High gradients in TESLA nine-cell cavities Lutz Lilje DESY -MPY- Lutz.Lilje@desy.de
Overview Standard etching Result of the CHECHIA test of an electropolished cavity Piezo compensation Lutz Lilje DESY 07.12.2018
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 07.12.2018
Lutz Lilje DESY 07.12.2018
Nine-cell Cavities for TESLA-800 TESLA 800 goal Lutz Lilje DESY 07.12.2018
First High Power Test of an Electropolished nine-cell cavity Lutz Lilje DESY 07.12.2018
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 07.12.2018
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 07.12.2018
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 07.12.2018
Piezoelectric tuner M. Liepe, S. Simrock, W.D.-Moeller Tuning mechanism Piezo Piezo-Actuator: l=39mm Umax=150V l=3m at 2K fmax,static=500Hz He-Tank & Cavity Lutz Lilje DESY 07.12.2018
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 07.12.2018
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 07.12.2018
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. Lutz Lilje DESY 07.12.2018
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 07.12.2018