IPAC2013 - List of Authors (Liepe, M.)

Paper	Title	Page
MOPWA070	Beam Position Monitor within the Cornell Energy Recovery Linac Cavity Assembly	840
	M.G. Billing, M. Liepe, V.D. Shemelin, N.R.A. Valles CLASSE, Ithaca, New York, USA
	In an energy recovery Linac (ERL) the low energy beam is very sensitive to deflections due to the RF fields as it passes through the accelerator cavities. Therefore, to avoid the possible effects of beam breakup, it will be important to determine the optimum transverse position for the beam within the first several sets of cavity cells in the cryostat assembly and to maintain this position over long periods. As a result a beam position monitor (BPM) has been designed to be located between the higher-order modes (HOM) loads and the seven-cell RF structures. This BPM’s design reduces the coupling of RF power from the fundamental mode and HOMs into the BPM, while maintaining acceptable position sensitivity and resolution. We analyzed the coupling of the probe to the HOMs of realistically shaped cavities by generating geometries for hundreds of cavities having small shape variations from the nominal dimensions consistent with present machining tolerances, and solved for their monopole and dipole spectra. Our results show that the peak, dissipated power within BPM cables, which pass through the cryostat, is well within the permissible levels.

WEPWO059	Cornell's HOM Beamline Absorbers	2441
	R. Eichhorn, J.V. Conway, Y. He, G.H. Hoffstaetter, M. Liepe, T.I. O'Connell, P. Quigley, J. Sears, V.D. Shemelin, N.R.A. Valles CLASSE, Ithaca, New York, USA
	The proposed energy recovery linac at Cornell aims for high beam currents and short bunch lengths, the combination of which requires efficient damping of the higher order modes (HOMs) being present in the superconducting cavities. Numerical simulations show that the expected HOM power could be as high as 200 W per cavity with frequencies ranging to 40 GHz. Consequently, a beam line absorber approach was chosen. We will review the design, report on first results from a prototype and discuss further improvements.

WEPWO060	The CW Linac Cryo-module for Cornell’s ERL	2444
	R. Eichhorn, Y. He, G.H. Hoffstaetter, M. Liepe, T.I. O'Connell, P. Quigley, D.M. Sabol, J. Sears, E.N. Smith, V. Veshcherevich CLASSE, Ithaca, New York, USA
	Cornell University has proposed an energy-recovery linac (ERL) based synchrotron-light facility which can provide greatly improved X-ray beams due to the high electron-beam quality that is available from a linac. As part of the phase 1 R&D program, critical challenges in the design were addressed, one of them being a full linac cryo-module. It houses 6 superconducting cavities- operated at 1.8 K in cw mode- HOM absorbers and a magnet/ BPM section. We will present the design being finalized recently and report on the fabrication status that started in late 2012.

WEPWO061	Readiness for the Cornell ERL	2447
	G.H. Hoffstaetter, A.C. Bartnik, I.V. Bazarov, D.H. Bilderback, M.G. Billing, J.D. Brock, J.A. Crittenden, L. Cultrera, D.S. Dale, J. Dobbins, B.M. Dunham, R.D. Ehrlich, M. P. Ehrlichman, R. Eichhorn, K. Finkelstein, E. Fontes, M.J. Forster, S.J. Full, F. Furuta, D. Gonnella, S.W. Gray, S.M. Gruner, C.M. Gulliford, D.L. Hartill, Y. He, R.G. Helmke, K.M.V. Ho, R.P.K. Kaplan, S.S. Karkare, V.O. Kostroun, H. Lee, Y. Li, M. Liepe, X. Liu, J.M. Maxson, C.E. Mayes, A.A. Mikhailichenko, H. Padamsee, J.R. Patterson, S.B. Peck, S. Posen, P. Quigley, P. Revesz, D.H. Rice, D. Sagan, J. Sears, V.D. Shemelin, D.M. Smilgies, E.N. Smith, K.W. Smolenski, A.B. Temnykh, M. Tigner, N.R.A. Valles, V. Veshcherevich, A.R. Woll, Y. Xie, Z. Zhao CLASSE, Ithaca, New York, USA
	Funding: Supported by NSF award DMR-0807731 and NY State Energy-Recovery Linacs (ERLs) are proposed as drivers for hard x-ray sources because of their ability to produce electron bunches with small, flexible cross sections and short lengths at high repetition rates. Cornell University has pioneered the design and hardware for ERL lightsources. This preparatory research for ERL-lightsource construction will be discussed. Important milestones have been achieved in Cornell's prototype ERL injector, including the production of a prototype SRF cavity that exceeds design specifications, the regular production of long-lived and low emittance cathodes, the acceleration of ultra-low emittance bunches, and the world-record of 65 mA current from a photoemission DC gun. We believe that demonstration of the practical feasibility of these technologies have progressed sufficiently to allow the construction of an ERL-based lightsource like that described in [erl.chess.cornell.edu/PDDR].

