IPAC2016 - List of Authors (Hoffstaetter, G.H.)

Paper	Title	Page
TUPOR031	Trapped Ion Effects and Mitigation During High Current Operation in the Cornell DC Photoinjector	1735
SUPSS054	use link to see paper's listing under its alternate paper code
	S.J. Full, A.C. Bartnik, I.V. Bazarov, J. Dobbins, B.M. Dunham, G.H. Hoffstaetter Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	Funding: U.S. Department of Energy (Grant No. DE-SC0012493), National Science Foundation (Award No. NSF-DMR 0807731) The Cornell high intensity photoinjector reaches a new regime of linac beam parameters where high continuous-wave electron beam currents lead to ion trapping. Above 10 mA, we have observed beam trips that limit stable machine operation to approximately 10^-15 minutes. By applying known ion clearing methods, the machine lifetime increases to at least 24 hours of continuous operation, suggesting that trapped ions are the most likely cause of the trips. In this paper we share some of our observations ion trapping in the photoinjector, as well as experimental tests of three common ion mitigation methods: clearing electrodes, beam shaking and bunch gaps.
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WEPMR015	Surface Topography Techniques at Cornell University: Optical Inspection and Surface Replica	2292
	G.M. Ge, F. Furuta, D. Gonnella, D.L. Hall, G.H. Hoffstaetter, M. Liepe, T.I. O'Connell, J. Sears Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	Surface imperfections significantly limit the performance of superconducting radio frequency (SRF) cavities. The development of surface topography techniques aims to locate the surface flaws in an SRF cavity and profile their geometry details. This effort plays an important role of quality control in cavity productions as well as provides contour information of the defects for understanding quench mechanisms. The surface topography techniques at Cornell University include an optical inspection system and surface replica technique. In this paper, we present the details of the techniques and show features found in the SRF cavities at Cornell.
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WEPMR018	Time Resolved Cryogenic Cooling Analysis of the Cornell Injector Cryomodule	2298
	R.G. Eichhorn, A.C. Bartnik, B.M. Dunham, G.M. Ge, G.H. Hoffstaetter, H. Lee, M. Liepe, S.R. Markham, 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
	To demonstrate key parameters of a an energy recovery linac (ERL) at Cornel, an injector based on a photo gun and an SRF cryomodule was designed and built. The goal was to demonstrate high current generation while achieving low emittances. While the emittance goal has been reached, the current achieved so far is 75 mA. Even though this is a world record, it is still below the targeted 100 mA. While ramping up the current we observed excessive heating in the fundamental power coupler which we were able to track down to insufficient cooling of the 80 K intercepts. These intercepts are cooled by a stream of parallel cryogenic flows which we found to be unbalanced. In this paper we will review the finding, describe the analysis we did, modeling of the parallel flow and the modifications made to the module to overcome the heating.
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WEPMR020	First Cool-down of the Cornell ERL Main Linac Cryo-Module	2305
	R.G. Eichhorn, J.V. Conway, F. Furuta, G.M. Ge, D. Gonnella, T. Gruber, G.H. Hoffstaetter, J.J. Kaufman, 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
	Cornell University has finished building a 10 m long superconducting accelerator module as a prototype of the main linac of a proposed ERL facility. This module houses 6 superconducting cavities- operated at 1.8 K in continuous wave (CW) mode with a design field of 16 MV/m and a Quality factor of 2x10¹⁰. We wil shortly review the design and focus on reporting on the first cool-down of this module. We will giving data for various cool-down scenarios (fast/ slow), uniformity and performance
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WEPMR021	HOM Measurements for Cornell's High-current CW ERL Cryomodule	2309
	F. Furuta, R.G. Eichhorn, G.M. Ge, D. Gonnella, G.H. Hoffstaetter, M. Liepe, P. Quigley, V. Veshcherevich Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	The main linac cryomodule (MLC) for the future energy-recovery linac (ERL) based synchrotron-light facility at Cornell had been designed, fabricated, and tested. It houses 6 SRF cavities with individual higher order-modes (HOMs)absorbers and one magnet/ BPM section. We will report the HOM study on MLC.
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WEPMR022	ERL Main Linac Cryomodule Cavity Performance and Effect of Thermal Cycling	2312
	F. Furuta, J. Dobbins, R.G. Eichhorn, G.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
	Cornell has designed, fabricated, and tested a high current (100 mA) CW SRF prototype cryomodule for the future energy-recovery linac (ERL) based synchrotron-light facility at Cornell . It houses six 7-cell SRF cavities with individual HOM absorbers and one magnet/ BPM section. Cavities are targeted to operate with high Qo of 2.0·10¹⁰ at 16.2 MV/m, 1.8 K in continuous wave (CW) mode. We will report the RF test results of 7-cell cavities in this cryomodule after initial cooldown and several thermal cycles with different cooldown method.
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WEPMR025	Improved N-Doping Protocols for SRF Cavities	2323
	D. Gonnella, R.G. Eichhorn, F. Furuta, G.M. Ge, T. Gruber, G.H. Hoffstaetter, J.J. Kaufman, P.N. Koufalis, M. Liepe, J.T. Maniscalco Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	Funding: NSF, DOE Nitrogen-doping has been shown to consistently produce better quality factors in SRF cavities than is achievable with standard preparation techniques. Unfortunately, nitrogen-doping typically brings with it lower quench fields and higher sensitivities of residual resistance to trapped magnetic flux. Here we present work to understand these effects in hopes of mitigating them while maintaining the high Q desired by future projects. Using a nitrogen diffusion simulation, material parameters of nitrogen-doped cavities can be predicted prior to doping. These simulations results are consistent with SIMS data taken from samples treated with cavities. The nature of doping's effect on quench field has also been studied using CW and pulsed measurements. These results have allowed us to better understand the nature of nitrogen-doping and its effect on cavity performance.
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WEPMR028	Studies on the Field Dependence of the BCS Surface Resistance	2335
SUPSS116	use link to see paper's listing under its alternate paper code
	J.T. Maniscalco, D. Gonnella, G.H. Hoffstaetter, P.N. Koufalis, M. Liepe Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	Experiments have shown that the temperature-dependent portion of the RF surface resistance of SRF materials also exhibits a dependence on the magnitude of the surface field, manifested as a "Q-slope" or "anti-Q-slope" in the medium field region. Recent theoretical work proposes an explanation of the anti-Q-slope in dirty-limit superconductors. In this report, we compare theoretical predictions with the results of systematic experimental studies on the RF field dependence of the surface resistance using 1.3 GHz niobium SRF cavities with a wide range of mean free paths. We find very good agreement between theory and experiment in the dirty limit, with some divergence as the cavities approach the clean limit.
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

