IPAC2013 - List of Authors (Shemelin, V.D.)

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.

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].

WEPWO065	Optimization of Elliptical SRF Cavities for β <1	2450
	V.D. Shemelin CLASSE, Ithaca, New York, USA J. Newbolt Rochester University, Rochester, New York, USA
	Funding: NSF award DMR-0807731 A systematic approach to optimization of SRF cavities which was done earlier for β=1 is extended to β<1 Some improvements for earlier developed designs are proposed.

WEPWO066	Frequency Control in the Cornell-ERL Main-Linac Cavity Production	2453
	V.D. Shemelin, B. Bullock, P.R. Carriere, B. Clasby, R. Eichhorn, B. Elmore, J.J. Kaufman, J. Sears CLASSE, Ithaca, New York, USA
	Funding: NSF award DMR-0807731 Cavity fabrication can be broken down into three main stages: deep-drawing cups, welding the cups in pairs to obtain “dumbbells” and end groups, and, finally, welding the obtained components into a completed cavity. Frequency measurements and precise machining were implemented after the second stage. A custom RF fixture and data acquisition system were used for this purpose. The system comprised of a mechanical press with RF contacts, a network analyzer, a load cell and custom LabVIEW and MATLAB scripts. To extract the individual frequencies of the cups from these measurements, algorithm of calculations was developed. Corrections for the ambient environment were also incorporated into the measurement protocol. Two 7-cell 1.3 GHz cavities were produced with high field flatness immediately after fabrication.

WEPWO067	Conditions for the Existence of 1- and 2-point Multipactor in SRF Cavities	2456
	V.D. Shemelin CLASSE, Ithaca, New York, USA
	Funding: NSF award DMR-0807731 One- and two-point multipactor (MP) in RF cavities are well-known phenomena. However, conditions when this or the other type of discharge develops were not clearly defined up to now. Here, an explicit description of these two types of the MP is presented, geometrical parameters, or figures of merit, responsible for initiation of the MP defined, and areas of their existence delineated. Small sizes of trajectories in the MP require a very precise calculation of fields for simulations. On the other hand, due to these small sizes, fields can be presented as the Taylor expansions and trajectories can be found solving ordinary differential equations of motion. Conditions of motion stability and influence of the Miller force are also accounted.

THPFI090	Accuracy of Measurements of ε and μ of Lossy Materials	3499
	V.D. Shemelin, J.J. Kaufman CLASSE, Ithaca, New York, USA
	Funding: NSF award DMR-0807731 Measurements of samples of lossy ceramic and ferrites for Higher Order Mode Loads are performed routinely in our Lab. Some difference of results for different batches of materials can be explained not only by technological deviations in the material production but also by errors in the dimensions of the measured samples. Simulations with MicroWave Studio for samples in the form of coaxial washers in the frequency range from 1 to 12.4 GHz helped to define the main sources of errors and to improve accuracy of measurements.

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.

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].

WEPWO065

Optimization of Elliptical SRF Cavities for β <1

2450

V.D. Shemelin
CLASSE, Ithaca, New York, USA
J. Newbolt
Rochester University, Rochester, New York, USA

Funding: NSF award DMR-0807731
A systematic approach to optimization of SRF cavities which was done earlier for β=1 is extended to β<1 Some improvements for earlier developed designs are proposed.

WEPWO066

Frequency Control in the Cornell-ERL Main-Linac Cavity Production

2453

V.D. Shemelin, B. Bullock, P.R. Carriere, B. Clasby, R. Eichhorn, B. Elmore, J.J. Kaufman, J. Sears
CLASSE, Ithaca, New York, USA

Funding: NSF award DMR-0807731
Cavity fabrication can be broken down into three main stages: deep-drawing cups, welding the cups in pairs to obtain “dumbbells” and end groups, and, finally, welding the obtained components into a completed cavity. Frequency measurements and precise machining were implemented after the second stage. A custom RF fixture and data acquisition system were used for this purpose. The system comprised of a mechanical press with RF contacts, a network analyzer, a load cell and custom LabVIEW and MATLAB scripts. To extract the individual frequencies of the cups from these measurements, algorithm of calculations was developed. Corrections for the ambient environment were also incorporated into the measurement protocol. Two 7-cell 1.3 GHz cavities were produced with high field flatness immediately after fabrication.

WEPWO067

Conditions for the Existence of 1- and 2-point Multipactor in SRF Cavities

2456

V.D. Shemelin
CLASSE, Ithaca, New York, USA

Funding: NSF award DMR-0807731
One- and two-point multipactor (MP) in RF cavities are well-known phenomena. However, conditions when this or the other type of discharge develops were not clearly defined up to now. Here, an explicit description of these two types of the MP is presented, geometrical parameters, or figures of merit, responsible for initiation of the MP defined, and areas of their existence delineated. Small sizes of trajectories in the MP require a very precise calculation of fields for simulations. On the other hand, due to these small sizes, fields can be presented as the Taylor expansions and trajectories can be found solving ordinary differential equations of motion. Conditions of motion stability and influence of the Miller force are also accounted.

THPFI090

Accuracy of Measurements of ε and μ of Lossy Materials

3499

V.D. Shemelin, J.J. Kaufman
CLASSE, Ithaca, New York, USA

Funding: NSF award DMR-0807731
Measurements of samples of lossy ceramic and ferrites for Higher Order Mode Loads are performed routinely in our Lab. Some difference of results for different batches of materials can be explained not only by technological deviations in the material production but also by errors in the dimensions of the measured samples. Simulations with MicroWave Studio for samples in the form of coaxial washers in the frequency range from 1 to 12.4 GHz helped to define the main sources of errors and to improve accuracy of measurements.