High gradients in TESLA nine-cell cavities

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High gradients in TESLA nine-cell cavities

• Lutz Lilje
• DESY -MPY-
• Lutz.Lilje_at_desy.de

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Overview

• Standard etching
• Result of the CHECHIA test of an electropolished
  cavity
• Piezo compensation

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High Gradient Performance
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(No Transcript)
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Nine-cell Cavities for TESLA-800
TESLA 800 goal
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First High Power Test of an Electropolished
nine-cell cavity
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High Power Test of an EP nine-cell cavity
HERA plant
Calib. Measurement

• 5 Hz, 500 us fill, 800us flat-top
• Feed-forward only
• No piezo compensation at the moment
• 33-35 MV/m with no interruption related to
  cavity-coupler-klystron since more than 100 hours
• 2 cryo problems at 95 and 130 hours resulting
  from connection to the HERA plant
• (scheduled calibration measurement at 65 hours
  shown in the plot)
• Very low activity in the high power coupler,
  temperature levels o.k. for 5 Hz
• No field emission observable

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High Power Test of an EP nine-cell cavity
HERA plant
Calib. Measurement

• 5 Hz, 500 us fill, 800us flat-top
• Feed-forward only
• No piezo compensation at the moment
• 33-35 MV/m with no interruption related to
  cavity-coupler-klystron since more than 130 hours
• 2 cryo problems at 95 and 130 hours resulting
  from connection to the HERA plant
• Cryo shutdown right now due to problem of
  impurities in He circuit (from HERA plant)
• (scheduled calibration measurement at 65 hours
  shown in the plot)
• Very low activity in the high power coupler,
  temperature levels o.k. for 5 Hz
• No field emission observable

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High Power Test of an EP nine-cell cavity
HERA plant
Calib. Measurement

• 5 Hz, 500 us fill, 800us flat-top
• Feed-forward only
• No piezo compensation at the moment
• 33-35 MV/m with no interruption related to
  cavity-coupler-klystron since more than 130 hours
• 2 cryo problems at 95 and 130 hours resulting
  from connection to the HERA plant
• (scheduled calibration measurement at 65 hours
  shown in the plot)
• Very low activity in the high power coupler,
  temperature levels o.k. for 5 Hz
• No field emission observable

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Piezoelectric tunerM. Liepe, S. Simrock,
W.D.-Moeller
Tuning mechanism
Piezo
Piezo-Actuator l39mm Umax150V ? l3?m at
2K ?fmax,static500Hz
He-Tank Cavity
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New Piezo-assisted Tuner setup

• Sensor-Actuator configuration
• To compensate for Lorentz force detuning during
  the 1 ms RF pulse
• Feed-Forward
• To counteract mechanical noise, microphonics
  
• Feed-Back

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Frequency detuning during RF pulse
Beam on
Frequency detuning due Lorentz forces of the
electromagnetic field in the cavities ?f K
Eacc2 where K 1 Hz / (MV/m)2 Remember Cavity
bandwidth with main coupler is 300 Hz
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Frequency stabilization during RF pulse using a
piezoelectric tuner
Blue With piezo Red Without piezo Frequency
detuning of 200 - 250 Hz compensated with
rectangular voltage pulse (120 V) on the piezo.
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Frequency stabilization at 35 MV/m
Blue With piezo Red Without piezo Frequency
detuning of 1000 Hz compensated with resonant
excitation of a mechanical cavity resonance at
230 Hz. NOTE This is rather an demonstration of
the capability of active tuning. Application in a
real machine is probably difficult/impossible.