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Space Charge and High Intensity Studies on ISIS. C M Warsop Reporting the work of D J Adams, B Jones, B G Pine, C M Warsop, R E Williamson ISIS Synchrotron Accelerator Physics and: S J Payne, J W G Thomason, ISIS Accelerator Diagnostics, ISIS Operations, ASTeC/IB. Contents Introduction - PowerPoint PPT Presentation
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Space Charge and High Intensity Studies on ISIS
C M Warsop
Reporting the work of
D J Adams, B Jones, B G Pine, C M Warsop, R E Williamson
ISIS Synchrotron Accelerator Physics
and: S J Payne, J W G Thomason,ISIS Accelerator Diagnostics, ISIS Operations, ASTeC/IB.
Contents
• Introduction
• Main Topics
1 - Profile Monitor Modelling
2 - Injection Painting
3 - Full Machine Simulations
4 - Half Integer Losses
5 - Image Effects & Set Code
• Summary
Introduction
• ISIS Spallation Neutron Source ~0.2 MW
- Commissioning Second Target Station
- Now ramping up operational intensity
- ISIS Megawatt Upgrade Studies started
• Will summarise our programme of Ring High Intensity R&D
- Underpins the work above (& has wider applications)
- Aim to understand intensity limits of present and upgraded machines
- Experimentally verify simulation and theory on ISIS where possible
- Broad: covers diagnostics, experiments, simulation, theory
0 2 4 6 8 10
0
0.5
1
1.5
2
2.5
Time (ms)
Beam
Inte
nsity p
pp x
1e13 /
Beam
Loss
Beam Intensity ppp x 1e13 Beam Loss
Circumference 163 m
Energy Range 70-800 MeV
Rep. Rate 50 Hz
Intensity 2.5x1013 → ~ 3.0x1013 protons per pulse
Mean Power 160 → ~ 200 kW
Losses Mean Lost Power ~ 1.6 kW (≤100 MeV)
Inj: 2% (70 MeV) Trap: 5% (<100 MeV)
Acceleration/Extraction: 0.1 – 0.01%
Injection 130 turn, charge-exchange paint injected beam of ~ 25 mm mr
Acceptances horizontal: 540 mm mr with dp/p 0.6% vertical: 430 mm mr
RF System h=2, frf =1.3-3.1 MHz, peak Vrf=140 kV/turn
h=4, frf =2.6-6.2 MHz, peak Vrf=80 kV/turn
Extraction Single Turn, Vertical
Tunes Qx=4.31, Qy=3.83 (variable with trim quads)
The ISIS Synchrotron
• Profile measurements essential for space charge study
- This work: Modelling & experiments to determine accuracy
- Overlaps with diagnostics R&D work - S J Payne et al
• Residual gas ionisation monitors
- Detect positive ions in 30-60 kV drift field
• Two main sources of error:
(1) - Drift Field Non-Linearities
(2) - Beam Space Charge
• Modelled dynamics of ions with
- CST Studio™ for fields
- “In house” particle trackers
ELECTRODE
DETECTOR
1. Profile Monitor Studies ~ 1
Rob Williamson, Ben Pine, Steve Payne
Potential from CST
y
zx
Φ(x,y)
Φ(y,z)
Introduction
Drift Field Error
2D Tracking Study
3D Tracking Study
1. Profile Monitor Studies ~ 2Rob Williamson, Ben Pine
(xs, ys)
xd
Particle Trajectory
- Field error distorts trajectories
- Measured position xd=F(xs,ys)
For given geometry find:
- Averaged scaling correction
- More complicated in 3D case
- Longitudinal fields – new effects
- Detected ions from many points
- Scaling corrections still work
- Ideas for modifications
Φ(x,y)
Φ(y,z) Blue: Trajectory of particles entering detector
Red: Origin of particles entering detector
Black: Transverse section of beam at given z
Trajectories as a function of z along beam
Space charge field distorts trajectories
Space Charge Error
-40 -20 0 20 40
-100
-75
-50
-25
0
25
50
-40 -20 0 20 40
-100
-75
-50
-25
0
25
50
-40 -20 0 20 40
-100
-75
-50
-25
0
25
50
1. Profile Monitor Studies ~ 3Rob Williamson, Ben Pine, Steve Payne
