1. High gradients in TESLA nine-cell cavities
Lutz Lilje
DESY -MPY-

2. Overview Standard etching
Result of the CHECHIA test of an electropolished cavity
Piezo compensation
Lutz Lilje DESY

3. High Gradient Performance
Cavity AC 67 has a cold leak which was not located so far
The Q vs. E curve‘s behaviour is due to Helium inside the cavity
16 cavities with standard treatment
Lutz Lilje DESY

4. Lutz Lilje DESY

5. Nine-cell Cavities for TESLA-800
TESLA 800 goal
Lutz Lilje DESY

6. First High Power Test of an Electropolished nine-cell cavity
Lutz Lilje DESY

7. High Power Test of an EP nine-cell cavity
Calib. Measurement
HERA plant
High Power Test of an EP nine-cell cavity
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
Lutz Lilje DESY

8. High Power Test of an EP nine-cell cavity
Calib. Measurement
HERA plant
High Power Test of an EP nine-cell cavity
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
Lutz Lilje DESY

9. High Power Test of an EP nine-cell cavity
Calib. Measurement
HERA plant
High Power Test of an EP nine-cell cavity
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
Lutz Lilje DESY

10. Piezoelectric tuner M. Liepe, S. Simrock, W.D.-Moeller
Tuning mechanism
Piezo
Piezo-Actuator:
l=39mm
Umax=150V
 l=3m at 2K
fmax,static=500Hz
He-Tank
& Cavity
Lutz Lilje DESY

11. 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
Lutz Lilje DESY

12. Frequency detuning during RF pulse
Beam on
Frequency detuning due Lorentz forces of the electromagnetic field in the cavities:
Δf = K • Eacc2
where K ≈ 1 Hz / (MV/m)2
Remember: Cavity bandwidth with main coupler is ≈ 300 Hz
Lutz Lilje DESY

13. Frequency stabilization during RF pulse using a piezoelectric tuner
Blue: With piezo
Red: Without piezo
Frequency detuning of Hz compensated with rectangular voltage pulse (~120 V) on the piezo.
Lutz Lilje DESY

14. 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.
Lutz Lilje DESY