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GOETHE
UNIVERSITÄT FRANKFURT AM MAIN
*Work supported by HIM, GSI, BMBF Contr. No. 05P12RFRBL
Institute for Applied Physics
Max-von-Laue-Straße 1
D-60438, Frankfurt am Main, Germany
The Piezo-Based Frequency Tuner for sc CH-Cavities
Figure 1: Piezo-based frequency tuner mounted on top of the helium vessel of the sc 325 MHz CH-Cavity (left) and complete frequency tuning system including the 3-cell dynamic bellow plunger (right)
• Piezo actuator ‚in series‘ with slow tuner arm
• Required stroke of at least 6 µm
Requirements • Max. stroke of slow tuner 1 mm • Required force of 600 N • Tuner arm (pivot with mechanical
advantage of ≈ 2:1) • Harmonic drive gear reduction 50:1
Dynamic bellow plunger
Slow tuner arm
Slow tuner (stepper motor)
Fast tuner (piezo actuator)
The Fast Piezo-Based Frequency Tuner for sc CH-Cavities*
M. Amberg#1,2, M. Busch2, F. Dziuba2, H. Podlech2, U. Ratzinger2, S. Mickat1,3, K. Aulenbacher1,4, W. Barth1,3 1Helmholtz-Institut Mainz (HIM), 55099 Mainz, Germany
2IAP Frankfurt University, 60438 Frankfurt am Main, Germany 3GSI Helmholtzzentrum, 64291 Darmstadt, Germany
4KPH Mainz University, 55128 Mainz, Germany
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Abstract Superconducting structures are very susceptible to external influences due to their thin walls and their narrow bandwidth. Even small mechanical deformations caused by dynamic effects like microphonic noise, pressure fluctuations of the liquid helium bath or Lorentz-Force-Detuning can lead to resonance frequency changes of the cavity which are much larger than the bandwidth. To compensate the slow and fast resonance frequency variations during operation a compact frequency tuner prototype equipped with a stepper motor and a piezo actuator has been developed at the Institute for Applied Physics (IAP) of Frankfurt University. In this contribution the tuner design and the results of first room temperature measurements of the tuner prototype are presented.
Michael Amberg – Max-von-Laue Str. 1 – 60438 Frankfurt am Main – [email protected] – www.linac-world.de
First Room Temperature Measurements
Probe indicator
1-cell bellow tuner
Piezo actuator P-843.20
(Physik Instrumente)
Stepper motor and harmonic drive
(Phytron VSS UHVC 52)
Screw nut (with WS2 LAMCOAT®coating)
CuBe spindle (with WS2 LAMCOAT®coating)
AISI 316L
SKF ball bearings (with WS2 LAMCOAT® coating)
Figure 3: Main components of the frequency tuner drive system
Components of the Frequency Tuner Drive
• A frequency tuner prototype has been built to validate the drive concept
• The stroke of a 1-cell bellow tuner prototype made of niobium has been measured
Figure 2: Measured frequency tuning range of the two dynamic bellow tuners of the sc 325 MHz CH-Cavity
Dynamic Bellow Tuner
• Dynamic capacitive bellow tuners are welded into the girders to act against fast frequency variations by changing their height
• First plunger type tuner in a sc cavity
Dynamic bellow #2 Dynamic bellow #1
• A part or the whole tuner is positioned at liquid nitrogen temperature and under vacuum
• Special materials and treatments are essential
Figure 4: First room temperature measurement results of a dynamic frequency tuner prototype made of stainless steel
Helium vessel
Slow tuner test
Fast tuner test
Laservibrometer (Polytec)
Mirror
1-cell bellow tuner
Test setup