HALO AND TAIL SIMULATIONS WITH APPLICATION TO THE CLIC DRIVE BEAM Miriam Fitterer * , Anke-Susanne M¨ uller, Universit¨ at Karlsruhe (TH), Germany Erik Adli, Helmut Burkhardt, Barbara Dalena, Giovanni Rumolo, Daniel Schulte, CERN, Geneva, Switzerland, Andrea Latina, FNAL, USA, Ijaz Ahmed, NCP, Islamabad, Pakistan Abstract We report about generic halo and tail simulations and es- timates. Previous studies were mainly focused on very high energies as relevant for the beam delivery systems of linear colliders. We have now studied, applied and extended these simulations to lower energies as relevant for the CLIC drive beam. INTRODUCTION Halo and Tail Generation Halo particles can be a major source of beam losses and radiation and can therefore lead to performance limitations of future accelerators. If the amplitude of a core particle increases significantly, it becomes a halo particle. The in- crease of the amplitude can be caused by the following par- ticle processes: • Beam gas scattering: elastic scattering (Mott scatter- ing), inelastic scattering (Bremsstrahlung), multiple scattering • Scattering of thermal photons (Compton scattering) • Touschek effect • Intrabeam scattering • Electron and Ion cloud effects • Space charge effects • Synchrotron radiation The most relevant processes for halo generation are usu- ally beam gas scattering and multiple scattering, which can be simulated with the halo and tail generation package HTGEN [1]. In addition to the scattering processes, op- tics related effects like mismatch, coupling, dispersion and nonlinearities can enlarge the halo. These as well as the ef- fect of synchrotron radiation are fully included in the track- ing code PLACET [2], which can be used in combination with HTGEN. Previous studies using PLACET-HTGEN were done for high energy beams like the 250 GeV beam of the ILC [3]. In the following we will describe the exten- sion of PLACET-HTGEN to low energy beams with high intensity like the CLIC drive beam decelerator. * at CERN CLIC Drive Beam Decelerator The CLIC Drive Beam decelerator will extract X-band RF power from a 100 A Drive Beam. The focussing and alignment systems must ensure transport of particles of all energies through the decelerator sectors, ensuring minimal losses. A short summary of relevant beam parameters is given in Table 1 and a more detailed description can be found in [4]. Table 1: CLIC drive beam decelerator parameters Parameter Unit Value Drive beam sector length m 1053 numb. of part. per bunch 10 9 52.5 numb. of bunches per train 2928 mean initial beam energy GeV 2.40 mean final beam energy GeV 0.40 ǫ N,y,initial μm 150 ǫ N,y,final μm 334 THEORY Elastic Scattering The electron is deflected by the Coulomb potential of the particles in the residual gas. Taking the spin of the electron into account the differential cross section is given by [5]: dσ dΩ =  Zr e 2γβ 2  2 1 - β 2 sin 2 θ 2 sin 4 θ 2 (1) where Z is the charge of the nucleus, r e the classical elec- tron radius, γ the Lorentz factor E/mc 2 of the electron and β the velocity of the electron in units of the speed of light. Relevant for halo production are only scattering angles ex- ceeding the beam divergence, so roughly: θ>θ min =  ǫ N,y /(γβ y ) (2) where ǫ N,y is the normalized emittance and β y the lo- cal vertical beta function. Integration over the solid angle yields the total cross section: WE6PFP085 Proceedings of PAC09, Vancouver, BC, Canada 2700 Lepton Accelerators A03 - Linear Colliders