dd
sc
VE
Ex
1
Profile widths parabolic simulation
0.11
0.12
0.13
0.14
0.15
0.16
5.0 25.0 45.0 65.0 85.0 105.0
Electrode voltage / kV
Det
ect
ed 9
0% W
idth
/m
Theory Simulations Experimental data
S J Payne
Ion Trajectories (2D)
increasingdE
90% Width vs Vd
Sim & Meas & Theory
k vs Width
Sim (3D) & Meas
Width vs Vd-1
Simulation (3D)
• Increase in given percentage width
• Also - for “normal” distributions
• So can correct a profile for space charge
• Confirmed experimentally & in 2D/3D simulations
Simple calculation: trajectory deflection
1%%
dxx VkW
1 dV
%% xx Wk
Width vs Vd-1
Measurement
D
SCptDpm V
pKwKw
,,
• Good understanding of monitors
- Correction scheme: good to ±3 mm
• Experimental verification
- Many checks and agrees well
- Final checks needed: EPB monitor
• Monitor Developments (S J Payne)
- Multi-channel, calibration, etc
- Drift field increase and optimisation
• Seems to work well
- See next section …
1. Profile Monitor Studies ~ 4
Summary Rob Williamson, Ben Pine
Basic correction scheme
- drift field and space charge
- for near-centred, “normal” beams
3D simulation: original, “measured” and corrected profile
angular acceptance of detector, reduces errors to ± 3 mm
Injection Septum
Vertical Sweeper
Injection Dipoles
Foil Injected Beam
Closed Orbit
Dispersive Closed Orbit
2. Injection Painting ~ 1 Bryan Jones, Dean Adams
• ISIS Injection
- 70 MeV H- injected beam: 130 turns
- 0.25 μm Al2O3stripping foil
- Four-dipole horizontal injection bump
- Horizontal: falling B[t] moves orbit
- Vertical: steering magnet
• Studies of injection important for:
- ISIS operations and optimisation
- ISIS Megawatt Upgrade Studies
- Space charge studies
• Want optimal painting
- Minimal loss from space charge, foil
• Start is Modelling-Measuring ISIS
Injection Studies: Aims and Background
2. Injection Painting ~ 2Bryan Jones, Dean Adams
• Direct measurement of painting
- Use “chopped” beams
- Low intensity (1E11 ppp); less than 1 turn
- Inject chopped pulse at different times
- Least squares fit to turn by turn positions
- Extract initial centroid betatron amplitude
Injection Painting Measurements
-500 -400 -300 -200 -100 00
20
40
60
80
100
120
140
160
Time Before Field Minimum (us)
Ce
ntro
id E
mitt
anc
e (
pi m
m m
r)
• Profiles measured on RGI monitors
- Corrections as described above
• Plus other data …
- Injected beam, sweeper currents, …
00
2
2cos2
exp cocon zznQnQnQn
Az
• Compare Measurement-Simulation
- Normal anti-correlated case
- Trial correlated case
• Change vertical sweeper to switch
- Reverse current vs time function
-0.4 -0.2 0
Time (ms)
Simulation and Measurement: Normal Painting
2.5x1013 ppp2.5x1012 ppp
-0.3ms
-0.2ms
-0.1ms
-0.3ms
-0.2ms
-0.1ms
2.5x1013 ppp2.5x1012 ppp-0.3ms
-0.2ms
-0.1ms
-0.3ms
-0.2ms
-0.1ms
2. Injection Painting ~ 3Bryan Jones, Dean Adams
Horizontal
Vertical
Painting
anti-correlated
Horizontal Profile Vertical Profile
Key - Measured (corrected) - Simulation (ORBIT)
Not the final iteration, but pretty good agreement
2.5x1013 ppp2.5x1012 ppp-0.3ms
-0.2ms
-0.1ms
-0.3ms
-0.2ms
-0.1ms
2.5x1013 ppp2.5x1012 ppp-0.3ms
-0.2ms
-0.1ms
-0.3ms
-0.2ms
-0.1ms
Anti-correlated Correlated
2. Injection Painting ~ 4Bryan Jones, Dean Adams
Horizontal
Vertical - correlated Vertical Profile
Simulation and Measurement: Painting Experiment
Vertical ProfilePainting
Vertical - anti-correlated
Key - Measured (corrected) - Simulation (ORBIT)
• Follows expectations … [ran at 50 Hz OK!]