WEPWO068	Cornell ERL Main Linac 7-cell Cavity Performance in Horizontal Test Cryomodule Qualifications	2459
	N.R.A. Valles, R. Eichhorn, F. Furuta, G.M. Ge, D. Gonnella, Y. He, K.M.V. Ho, G.H. Hoffstaetter, M. Liepe, T.I. O'Connell, S. Posen, P. Quigley, J. Sears, V. Veshcherevich CLASSE, Ithaca, New York, USA
	Funding: NSF DMR-0807731 Cornell has recently ﬁnished producing and testing the ﬁrst prototype 7-cell main linac cavity for the Cornell Energy Recovery Linac, and completed the prototype cavity qualification program. This paper presents quality factor results from the horizontal test cryomodule (HTC) measurements, from the HTC-1 through HTC-3 experiments, reaching Q's up to 6 x 10¹⁰ at 1.6 K. We investigate the effect of thermal cycling on cavity quality factor and show that high quality factors can be preserved from initial mounting to fully outfitting the cavity with side-mounted input coupler and beam line absorbers. We also discuss the production of six additional main-linac cavities as we progress toward constructing a full 6-cavity cryomodule.

WEPWO069	HOM Studies of the Cornell ERL Main Linac Cavity: HTC-1 Through HTC-3	2462
	N.R.A. Valles, R. Eichhorn, G.H. Hoffstaetter, M. Liepe CLASSE, Ithaca, New York, USA
	Funding: Supported by NSF grant DMR-0807731 The Cornell energy recovery linac is designed to run a high energy (5 GeV), high current (100 mA), very low emittance beam (30 pm at 77 pC bunch charge). A major challenge to running such a large current continuously through the machine is the effect of strong higher-order modes(HOMs) that can lead to beam breakup. This paper presents the results of HOM studies for the prototype 7-cell cavity installed in a horizontal test cryomodule (HTC) from initial RF test, to being fully outfitted with side-mounted input coupler and beam line absorbers. We compare the simulated results of the optimized cavity geometry with measurements from all three HTC experiments.

WEPWO071	Quench and High Field Q-SLOP Studies using a Single Cell Cavity with Artificial Pits	2465
	Y. Xie, G.H. Hoffstaetter, M. Liepe CLASSE, Ithaca, New York, USA
	Surface defects such as pits have been identified as some of the main sources of limitations of srf cavity performance. A single cell cavity was made with 30 artificial pits in the high magnetic field region to gain new insight in how pits limit the cavity performance. The test of the pit cavity showed clear evidence that the edges of two of the largest radius pits transitioned into the normal conducting state at field just below the quench field of the cavity, and that the quench was indeed induced by these two pits. Insights about quench and non-linear rf resistances will be presented.

WEPFI076	Experience with a 5 kW, 1.3 GHz Solid State Amplifier	2869
	K.M.V. Ho, R. Eichhorn, D.L. Hartill, M. Liepe CLASSE, Ithaca, New York, USA
	This study describes the experience with and performance of a commercially available 1.3 GHz 5kW Solid State Amplifier in various experiments at Cornell University. This paper focuses on several key factors in testing the performance of the amplifier. Among those are phase and amplitude stability, gain linearity, and phase shift vs. power. High power amplifiers are usually built with multiple RF power modules and the individual output signals are then combined in a power combiner. Therefore, the phases of the individual RF output power signals have to be adjusted within tight tolerances. The relative phases can be affected by different lengths cables and also affect the overall gain performance of the amplifier.

