ISIS Accelerator Division Upgrades to the ISIS Facility John Thomason ISIS Accelerator Division

ISIS Accelerators H ion source (17 kV) 665 kV H RFQ 70 MeV H linac 800 MeV proton synchrotron Extracted proton beam lines The accelerator produces a pulsed beam of 800 MeV (84% speed of light) protons at 50 Hz, average beam current is 230 A (2.9× 1013 ppp) therefore 184 kW on target (148 kW to TS-1 at 40 pps, 36 kW to TS-2 at 10 pps).

ISIS Upgrades Present operations for two target stations Operational Intensities: 220 – 230 μA (185 kW) Experimental Intensities of 31013 ppp (equiv. 240 μA) DHRF operating well: High Intensity & Low Loss Now looking at overall high intensity optimisation Study ISIS upgrade scenarios 0) Linac and TS1 refurbishment 1) Linac upgrade leading to ~0.5 MW operations on TS1 2) ~3.3 GeV booster synchrotron: MW Target 3) 800 MeV direct injections to booster synchrotron: 2 – 5 MW Target 4) Upgrade 3) + long pulse mode option

ISIS MW Upgrade Scenarios 1) Replace ISIS linac with a new ≈ 180 MeV linac (≈ 0.5MW) 2) Based on a ≈ 3.3 GeV RCS fed by bucket-to-bucket transfer from ISIS 800 MeV synchrotron (1MW, perhaps more) 3) RCS design also accommodates multi-turn charge exchange injection to facilitate a further upgrade path where the RCS is fed directly from an 800 MeV linac (2 – 5 MW)

Power / Benefit / Cost Neutrons £ + Risk Power Upgraded TS1 TS2 Existing TS1 Power

ISIS Upgrades, Developments and R&D Work We have on-going research and studies to develop and fully exploit the machine map out the best development routes define principle upgrades undertake basic R&D into physics of high intensity beams Main focus presently ~180 MeV Injector Upgrade summarised in the following pages holistic optimisation including targets, neutronics, … “at the user” Next steps Exploring the possibilities for optimistic & less optimistic funding scenarios Mapping out the best options for a 1-2 MW short pulse neutron source Development and research on present machine

ISIS Injection Upgrade New 180 MeV Linac ISIS Injection Upgrade 70 MeV Linac A New 180 MeV Injector Update old linac Increase beam power ~0.5 MW Advantages Reduces Space Charge (factor 2.6) Chopped, Optimised Injection & Trapping Challenges Injection straight Activation (180 MeV) Space charge, beam stability, .... MICE 800 MeV Synchrotron TS1 TS2

ISIS Injection Upgrade Ring Physics Study Snapshots of the work: challenges of getting 0.5 MW in the ISIS Ring Injection Longitudinal Dynamics Injection Straight Modelling Injection Straight Analytical Work Simulation Results Test Distribution Evolution of bunch Foil temperatures Injected distributions in (x,x’),(y,y’),(,dE) RF Bucket Variation of key parameters Transverse & Full Cycle 3D Dynamics Other Essentials: Activation, Diagnostics Predicted Space Charge Limit Single particle tune shift distributions at 0.5 MW Activation vs Energy Activation Measurements Coherent Tune Shift and Resonance Electron Cloud Monitor Strip-line Monitor/Kicker Accelerated distributions in (x,x’),(y,y’),(,dE)

Possible ≈ 3.3 GeV RCS Rings

Bucket-to-Bucket Transfer

5SP RCS Ring Energy 0.8 – 3.2 GeV Rep Rate 50 Hz C, R/R0 367.6 m, 9/4 Gamma-T 7.2 h 9 frf sweep 6.1-7.1 MHz Peak Vrf ≈ 750 kV Peak Ksc ≈ 0.1 εl per bunch ≈ 1.5 eV s B[t] sinusoidal

Accelerating Structures DTL/SC Elliptical Cavities Frequency Grahame Rees, Ciprian Plostinar ( ) 800 MeV, Hˉ Linac Design Parameters Ion Species H- Output Energy 800 MeV Accelerating Structures DTL/SC Elliptical Cavities Frequency 324/648 MHz Beam Current 43 mA Repetition Rate 30 Hz (Upgradeable to 50 ) Pulse Length 0.75 ms Duty Cycle 2.25 % Average Beam Power 0.5 MW Total Linac Length 243 m

Design Options

Capacity upgrade scenarios “Traditional” 3-stage MW upgrade scenario could be extended so 3.2 GeV RCS includes multiple extraction straights (or switchyard in EPB), with or without 800 MeV linac. Stacked rings (as at CERN PSB) could be implemented as part of AC magnet replacement programme. Would require increased linac performance, but otherwise it is an engineering challenge to minimise off time during installation rather than an accelerator physics challenge, and would be a very predictable upgrade.

One synchrotron with several extraction straights? Target station #1 Target station #2 “Efficient” footprint Maximises total number of neutron beam lines Flexible Easy extraction of proton beams of different energies, intensities and repetition rates to suit wide range of neutron experiments Linac Synchrotron Would need to drive trim quads. and steerers differently for different energies and intensities, but trim quads. and steerers are pulsed anyway, and so changing trim magnet current profiles from acceleration cycle to acceleration cycle should raise no fundamental complications. Target station #4 Target station #3

Ring High Intensity Beam Studies on ISIS Some of our R&D Studies Half-integer intensity limit in proton rings Using the ISIS ring to study halo formation New simulation code: Set 3Di Model losses, benchmark on ISIS Simulation Simulation Measurement (Y,Y) Y profile Y profile Higher order loss effects and images Investigating complex loss mechanisms Head-tail instability Key for high intensity proton rings Image driven resonance Vertical dipole motion along bunch on successive turns Vertical difference signal (along bunch, many turns) Loss vs Q measurement Samples along bunch Turn 

Necessary Hardware R&D High power front end (FETS) RF Systems Stripping Foils Diagnostics Targets Kickers etc. To realise ISIS upgrades and generic high power proton driver development, common hardware R&D will be necessary in key areas: In the neutron factory context SNS and J-PARC are currently dealing with many of these issues during facility commissioning and we have a watching brief for all of these Active programmes in some specific areas