• Plan to develop and extend to study
- other painting functions: optimal distributions
- emittance growth (during & after injection)
- foil hits & related losses
Injection Simulation Details
- ORBIT multi-turn injection model
- Painting: H - Dispersive orbit movement; V - Sweeper Magnet
- Injection bump, momentum spread and initial bunching
- 2D transverse (with space charge)
- 1D longitudinal (no space charge yet)
3. Machine Modelling ~ 1 Dean Adams, Bryan Jones
(x,x’) (y,y’)
(x,y) (dE, phi)
Turn 9 Turn 39 Turn 69 Turn 99 Turn 129
Example: Normal anti-correlated case 2.5E13 ppp
ORBIT
Longitudinal Studies ~ work in progress
- TRACK1D - works well - basis of DHRF upgrade (C R Prior)
- Now working to model in detail in ORBIT (1D then 2.5D)
- Collaborating on tomography (S Hancock, M Lindroos, CERN)
3. Machine Modelling ~ 2
TRACK1D ORBIT 1D
Dean Adams
Tomography trialsComparisons and trials at 0.5 ms after field
minimum on ISIS for ~ 2.5x1013 ppp
(real data!)
Full Machine Modelling in ORBIT ~ work in progress
• Simulation of full machine cycle 2.5D – some reasonable results
- time variation of loss
→ reproduces main loss 0 - 3 ms
• Collimators now included
~ space variation of loss
→ good results (normal ops & Mice target)
3. Machine Modelling ~ 3 Dean Adams
Loss vs Time
Simulation
MeasurementB
LM s
igna
l*
* some energy dependence
Spatial LossLo
st P
artic
les
Incr
ea
se in
ten
sity
Importance for the ISIS RCS
• Transverse space charge - key loss mechanism
- Peaks at ~0.5 ms during bunching ΔQinc~-0.4
- In RCS is 3D problem: initially study simpler 2D case
4. Half Integer Losses ~ 1Chris Warsop
3.8 3.9 4 4.1 4.2 4.3 4.4 4.5Qx3.4
3.5
3.6
3.7
3.8
3.9
4Qy
1 ms
10 ms
Incoh Q Shift
• First step: envelope equation calculations
- ISIS large tune split case: independent h and v
- Get 8/5 “coherent advantage” (e.g. Baartman)
- Numerical solutions confirm behaviour
20 40 60 80 100 120
0.25
0.5
0.75
1
1.25
1.5
x
6 7 8 9f
10
20
30
40
amplitude20 40 60 80 100 120
0.25
0.5
0.75
1
1.25
1.5
x
6 7 8 9f
2
4
6
8
amplitude
20 40 60 80 100 120
0.25
0.5
0.75
1
1.25
1.5
x
6 7 8 9f
0.5
1
1.5
2
amplitude
20 40 60 80 100 120
0.2
0.4
0.6
0.8
1
1.2
y
6 7 8 9fy
5
10
15
20
amplitude
20 40 60 80 100 120
0.2
0.4
0.6
0.8
1
1.2
x
6 7 8 9fx
0.5
1
1.5
2
2.5
amplitude
1D 2DEnvelope Amplitude Frequency Amplitude Frequency
Envelope
Horizontal
Vertical
(Qh,Qv)=(4.31,3.83)
ORBIT 2D Simulation Results
- 5E4 macro particles; ~RMS matched waterbag beam
- Tracked for 100 turns; driven 2Qv=7 term
390 395 400 405 410 415 420 425 430 435 4400
500
1000
1500
2000
2500
3000
3500
Frequency of Dipole Motion: Horizontal
100 x azimuthal frequency
Am
plitu
de
340 345 350 355 360 365 370 375 380 385 3900
500
1000
1500
2000
2500
3000
Frequency of Dipole Motion: Vertical
100 x azimuthal frequency
Am
plitu
de
780 790 800 810 820 830 840 850 860 870 8800
