SRF2011 - List of Authors (Sergatskov, D.A.)

Paper

Title

Page

Optical Inspection of SRF Cavities at Fermilab

515

E. Toropov, D.A. Sergatskov
Fermilab, Batavia, USA

The production of an SRF cavity includes a string of multiple treatments at different facilities before the cavity can be RF-tested in a cryogenic system. Many of the processing steps change the cavity surface and affect the RF performance of the cavity. Interjection of optical inspections between these steps provides us with an instant feedback on the processes involved as well as giving us new insight on the mechanisms responsible for forming surface abnormalities. The major drawback of inclusion of frequent optical inspections is the increased amount of time and labor in the cavity production cycle. An optical inspection of equatorial and iris welds of a 1.3GHz TESLA-shape cavity produces about two thousand pictures. We developed an automated procedure where a computer takes over the most of the routine operations including adjusting the camera focus. With that automation, the inspection currently takes about three hours and little operator time. We will describe the developed system including the focusing algorithm and discuss the ways to further optimize the procedure.

Poster TUPO053 [0.736 MB]

TUPO054

SRF Cavity Surface Topography From Optical Inspection

519

E. Toropov, D.A. Sergatskov
Fermilab, Batavia, USA

Characteristics of the cavity surface geometry such as roughness affect cavity performance. The optical cavity inspection system at Fermilab allows us to obtain pictures of cavity surface at different lightning conditions. By analyzing the images of some fixed location inside the cavity taken while the light source moves progressively along the axis we can deduce some topographical information of that surface. In the large-grain cavities after BCP, grains are oriented at distinct angles to the surface and, therefore, reflect light in different directions. We developed a simple algorithm to calculate the angle distribution of the grains and thus to estimate the roughness. We discuss this method and the results of the analysis of the actual cavity surface.

Poster TUPO054 [0.643 MB]

THPO015

Repair SRFCavity by Re-Melting Surface Defects via High Power Laser Technique

740

G.M. Ge
CLASSE, Ithaca, New York, USA
E. Borissov, L.D. Cooley, D.T. Hicks, T.H. Nicol, J.P. Ozelis, J. Ruan, D.A. Sergatskov
Fermilab, Batavia, USA
G. Wu
ANL, Argonne, USA

As the field emission is gradually under control in recent SRF activities, cavity performance is limited by hard quench in the most case. Surface defect has been identified as one of main reasons caused cavity quench scattering cavity accelerating gradient from 12 MV/m to 40 MV/m. Laser processing is able to re-shape the steep flaws to be flat and smooth surface. In Fermilab, a sophisticated laser repair system has been built for 1.3GHz low performance SRF cavity which is limited by surface defect. The pit in a 1.3GHz single-cell cavity was re-melted by high power laser pulse, cavity took 30 μm light Electropolishing after that. The gradient achieved 39MV/m in initial run; after another 30 μm Electropolishing, it achieved 40 MV/m. The improved laser repair system is able to re-melt the surface defect in one meter long 9-cell SRF cavity. It successfully re-melted a pit in 9-cell SRF cavity TB9ACC017.

THPO023

External Magnetic Fields and Operating SRF Cavity

763

D.A. Sergatskov, T.N. Khabiboulline, R.L. Madrak, J.P. Ozelis, I. Terechkine
Fermilab, Batavia, USA

Funding: The work herein has been performed at Fermilab, which is operated by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the United States Department of Energy.
When an SRF cavity is undergoing a transition to the superconducting state in an external magnetic field it traps some of the flux which results in an increase of surface resistance. This effect was extensively studied, is well understood by now and results in stringent requirements for an ambient magnetic field on the surface of an SRF cavity. The situation is quite different when magnetic field is applied to a cavity already in the superconducting state. During normal operation the bulk of the superconducting Nb should protect the RF surface of the cavity from fields on the outside. So we expect that the requirements on an external magnetic field applied to an operating cavity could be significantly relaxed. One possible failure mode is when the cavity quenches while the external field is applied. The magnetic field would penetrate through a normal zone formed during the quench and can get trapped during the subsequent post-quench cooling. We studied the effects of an external magnetic field applied to an operating SRF cavity and report the results.

Poster THPO023 [1.370 MB]

THPO024

Quench Dynamics in SRF Cavities

764

Y.B. Maximenko
MIPT, Dolgoprudniy, Moscow Region, Russia
D.A. Sergatskov, V.P. Yakovlev
Fermilab, Batavia, USA

Funding: The work herein has been performed at Fermilab, which is operated by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the United States Department of Energy.
We have developed a time-dependent model of quench process in an SRF cavity. We discuss peculiarities of the numerical solution and the results of simulation.

