NAPAC2016 - List of Authors (Ge, M.)

Paper	Title	Page
MOPOB60	Performance of the Cornell Main Linac Prototype Cryomodule for the CBETA Project	204
	F. Furuta, N. Banerjee, J. Dobbins, R.G. Eichhorn, M. Ge, D. Gonnella, G.H. Hoffstaetter, M. Liepe, T.I. O'Connell, P. Quigley, D.M. Sabol, J. Sears, E.N. Smith, V. Veshcherevich Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	The main linac prototype cryomodule (MLC) is a key component for the Cornell-BNL ERL Test Accelerator (CBETA), which is a 4-turn FFAG ERL under construction at Cornell University. The MLC has been designed for high current and efficient continuous wave (CW) SRF cavity operation, and houses six high Q0 7-cell SRF cavities with individual beamline higher order-modes (HOMs) absorbers for strong HOM suppression in high beam current operation. Cavities have achieved specification values of 16.2MV/m with high Q0 of 2.0·10¹⁰ at 1.8K in CW operation after cooldown optimizations and RF processing. Damping of the HOMs has been measured in detail, indicating that the loaded quality-factors of all critical modes are low enough to avoid BBU in high current, multi-turn ERL operation. Microphonics measurements have been carried out as well, and vibration sources have been determined and eliminated. Here we report on these cryomodule performance studies.
	Poster MOPOB60 [3.321 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-NAPAC2016-MOPOB60
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MOPOB61	Updates of Vertical Electropolishing Studies at Cornell with KEK and Marui Galvanizing Co. Ltd .	208
	F. Furuta, M. Ge, T. Gruber, J.J. Kaufman, M. Liepe, J. Sears Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA V. Chouhan, Y.I. Ida, K.N. Nii, T.Y. Yamaguchi MGH, Hyogo-ken, Japan H. Hayano, S. Kato, T. Saeki KEK, Ibaraki, Japan
	Cornell, KEK, and Marui Galvanizing Co. Ltd (MGI) have started new Vertical Electro-Polishing (VEP) R&D collaboration in 2014. MGI and KEK has developed their original VEP cathode named 'i-cathode Ninja'® which has four retractable wing-shape parts per cell for single-/9-cell cavities. One single cell cavity had processed with VEP using i-cathode Ninja at Cornell. Cornell also performed the vertical test on that cavity. We will present the details of process and RF test result at Cornell.
	Poster MOPOB61 [2.251 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-NAPAC2016-MOPOB61
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MOPOB62	SRF Half Wave Resonator Activities at Cornell for the RAON Project	211
	M. Ge, F. Furuta, T. Gruber, S.W. Hartman, C. Henderson, M. Liepe, S. Lok, T.I. O'Connell, P.J. Pamel, J. Sears, V. Veshcherevich Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA J. Joo, J.-W. Kim, W.K. Kim, J. Lee, I. Shin IBS, Daejeon, Republic of Korea
	The RAON heavy-ion accelerator requires ninety-eight 162.5MHz Half-Wave-Resonators (HWR) with a geometrical β=0.12. Cornell University will test a prototype HWR as well as develop a frequency tuner for this cavity. In this paper we report on the progress in designing, fabricating, and commissioning of new HWR preparation and testing infrastructure at Cornell. The HWR infrastructure work includes new input and pick-up couplers, a modified vertical test insert with a 162.5MHz RF system, a new High-Pressure-Water-Rinsing (HPR) setup, and a modified chemical etching system.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-NAPAC2016-MOPOB62
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MOPOB63	Impact of Cooldown Procedure and Ambient Magnetic Field on the Quality Factor of State-of-the-Art Nb3Sn Single-Cell ILC Cavities	215
	D.L. Hall, M. Ge, J.J. Kaufman, M. Liepe, R.D. Porter Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	Funding: DOE Single-cell Nb3Sn cavities coated at Cornell University have demonstrated quality factors of 10¹⁰ at 16 MV/m and 4.2 K in vertical tests, achieving the performance requirements of contemporary modern accelerator designs. In this paper, we present results demonstrating the impact of the cooldown procedure and ambient magnetic fields on the cavity's ability to achieve these quality factors and accelerating gradients. The impact of the magnetic fields from thermoelectric currents, generated by thermal gradients across the cavity during cooldown, are shown to be equivalent to the impact of magnetic fields trapped from ambient sources. Furthermore, the increase in the residual surface resistance due to trapped magnetic flux, from both ambient sources and thermoelectric currents, is found to be a function of the applied RF magnetic field amplitude. A hypothesis for this observation is given, and conclusions are drawn regarding the demands on the cooldown procedure and ambient magnetic fields necessary to achieve quality factors of 10¹⁰ at 4.2 K and 16 MV/m or higher.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-NAPAC2016-MOPOB63
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MOPOB65	Investigation of the Origin of the Anti-Q-Slope	218
	J.T. Maniscalco, M. Ge, D. Gonnella, M. Liepe Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	The surface resistance of a superconductor, a property very relevant to SRF accelerators, has long been known to depend on the strength of the surface magnetic field. A recent discovery showed that, for certain surface treatments, microwave cavities can be shown to have an inverse field dependence, dubbed the ‘‘anti-Q-slope'', in which the surface resistance decreases over an increasing field. Here we present an investigation into what causes the anti-Q-slope in nitrogen-doped niobium cavities, drawing a direct connection between the electron mean free path of the SRF material and the magnitude of the anti-Q-slope. Further, we incorporate residual resistance due to flux trapping to calculate an optimal mean free path for a given trapped flux.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-NAPAC2016-MOPOB65
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Paper

