IPAC2012 - List of Authors (Posen, S.)

Paper	Title	Page
WEPPC071	Quench Studies of a Superconducting RF Cavity	2375
	D. Gonnella, M. Liepe, S. Posen CLASSE, Ithaca, New York, USA
	In tests of superconducting RF cavities, it is important to understand the cause of high field quenches. Quenches at high field above 25 MV/m are a limiting factor in the performance of high accelerating field cavities but their causes are currently not well understood. An ILC shaped single cell cavity with quench field near 40 MV/m was tested with temperature mapping to determine the cause of its hard quench. Prior to quench, heating on the order of 25 mK was concentrated in two hot spots. After a quench, these two hot spots remain and a new one appears with much higher heating (about 40 mK). The quench location was found by the temperature mapping system to be centered at the new hot spot, not at the two hot spot locations before that dominated quench. By studying the quench location and heating on the surface of the cavity, some hints were gained as to the cause of this quench.

WEPPC072	High Current Operation of the Cornell ERL Superconducting RF Injector Cryomodule	2378
	M. Liepe, G.H. Hoffstaetter, S. Posen, P. Quigley, V. Veshcherevich CLASSE, Ithaca, New York, USA
	Cornell University has developed a SCRF injector cryomodule for the acceleration of high current, low emittance beams in continuous wave operation. This cryomodule is based on superconducting RF technology, and is currently under extensive testing in the Cornell ERL injector prototype with CW beam currents exceeding 25 mA. Strong damping of Higher-Order-Modes in the cavities is essential for high beam current operation, and is achieved by beamline RF absorber located at cryogenic temperatures in the beam pipe sections between the cavities. This paper gives an overview of the experience gained during the high beam current operation of the cryomodule.

WEPPC073	Progress on Superconducting RF Work for the Cornell ERL	2381
	M. Liepe, F. Furuta, G.M. Ge, Y. He, G.H. Hoffstaetter, T.I. O'Connell, S. Posen, J. Sears, M. Tigner, N.R.A. Valles, V. Veshcherevich CLASSE, Ithaca, New York, USA
	Cornell University is developing the superconducting RF technology required for the construction of a 100 mA hard X-ray light source driven by an Energy-Recovery Linac. Prototypes of all beam line components of the 5 GeV cw SRF main linac cryomodule have been fabricated and tested in detail. This work includes an optimized 7-cell SRF cavity, a broadband HOM beamline absorber, a cold frequency tuner, and a 5 kW CW RF input coupler. A one-cavity test cryomodule has been assembled for a first full cryomodule test of the main linac cavity, and is currently under testing. In this paper we give an overview of these extensive R&D activities at Cornell.

WEPPC075	Testing of the Main-Linac Prototype Cavity in a Horizontal Test Cryomodule for the Cornell ERL	2387
	N.R.A. Valles, F. Furuta, G.M. Ge, Y. He, K.M.V. Ho, G.H. Hoffstaetter, M. Liepe, T.I. O'Connell, S. Posen, P. Quigley, J. Sears, M. Tigner, V. Veshcherevich CLASSE, Ithaca, New York, USA
	Cornell has recently finished producing and testing the first prototype 7-cell main linac cavity for the Cornell Energy Recovery Linac (ERL). The cavity construction met all necessary fabrication constraints. After a bulk BCP, 650C outgassing, final BCP, and 120C bake the cavity was vertically tested. The cavity met quality factor and gradient specifications (2·10¹⁰ at 16.2 MV/m) in the vertical test. Progressing with the ERL linac development, the cavity was installed in a horizontal test cryomodule and the quality factor versus accelerating gradient was again measured. This baseline measurement is the first test in a sequence of tests of the main linac cavity in the test cryomodule. Subsequent tests will be with increased complexity of the beam line, e.g. with HOM beamline loads installed, to study potential sources of reducing the cavity’s quality factor.

WEPPC078	Recent Developments in the Cornell Nb3Sn Initiative	2390
	S. Posen, G.H. Hoffstaetter, M. Liepe, Y. Xie CLASSE, Ithaca, New York, USA
	Superconducting accelerator cavities coated with Nb3Sn have already demonstrated significantly higher unloaded quality factors than standard niobium cavities at surface magnetic fields <30 mT. Theoretical predictions suggest that the maximum critical field of such cavities could be twice that of niobium cavities. Significant facilities have been developed at Cornell University to fabricate Nb3Sn using the vapor diffusion technique. In this paper, recent progress is presented from our Nb3Sn program. The first RF results from a test of a Nb3Sn sample in a TE pillbox sample cavity are presented as well as first images of the newly constructed apparatus for coating full 1.3 GHz single cell cavities.

