RHUL Physics Department TWiki> PP/JAI Web>RFLab>BeamPosition>ClicBpm>Ctf3Sensitivity (11 Feb 2014, FrankieCullinan)

The dipole mode sensitivity was estimated from the following formula, the measured external quality factor of 617 and R/Q from simulation in several codes, of which CST and GdfidL use a hexahedral mesh while Ace3p uses a tetrahedral mesh:

Code | R/Q /Ω | Sensitivity/V nC^{-1} mm^{-1} |
---|---|---|

GdfidL | 0.85 | 8.7 |

Ace3p | 0.77 | 8.3 |

CST | 0.77 | 8.3 |

The measured external quality factor of the reference cavity is 203.

Code | R/Q /Ω | Sensitivity/V nC^{-1} |
---|---|---|

GdfidL | 28.2 | 87 |

Ace3p | 9.8 | 52 |

CST | 10 | 52 |

Electronics gain/dB | 5 |
---|---|

Cable loss/dB | -2.6 |

Position cavity attenuation/dB | 6 |

Reference cavity attenuation/dB | 20 |

Position signal (offset=1mm, charge=1nC) | Reference signal (Charge=1nC) | |||
---|---|---|---|---|

Location | Volts | dBm | Volts | dBm |

Cavity out | 8.3 | 31.4 | 52.0 | 47.3 |

Electronics in | 4.2 | 25.4 | 5.2 | 27.3 |

Electronics out | 7.4 | 30.4 | 9.2 | 32.3 |

Digitiser in | 5.5 | 27.8 | 6.9 | 29.7 |

- Position scale factor: 1.25 mm

The mode R/Qs were now calculated by integrating over the full geometry instead of just the cavity length:. The results for the position cavity are:

Code | R/Q /Ω | Sensitivity/V nC^{-1} mm^{-1} |
---|---|---|

GdfidL | 3.26 | 17.08 |

Ace3p | 3.27 | 17.11 |

CST | 4.55 | 20.2 |

The results for the reference cavity are:

Code | R/Q /Ω | Sensitivity/V nC^{-1} |
---|---|---|

GdfidL | 50.3 | 117 |

Ace3p | 50.7 | 118 |

Position signal (offset=1mm, charge=1nC) | Reference signal (Charge=1nC) | |||
---|---|---|---|---|

Location | Volts | dBm | Volts | dBm |

Cavity out | 14.7 | 36.4 | 118 | 54.4 |

Electronics in | 3.37 | 23.6 | 5.39 | 27.6 |

Electronics out | 5.99 | 9.60 | 9.2 | 32.6 |

Digitiser in | 4.44 | 26.0 | 7.11 | 30.0 |

- Position scale factor: 0.62 mm

Because the signal decays with a finite decay time, the assumption that the root mean square voltage over one period is the peak voltage divided by is no longer valid. The corresponding value can be found by

where f is the signal frequency, τ is the decay time and T is the time of one period in time t and is equal to 1/f. Evaluating the definite integral gives This is one case where the signal is given by a sine function. In the opposing case, where a cosine function is used instead, the expression evaluates to The median of these two cases is Another effect is the signal decaying before the first peak in the oscillation is seen. The peak time in the case of a

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Topic revision: r16 - 11 Feb 2014 - FrankieCullinan

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