Title

Page

Performance of the Cornell Main Linac Prototype Cryomodule for the CBETA Project

204

F. Furuta, N. Banerjee, J. Dobbins, R.G. Eichhorn, M. Ge, D. Gonnella, G.H. Hoffstaetter, M. Liepe, T.I. O'Connell, P. Quigley, D.M. Sabol, J. Sears, E.N. Smith, V. Veshcherevich
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

The main linac prototype cryomodule (MLC) is a key component for the Cornell-BNL ERL Test Accelerator (CBETA), which is a 4-turn FFAG ERL under construction at Cornell University. The MLC has been designed for high current and efficient continuous wave (CW) SRF cavity operation, and houses six high Q0 7-cell SRF cavities with individual beamline higher order-modes (HOMs) absorbers for strong HOM suppression in high beam current operation. Cavities have achieved specification values of 16.2MV/m with high Q0 of 2.0·10¹⁰ at 1.8K in CW operation after cooldown optimizations and RF processing. Damping of the HOMs has been measured in detail, indicating that the loaded quality-factors of all critical modes are low enough to avoid BBU in high current, multi-turn ERL operation. Microphonics measurements have been carried out as well, and vibration sources have been determined and eliminated. Here we report on these cryomodule performance studies.

Poster MOPOB60 [3.321 MB]

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-NAPAC2016-MOPOB60

Export •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

MOPOB61

Updates of Vertical Electropolishing Studies at Cornell with KEK and Marui Galvanizing Co. Ltd .

208

F. Furuta, M. Ge, T. Gruber, J.J. Kaufman, M. Liepe, J. Sears
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
V. Chouhan, Y.I. Ida, K.N. Nii, T.Y. Yamaguchi
MGH, Hyogo-ken, Japan
H. Hayano, S. Kato, T. Saeki
KEK, Ibaraki, Japan

Cornell, KEK, and Marui Galvanizing Co. Ltd (MGI) have started new Vertical Electro-Polishing (VEP) R&D collaboration in 2014. MGI and KEK has developed their original VEP cathode named 'i-cathode Ninja'® which has four retractable wing-shape parts per cell for single-/9-cell cavities. One single cell cavity had processed with VEP using i-cathode Ninja at Cornell. Cornell also performed the vertical test on that cavity. We will present the details of process and RF test result at Cornell.

Poster MOPOB61 [2.251 MB]

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-NAPAC2016-MOPOB61

Export •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

MOPOB62

SRF Half Wave Resonator Activities at Cornell for the RAON Project

211

M. Ge, F. Furuta, T. Gruber, S.W. Hartman, C. Henderson, M. Liepe, S. Lok, T.I. O'Connell, P.J. Pamel, J. Sears, V. Veshcherevich
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
J. Joo, J.-W. Kim, W.K. Kim, J. Lee, I. Shin
IBS, Daejeon, Republic of Korea

The RAON heavy-ion accelerator requires ninety-eight 162.5MHz Half-Wave-Resonators (HWR) with a geometrical β=0.12. Cornell University will test a prototype HWR as well as develop a frequency tuner for this cavity. In this paper we report on the progress in designing, fabricating, and commissioning of new HWR preparation and testing infrastructure at Cornell. The HWR infrastructure work includes new input and pick-up couplers, a modified vertical test insert with a 162.5MHz RF system, a new High-Pressure-Water-Rinsing (HPR) setup, and a modified chemical etching system.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-NAPAC2016-MOPOB62

Export •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

MOPOB63

Impact of Cooldown Procedure and Ambient Magnetic Field on the Quality Factor of State-of-the-Art Nb3Sn Single-Cell ILC Cavities

215

D.L. Hall, M. Ge, J.J. Kaufman, M. Liepe, R.D. Porter
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

Funding: DOE
Single-cell Nb3Sn cavities coated at Cornell University have demonstrated quality factors of 10¹⁰ at 16 MV/m and 4.2 K in vertical tests, achieving the performance requirements of contemporary modern accelerator designs. In this paper, we present results demonstrating the impact of the cooldown procedure and ambient magnetic fields on the cavity's ability to achieve these quality factors and accelerating gradients. The impact of the magnetic fields from thermoelectric currents, generated by thermal gradients across the cavity during cooldown, are shown to be equivalent to the impact of magnetic fields trapped from ambient sources. Furthermore, the increase in the residual surface resistance due to trapped magnetic flux, from both ambient sources and thermoelectric currents, is found to be a function of the applied RF magnetic field amplitude. A hypothesis for this observation is given, and conclusions are drawn regarding the demands on the cooldown procedure and ambient magnetic fields necessary to achieve quality factors of 10¹⁰ at 4.2 K and 16 MV/m or higher.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-NAPAC2016-MOPOB63

Export •

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MOPOB65

Investigation of the Origin of the Anti-Q-Slope

218

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

The surface resistance of a superconductor, a property very relevant to SRF accelerators, has long been known to depend on the strength of the surface magnetic field. A recent discovery showed that, for certain surface treatments, microwave cavities can be shown to have an inverse field dependence, dubbed the ‘‘anti-Q-slope'', in which the surface resistance decreases over an increasing field. Here we present an investigation into what causes the anti-Q-slope in nitrogen-doped niobium cavities, drawing a direct connection between the electron mean free path of the SRF material and the magnitude of the anti-Q-slope. Further, we incorporate residual resistance due to flux trapping to calculate an optimal mean free path for a given trapped flux.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-NAPAC2016-MOPOB65

Export •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)