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Analysis of PS detector in MU98
A. Romano, G. Iadarola, G. Rumolo
Many thanks to: C. Alaggio, Christina Yin Vallgren
Electron Cloud meeting 27-06-2014
Outline
• Introduction
• Simulation of new PS EC detector
– Geometrical properties
– Numerical issues and their resolution
• Summary and future work
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Outline
• Introduction
• Simulation of new PS EC detector
– Geometrical properties
– Numerical issues and their resolution
• Summary and future work
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PS detector in MU98
• New electron cloud (EC) detectors have been installed in one of the
PS main magnets to study EC effects in strong magnetic field
conditions (B>1 T)
Grid
[By Teddy Capelli EN/MME]
Biased Electrode:
Measure current from EC
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New PS EC Detector
Endoscopy of EC detector inside the
chamber
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New PS EC Detector-Structure
• The detector is mounted in the right part of the
beam pipe, at bottom; the distance between the
end of the pick-up and the vertical axis of vacuum
chamber is 1.2 cm
EC detector
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New PS EC Detector-Structure
[By T. Capelli and C.F Eymin]
•
The pick-up is made by a ceramic block shielded from the main chamber with a 0.2 mm
thick stainless steel sheet consisting of a series of holes (1 mm diameter and 2 mm pitch).
The practical difficulty of pick-up is the limited distance from the magnetic gap
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Outline
• Introduction
• Simulation of new PS EC detector
– Geometrical properties
– Numerical problems of simulations and their resolution
• Summary and future Work
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Simulation Strategy
How we have implemented it in PyEcloud?
Realistic chamber
1.2
•
The chamber can be schematically
represented as combination of arcs of
circumferences
•
The size of chamber is :
x_aper= 73 mm
y_aper= 35mm
•
The shielded pick-up is fully inserted
in the green arc of circumference
(bottom-right)
Thanks to C. Alaggio
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Simulation strategy
How have we implemented it in PyEcloud?
Realistic chamber with EC detector implemented in PyEcloud code
•
The surface of beam pipe is
made of adjacent segments of
different size and SEY
hole
chamber
• d= 1 mm
• SEY = 0 (absorbing
surface)
• SEY= [1.0-2.2]
EC detector
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Simulation strategy
How we have implemented it in PyEcloud?
Realistic chamber with EC detector implemented in PyEcloud code
•
The surface of beam pipe is
made of adjacent segments of
different size and SEY
hole
chamber
• d= 1 mm
• SEY = 0 (absorbing
surface)
• SEY= [1.0-2.2]
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Magnetic Field in PS
Distribution of electrons inside the chamber
Combined function
•
The distribution of electrons inside the chamber follows the B field lines of the
combined function magnet
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Simulation Development
Numerical issues of simulations :
1. Simulation with two different algorithms: Boris vs StrongBgen
 Both methods are used to compute the MP motion in a general magnetic field
of magnitude B. Which is the better one?
2. Study of Boris convergence 
Define the value of some important
parameters to give a good balance between accuracy and computational burden
3. Effects of initial distribution of electrons 
How the initial
distribution influences the results of simulations?
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StrongBgen VS Boris
1. Methods Comparison
SEY=1.6 ; llDt= 18ps
StrongBgen1.2T Dipole_field
•
StrongBgenCombined function
StrongBgen method introduces an artificial shift of the electron distribution  electrons
are killed in the detector region
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StrongBgen VS Boris
1. Methods Comparison
SEY=1.6 ; Dt= 18ps
StrongBgen1.2T Dipole_field
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Boris Combined function
Boris method corrects the artificial shift of the electrons
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Study of convergence
2. Boris convergence
Electron flux through the chamber
Very good convergence for each Dt and SubStep
We can choose
Dt=25ps
SubStep=10
(good balance between accuracy and acceptable simulation time)
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Study of convergence
2. Boris convergence
Electron flux through the holes
Good convergence for each Dt and SubStep
We can choose
Dt=25ps
SubStep=10
(good balance between accuracy and acceptable simulation time)
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Electrons Distribution
3. Effect of different initial distribution
SEY=1.5
SubStep=10
Dt=18 ps
Passage= 60
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The different initial distribution of electrons influences the profile of electrons inside
the chamber. Increasing the number of seeds it is possible to attenuate the noise and to
obtain a smoother profile
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Outline
• Introduction
• Simulation of new PS EC detector
– Geometrical properties
– Numerical issues and their resolution
• Summary and future work
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Summary and future work
In conclusion:
• Simulations for EC detector installed in PS combined function
have been set-up
• Main results so far:
- Boris algorithm should be used to simulate the new PS EC detector
- Setting Dt= 25 ps and SubStep=10 it is possible to achieve a good
balance between accuracy and an acceptable simulation time
- Large number of seeds is needed to correctly initiate multipacting
processes in the detector region
• Next steps
- Parameter scans  bunch intensity, bunch length, radial position ..
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Thanks for your attention!
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