s.ratschow, s.setzer, t.weiland, i. zagorodnov report from
TRANSCRIPT
Darmstadt University of TechnologyDarmstadt University of TechnologyDepartment of Electrical Engineering and Information-Technology
Computational Electromagnetics Laboratory (TEMF)SchloßgartenstrSchloßgartenstr. 8 , 64289 Darmstadt, Germany. 8 , 64289 Darmstadt, Germany
[email protected], [email protected], www.TEMF.de
Computational Electromagnetics Laboratory
Report from TU-Darmstadt
R.Cee, M.Krassilnikov,T.Lau, W.F.O.Müller,S.Ratschow, S.Setzer, T.Weiland, I. Zagorodnov
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Com
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tiReports from TU-Darmstadt
• Computational Electromagnetics Laboratory♦ Results from W. Mueller♦ Detailed Numerical Study of Space Charge Effects in
the FEL rf-gun (PITZ)♦ V-Code Alignment Utility♦ A Code for Longitudinal Wake Field Calculation♦ Investigation of Surface Roughness Wake Fields
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Com
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tiSimulation of Production Procedure
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tiDifferent Methods of Deformation
• Linear Expansion• Constant Length of 2D-Contours• Constant Contours with Stiffening Ring• Deformation from Numerical Simulation
××××
××××
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• Detuning of a Half Cell in MHz/mm:
Detuning
-2
0
2
4
6
8
10
12
14
-1,5 -0,5 0,5 1,5
elongation / mm
Df/D
L / M
Hz/m
m expansioncontourstiffening ringdeformationmeasurement
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0,0E+00
2,0E-04
4,0E-04
6,0E-04
8,0E-04
1,0E-03
1,2E-03
1,4E-03
1,6E-03
0,0E+00 1,0E-04 2,0E-04 3,0E-04 4,0E-04 5,0E-04 6,0E-04 7,0E-04 8,0E-04
MacroparticlesLayer 1Layer 2Layer 3
Beam slices
Space Charge Effects in the RF-Gun:Emittance Formation Study
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Space Charge Effects in the RF-Gun:Emittance Formation Study
0 100 200z - Position / mm
0
5
10Tr
ans.
Em
ittan
ce /
mm
- m
rad
0 100 2000
5
10
Long. Emittance
/keV-m
m
Long. Emittance
Projected Emittance
Slice Emittance
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Space Charge Effects in the RF-Gun:Emittance Formation Study
0.0 0.5 1.0 1.5r - Position / mm
-1e-03
0e+00
1e-03
2e-03
3e-03
4e-03
Trans
. Mo
men
tβγ z = 31 mµ
z = 253 mµz = 696 mµ
a)
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Space Charge Effects in the RF-Gun:Emittance Formation Study
0.0 0.5 1.0 1.5 2.0 2.5r - Position / mm
0e+00
5e-02
1e-01Tra
ns. M
om
ent
βγ
z = 0.3 mmz = 1.9 mmz = 4.9 mmz = 8.8 mm
b)
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0.0 0.5 1.0 1.5r-Position / mm
0.0
0.5
1.0
1.5
2.0
Nor
ma
lize
d In
tesit
y
Int. Ratio = 1.0
Int. Ratio = 0.75
Int. Ratio = 0.5
Int. Ratio = 0.25
Influence of Transverse Laser Profiles on Beam Emittance at Gun Exit
(Laser Pulse Length 10 ps FWHM, 2 ps rise/fall time)
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Influence of Transverse Laser Profiles on Beam Emittance at Gun Exit
0.2 0.4 0.6 0.8 1.0Intensity Ratio
0
2
4
6
8
Tran
s. E
mitt
ance
/ m
m-m
rad
0.2 0.4 0.6 0.8 1.015
20
25Long. Em
ittance/keV-m
m
Projected Emittance
Long. Emittance
Slice Emittance
(Laser Pulse Length 10 ps FWHM, 2 ps rise/fall time)
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0 2 4 6 80
2
4
6
8
Tran
s. E
mitt
ance
/ m
m-m
rad
0 2 4 6 8Rise-Time / ps
0
5
10
Long.Emittance
/keV-mm
Slice Emittance
Projected Emittance
Long. Emittance
Dependency of the Emittances at the Gun Exit On the Laser Rise Time
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-6
-4
-2
0
2
4
6
-6 -4 -2 0 2 4 6x / mm
y / m
m
TTF Gun Alignment Study: Measurements&Simulations
Secondary solenoid magnetic
center (simulated )
Primary solenoid magnetic
center (simulated )
Laser beam position on the cathode (simulated )
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-6
-4
-2
0
2
4
6
-6 -4 -2 0 2 4 6
xBPM1 / mm
y BPM
1 / m
m
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0
0.2
0.4
0.6
0.8
1
1.2
1.4
-0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8x / mm
y / m
m
BPM1 Readings vs RF-Phase(with both solenoids off)
BPM center
70deg
10deg
RF mode offset is to be taken into account
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E-Field
H-Field
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π-mode Offset Study :Magnetic Field Isolines
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π-mode Offset Study: Hx on the cavity axis
-250
-200
-150
-100
-50
0
50
0 50 100 150 200 250
z / mm
a.u.