1
2
3
4
5
x 104 Frequency of Envelope Motion: Horizontal
100 x azimuthal frequency
Am
plitu
de
680 690 700 710 720 730 740 750 760 770 7800
1
2
3
4
5
6
7
8
x 104 Frequency of Envelope Motion: Vertical
100 x azimuthal frequency
Am
plitu
de
0 2000 4000 6000 8000 10000 12000 14000 16000 18000-10
0
10
20
30
40
50
60
70x (3,1), x-y (2,2) and y (1,3) envelopes - 2nd Order
x (2,0)
x-y (1,1)
y (0,2)
390 395 400 405 410 415 420 425 430 435 4400
500
1000
1500
2000
2500
3000
3500
Frequency of Dipole Motion: Horizontal
100 x azimuthal frequency
Am
plitu
de
340 345 350 355 360 365 370 375 380 385 3900
500
1000
1500
2000
2500
3000
Frequency of Dipole Motion: Vertical
100 x azimuthal frequency
Am
plitu
de
780 790 800 810 820 830 840 850 860 870 8800
2
4
6
8
10
12
x 104 Frequency of Envelope Motion: Horizontal
100 x azimuthal frequency
Am
plitu
de
680 690 700 710 720 730 740 750 760 770 7800
2
4
6
8
10
12
14
16
18
x 104 Frequency of Envelope Motion: Vertical
100 x azimuthal frequency
Am
plitu
de
0 2000 4000 6000 8000 10000 12000 14000 16000 18000-10
0
10
20
30
40
50
60
70
80
90x (3,1), x-y (2,2) and y (1,3) envelopes - 2nd Order
x (2,0)
x-y (1,1)
y (0,2)
390 395 400 405 410 415 420 425 430 435 4400
500
1000
1500
2000
2500
3000
3500
Frequency of Dipole Motion: Horizontal
100 x azimuthal frequency
Am
plitu
de
340 345 350 355 360 365 370 375 380 385 3900
500
1000
1500
2000
2500
3000
Frequency of Dipole Motion: Vertical
100 x azimuthal frequency
Am
plitu
de
780 790 800 810 820 830 840 850 860 870 8800
2
4
6
8
10
12
x 104 Frequency of Envelope Motion: Horizontal
100 x azimuthal frequency
Am
plitu
de
680 690 700 710 720 730 740 750 760 770 7800
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
x 105 Frequency of Envelope Motion: Vertical
100 x azimuthal frequency
Am
plitu
de
0 2000 4000 6000 8000 10000 12000 14000 16000 18000-20
0
20
40
60
80
100
120x (3,1), x-y (2,2) and y (1,3) envelopes - 2nd Order
x (2,0)
x-y (1,1)
y (0,2)
6x1013 ppp
5x1013 ppp
7x1013ppp
(x,x’) (y,y’)
(x,y) (εx,εy)
4. Half Integer Losses ~2Chris Warsop
Envelope Frequencies Incoherent Q’s EnvelopesHorizontal Vertical
Turn 100
ORBIT 2D Simulation Results
- Repeat similar simulations, but driven by representative 2Qh=8 & 2Qv=7 terms
- If allow for BF and energy is compatible with loss observation on ISIS
4. Half Integer Losses ~3Chris Warsop
Driven both planes 2Qh=8 & 2Qv=7
0 1 2 3 4 5 6 7 8 9 107
7.5
8
8.5
9
Env
Osc
/Tur
n
Coherent Envelope Frequency
0 1 2 3 4 5 6 7 8 9 103
3.5
4
4.5
Inco
h O
sc/T
urn
Minimum Incoherent Frequency (Peak Q Depression)
0 1 2 3 4 5 6 7 8 9 1060
80
100
120
140
Circulating Protons (x1E13)
RM
S E
mitt
ance
(pi
mm
mr) RMS Emittance on Turn 100
Horizontal
Vertical
Coherent Limit
Incoherent Limit
Emittance Growth
Questions important for real machines …
• What causes εrms growth?
