Scattering Parameter Calculation for the 2x7 Superstructure

1
Scattering Parameter Calculationfor the 2x7
Superstructure

• TESLA Collaboration Meeting
• INFN Frascati May 26-28, 2003
• Karsten Rothemund, Dirk Hecht, Ulla van Rienen

2
2x7-Superstructure
Images I.Ibendorf
3
2x7-Superstructure
Images I.Ibendorf
4
Radius Adaptor
5
HOM-Input-Coupler
Geometry data taken from drawing Formteil F (3
99 9177/D.001),1
1 coutesy DESY
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HOM-Coupler (HOM 2 HOM 3)
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7 Cell TESLA Cavity
S../dB
Plot MWS, simulation MAFIA, 2D, time domain
S../dB
S../dB
f/GHz
f1.5-3.0 GHz
f/GHz
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Analytical Sections

• Rotation between HOM-Couplers
• Rotate reference frame of dipole and quadrupole
  modes
• length of section is 0
• Wave Guide (neg. and pos.)
• shift reference plane of cavity
• shift HOM 3 to correct position

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Subsections
Subsection Port-Modes of this
type HOM-Input-coupler 5 5 11 1 HOM
coupler 2 3 5 5 1 2 TESLA cavity 5
5 2 Plane shift cavity 5 5 4 Shift of
HOM 3 5 5 2 Rotation 5 5 4 Radius
adaptor 5 5 2 Total number of
subsections 17 Total number of modes
S-matrix dimension 174 (to be computed for each
frequency point)
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CSC-Computation
Calculation of overall S-matrix open ports beam
pipe, 3x HOM-, 1x Input-coupler 1500 values
computed in 1.5-3 GHz frequency range shown
here 2.46-2.58 GHz (3rd dipole passband) 481
frequency-points interpolation
S../dB
S-values of 7-cell cavity
f/GHz
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Results
Coupling between HOM1 and HOM2 to beam pipe modes
S../dB
upstream beam pipe
HOM2
S../dB
HOM1
f/GHz
downstream beam pipe
f/GHz
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Results
S../dB
S../dB
f/GHz
f/GHz
13
Timing S-Parameter

• CST-MicrowaveStudioTM (2.4 GHz Pentium 4, 4GB
  RAM)
• HOM-Input-Coupler
• 316,160 mesh points (20 lines/lambda),
• 5 beam pipe modes 2 koaxial modes
• Total computation time 100 h (12 runs)
• HOM-Coupler
• 178,920 mesh points (20 lines/lambda),
• 5 beampipe modes 1 koaxial mode
• Total computation time 24 h (11 runs)
• MAFIA (SUN Enterprise, 400 MHz, 4GB RAM)
• TESLA 7 cell cavity
• 2D-geometry (rz)
• 31,158 mesh points
• Total computation time 2h 6.5h 6.75h

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Timing CSC
CSC platform Mathematica 4.1 17 subsections 5
modes in structure dimension of matrix 174 481
frequency points, 2.46 2.58 GHz 430 s on
Pentium 3 (1 GHz, 512 MB RAM)
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Summary

• S-parameter of 2x7 TESLA-Superstructure have
  been
• calculated (an open structure) with CSC
• 5 modes have been considered in the structure
• S-parameter of subsections were computed with
• CST-MicrowaveStudioTM (coupler sections, 3D)
• MAFIA (TESLA cavity, 2D-rz-geometry)
• analytically (shifting planes, rotation)
• some exemplary coupling parameters have been
• presented
• computation times for S-parameters of
  subsections
• in order of days
• additional computation times whole structure
  then in
• the order of minutes
• parameter tuning (e.g. rotation angles,
  distances)
• possible