TTC/ARIES topical workshop on flux trapping and magnetic shielding

Session

Sensitivity to trapped flux

9 Nov 2018, 09:00

31/3-004 - IT Amphitheatre (CERN)

Conveners

Sensitivity to trapped flux: Part 1

• Akira Miyazaki (University of Manchester (GB))
• Mattia Checchin (FNAL)

Sensitivity to trapped flux: Part 2

• Akira Miyazaki (University of Manchester (GB))
• Mattia Checchin (FNAL)

34. Introduction to the session

Akira Miyazaki (University of Manchester (GB))

09/11/2018, 09:00

35. Trapped flux sensitivity studies as a function of: treatment, RF field and frequency

Martina Martinello (Fermilab - IIT)

09/11/2018, 09:03

The trapped flux surface resistance dependence on surface treatment, RF field and resonance frequency has been intensively studied at FNAL. The findings of this study are here presented, with a particular focus on the level of sensitivity at high fields given by the state-of-the-art high-gradient treatments such as 120C baking, N-infusion and modified 75-120C baking . Analyzing these results...

36. Overview of flux trapping at Cornell

James Maniscalco (Cornell University)

09/11/2018, 09:20

We report an overview of Cornell's measurements of residual resistance due to trapped flux in Nb3Sn and impurity-doped niobium in single-cell 1.3 GHz and 2.6 GHz TESLA-shape cavities

37. Sensitivity to trapped flux in high-purity large-grain niobium based on cavity measurements

Rongli Geng (Jefferson Lab)

09/11/2018, 09:37

Surface resistance arising from trapped flux is experimentally measured, by which the sensitivity to trapped flux is derived. Measurements are carried out with single-cell L-band SRF cavities made of high-purity large-grain niobium materials, immersed in a uniform externally applied magnetic field generated by a solenoid whose axis overlaps the cavity axis. The surface resistance is found by...

38. Flux trapping investigation in superconducting samples via the quadrupole resonator

Marco Arzeo (CERN)

09/11/2018, 09:54

Magnetic flux trapping has been demonstrated to be very detrimental for the performances of superconducting radio frequency (SRF) cavities for accelerators. How exactly the flux, trapped in pinning centers in the form of vortices, results in dissipation of the RF power is an interesting open question. Theoretical models have been proposed to explain the experimental observations. A possible...

39. Reports on sensitivity measurements at KEK

Kensei Umemori (KEK)

09/11/2018, 10:11

"Sensitivity measurements have been performed for several
kinds of surface treatment in SRF cavities. Experimental setup
and results will be shown"

40. Optimization of High Temperature N2 Doping for Minimization of Sensitivity to Trapped Flux and Maximization of Quench Fields

Daniel Bafia (Fermi National Accelerator Laboratory)

09/11/2018, 10:18

We will describe Fermilab experiments that focus on the optimization of doping parameters to achieve low sensitivity to magnetic flux while maintaining very high Q characteristic of nitrogen doped cavities and same or higher quench fields. One of the directions pursued is using lighter doping recipes which have been shown in the past to increase the mean free path of the resonator and decrease...

41. Dissipation caused by oscillating vortices in the SRF cavities

Alexander Gurevich (Old Dominion University)

09/11/2018, 11:00

In this talk I discuss the RF dissipation of trapped vortices which contribute to the residual surface resistance in SRF cavities. In particular, the power caused by oscillations of flexible pinned vortex segments driven by a weak RF field, and the dependencies of the RF power on frequency, spatial distribution of pinning centers and purity of the material are considered. A brief overview of...

42. Trapped flux sensitivity in the low amplitude radio-frequency regime

Dr Mattia Checchin (FNAL)

09/11/2018, 11:25

In this study, the radio-frequency complex response of trapped vortices in superconductors calculated for small values of applied radio-frequency field, will be presented. In agreement with experimental data on bulk niobium radio-frequency cavities, the calculated surface resistance shows a non-monotonic trend as a function of the mean-free-path and a sigmoidal-like trend as a function of the...

43. A simple model for the RF field dependence of the trapped flux sensitivity based on a non-linear pinning force

Ruggero Vaglio (1950)

09/11/2018, 11:42

The improvement of the performance of RF superconducting cavities has recently motivated a considerable research effort to elucidate the effect of trapped magnetic flux on the surface resistance . In this paper we show that by introducing a non-linear pinning force in the Gittleman-Rosenblum equations for the RF power dissipation due to a trapped magnetic flux in a superconductor, we can...

44. Vortex dynamics and hysteretic flux losses due to pinning

Danilo Liarte (Cornell University)

09/11/2018, 11:59

In this talk, I will explain the hysteretic mechanisms that are responsible for field-dependent residual losses of SRF cavities due to the motion of isolated trapped vortex lines under the action of parallel oscillating fields at the surface. By invoking collective weak pinning theory in the context of the Bardeen-Stephen model of vortex dynamics, I will present simple estimates, approximate...

45. Discussion

09/11/2018, 12:16