Mis-match, non stationary distributions,
driving terms from lattice, … ?
• Can we minimise it?
• Do codes give good predictions?
- can they predict emittance growth & loss?
Have compared ORBIT with theory
- to see if behaviour follows models
Study of Halo & Future Work
Vertical (YN, YN')
Simulation
Theory [*]
Incr
easi
ng Inte
nsi
ty
7.00 x1013 ppp 7.25 x1013 ppp
8.00 x1013 ppp 7.50 x1013 ppp
8.50 x1013 ppp 7.75 x1013 ppp
4. Half Integer Losses ~ 4
• Comparison of halo structure with theory
- ORBIT: Poincare routines: AG ISIS Lattice; RMS Matched WB; quad driving term; large tune split;
- Theoretical model: Smooth, RMS equivalent KV,quad driving term; “small tune split” (equal) [*Venturini & Gluckstern PRST-AB V3 p034203,2000]
- Main features agree …
Chris Warsop
• Next
- Check number of particles migrating into halo …?
- Introduce momentum spread (then extend to 3D)
- Comparison with ISIS in Storage ring mode~ trials now underway
Normalised vertical phase space
Developing a space charge code “Set"
(1) Model and Study Rectangular Vacuum Vessels in ISIS
- implement the appropriate field solvers
- study image effects: rectangular vs elliptical geometry
(2) Develop our own code
- allow us to understand operation and limitations
- develop and enhance areas of particular interest
- presently 2D: will extend …
- plus use of ORBIT, SIMBAD, TRACKnD, etc
5. Images and Set Code ~ 1 Ben Pine
View inside ISIS vacuum vessels
Field Solver Benchmarking: Set solver vs CST Studio
5. Images and Set Code ~ 2
(xc,yc)=(0,0)
(xc,yc)=(5,5)
(xc,yc)=(15,0)
Set solver and CST agree to <0.1%
Ben Pine
ρ(x,y) Ф(x,y) Relative Error Ф(x,y)
Comparisons of Set with ORBIT
5. Images and Set Code ~ 3 Ben Pine
(x,x’) (y,y’)
(x,y)
(x,x’) (y,y’)
(x,y)
Incoherent Tune Shifts• ISIS half integer resonance (as above)
- ~ RMS matched WB beam, 2Qv=7 term etc
- Track for 100 turns; vary intensity
• Good Agreement - where expected
- Incoherent tunes, envelope frequencies
- evolution of εrms, beam distributions
ORBIT Set
Distributions on turn 100
ORBIT Set
Set: Dipole Tune Shift and Next Steps
5. Images and Set Code ~ 4Ben Pine
Coherent tune shifts from Set
• Next Steps
- Are now modelling closed orbits with images
- See expected variations in orbit with intensity
- evidence of non linear driving terms …
- planning experiments to probe images …
• Coherent Dipole Tune Shift in Set
- Expect some differences between ORBIT & Set
- ORBIT - just direct space charge (as we used it)
- Set - images give coherent tune shift
• Making good progress in key areas
- experimental study (collaboration on diagnostics)
- machine modelling and bench marking
- code development and study of loss mechanisms
• Topics covered
- Current priorities: Space charge and related loss, injection.
- Next: Instabilities, e-p, …
• Essential for ISIS upgrades
• Comments and suggestions welcome!
Summary
Acknowledgements:
ASTeC/IB - S J Brooks, C R Prior ~ useful discussions
STFC e-Science Group ~ code development
ORNL/SNS ~ for the use of ORBIT
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