalignments of the cavities.
CERN, Geneva
UMAN, Manchester
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire
The High Intensity and Energy ISOLDE (HIE-ISOLDE) proposal 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 beam. For the energy increase a staged construction of a superconducting linac based on sputtered quarter wave cavities is foreseen downstream of the present normal conducting linac. A funded R&D program has been launched at the end of 2007 in order to prepare a full Technical Design Report covering all the issues of such a linac, including cavity prototyping and testing, cryomodule design, beam dynamics and beam diagnostics. We report here on the status and planning of the R&D activities for the SCREX-ISOLDE linac.
CERN, Geneva
UMAN, Manchester
For the REX-ISOLDE upgrade a superconducting linac based on 101.28 MHz Quarter Wave Resonators (QWRs) is foreseen downstream the normal conducting (NC) linac. Currently the REX-ISOLDE linac can accelerate ions with a mass to charge ratio in the range of 3 < A/q < 4.5 and up to an energy of 3 MeV/u. The upgrade aims to reach a final beam minimum energy of 10 MeV/u for A/q=4.5 in two main stages. The first stage consists of installing two cryomodules loaded with 10 cavities able to reach 5.5 MeV/u at the end of the present linac and the second consists of replacing part of the existing NC linac and adding further cryomodules. We report here on a beam dynamics study of the accelerator for the two installation stages and the transport line to the experimental station.
UMAN, Manchester
Higher order modes (HOMs) are simulated with finite element and finite difference computer codes for the ILC superconducting cavities currently under investigation for the ILC. In particular, HOMs in KEK's Ichiro type of cavity and Cornel University's Re-entrant design are focussed on in this work. The aim, at these Universities and laboratories, is to achieve an accelerating gradient in excess of 50 MV/m in 9-cell superconducting cavities whilst maintaining a high quality and stable electron beam. At these high gradients, electrical breakdown is an important cause for concern and the wakefields excited by the energetic electron beams are also potentially damaging to the beam's emittance. Here we restrict the analysis to performing detailed simulations, on emittance dilution due to beams initially injected with realistic offsets from the electrical centre of the cavities and due to statistical misalignments of the cavities. We take advantage of the latest beam dynamics codes in order to perform these simulations.
UMAN, Manchester
The globalised scattering matrix (GSM) method provides an efficient means of obtaining the electromagnetic field in interconnected multi-cavity structures. In the proposed XFEL at DESY and the ILC facilities, energetic electron beams can readily excite higher order modes which if left unchecked can dilute the emittance of the beams. The GSM in conjunction with finite element modelling of the scattering matrices of the linac cavities is used to enable the characteristic eigenmodes to be rapidly obtained and the potential for trapped modes is investigated. This characteristic eigensystem allows the wakefield experienced by the beam to be analysed and the consequences on beam quality ascertained. The impact of fabrication errors on the transverse electromagnetic field and corresponding resonant frequencies of the modes is also explored in detailed simulations.
UMAN, Manchester
The Hashemite University, Zarka
Based on Lienard-Weichert method of retarded potentials and the potential due to the image of charges on the cathode, a rigorous relativistic description of the beam transport inside the rf-photoinjector is presented. The velocity dependent effects are explicitly taken into account in a complete analytical description. Simulations are presented for parameters of the ELSA photo-cathode.
Cockcroft Institute, Lancaster University, Lancaster
UMAN, Manchester
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire
The CLIC linear collider will require a crab cavity to align bunches prior to collision. Consideration of the bunch structure leads us to favour the use of X-band copper cavities. Due to the large variation of train to train beam loading, it is necessary to minimise the consequences of beam loading. One solution is to use a travelling wave structure with a large group velocity allowing rapid propagation of amplitude errors from the system. Such a design makes this structure significantly different from previous travelling wave deflecting structures. This paper will look at the implications of this on other cavity parameters and the optimization of the cavity geometry.
Cockcroft Institute, Lancaster University, Lancaster
SLAC, Menlo Park, California
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire
Fermilab, Batavia
UMAN, Manchester
CERN, Geneva
Crab cavities have been proposed for a wide number of accelerators and interest in crab cavities has recently increased after the successful operation of a pair of crab cavities in KEK-B. In particular crab cavities are required for both the ILC and CLIC linear colliders for bunch alignment. Consideration of bunch structure and size constraints favours a 3.9 GHz superconducting, multi-cell cavity as the ILC solution, whilst bunch structure and beam-loading considerations suggest an X-band copper travelling wave structure for CLIC. These two cavity solutions are very different in design but share complex design issues. Phase stabilisation, beam loading, wakefields and mode damping are special issues for these crab cavities. Requirements and potential design solutions will be discussed for both colliders.