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1.3GHz Large-aperture bpm’s

1.3GHz Large-aperture bpm’s. Jim Crisp Fermilab. Design Information. 1.3GHz bunch spacing /4 = 5.8cm 3 to 5 cm aperture Fit inside a quadrupole ~66nsec rotation period ~86 bunches/turn Turn by turn for 10 turns 1e10 electrons/bunch 2amps average / ~10amps peak. Bpm.

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1.3GHz Large-aperture bpm’s

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  1. 1.3GHz Large-aperture bpm’s Jim Crisp Fermilab

  2. Design Information • 1.3GHz bunch spacing • /4 = 5.8cm • 3 to 5 cm aperture • Fit inside a quadrupole • ~66nsec rotation period • ~86 bunches/turn • Turn by turn for 10 turns • 1e10 electrons/bunch • 2amps average / ~10amps peak

  3. Bpm • Suggest 4 plates • 5.8cm long • 1cm wide • ~1/15 of the beam current on each plate • Shorted at one end (not directional) • SMA feedthroughs • Roughly similar plate spacing as Fermi MI bpm’s

  4. Fermilab Main Injector bpm • Measured with wire using 5mm steps • Use simple linear fit along the axis in both directions • 45º rotation would change the shape but not necessarily the error

  5. Linearity error • Error would be ½ as much with 5cm bpm • Using simple linear fit in both directions • Could be reduced with a 2 dimensional fit

  6. Bpm Receiver • Suggest digital receiver • 12bit resolution 210MHz sample rate • 14 samples/turn • 20MHz bandpass filter • ~1 rotation harmonic • Mix 1.3GHz down to ~20MHz • (Requires good quality mixer)

  7. Digital Receiver • 12 bit converter has 64.5db sinad (10.75 bits) • sinad = signal to noise and distortion • noise ~2um distortion ~10um • (Noise improves with N) • 12bit 210MHz adc • 14 samples • 25mm radius bpm • Full scale plate signal • (Xnoise goes like 1/Vplate)

  8. Recycler digital receivers • 14 bit 80MHz adc’s, 120 samples, 63mm radius • each position measured 100 times • Mean is plotted on the left and the standard deviation is on the right

  9. Single bunch position • A single bunch could be used to excite a filter as shown • 210MHz adc sample frequency • 105MHz center frequency • 10MHz bandwidth

  10. Single bunch noise • The wavelet generated from a single bunch has an average voltage 25% of full scale • (Provided the bpm and filter produce a full scale signal for the adc) • The resulting noise and distortion would thus be 4 times larger • Noise ~8um distortion ~40um • About 1.6% of the signal remains after 1 turn • This would allow 1.6% of the previous position to contaminate the subsequent measurement • This could be eliminated by selecting a resonant filter center frequency that puts the previous signal in quadrature • The filters need to be stable and matched • The adc must be synchronized with the beam

  11. Summary • Bunch frequency suggests either buttons or short striplines • The ability to correct for linearity will determine bpm accuracy • Although the electrodes may fit inside a quadrupole, the coaxial feedthroughs likely won’t • Digital receivers are the only way to go • Single bunch measurements are possible with some compromise in noise and accuracy

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