SRF2011 - List of Authors (Posen, S.)

Paper

Title

Page

Superconducting RF for the Cornell Energy-Recovery Linac Main Linac

90

M. Liepe, Y. He, G.H. Hoffstaetter, S. Posen, J. Sears, V.D. Shemelin, M. Tigner, N.R.A. Valles, V. Veshcherevich
CLASSE, Ithaca, New York, USA

Funding: Supported by NSF award DMR-0807731.
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. Prototype components of the 5 GeV cw SRF main linac cryomodule are under development, fabrication and testing. This work includes an optimized 7-cell SRF cavity, a broadband HOM beamline absorber, and a 5 kW cw RF input coupler. In this paper we give an overview of these activities at Cornell.

MOPO019

Minimizing Microphonics Detuning by Optimization of Stiffening Rings

103

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

Maintaining a constant gradient in a superconducting cavity requires can require much more power if the cavity is not driven on resonance. Significant cost savings in both power consumption and power supplies can be realized by minimizing the detuning of the cavity away from the drive frequency. One of the largest contributions to detuning is microphonics. In this paper, simulations of microphonics detuning by LHe bath pressure fluctuations in a Cornell ERL cavity are presented, and the effect of varying stiffening ring radius is investigated. The consequences of using optimal stiffening ring radii are explored as well, including bandwidth limitations in active detuning compensation due to mechanical resonances and requirements for the frequency tuner.

MOPO063

HOM Measurements with Beam at the Cornell Injector Cryomodule

251

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

The Cornell ERL injector prototype is undergoing commissioning and testing for running unprecedented currents in an electron cw injector. This paper discusses preliminary measurements of HOMs in the injector prototype’s superconducting RF cryomodule. These include HOM spectra up to 30 GHz measured via small antennae located at the HOM beam line absorbers between the SRF cavities. The spectra are compared at different beam currents and repetition rates. The shape of the spectra are compared to ABCI simulations of the loss factor spectrum of the cryomodule beam line. The total HOM power dissipated in the HOM loads was also measured with beam on, which allowed for an estimate of the loss factor. This measurement was accomplished via temperature sensors on the loads, calibrated to input power by heaters on the loads.

Poster MOPO063 [5.567 MB]

THPO009

Quench Studies in Large and Fine Grain Nb Cavities

714

S. Posen, M. Liepe, N.R.A. Valles
CLASSE, Ithaca, New York, USA

Quenches without radiation are sometimes observed at accelerating fields between 25 and 40 MV/m in niobium SRF cavities. The cause for this limitation is not well understood. This work presents results from vertical tests of seven 1.3 GHz single-cell cavities performing above 25 MV/m. Studies were carried out on both fine grain and large grain cavities in ILC and Cornell Reentrant shape geometries. The quenches were located by triangulation using Cornell oscillating superleak transducers and then cavities were optically inspected to determine the surface conditions of the cavity at the quench location. Optical inspection images are presented as well as 3D recreations of quench spots generated using a surface mold and a confocal microscope.

Poster THPO009 [2.013 MB]

THPO066

Stoichiometric Nb3Sn in First Samples Coated at Cornell

886

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

A cavity coated with the superconductor Nb3Sn theoretically will be able to reach more than twice the maximum accelerating field of Nb in a cavity under the same operating conditions and will have a much lower BCS surface resistance at a given temperature. The SRF group at Cornell has recently developed facilities to fabricate Nb3Sn on Nb. The first samples have been coated, and several tests have been performed to characterize them. Results presented include SEM images of the surface, anodization tests, a critical temperature measurement, a test for RRR degradation, and stoichiometry measurements using EDX and XPS.

Poster THPO066 [36.490 MB]

Paper	Title	Page
MOPO016	Superconducting RF for the Cornell Energy-Recovery Linac Main Linac	90
	M. Liepe, Y. He, G.H. Hoffstaetter, S. Posen, J. Sears, V.D. Shemelin, M. Tigner, N.R.A. Valles, V. Veshcherevich CLASSE, Ithaca, New York, USA
	Funding: Supported by NSF award DMR-0807731. 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. Prototype components of the 5 GeV cw SRF main linac cryomodule are under development, fabrication and testing. This work includes an optimized 7-cell SRF cavity, a broadband HOM beamline absorber, and a 5 kW cw RF input coupler. In this paper we give an overview of these activities at Cornell.

MOPO019	Minimizing Microphonics Detuning by Optimization of Stiffening Rings	103
	S. Posen, M. Liepe CLASSE, Ithaca, New York, USA
	Maintaining a constant gradient in a superconducting cavity requires can require much more power if the cavity is not driven on resonance. Significant cost savings in both power consumption and power supplies can be realized by minimizing the detuning of the cavity away from the drive frequency. One of the largest contributions to detuning is microphonics. In this paper, simulations of microphonics detuning by LHe bath pressure fluctuations in a Cornell ERL cavity are presented, and the effect of varying stiffening ring radius is investigated. The consequences of using optimal stiffening ring radii are explored as well, including bandwidth limitations in active detuning compensation due to mechanical resonances and requirements for the frequency tuner.

MOPO063	HOM Measurements with Beam at the Cornell Injector Cryomodule	251
	S. Posen, M. Liepe CLASSE, Ithaca, New York, USA
	The Cornell ERL injector prototype is undergoing commissioning and testing for running unprecedented currents in an electron cw injector. This paper discusses preliminary measurements of HOMs in the injector prototype’s superconducting RF cryomodule. These include HOM spectra up to 30 GHz measured via small antennae located at the HOM beam line absorbers between the SRF cavities. The spectra are compared at different beam currents and repetition rates. The shape of the spectra are compared to ABCI simulations of the loss factor spectrum of the cryomodule beam line. The total HOM power dissipated in the HOM loads was also measured with beam on, which allowed for an estimate of the loss factor. This measurement was accomplished via temperature sensors on the loads, calibrated to input power by heaters on the loads.
	Poster MOPO063 [5.567 MB]

THPO009	Quench Studies in Large and Fine Grain Nb Cavities	714
	S. Posen, M. Liepe, N.R.A. Valles CLASSE, Ithaca, New York, USA
	Quenches without radiation are sometimes observed at accelerating fields between 25 and 40 MV/m in niobium SRF cavities. The cause for this limitation is not well understood. This work presents results from vertical tests of seven 1.3 GHz single-cell cavities performing above 25 MV/m. Studies were carried out on both fine grain and large grain cavities in ILC and Cornell Reentrant shape geometries. The quenches were located by triangulation using Cornell oscillating superleak transducers and then cavities were optically inspected to determine the surface conditions of the cavity at the quench location. Optical inspection images are presented as well as 3D recreations of quench spots generated using a surface mold and a confocal microscope.
	Poster THPO009 [2.013 MB]

THPO066	Stoichiometric Nb3Sn in First Samples Coated at Cornell	886
	S. Posen, M. Liepe CLASSE, Ithaca, New York, USA
	A cavity coated with the superconductor Nb3Sn theoretically will be able to reach more than twice the maximum accelerating field of Nb in a cavity under the same operating conditions and will have a much lower BCS surface resistance at a given temperature. The SRF group at Cornell has recently developed facilities to fabricate Nb3Sn on Nb. The first samples have been coated, and several tests have been performed to characterize them. Results presented include SEM images of the surface, anodization tests, a critical temperature measurement, a test for RRR degradation, and stoichiometry measurements using EDX and XPS.
	Poster THPO066 [36.490 MB]