WEPPC079	Residual Resistance Studies at Cornell	2393
	S. Posen, D. Gonnella, G.H. Hoffstaetter, M. Liepe CLASSE, Ithaca, New York, USA J. Oh Cornell University, Ithaca, New York, USA
	The Cornell single-cell temperature mapping system has been adapted for use with ILC and Cornell ERL-shape superconducting accelerator cavities. The system was optimized for low-noise, high-precision measurements with the goal of measuring resistances as low as 1 nohms. Using this system, a T-map of an ILC single cell was obtained at accelerating fields below the onset of Q-slope and at temperatures at which BCS resistance is small, producing a measurement of the distribution of residual resistance over the surface of the cavity. Standard procedures were used in preparing the cavity to avoid Q-disease and trapped flux caused by cooling the cavity through its transition in the presence of magnetic fields. Studying the T-map gives clues to the source of residual resistance, so that steps can be taken to reduce it, thereby lowering losses and increasing Q0. The temperature map noise-reduction studies as well as the residual resistance results are presented in this paper.

WEPPC080	Minimizing Helium Pressure Sensitivity in Elliptical SRF Cavities	2396
	S. Posen, M. Liepe CLASSE, Ithaca, New York, USA
	Superconducting cavities in CW operation with small beam loading can operate at high QL to significantly reduce power requirements. However, the resulting small bandwidth makes them vulnerable to microphonics from helium pressure fluctuations, which can detune the cavity and cause it to trip. In this paper, we present a mechanical optimization of elliptical cavities for minimization of df/dp, the sensitivity to helium pressure changes. Using the Cornell ERL main linac cavity as an example, an analytical model is developed to illustrate the factors that contribute to df/dp. Methods to reduce df/dp are presented. In addition, df/dp measurements made at the Cornell Horizontal Test Cryostat are presented and corrections to the model are made to account for the thickness of the welds in the helium vessel.

WEPPC081	Measurement of the Mechanical Properties of Superconducting Cavities During Operation	2399
	S. Posen, M. Liepe CLASSE, Ithaca, New York, USA
	The Horizontal Test Cryostat (HTC) contains the first prototype 7-cell 1.3 GHz superconducting cavity for the Cornell ERL main linac. In this paper, experimental measurements of the cavity's mechanical properties are presented. The mechanical resonances were studied using a Dynamic Signal Analyzer, which measured the transfer function from the fast piezo tuner to itself and the cavity frequency. The microphonics detuning of the cavity was measured, and found to satisfy the specification that the maximum detuning be below 20 Hz, even without feedback from the piezos. Correlations were studied between the microphonics detuning and the helium pressure, piezo sense signal, and the ground vibrations. The Lorentz force detuning (LFD) coefficient was also measured. The frequencies of the mechanical resonances were compared to simulation. In addition, the performance of the frequency tuners was evaluated. Both the mechanical tuner and the piezo were found to be highly linear with very little hysteresis even on small scales.

Paper

Title

Page

Quench Studies of a Superconducting RF Cavity

2375

D. Gonnella, M. Liepe, S. Posen
CLASSE, Ithaca, New York, USA

In tests of superconducting RF cavities, it is important to understand the cause of high field quenches. Quenches at high field above 25 MV/m are a limiting factor in the performance of high accelerating field cavities but their causes are currently not well understood. An ILC shaped single cell cavity with quench field near 40 MV/m was tested with temperature mapping to determine the cause of its hard quench. Prior to quench, heating on the order of 25 mK was concentrated in two hot spots. After a quench, these two hot spots remain and a new one appears with much higher heating (about 40 mK). The quench location was found by the temperature mapping system to be centered at the new hot spot, not at the two hot spot locations before that dominated quench. By studying the quench location and heating on the surface of the cavity, some hints were gained as to the cause of this quench.

WEPPC072

High Current Operation of the Cornell ERL Superconducting RF Injector Cryomodule

2378

M. Liepe, G.H. Hoffstaetter, S. Posen, P. Quigley, V. Veshcherevich
CLASSE, Ithaca, New York, USA

Cornell University has developed a SCRF injector cryomodule for the acceleration of high current, low emittance beams in continuous wave operation. This cryomodule is based on superconducting RF technology, and is currently under extensive testing in the Cornell ERL injector prototype with CW beam currents exceeding 25 mA. Strong damping of Higher-Order-Modes in the cavities is essential for high beam current operation, and is achieved by beamline RF absorber located at cryogenic temperatures in the beam pipe sections between the cavities. This paper gives an overview of the experience gained during the high beam current operation of the cryomodule.

WEPPC073

Progress on Superconducting RF Work for the Cornell ERL

2381

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

Cornell University is developing the superconducting RF technology required for the construction of a 100 mA hard X-ray light source driven by an Energy-Recovery Linac. Prototypes of all beam line components of the 5 GeV cw SRF main linac cryomodule have been fabricated and tested in detail. This work includes an optimized 7-cell SRF cavity, a broadband HOM beamline absorber, a cold frequency tuner, and a 5 kW CW RF input coupler. A one-cavity test cryomodule has been assembled for a first full cryomodule test of the main linac cavity, and is currently under testing. In this paper we give an overview of these extensive R&D activities at Cornell.