Paper

Title

Page

TUPOR031

Trapped Ion Effects and Mitigation During High Current Operation in the Cornell DC Photoinjector

1735

SUPSS054

use link to see paper's listing under its alternate paper code

S.J. Full, A.C. Bartnik, I.V. Bazarov, J. Dobbins, B.M. Dunham, G.H. Hoffstaetter
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

Funding: U.S. Department of Energy (Grant No. DE-SC0012493), National Science Foundation (Award No. NSF-DMR 0807731)
The Cornell high intensity photoinjector reaches a new regime of linac beam parameters where high continuous-wave electron beam currents lead to ion trapping. Above 10 mA, we have observed beam trips that limit stable machine operation to approximately 10^-15 minutes. By applying known ion clearing methods, the machine lifetime increases to at least 24 hours of continuous operation, suggesting that trapped ions are the most likely cause of the trips. In this paper we share some of our observations ion trapping in the photoinjector, as well as experimental tests of three common ion mitigation methods: clearing electrodes, beam shaking and bunch gaps.

Export •

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

WEPMR015

Surface Topography Techniques at Cornell University: Optical Inspection and Surface Replica

2292

G.M. Ge, F. Furuta, D. Gonnella, D.L. Hall, G.H. Hoffstaetter, M. Liepe, T.I. O'Connell, J. Sears
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

Surface imperfections significantly limit the performance of superconducting radio frequency (SRF) cavities. The development of surface topography techniques aims to locate the surface flaws in an SRF cavity and profile their geometry details. This effort plays an important role of quality control in cavity productions as well as provides contour information of the defects for understanding quench mechanisms. The surface topography techniques at Cornell University include an optical inspection system and surface replica technique. In this paper, we present the details of the techniques and show features found in the SRF cavities at Cornell.

