ISIS Upgrade Modelling Dean Adams On behalf of STFC/ISIS C Warsop, B Jones, B Pine, R Williamson, H Smith, M Hughes, A McFarland, A Seville, I Gardner, R Mathieson, S Payne, A Pertica, S Fisher, S Jago, J Thomason and Imperial College London J Pasternack PASI, Friday 5 th April 2012, RAL

A 0.5 MW ISIS Replace old 70 MeV Linac with 180 MeV version and upgrade injection beam lines and ring injection region. Synchrotron Space charge limit scales as β 2 γ 3 hence 80 to 180 MeV ≈ factor of 2.60 so output scales from 0.2 to 0.5 MW. Presentation focuses on Ring Studies/Modelling: Transverse and longitudinal dynamics, injection, foils, magnets, RF and beam loss control.

Injection Scheme M1 M2 M3 M4 inner radius stripping foil h. & v. sweeper magnets H-H- p+p+ 4  pulsed ferrite, magnets (0.17 T, 45 – 55 mrad, 26,000 A in ~500  s) beam dump H- charge exchange injection over 500 turns on either falling rising or symmetric point of main magnet field. Horizontal painting using dynamic injection bump ( π mm mrad) Vertical painting via sweeper magnets ( π mm mrad). Longitudinal paint ±0-1.3 MeV using Linac injection energy and Ring RF bucket frequency errors. Chopped at ± 110° wrt Ring RF phase.

1D studies

3D Studies Centred around use of ORBIT code (Fermilab, SNS). Version used here modified to include RF Offsets and Acceleration. Models: Injection/Acceleration with Ramping Tunes and Harmonic Envelope Errors. Machine apertures and collimators (Beam Loss). ‘3D space charge’ routine. Foil scattering. Run in parallel environment using ~ 2M macro particles. Produces: 6D phase space, emittance evolution, beam losses, foil hits, beam moments etc

ORBIT Injection Studies 3D Injection painting simulated. Produce beam with maximum emittance 300 π mm mrad (un- normalised) Centroid painting roughly constant at 100 π mm mrad. 6D phase space at end of injection H and V 99% emittance evolution Dynamic injection bump

Foil:3.3σ RMS width Injected Beam Re-circulating beam Foils p H0H0 H-H- ORBIT model simulates foil hits In-house codes simulates striping efficiencies and foil temperatures. ~ 3.5 re-circulations/injected proton, 1322 K on hottest point. Temperature Per Pixel ANSYS modelling agrees well. Double foils studies in progress Pixel temperatures reach steady state after 10 pulses, 0.2s (200 µg/cm 2 carbon (as per JPARC) >99.6% stripping efficiency

Injection Magnets modelled using Opera Injection dipole, peak field A Blue zone 0.125% uniformity Injection Straight Magnets Particle tracking through complex fringe fields

Beam Losses and Activation MARS modelling (below) indicates ~ 5x increase in activation between 70 and180 MeV mSv/h Kinetic energy, MeV Cu Fe steel graphite concrete Loss, Horizontal, Vertical, Total ORBIT simulation (right) predicts < 1 % beam loss mainly located on collimators.

ORBIT used to model incoherent tune spread over injection and acceleration F=1 KV, 2 WB Tune Space max mode

Working point studies Other working points under investigation to avoid instabilities, half integer, head-tail SET code developed in-house, 2D particle tracker with images. Raising Vertical tune leads to loss of dynamic aperture (right) and coupling resonances Lowering Vertical Tune below half integer leads to sextupole resonance driven by images. 3D version of SET (SET3D) in development to complement ORBIT studies Nominal design tune

Simplified 2D beam dynamics Drive beam onto coherent resonance Loss observations as expect What causes growth? Simulations and theory suggest parametric halo Measuring halo development in new experiments Giving a deeper understanding of main loss mechanism Confirmation of codes and methods used in new designs Study of Loss Mechanisms Predicted Resonance Measured Loss Halo Experiment Transverse Profiles ExperimentSimulation Drive phase 1 Drive phase 2 Loss vs Intensity (Y,Y) New Storage Ring Mode Experiments High intensity “space charge limit”: half integer resonance

Diagnostics Stripline (monitor/kicker) Multi Channel Profile Monitor Electron Clouds ANSYS – HFSS Software CST

Summary Installing a new 180 MeV linac could increase ISIS power to ~ 0.5 MW Looks technically challenging but studies have shown no ‘show stoppers’. A variety of modelling software for beams and hardware used: ORBIT, in-house foil code, ANSYS, Opera, CST, SET (in-house) and HFSS 3D beam code SET3D in development to benchmark against ORBIT. Feasibility study almost complete. Report finalised in ~ 3 months.