Modelling of diagnostics for the ISIS ring
Ben Pine, Chris Warsop, Steve Payne
Motivation
It is important to understand and predict high intensity behaviour on ISIS
In order to compare theory and simulation with experimental results, we must
have confidence in the accuracy of our diagnostic instruments
A detailed analysis of instruments’ physical operation compliments the
diagnostic hardware upgrades
This talk describes work in progress studying the ISIS Residual Gas Profile
Monitors with CST Studio Suite and other tools
Modern computing power and software used to look for new insights into
these well known devices
2
Profile Monitor: Principle of Operation
ISIS Profile Monitor
Working Principle
Typical 10ms ISIS Profile
Electrode
Electric
field
Beam
Ions
Detector
Residual gas atoms left in the beam pipe are ionised as the beam comes past
The ions are swept with an electric field and the resulting current plotted
against transverse position
The gas ions will also be affected by the electric field of the beam itself
Radial electric field of beam may distort the detected profile
3
Profile Monitor: Focus of Work
Two major effects limiting resolution:
Non-linear drift field
Space charge of the beam
Effect of space charge can be minimised by increasing the electrode voltage
When will the drift field dominate over space charge?
What are the errors associated with the drift field alone?
Longitudinal electrode potential
Transverse electrode potential
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Profile Monitor: Drift Field Errors (1)
Aperture scan under drift-field: detected ion position as a function of
starting coordinate
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InIni
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itiatia
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l yl y
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popos
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sitiiti
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onon
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/m
/m
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mm
A new technique was
developed to overcome
(Initial x, Initial
y)
limitations
in particle
creation
and number in CST, and the
results compared with the
previous simulations
Detetecte
De
cteddpopo
ion/m/m
sitsit
ion
mm
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m
/m
mm
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tionn /
ossiitio
0
po
0
p
x
l
itiiaal x
IInnit
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0
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8080
6060
(Detected x)
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IniInit
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tia ial
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lyy
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popos
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sitiiti
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onon
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/
/mmm
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m
5
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m
mm
nn //m
ssittiioo
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In t
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cte
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Profile Monitor: Drift Field Errors (2)
Mathematica tracking program and CST field
used to calculate profile error and position
offset due to drift field
WORK IN PROGRESS
Initial Results
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Profile Monitor: Space Charge Effects
Simple model of ion trajectories and
profile under effect of analytical space
charge and ideal electrode field
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Results plotted as electrode voltage
is increased
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Ideal
Ideal
Detected
Detected
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Profile Monitor: HV Testing
Experiment increased
electrode voltage from
10-30 KV
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0ms data
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fit to data
Beam Width (cm)
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30kV width
60kV width
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Fitted curve changes
by less than 1cm
between 60-100 KV
80kV width
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New HV Towers for
monitors will provide 60
KV
10
9
8
0
20
40
60
80
100
Drift Field (kV)
‘Investigations into the relationship between the Drift Field Voltage and the
measure Beam Width in the ISIS Ring Beam Profile Monitor System‘, [S. J.
Payne, C. M. Warsop, A. H. Kershaw, D. M. Wright]
(Measurements taken at 0ms in the ISIS cycle, with 2.12x1013 ppp)
8
Profile model will be
compared directly with
experimental results
Conclusion
Understanding diagnostics is an essential part of machine development
What is being learnt about the diagnostics will help optimisation of the
synchrotron and prepare for the detailed measurements required to study
high intensity behaviour
This is work in progress - results will be compared with experiment as new
hardware becomes operational
Aim to model any 2D beam distribution, with arbitrary beam intensity and
electrode voltage, then predict the detected profile
Split-electrode beam position monitors have also been modelled; Envelope
monitors will hopefully follow by the summer
9