WEYGBF1
FRIB, East Lansing, USA
WEYGBF2
Fermilab, Batavia, Illinois, USA
It is currently believed in the field of SRF that the limit of the achievable accelerating gradients is set by the DC superheating field value, which guides most of the theoretical and experimental studies in this direction. However, it was recently proposed* that another mechanism is currently enabling both the existing SRF cavities with the quench field in excess of niobium Hc1, and providing the path forward to higher gradients, namely the vortex nucleation time slower than the rf period. If true, differently from currently pursued higher DC Hsh materials (e.g. Nb3Sn, MgB2 etc) or multi-layered structures, the new proposed directions are doping of the top niobium surface with special types of inelastic electron-phonon scattering "slowing down" impurities, or coating with thin layers of LOW (and not high) Tc superconductors. Both experimental and theoretical progress at Fermilab in this new area will be presented.
*A. Romanenko, TTC Topical Workshop - RF Superconductivity: Pushing Cavity Performance Limits, Fermilab, Batavia, IL, 2017, https://indico.fnal.gov/event/15177/session/3/contribution/27
The College of William and Mary, Williamsburg, Virginia, USA
JLab, Newport News, Virginia, USA
Virginia Polytechnic Institute and State University, Blacksburg, USA
ODU, Norfolk, Virginia, USA
Following encouraging results with Nb3Sn-coated R&D cavities, the existing coating system was upgraded to allow for Nb3Sn coating of CEBAF accelerator cavities. The upgrade was designed to allow Nb3Sn coating of original CEBAF 5-cell cavities with the vapor diffusion technique. Several CEBAF cavities were coated in the upgraded system to investigate vapor diffusion coatings on extended structures. Witness samples coated along with the cavities were characterized with material science techniques, while coated cavities were measured at 4 and 2 K. The progress, lessons learned, and the pathforward are discussed.
RIKEN SPring-8 Center, Sayo-cho, Sayo-gun, Hyogo, Japan
Nihon Koshuha Co. Ltd, Yokohama, Japan
Japan Synchrotron Radiation Research Institute (JASRI), RIKEN SPring-8 Center, Hyogo, Japan
A next generation electron storage ring represented by a diffraction-limited light source pursues an extremely low emittance leading to a small dynamic aperture and short beam lifetime. The top-up injection is hence indispensable to keep the stored beam current. The beam orbit fluctuation caused by the injection magnets should seriously obstruct utilization of an electron beam with sharp transverse profile. In order to solve these problems, a novel off-axis in-vacuum beam injection system was proposed. In the system, twin kicker magnets driven by a single solid-state pulsed power supply to launch a linear pi- bump orbit is the key to suppress the horizontal orbit fluctuation down to a level of several microns. Here, a big challenge is to achieve the magnetic field identity of the two kickers within an accuracy of 0.1%. This presentation overviews the proposed injection system and reports the development status focusing on the solid-state pulse generator.