Paper

Title

Page

Beam Position Monitor within the Cornell Energy Recovery Linac Cavity Assembly

840

M.G. Billing, M. Liepe, V.D. Shemelin, N.R.A. Valles
CLASSE, Ithaca, New York, USA

In an energy recovery Linac (ERL) the low energy beam is very sensitive to deflections due to the RF fields as it passes through the accelerator cavities. Therefore, to avoid the possible effects of beam breakup, it will be important to determine the optimum transverse position for the beam within the first several sets of cavity cells in the cryostat assembly and to maintain this position over long periods. As a result a beam position monitor (BPM) has been designed to be located between the higher-order modes (HOM) loads and the seven-cell RF structures. This BPM’s design reduces the coupling of RF power from the fundamental mode and HOMs into the BPM, while maintaining acceptable position sensitivity and resolution. We analyzed the coupling of the probe to the HOMs of realistically shaped cavities by generating geometries for hundreds of cavities having small shape variations from the nominal dimensions consistent with present machining tolerances, and solved for their monopole and dipole spectra. Our results show that the peak, dissipated power within BPM cables, which pass through the cryostat, is well within the permissible levels.

WEPWO059

Cornell's HOM Beamline Absorbers

2441

R. Eichhorn, J.V. Conway, Y. He, G.H. Hoffstaetter, M. Liepe, T.I. O'Connell, P. Quigley, J. Sears, V.D. Shemelin, N.R.A. Valles
CLASSE, Ithaca, New York, USA

The proposed energy recovery linac at Cornell aims for high beam currents and short bunch lengths, the combination of which requires efficient damping of the higher order modes (HOMs) being present in the superconducting cavities. Numerical simulations show that the expected HOM power could be as high as 200 W per cavity with frequencies ranging to 40 GHz. Consequently, a beam line absorber approach was chosen. We will review the design, report on first results from a prototype and discuss further improvements.

WEPWO060

The CW Linac Cryo-module for Cornell’s ERL

2444

R. Eichhorn, Y. He, G.H. Hoffstaetter, M. Liepe, T.I. O'Connell, P. Quigley, D.M. Sabol, J. Sears, E.N. Smith, V. Veshcherevich
CLASSE, Ithaca, New York, USA

Cornell University has proposed an energy-recovery linac (ERL) based synchrotron-light facility which can provide greatly improved X-ray beams due to the high electron-beam quality that is available from a linac. As part of the phase 1 R&D program, critical challenges in the design were addressed, one of them being a full linac cryo-module. It houses 6 superconducting cavities- operated at 1.8 K in cw mode- HOM absorbers and a magnet/ BPM section. We will present the design being finalized recently and report on the fabrication status that started in late 2012.

WEPWO061

Readiness for the Cornell ERL

2447

G.H. Hoffstaetter, A.C. Bartnik, I.V. Bazarov, D.H. Bilderback, M.G. Billing, J.D. Brock, J.A. Crittenden, L. Cultrera, D.S. Dale, J. Dobbins, B.M. Dunham, R.D. Ehrlich, M. P. Ehrlichman, R. Eichhorn, K. Finkelstein, E. Fontes, M.J. Forster, S.J. Full, F. Furuta, D. Gonnella, S.W. Gray, S.M. Gruner, C.M. Gulliford, D.L. Hartill, Y. He, R.G. Helmke, K.M.V. Ho, R.P.K. Kaplan, S.S. Karkare, V.O. Kostroun, H. Lee, Y. Li, M. Liepe, X. Liu, J.M. Maxson, C.E. Mayes, A.A. Mikhailichenko, H. Padamsee, J.R. Patterson, S.B. Peck, S. Posen, P. Quigley, P. Revesz, D.H. Rice, D. Sagan, J. Sears, V.D. Shemelin, D.M. Smilgies, E.N. Smith, K.W. Smolenski, A.B. Temnykh, M. Tigner, N.R.A. Valles, V. Veshcherevich, A.R. Woll, Y. Xie, Z. Zhao
CLASSE, Ithaca, New York, USA

