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
2
Outline
• Introduction
• Simulation of new PS EC detector
– Geometrical properties
– Numerical issues and their resolution
• Summary and future work
3
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
4
New PS EC Detector
Endoscopy of EC detector inside the
chamber
5
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
6
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
7
Outline
• Introduction
• Simulation of new PS EC detector
– Geometrical properties
– Numerical problems of simulations and their resolution
• Summary and future Work
8
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
9
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
10
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]
11
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
12
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?
13
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
14
StrongBgen VS Boris
1. Methods Comparison
SEY=1.6 ; Dt= 18ps
StrongBgen1.2T Dipole_field
•
Boris Combined function
Boris method corrects the artificial shift of the electrons
15
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)
16
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)
17
Electrons Distribution
3. Effect of different initial distribution
SEY=1.5
SubStep=10
Dt=18 ps
Passage= 60
•
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
18
Outline
• Introduction
• Simulation of new PS EC detector
– Geometrical properties
– Numerical issues and their resolution
• Summary and future work
19
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 ..
20
Thanks for your attention!
21