Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
The temperature-dependent part of the microwave surface resistance of superconducting radio-frequency (SRF) cavities has been shown experimentally to depend on the strength of the applied magnetic surface field. Several theories have recently been proposed to describe this phenomenon. In this paper we present work on the development of a microwave cavity setup for measuring the field-dependence with an applied DC magnetic field.
TRIUMF, Canada's National Laboratory for Particle and Nuclear Physics, Vancouver, Canada
TU Dresden, Dresden, Germany
CERN, Geneva, Switzerland
KIT, Karlsruhe, Germany
Michigan State University, East Lansing, Michigan, USA
FRIB, East Lansing, Michigan, USA
An understanding of the relationship between mechanical and functional properties, and processing history is essential in order to manufacture polycrystalline niobium cavities with consistent performance. The crystallographic texture (preferred crystal orientation) and microstructure in polycrystalline sheet varies considerably, so identifying its influence on properties is needed to achieve a better understanding of how to control properties of high purity niobium. Samples extracted from many lots produced by Tokyo Denkai and Ningxia sheet were examined. Through-thickness texture of the undeformed niobium samples was measured using electron backscattered pattern mapping. Texture is identified with pole figures, orientation distribution function, and grain misorientation relationships. Stress-strain tests were done to identify ultimate tensile stress, elongation, 0.2% yield strength, and hardening rate. From tests on many lots, there is no clear trend between the mechanical and material properties in high purity niobium and correlations between various microstructural and mechanical properties show significant scatter and few apparent correlations.
MSU, East Lansing, Michigan, USA
Michigan State University, East Lansing, Michigan, USA
FRIB, East Lansing, Michigan, USA
Deformation behavior of niobium (Nb) is not thoroughly studied, although it is widely used in manufacturing superconducting cavities. This deficiency of knowledge limits the predictibality in raw material properties for fine grain sheets, which are less anisotropic and easier to deform uniformly than large grain sheets. Studies on modeling and simulation of deformation of Nb are also limited. Therefore design of a new manufacturing procedure becomes a costly process, because models predicting the deformation of Nb are not accurate. A polycrystal is an aggregate of single crystals. Tensile tests were performed on single crystal with different orientations, to study the deformation behavior of Nb. A number of crystal plasticity models were developed, calibrated and finally used to predict the deformation of single crystal tensile samples. This study compares the predictions of these models. This provides a foundation for physically realistic polycrystal deformation models.
ORNL, Oak Ridge, Tennessee, USA
ORNL RAD, Oak Ridge, Tennessee, USA
The Spallation Neutron Source (SNS) has developed a vertical test area (VTA) for the testing and qualification of superconducting radio frequency cavities. The associated RF System successfully supported the initial commissioning of the VTA system and has been utilized for cavity testing at both 4 and 2 K. As operational experience was gained, improvements to the RF system were implemented to better utilize the dynamic range of the system, and software updates and additions were made to meet the operational needs. The system continues to evolve as we gain better understanding of the testing needs.
JLab, Newport News, Virginia, USA
RF systems for testing critically coupled SRF cavities require the ability to track the cavity frequency excursions while making accurate measurements of the radio frequency (RF) signals associated with the cavity. Two types of systems are being used at Jefferson Lab. The first, the traditional approach, is to use a voltage controlled oscillator configured as a phase locked loop such that it will track the cavity frequency. The more recently developed approach is to use a digital low level RF (LLRF) system in self excited loop (SEL) mode to track the cavity frequency. Using a digital LLRF system in SEL mode has the advantage that it is much easier to lock to the cavity’s resonant frequencies and they tend to have a wider capture range. This paper will report on the system designs used to implement the 12 GeV digital LLRF system in the JLAB vertical test area. Additionally, it will report on the system modifications which are being implemented so that the RF infrastructure in the VTA will be ready to support the LCLS II cryomodule production effort, which is scheduled to begin in calendar year 2016.