Funding: Supported by NSF award DMR-0807731 and NY State
Energy-Recovery Linacs (ERLs) are proposed as drivers for hard x-ray sources because of their ability to produce electron bunches with small, flexible cross sections and short lengths at high repetition rates. Cornell University has pioneered the design and hardware for ERL lightsources. This preparatory research for ERL-lightsource construction will be discussed. Important milestones have been achieved in Cornell's prototype ERL injector, including the production of a prototype SRF cavity that exceeds design specifications, the regular production of long-lived and low emittance cathodes, the acceleration of ultra-low emittance bunches, and the world-record of 65 mA current from a photoemission DC gun. We believe that demonstration of the practical feasibility of these technologies have progressed sufficiently to allow the construction of an ERL-based lightsource like that described in [erl.chess.cornell.edu/PDDR].

WEPWO068

Cornell ERL Main Linac 7-cell Cavity Performance in Horizontal Test Cryomodule Qualifications

2459

N.R.A. Valles, R. Eichhorn, F. Furuta, G.M. Ge, D. Gonnella, Y. He, K.M.V. Ho, G.H. Hoffstaetter, M. Liepe, T.I. O'Connell, S. Posen, P. Quigley, J. Sears, V. Veshcherevich
CLASSE, Ithaca, New York, USA

Funding: NSF DMR-0807731
Cornell has recently ﬁnished producing and testing the ﬁrst prototype 7-cell main linac cavity for the Cornell Energy Recovery Linac, and completed the prototype cavity qualification program. This paper presents quality factor results from the horizontal test cryomodule (HTC) measurements, from the HTC-1 through HTC-3 experiments, reaching Q's up to 6 x 10¹⁰ at 1.6 K. We investigate the effect of thermal cycling on cavity quality factor and show that high quality factors can be preserved from initial mounting to fully outfitting the cavity with side-mounted input coupler and beam line absorbers. We also discuss the production of six additional main-linac cavities as we progress toward constructing a full 6-cavity cryomodule.

WEPWO069

HOM Studies of the Cornell ERL Main Linac Cavity: HTC-1 Through HTC-3

2462

N.R.A. Valles, R. Eichhorn, G.H. Hoffstaetter, M. Liepe
CLASSE, Ithaca, New York, USA

Funding: Supported by NSF grant DMR-0807731
The Cornell energy recovery linac is designed to run a high energy (5 GeV), high current (100 mA), very low emittance beam (30 pm at 77 pC bunch charge). A major challenge to running such a large current continuously through the machine is the effect of strong higher-order modes(HOMs) that can lead to beam breakup. This paper presents the results of HOM studies for the prototype 7-cell cavity installed in a horizontal test cryomodule (HTC) from initial RF test, to being fully outfitted with side-mounted input coupler and beam line absorbers. We compare the simulated results of the optimized cavity geometry with measurements from all three HTC experiments.

WEPWO071

Quench and High Field Q-SLOP Studies using a Single Cell Cavity with Artificial Pits

2465

Y. Xie, G.H. Hoffstaetter, M. Liepe
CLASSE, Ithaca, New York, USA

Surface defects such as pits have been identified as some of the main sources of limitations of srf cavity performance. A single cell cavity was made with 30 artificial pits in the high magnetic field region to gain new insight in how pits limit the cavity performance. The test of the pit cavity showed clear evidence that the edges of two of the largest radius pits transitioned into the normal conducting state at field just below the quench field of the cavity, and that the quench was indeed induced by these two pits. Insights about quench and non-linear rf resistances will be presented.

WEPFI076

Experience with a 5 kW, 1.3 GHz Solid State Amplifier

2869

K.M.V. Ho, R. Eichhorn, D.L. Hartill, M. Liepe
CLASSE, Ithaca, New York, USA

This study describes the experience with and performance of a commercially available 1.3 GHz 5kW Solid State Amplifier in various experiments at Cornell University. This paper focuses on several key factors in testing the performance of the amplifier. Among those are phase and amplitude stability, gain linearity, and phase shift vs. power. High power amplifiers are usually built with multiple RF power modules and the individual output signals are then combined in a power combiner. Therefore, the phases of the individual RF output power signals have to be adjusted within tight tolerances. The relative phases can be affected by different lengths cables and also affect the overall gain performance of the amplifier.