ZS review: impedance . B. Salvant Many thanks to B. Bahlan , J. Borburgh, K. Cornelis. Agenda. Previous RF measurements Attempts to simulate the complex ZS geometry Replacing the wires with a solid on a simplified model Studying the full geometry Frequency domain simulations
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ZS review: impedance
Many thanks to B. Bahlan, J. Borburgh, K. Cornelis
1 TCE + 1 TCSP
Other elements to consider?
With wire (spacing
between wires =20 mm, larger than in reality)
Wire replaced by a solid (much easier for the code)
Im(Zlong/n) ~14 mOhm
It seems we can model the wires as solids for the longitudinal impedance.
Wakefields were not damped, hence the
Im(Zy_eff)=40(/5mm)=8 kOhm/m for this simplified model
Different amplitudes for both models can be due to different wake lengths
Im(Zx_eff)= 12 Ohm (/5mm)= 2.4 kOhm/m for this simplified model
As a conclusion from these studies, the ZS wires do not seem to be contributing significantly to the ZS impedance (at frequencies < 1GHz).
Simplified geometry generated from the drawing
Full geometry imported from CATIA
Quite different behaviour, in particular above 500 MHz!
These harmonics of ~40 MHz should be linked to the length of the ZS (3.2 m)
The smaller frequency for the full structure could be due to the presence of the dielectric rods.
Similar effective longitudinal impedance at low frequency is therefore predicted for the full and for the simplified geometry
Very different behaviour.
Full structure: Im(Zeff_y)~40 KOhm/m
Simplified structure: Im(Zeff_y)~10 KOhm/m
Effective impedances at low frequency
Im(Zlong/n)~ 7 mOhm
Im(Zx)~ 2 kOhm/m
Im(Zy)~ 8 kOhm/m
Rs=1.1 MOhm (stainless steel)
Q=14000 (stainless steel)
(6 ZS (6*40 mOhm/m) +7 transitions (7*8 kOhm/m)~300 kOhm/m, i.e. ~1.5% of the SPS transverse effective imaginary impedance).
More studies are needed, and the new powerful PCs are helping greatly.