Sub nano-Ohm resolution surface resistance measurements in a cryo-free environment
State of the art superconducting cavities made of niobium are reaching fundamental limitations in terms of maximum accelerating gradient and power dissipation. New materials such as Nb3Sn can potentially allow for muli-million-pound savings for large scale projects due to lower power dissipation and enable new applications of SRF technology in research and industry such as security and waste water treatment.
AsTeC/STFC is developing an infrastructure to produce and test samples of such materials. It has the potential to be world leading if high sample throughput can be achieved. Previous experience at several laboratories world-wide has shown that RF testing of superconducting samples is a task with challenging and often opposing requirements . Sample test cavities are available at several laboratories world-wide; none has become the workhorse for systematic sample studies yet . In order to assess the applicability to particle accelerators sub nano-Ohm resolution measurements are key. Up till now this has only been proven to be successful using an instrument named the Quadrupole Resonator . However, this device requires a complicated sample shape and operation in a liquid helium bath cryostat. Turn-around times for sample tests are therefore limited below the requirements for systematic studies. In order to overcome this limitation AsTeC in collaboration with Lancaster University has designed a Choked Resonator to be operated in cryo-free environment .
The student´s first task is to commission the test cavity and develop a measurement system (calorimeter) which will allow for sub nano-Ohm resolution surface resistance measurements. This includes a detailed study of the limits of surface resistance resolution and identifying and implementing methods for improvement. This will require to become familiar with cryogenic, radiofrequency and superconductivity techniques alike. The aim is to establish a test program which allows quick turnaround of samples to provide efficient feedback to colleagues working on thin film deposition. The student will learn the basics of this field to allow for efficient communication and decision making in a team effort. AsTeC/STFC is investigating several new materials and deposition techniques for superconducting cavities. Currently the most promising one is High-power Impulse Magnetron Sputtering (HIPIMS) of Nb3Sn on copper substrates, which will be the focus of the investigations.
 Goudket, Philippe, T. Junginger, and B. P. Xiao. "Devices for SRF material characterization." Superconductor Science and Technology 30.1 (2016): 013001.
 Junginger, Tobias, Wolfgang Weingarten, and Carsten Welsch. "Extension of the measurement capabilities of the quadrupole resonator." Review of Scientific Instruments 83.6 (2012): 063902.
 P. Goudket, L. Bizel-Bizellot, L. Gurran, O.B. Malyshev, S.M. Pattalwar, R. Valizadeh, G. Burt, L. Gurran, T. Junginger, L. Gurran. "Superconducting Thin Film RF Measurements" Proceedings of IPAC18 Pre-press
The project is fully funded by the Science and Technology Facilities Council for 3.5 years. A full package of training and support will be provided and the student will take part in a vibrant accelerator research and education community of over 150 people. The project is fully funded by the STFC for years; the UK and other EU citizens are eligible to apply. The student will receive a standard stipend of around £14.5k/yr.
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