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0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
-0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8x / mm
y / m
m
BPM1 Reading vs RF-Phase
MeasuredSimulated using
mode offset
Laser Position on the
cathode
BPM center
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0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
-0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8x / mm
y / m
m
BPM1: Final Measurements&Simulations
0.5x0.4mm
AngleXSol1 0.0109052 degAngleXSol2 0.0923767 degAngleYSol1 0.0209942 degAngleYSol2 0.151047 degLaser_Beam_CenterX 0.244745 mmLaser_Beam_CenterY 0.330667 mmXSol1Center -0.202089 mmXSol2Center -0.172699 mmYSol1Center 0.172081 mmYSol2Center 0.392517 mmY_nonsym 0.81112 mm
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-4
-2
0
2
4
6
8
-6 -4 -2 0 2 4 6x / mm
y / m
m
TTF RF-Gun Alignment: Before and After
Secondary solenoid magnetic
center before BBA (simulated )
Primary solenoid magnetic
center before BBA (simulated )
Laser beam position on the cathode before BBA (simulated )
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A Code for Longitudinal Wake Field Calculation
Geometry editor
Boundary shape
The implicit scheme [A.Novokhatski]:
• does not havedispersionin longitudinal direction.
• allows calculation for very long structures
• travelling mesh
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A Code for Longitudinal Wake Field Calculation
Flux Bunch
∫=Φr
z rdErtzr0
ˆˆ),,(
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A Code for Longitudinal Wake Field Calculation
Longitudinal wake potential
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A Code for Longitudinal Wake Field Calculation
O(h)
Staircase boundary approximation
Perfect boundary approximation
O(h2)
The new implicit scheme with perfect boundary approximation is developed.
It will allow calculation of longitudinal wake potential for long smooth structures.
The staircase boundary approximation is realized in the code.
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Investigation of Surface Roughness Wake Fields
• Further studies on the rough tube model according to A.Novokhatski and M. Timm.
♦ considered forms of 2D surface corrugations
♦ these corrugations are replaced by a single homogeneous layer of some equivalent dielectric constant
♦ So far always εr = 2 was assumed, whilst the theoretical justification for this assumption was missing.
periodic
non-periodic
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• anisotropic averaging of the material distribution in the corrugation layer
• new result for the wave number of the rough tube mode in contrast to the wave number of the thin dielectric layer mode
• this wavenumber is consistent with a mode matching calculation done by K. Bane and G. Stupakov
• further details see:• S.Ratschow, T. Weiland, M.Timm: On the mechanism of surface roughness wake
field excitation. presented at PAC2001, Chicago, TOAA010.
x
y
z
sh
1d2d
1
211 d
ddz
+≅ εε
21
22, dd
diyx +
≅ω
κε
2 1 20,
1
2 2zRTM
d dkR R dεδ δ
+= = 2
0,2
1r
TDLMr
kR
εδ ε
=−