WEPPC075

Testing of the Main-Linac Prototype Cavity in a Horizontal Test Cryomodule for the Cornell ERL

2387

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

Cornell has recently finished producing and testing the first prototype 7-cell main linac cavity for the Cornell Energy Recovery Linac (ERL). The cavity construction met all necessary fabrication constraints. After a bulk BCP, 650C outgassing, final BCP, and 120C bake the cavity was vertically tested. The cavity met quality factor and gradient specifications (2·10¹⁰ at 16.2 MV/m) in the vertical test. Progressing with the ERL linac development, the cavity was installed in a horizontal test cryomodule and the quality factor versus accelerating gradient was again measured. This baseline measurement is the first test in a sequence of tests of the main linac cavity in the test cryomodule. Subsequent tests will be with increased complexity of the beam line, e.g. with HOM beamline loads installed, to study potential sources of reducing the cavity’s quality factor.

WEPPC078

Recent Developments in the Cornell Nb3Sn Initiative

2390

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

Superconducting accelerator cavities coated with Nb3Sn have already demonstrated significantly higher unloaded quality factors than standard niobium cavities at surface magnetic fields <30 mT. Theoretical predictions suggest that the maximum critical field of such cavities could be twice that of niobium cavities. Significant facilities have been developed at Cornell University to fabricate Nb3Sn using the vapor diffusion technique. In this paper, recent progress is presented from our Nb3Sn program. The first RF results from a test of a Nb3Sn sample in a TE pillbox sample cavity are presented as well as first images of the newly constructed apparatus for coating full 1.3 GHz single cell cavities.

WEPPC079

Residual Resistance Studies at Cornell

2393

S. Posen, D. Gonnella, G.H. Hoffstaetter, M. Liepe
CLASSE, Ithaca, New York, USA
J. Oh
Cornell University, Ithaca, New York, USA

The Cornell single-cell temperature mapping system has been adapted for use with ILC and Cornell ERL-shape superconducting accelerator cavities. The system was optimized for low-noise, high-precision measurements with the goal of measuring resistances as low as 1 nohms. Using this system, a T-map of an ILC single cell was obtained at accelerating fields below the onset of Q-slope and at temperatures at which BCS resistance is small, producing a measurement of the distribution of residual resistance over the surface of the cavity. Standard procedures were used in preparing the cavity to avoid Q-disease and trapped flux caused by cooling the cavity through its transition in the presence of magnetic fields. Studying the T-map gives clues to the source of residual resistance, so that steps can be taken to reduce it, thereby lowering losses and increasing Q0. The temperature map noise-reduction studies as well as the residual resistance results are presented in this paper.

WEPPC080

Minimizing Helium Pressure Sensitivity in Elliptical SRF Cavities

2396

S. Posen, M. Liepe
CLASSE, Ithaca, New York, USA

Superconducting cavities in CW operation with small beam loading can operate at high QL to significantly reduce power requirements. However, the resulting small bandwidth makes them vulnerable to microphonics from helium pressure fluctuations, which can detune the cavity and cause it to trip. In this paper, we present a mechanical optimization of elliptical cavities for minimization of df/dp, the sensitivity to helium pressure changes. Using the Cornell ERL main linac cavity as an example, an analytical model is developed to illustrate the factors that contribute to df/dp. Methods to reduce df/dp are presented. In addition, df/dp measurements made at the Cornell Horizontal Test Cryostat are presented and corrections to the model are made to account for the thickness of the welds in the helium vessel.

WEPPC081

Measurement of the Mechanical Properties of Superconducting Cavities During Operation

2399

S. Posen, M. Liepe
CLASSE, Ithaca, New York, USA

The Horizontal Test Cryostat (HTC) contains the first prototype 7-cell 1.3 GHz superconducting cavity for the Cornell ERL main linac. In this paper, experimental measurements of the cavity's mechanical properties are presented. The mechanical resonances were studied using a Dynamic Signal Analyzer, which measured the transfer function from the fast piezo tuner to itself and the cavity frequency. The microphonics detuning of the cavity was measured, and found to satisfy the specification that the maximum detuning be below 20 Hz, even without feedback from the piezos. Correlations were studied between the microphonics detuning and the helium pressure, piezo sense signal, and the ground vibrations. The Lorentz force detuning (LFD) coefficient was also measured. The frequencies of the mechanical resonances were compared to simulation. In addition, the performance of the frequency tuners was evaluated. Both the mechanical tuner and the piezo were found to be highly linear with very little hysteresis even on small scales.