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Feedthrough Simulations

  • The results of the RF measurements showed that the external Q of the BPM was much higher than anticipated.
  • A study was done to reduce the Q factor and return the Q to its goal value of 500.

Position Cavity RF Measurement

  • Results from RF measurement

S Parameter Frequency /GHz Unloaded Q External Q Loaded Q Loaded Q check
S11 14.996 1154 2450 789 789
S22 14.995 1250 2999 869 882
S33 14.996 1200 2222 779 779
S44 14.995 1394 2221 857 857

  • Effect of removing seals, i.e. the antennae protrude 0.45 mm further into the waveguides.

Frequency /GHz Unloaded Q External Q Loaded Q Loaded Q check
14.999 444 714 280 274

  • The external Q has reduced to a value closer to the expected number.
  • However, the loaded Q is too small, caused by a low internal Q.

Position Cavity Simulation

  • The effect of the antenna length on the Q was studied in simulation.

Antenna separation change /um Frequency /GHz Loaded Q
-0.45 15.005 343
-0.30 15.011 348
-0.15 15.030 504
0.0 15.030 666
+0.30 15.036 1188
+0.45 15.031 1710

ant_sep.png

  • Removing the seals means the antenna separation changes by -0.45 mm, decreasing the overall Q.
  • Comparing the simulated and measured Q's, the measured value was 444 and the simulated was 343.
  • The separation change that gives a loaded Q of ~500 is about -0.15 mm.

Reference Cavity Simulation

  • The above simulations were performed for the reference cavity

Antenna separation change /um Frequency /GHz Loaded Q
-0.30 14.750 276
-0.15 14.742 401
0.0 14.753 575
+0.15 14.740 828
+0.30 14.744 1192

ant_sep_ref.png

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Topic revision: r4 - 31 Oct 2014 - JackTowler

 
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