TUNER SYSTEM SIMULATION AND TESTS FOR THE 201-MHZ MICE CAVITY L. Somaschini, INFN-Pisa, Pisa, Italy J. H. Gaynier, R. J. Pasquinelli, D. W. Peterson, R. Schultz, Fermilab, Batavia, IL, USA Y. Torun, IIT, Chicago, USA A. J. DeMello, A. R. Lambert, S. Virostek, LBNL, Berkeley, CA, USA Abstract The frequency of MICE cavities is controlled by pneumatic tuners as their operation is impervious due to large magnetic fields. The mechanical and RF transfer functions of the tuner were simulated in ANSYS. The first of these tuning systems was assembled and tested at Fermilab. The mechanical response and the RF tuning transfer function have been measured and compared with simulation results. Finally the failure of different actuators has been simulated and tested to predict the operational limits of the tuner. MICE CAVITY AND TUNER Each acceleration module (RFCC) of the MICE experiment [1] is composed of four normal-conducting cavities made of copper with a nominal resonant frequency of 201.25 MHz (fig. 1) [2]. The four cavities will be mounted into a vacuum vessel in order to have the same pressure on both sides and avoid deformation of the cavity when pulling vacuum. The cavities will have to work in a high magnetic field that can reach 3T on some points of the cavities surface [3]: a tuning system able to work in such an environment had to be designed. Each cavity will be equipped with a pneumatic system of 6 tuners composed of an actuator and a fork. Each fork, made of stainless steel, will be inside the vacuum vessel and it will stretch and squeeze the cavity when operated by the respective actuator. The actuators will be located outside of the vacuum vessel and will share vacuum with the vessel by means of bellows. All 6 actuators will be connected in parallel and will be controlled by two electronic valves, one responsible for pushing the actuator shaft and the other one for pulling the shaft. The main aim of the tuner will be to compensate for thermal drift of the cavity and for structural differences between the 4 of them, keeping all the cavities at the same resonant frequency. A test module with only one cavity has been built and is about to be tested in the MuCool Test Area (MTA) at FNAL [4]. TUNER CONTROLS Pneumatic System A control system for the MICE cavity tuner was developed in order to operate the tuner both during test and regular operation in the MTA. Compressed air is provided by a compressor and is filtered to remove any moisture. A relief valve prevents over-pressurization of pneumatic system providing a relief at 120PSI. The incoming air is routed to two proportional valves manufactured by ProportionAir, respectively responsible for the pressurization of the squeeze and stretch circuit of the tuning system. Proportional valves are solenoidal valves with a built in feedback loop. Once they are set to reach a target output pressures, they regulate the airflow to keep the output pressure constant, independently on the input. Three additional electronic pressure gauges by Omega with 4-20 mA current output provide a control over input pressure, stretch and squeeze pressures. All this pneumatic instrumentation is mounted on an aluminum panel and every connection is realized with copper plumbing. Two air lines connect the control panel, placed away from the cavity, to the vacuum vessel. Here a system of manual valves and manifold distributes the air supply to each of the six actuators, allowing for an independent exclusion of each actuator. Every connection on this manifold panel is realized with copper while radiation compatible sealant is used. Manual valves are all made in stainless steel to be radiation compatible and survive operations in the MTA. Electronic System The test system is equipped with dedicated control electronics. The measured variables are pressure, resonant frequency of the cavity and movement of actuator shafts. The interface with the user is developed in LabView. Here we have the possibility to set different target pressures, to read digital pressure gauges, to monitor the frequency read by a Network Analyzer and to monitor the movement of each actuator shaft. The PC is directly connected to the NWA and to an ADC by NI to acquire the reading of 6 linear potentiometers used to monitor the movement of each actuator shaft. At the same time the Figure 1: The MTA cavity module and the tuning system. 5th International Particle Accelerator Conference IPAC2014, Dresden, Germany JACoW Publishing ISBN: 978-3-95450-132-8 doi:10.18429/JACoW-IPAC2014-THPRI070 07 Accelerator Technology Main Systems T06 Room Temperature RF THPRI070 3927 Content from this work may be used under the terms of the CC BY 3.0 licence (© 2014). Any distribution of this work must maintain attribution to the author(s), title of the work, publisher, and DOI.