Export •

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

WEPMR018

Time Resolved Cryogenic Cooling Analysis of the Cornell Injector Cryomodule

2298

R.G. Eichhorn, A.C. Bartnik, B.M. Dunham, G.M. Ge, G.H. Hoffstaetter, H. Lee, M. Liepe, S.R. Markham, 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

To demonstrate key parameters of a an energy recovery linac (ERL) at Cornel, an injector based on a photo gun and an SRF cryomodule was designed and built. The goal was to demonstrate high current generation while achieving low emittances. While the emittance goal has been reached, the current achieved so far is 75 mA. Even though this is a world record, it is still below the targeted 100 mA. While ramping up the current we observed excessive heating in the fundamental power coupler which we were able to track down to insufficient cooling of the 80 K intercepts. These intercepts are cooled by a stream of parallel cryogenic flows which we found to be unbalanced. In this paper we will review the finding, describe the analysis we did, modeling of the parallel flow and the modifications made to the module to overcome the heating.

Export •

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

WEPMR020

First Cool-down of the Cornell ERL Main Linac Cryo-Module

2305

R.G. Eichhorn, J.V. Conway, F. Furuta, G.M. Ge, D. Gonnella, T. Gruber, G.H. Hoffstaetter, J.J. Kaufman, 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

Cornell University has finished building a 10 m long superconducting accelerator module as a prototype of the main linac of a proposed ERL facility. This module houses 6 superconducting cavities- operated at 1.8 K in continuous wave (CW) mode with a design field of 16 MV/m and a Quality factor of 2x10¹⁰. We wil shortly review the design and focus on reporting on the first cool-down of this module. We will giving data for various cool-down scenarios (fast/ slow), uniformity and performance

Export •

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

WEPMR021

HOM Measurements for Cornell's High-current CW ERL Cryomodule

2309

F. Furuta, R.G. Eichhorn, G.M. Ge, D. Gonnella, G.H. Hoffstaetter, M. Liepe, P. Quigley, V. Veshcherevich
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

The main linac cryomodule (MLC) for the future energy-recovery linac (ERL) based synchrotron-light facility at Cornell had been designed, fabricated, and tested. It houses 6 SRF cavities with individual higher order-modes (HOMs)absorbers and one magnet/ BPM section. We will report the HOM study on MLC.

Export •

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

WEPMR022

ERL Main Linac Cryomodule Cavity Performance and Effect of Thermal Cycling

2312

F. Furuta, J. Dobbins, R.G. Eichhorn, G.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

Cornell has designed, fabricated, and tested a high current (100 mA) CW SRF prototype cryomodule for the future energy-recovery linac (ERL) based synchrotron-light facility at Cornell . It houses six 7-cell SRF cavities with individual HOM absorbers and one magnet/ BPM section. Cavities are targeted to operate with high Qo of 2.0·10¹⁰ at 16.2 MV/m, 1.8 K in continuous wave (CW) mode. We will report the RF test results of 7-cell cavities in this cryomodule after initial cooldown and several thermal cycles with different cooldown method.

Export •

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

WEPMR025

Improved N-Doping Protocols for SRF Cavities

2323

D. Gonnella, R.G. Eichhorn, F. Furuta, G.M. Ge, T. Gruber, G.H. Hoffstaetter, J.J. Kaufman, P.N. Koufalis, M. Liepe, J.T. Maniscalco
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

Funding: NSF, DOE
Nitrogen-doping has been shown to consistently produce better quality factors in SRF cavities than is achievable with standard preparation techniques. Unfortunately, nitrogen-doping typically brings with it lower quench fields and higher sensitivities of residual resistance to trapped magnetic flux. Here we present work to understand these effects in hopes of mitigating them while maintaining the high Q desired by future projects. Using a nitrogen diffusion simulation, material parameters of nitrogen-doped cavities can be predicted prior to doping. These simulations results are consistent with SIMS data taken from samples treated with cavities. The nature of doping's effect on quench field has also been studied using CW and pulsed measurements. These results have allowed us to better understand the nature of nitrogen-doping and its effect on cavity performance.

Export •

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

WEPMR028

Studies on the Field Dependence of the BCS Surface Resistance

2335

SUPSS116

use link to see paper's listing under its alternate paper code

J.T. Maniscalco, D. Gonnella, G.H. Hoffstaetter, P.N. Koufalis, M. Liepe
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

Experiments have shown that the temperature-dependent portion of the RF surface resistance of SRF materials also exhibits a dependence on the magnitude of the surface field, manifested as a "Q-slope" or "anti-Q-slope" in the medium field region. Recent theoretical work proposes an explanation of the anti-Q-slope in dirty-limit superconductors. In this report, we compare theoretical predictions with the results of systematic experimental studies on the RF field dependence of the surface resistance using 1.3 GHz niobium SRF cavities with a wide range of mean free paths. We find very good agreement between theory and experiment in the dirty limit, with some divergence as the cavities approach the clean limit.

Export •

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