ISIS Upgrade ModellingDean Adams

On behalf ofSTFC/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 LondonJ Pasternack

PASI , Friday 5th 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 β2γ3 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 foilh. & v.sweepermagnets

H-

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 (50-200 π mm mrad)

• Vertical painting via sweeper magnets (50-200 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• In house 1D code with longitudinal space charge.• Paint chopped beam (±110 °) using injection

energy and ring RF bucket energy offset.• Use a dual harmonic volts system • High bunching factor , transverse stability by Keil-

Schnell-Boussard Criterion (KSB) for bunched beams < 1

3D StudiesCentred 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 Studies3D 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

H0

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 PixelANSYS modelling agrees well. Double foils studies in progress

Pixel temperatures reach steady state after 10 pulses, 0.2s

(200 µg/cm2 carbon (as per JPARC)>99.6% stripping efficiency

Injection Magnets modelled using OperaInjection dipole, peak field 0.165 T @ 26000 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

mS

v/h

Kinetic energy, MeV

Cu

Fe

steel

graphiteconcrete

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 accelerationF=1 KV, 2 WB

Tune Space

0 1 2 3 4 5 6 7 8 9 100

0.1

0.2

0.3

0.4

0.5

0.6Horizontal Incoherent Tune

Shift

0 1 2 3 4 5 6 7 8 9 100

0.1

0.2

0.3

0.4

0.5

0.6 Vertical Incoherent Tune Shift

ORBIT maxKVWaterbagORBIT mode

max

mode

Working point studiesOther working points under investigation to avoid instabilities, half integer, head-tailSET 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

0 . 6 0 . 8 1 . 0 1 . 2 1 . 4 1 . 6 1 . 8 2 . 00 . 00 . 10 . 20 . 30 . 40 . 5

I n t e n s i t y x 1 . 0 E 1 3 p p p Loss

1.0E13Study of Loss Mechanisms

Predicted Resonance

Measured Loss

Halo Experiment Transverse ProfilesExperiment Simulation

Drive phase 1

Drive phase 2

Loss vs Intensity

(Y,Y)

(Y,Y)

(Y,Y)

New Storage Ring Mode Experiments

• High intensity “space charge limit”: half integer resonance

Diagnostics

9.952 9.953 9.954 9.955 9.956-0.15-0.050.050.150.250.35

R5VMS Sum Position MonitorR5 Electron Cloud Monitor

Acceleration Cycle Time (ms)

Mag

nitu

de (

arbi

trar

y un

its)

Stripline (monitor/kicker)

Multi Channel Profile MonitorElectron Clouds

ANSYS – HFSSSoftware

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.