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Position Cavity Waveguide Geometry

  • To improve simulation time, the coaxials were ignored and the waveguide end cut short with ports added at the end of the waveguide. Perfect Electrical Conductor (PEC) was used as the background material to further speed up the simulation

coax.PNG wg.PNG

  • The loaded Q was recorded while changing the geometry of the design. This included the offset of the waveguides from the beampipe, the width of the waveguides and the length of the resonating cavity. The geometry was simulated in Copper.

length.png wgodd.png

  • The only factor that significantly affects the Q above is the waveguide width. Reducing the waveguide width will reduce the Q.
  • However the results above show that a copper cavity rather than stainless steel yields an acceptable Q value. The measured loaded of Q of 517 corresponds to 1.0% signal level at 50 ns. The measured loaded Q for stainless steel was 268.

ACE3P Simulation

  • Attempts at measuring the loaded Q of the full geometry (cavity, waveguides and coaxial) in CST were unsatisfactory. However ACE3P was later used succesfully, yielding a Q factor of 579 at a resonant dipole frequency of 14.988 GHz
  • This corresponds to a time decay of 6.1 ns, after 50 ns the signal will decay to 1.7%.
  • The external Q is 702 and the loaded Q with stainless steel is 292.

Cavity Simulation With New Feedthrough Design

  • ACE3P was also used to simulate the BPM with the beaded antenna designed here: ClicFTSim. The geometry is shown below.


  • A loaded Q factor of 670 was found at a resonant frequency of 14.991 GHz. This corresponds to a signal level of 3.0% after 50 ns.
  • The external Q was found to be 702.

-- JackTowler - 30 Apr 2013

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Topic revision: r18 - 29 Jan 2014 - JackTowler

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