LINAC2014 - List of Authors (Ge, G.M.)

Paper

Title

Page

Extracting Superconducting Parameters from Surface Resistivity by Using Inside Temperature of SRF Cavities

80

G.M. Ge, G.H. Hoffstaetter, M. Liepe, H. Padamsee, V.D. Shemelin
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

The surface resistance of an RF superconductor depends on the surface temperature, the residual resistance and various superconductor parameters. These parameters can be determined by measuring the quality factor of a SRF cavity in helium-baths of different temperatures. The surface resistance can be computed from Q0 for any cavity geometry, however it is less simple to determine the temperature of the surface when only the temperature of the helium bath is known. Traditionally, it was approximated that the surface temperature on the inner surface of the cavity is the same as the temperature of the bath. This is a good approximation at small RF-field losses on the surface, but to determine the field dependence of Rs, one cannot be restricted to small field losses. Here we show how computer simulations can be used to determine the inside temperature so that Rs(Tin) can then be used to extract superconductor parameters. The computer code combines the well-known programs HEAT and SRIMP. We find that the error of the incorrect fitting method is about 10% at high RF-fields.

MOPP018

Nitrogen-Doped 9-Cell Cavity Performance in the Cornell Horizontal Test Cryomodule

88

D. Gonnella, R.G. Eichhorn, F. Furuta, G.M. Ge, D.L. Hall, Y. He, G.H. Hoffstaetter, M. Liepe, T.I. O'Connel, S. Posen, P. Quigley, J. Sears, V. Veshcherevich
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
A. Grassellino, A. Romanenko
Fermilab, Batavia, Illinois, USA

Funding: U.S. Department of Energy
Cornell has recently completed construction and qualification of a horizontal cryomodule capable of holding a 9-cell ILC cavity. A nitrogen-doped niobium 9-cell cavity was assembled into the Horizontal Test Cryomodule (HTC) with a high Q input coupler and tested. We report on results from this test of a nitrogen-doped cavity in cryomodule and discuss the effects of cool down rate and thermal cycling on the residual resistance of the cavity.

TUPP016

Cornell ERL cavity production and vertical test results

F. Furuta, B. Bullock, B. Clasby, R.G. Eichhorn, B. Elmore, A. Ganshin, G.M. Ge, G.H. Hoffstaetter, J.J. Kaufman, M. Liepe, J. Sears
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

The Cornell ERL 7-cell cavities for the Main Linac Cryomodule (MLC), six 7-cells in total- have been fabricated, processed, and tested in the Cornell Laboratory for Accelerator-based Sciences and Education (CLASSE) vertical test pit. All have surpassed the specification values (Eacc=16.2MV/m with Qo of 2.0·10¹⁰ at 1.8K). In fact, the achieved Qo during vertical test were much higher than specs, the average of Qo is almost 3·10¹⁰ at 1.8K. In this poster, we will describe about our ERL cavity fabrication, preparation, and vertical testing results.

THPP016

Nitrogen-Treated Cavity Testing at Cornell

866

D. Gonnella, F. Furuta, G.M. Ge, M. Liepe
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

Funding: U.S. Department of Energy
Recent results from Cornell, FNAL, and TJNAF have shown that superconducting RF cavities given a heat treatment in a nitrogen atmosphere show higher Q₀ at operating gradients at 2.0 K than standard SRF cavities. Here we present on recent results at Cornell in which five single cell cavities and three 9-cell cavities were tested after receiving various nitrogen-doping treatments. Cavity performance was correlated with treatment, and samples treated with the cavities were analyzed with SIMS. These results provide new insights into the science behind the excellent performance that is observed in these cavities.

Paper	Title	Page
MOPP016	Extracting Superconducting Parameters from Surface Resistivity by Using Inside Temperature of SRF Cavities	80
	G.M. Ge, G.H. Hoffstaetter, M. Liepe, H. Padamsee, V.D. Shemelin Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	The surface resistance of an RF superconductor depends on the surface temperature, the residual resistance and various superconductor parameters. These parameters can be determined by measuring the quality factor of a SRF cavity in helium-baths of different temperatures. The surface resistance can be computed from Q0 for any cavity geometry, however it is less simple to determine the temperature of the surface when only the temperature of the helium bath is known. Traditionally, it was approximated that the surface temperature on the inner surface of the cavity is the same as the temperature of the bath. This is a good approximation at small RF-field losses on the surface, but to determine the field dependence of Rs, one cannot be restricted to small field losses. Here we show how computer simulations can be used to determine the inside temperature so that Rs(Tin) can then be used to extract superconductor parameters. The computer code combines the well-known programs HEAT and SRIMP. We find that the error of the incorrect fitting method is about 10% at high RF-fields.

MOPP018	Nitrogen-Doped 9-Cell Cavity Performance in the Cornell Horizontal Test Cryomodule	88
	D. Gonnella, R.G. Eichhorn, F. Furuta, G.M. Ge, D.L. Hall, Y. He, G.H. Hoffstaetter, M. Liepe, T.I. O'Connel, S. Posen, P. Quigley, J. Sears, V. Veshcherevich Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA A. Grassellino, A. Romanenko Fermilab, Batavia, Illinois, USA
	Funding: U.S. Department of Energy Cornell has recently completed construction and qualification of a horizontal cryomodule capable of holding a 9-cell ILC cavity. A nitrogen-doped niobium 9-cell cavity was assembled into the Horizontal Test Cryomodule (HTC) with a high Q input coupler and tested. We report on results from this test of a nitrogen-doped cavity in cryomodule and discuss the effects of cool down rate and thermal cycling on the residual resistance of the cavity.

TUPP016	Cornell ERL cavity production and vertical test results
	F. Furuta, B. Bullock, B. Clasby, R.G. Eichhorn, B. Elmore, A. Ganshin, G.M. Ge, G.H. Hoffstaetter, J.J. Kaufman, M. Liepe, J. Sears Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	The Cornell ERL 7-cell cavities for the Main Linac Cryomodule (MLC), six 7-cells in total- have been fabricated, processed, and tested in the Cornell Laboratory for Accelerator-based Sciences and Education (CLASSE) vertical test pit. All have surpassed the specification values (Eacc=16.2MV/m with Qo of 2.0·10¹⁰ at 1.8K). In fact, the achieved Qo during vertical test were much higher than specs, the average of Qo is almost 3·10¹⁰ at 1.8K. In this poster, we will describe about our ERL cavity fabrication, preparation, and vertical testing results.

THPP016	Nitrogen-Treated Cavity Testing at Cornell	866
	D. Gonnella, F. Furuta, G.M. Ge, M. Liepe Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	Funding: U.S. Department of Energy Recent results from Cornell, FNAL, and TJNAF have shown that superconducting RF cavities given a heat treatment in a nitrogen atmosphere show higher Q₀ at operating gradients at 2.0 K than standard SRF cavities. Here we present on recent results at Cornell in which five single cell cavities and three 9-cell cavities were tested after receiving various nitrogen-doping treatments. Cavity performance was correlated with treatment, and samples treated with the cavities were analyzed with SIMS. These results provide new insights into the science behind the excellent performance that is observed in these cavities.