Paper	Title	Page
TUPO053	Optical Inspection of SRF Cavities at Fermilab	515
	E. Toropov, D.A. Sergatskov Fermilab, Batavia, USA
	The production of an SRF cavity includes a string of multiple treatments at different facilities before the cavity can be RF-tested in a cryogenic system. Many of the processing steps change the cavity surface and affect the RF performance of the cavity. Interjection of optical inspections between these steps provides us with an instant feedback on the processes involved as well as giving us new insight on the mechanisms responsible for forming surface abnormalities. The major drawback of inclusion of frequent optical inspections is the increased amount of time and labor in the cavity production cycle. An optical inspection of equatorial and iris welds of a 1.3GHz TESLA-shape cavity produces about two thousand pictures. We developed an automated procedure where a computer takes over the most of the routine operations including adjusting the camera focus. With that automation, the inspection currently takes about three hours and little operator time. We will describe the developed system including the focusing algorithm and discuss the ways to further optimize the procedure.
	Poster TUPO053 [0.736 MB]

TUPO054	SRF Cavity Surface Topography From Optical Inspection	519
	E. Toropov, D.A. Sergatskov Fermilab, Batavia, USA
	Characteristics of the cavity surface geometry such as roughness affect cavity performance. The optical cavity inspection system at Fermilab allows us to obtain pictures of cavity surface at different lightning conditions. By analyzing the images of some fixed location inside the cavity taken while the light source moves progressively along the axis we can deduce some topographical information of that surface. In the large-grain cavities after BCP, grains are oriented at distinct angles to the surface and, therefore, reflect light in different directions. We developed a simple algorithm to calculate the angle distribution of the grains and thus to estimate the roughness. We discuss this method and the results of the analysis of the actual cavity surface.
	Poster TUPO054 [0.643 MB]

THPO015	Repair SRFCavity by Re-Melting Surface Defects via High Power Laser Technique	740
	G.M. Ge CLASSE, Ithaca, New York, USA E. Borissov, L.D. Cooley, D.T. Hicks, T.H. Nicol, J.P. Ozelis, J. Ruan, D.A. Sergatskov Fermilab, Batavia, USA G. Wu ANL, Argonne, USA
	As the field emission is gradually under control in recent SRF activities, cavity performance is limited by hard quench in the most case. Surface defect has been identified as one of main reasons caused cavity quench scattering cavity accelerating gradient from 12 MV/m to 40 MV/m. Laser processing is able to re-shape the steep flaws to be flat and smooth surface. In Fermilab, a sophisticated laser repair system has been built for 1.3GHz low performance SRF cavity which is limited by surface defect. The pit in a 1.3GHz single-cell cavity was re-melted by high power laser pulse, cavity took 30 μm light Electropolishing after that. The gradient achieved 39MV/m in initial run; after another 30 μm Electropolishing, it achieved 40 MV/m. The improved laser repair system is able to re-melt the surface defect in one meter long 9-cell SRF cavity. It successfully re-melted a pit in 9-cell SRF cavity TB9ACC017.

THPO023	External Magnetic Fields and Operating SRF Cavity	763
	D.A. Sergatskov, T.N. Khabiboulline, R.L. Madrak, J.P. Ozelis, I. Terechkine Fermilab, Batavia, USA
	Funding: The work herein has been performed at Fermilab, which is operated by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the United States Department of Energy. When an SRF cavity is undergoing a transition to the superconducting state in an external magnetic field it traps some of the flux which results in an increase of surface resistance. This effect was extensively studied, is well understood by now and results in stringent requirements for an ambient magnetic field on the surface of an SRF cavity. The situation is quite different when magnetic field is applied to a cavity already in the superconducting state. During normal operation the bulk of the superconducting Nb should protect the RF surface of the cavity from fields on the outside. So we expect that the requirements on an external magnetic field applied to an operating cavity could be significantly relaxed. One possible failure mode is when the cavity quenches while the external field is applied. The magnetic field would penetrate through a normal zone formed during the quench and can get trapped during the subsequent post-quench cooling. We studied the effects of an external magnetic field applied to an operating SRF cavity and report the results.
	Poster THPO023 [1.370 MB]

THPO024	Quench Dynamics in SRF Cavities	764
	Y.B. Maximenko MIPT, Dolgoprudniy, Moscow Region, Russia D.A. Sergatskov, V.P. Yakovlev Fermilab, Batavia, USA
	Funding: The work herein has been performed at Fermilab, which is operated by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the United States Department of Energy. We have developed a time-dependent model of quench process in an SRF cavity. We discuss peculiarities of the numerical solution and the results of simulation.