1 3ghz large aperture bpm s
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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 3ghz large aperture bpm s

1.3GHz Large-aperture bpm’s

Jim Crisp Fermilab


Design information

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


1 3ghz large aperture bpm s

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


Fermilab main injector bpm

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


Linearity error

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


Bpm receiver

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)


Digital receiver

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)


Recycler digital receivers

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


Single bunch position

Single bunch position

  • A single bunch could be used to excite a filter as shown

    • 210MHz adc sample frequency

    • 105MHz center frequency

    • 10MHz bandwidth


Single bunch noise

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


  • Summary

    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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