SRF2015 - List of Authors (Gajewski, K.J.)

Paper	Title	Page
TUPB026	Cryogenic Performance of the HNOSS Test Facility at Uppsala University	612
	R. Santiago Kern, K.J. Gajewski, L. Hermansson, R.J.M.Y. Ruber Uppsala University, Uppsala, Sweden P. Bujard, T. Junquera, J.P. Thermeau Accelerators and Cryogenic Systems, Orsay, France
	Funding: Knut and Alice Wallenbergs foundation The FREIA Laboratory at Uppsala University, Sweden, is developing part of the RF system and testing the superconducting double spoke cavitites for ESS. During 2014 it was equipped with HNOSS, a versatile horizontal cryostat system for testing superconducting cavities. HNOSS is designed for high power RF testing of up to two superconducting accelerating cavities equipped with helium tank, fundamental power coupler and tuning system. In particular it will be used to characterise the performance of spoke cavities like used in the accelerator for the ESS project. HNOSS is connected to a cryogenic plant providing liquid helium and a sub-atmospheric pumping system enabling operation in the range 1.8 to 4.5~K. We present a brief description of the major components, installation and results from the recent operation and tests.
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TUPB089	High-Precision Measurements of the Quality Factor of Superconducting Cavities at the FREIA Laboratory	810
	V.A. Goryashko, K.J. Gajewski, L. Hermansson, H. Li, H. Nicander, R.J.M.Y. Ruber, R. Santiago Kern, S. Teerikoski Uppsala University, Uppsala, Sweden D.S. Dancila Uppsala University, Department of Engineering Sciences, Uppsala, Sweden
	In this paper we propose a high-precision method of measuring Q0 of SRF cavities. A common way to study the performance of an SRF cavity is to build an oscillator around it that is referred to as a self-exciting loop. In the standard approach, by tuning the loop phase for a maximum field level in the cavity and measuring forward and reflected waves, one finds the cavity coupling. Then, performing a time-decay measurement and finding the total quality factor, one gets Q0. However, this approach suffers from a deficiency originating from a single data-point measurement of the reflection coefficient. In our method by varying the loop phase shift, one obtains amplitudes of the reflection coefficient of the cavity as a function of its phases. The complex reflection coefficient describes a perfect circle in polar coordinates. Fitting the overdetermined set of data to that circle allows more accurate calculation of Q0 via the least-squares procedure. The method has been tested at the FREIA Laboratory on two cavities from IPN Orsay: a single spoke and a prototype ESS double spoke.
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Paper

Title

Page

Cryogenic Performance of the HNOSS Test Facility at Uppsala University

612

R. Santiago Kern, K.J. Gajewski, L. Hermansson, R.J.M.Y. Ruber
Uppsala University, Uppsala, Sweden
P. Bujard, T. Junquera, J.P. Thermeau
Accelerators and Cryogenic Systems, Orsay, France

Funding: Knut and Alice Wallenbergs foundation
The FREIA Laboratory at Uppsala University, Sweden, is developing part of the RF system and testing the superconducting double spoke cavitites for ESS. During 2014 it was equipped with HNOSS, a versatile horizontal cryostat system for testing superconducting cavities. HNOSS is designed for high power RF testing of up to two superconducting accelerating cavities equipped with helium tank, fundamental power coupler and tuning system. In particular it will be used to characterise the performance of spoke cavities like used in the accelerator for the ESS project. HNOSS is connected to a cryogenic plant providing liquid helium and a sub-atmospheric pumping system enabling operation in the range 1.8 to 4.5~K. We present a brief description of the major components, installation and results from the recent operation and tests.

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

TUPB089

High-Precision Measurements of the Quality Factor of Superconducting Cavities at the FREIA Laboratory

810

V.A. Goryashko, K.J. Gajewski, L. Hermansson, H. Li, H. Nicander, R.J.M.Y. Ruber, R. Santiago Kern, S. Teerikoski
Uppsala University, Uppsala, Sweden
D.S. Dancila
Uppsala University, Department of Engineering Sciences, Uppsala, Sweden

In this paper we propose a high-precision method of measuring Q0 of SRF cavities. A common way to study the performance of an SRF cavity is to build an oscillator around it that is referred to as a self-exciting loop. In the standard approach, by tuning the loop phase for a maximum field level in the cavity and measuring forward and reflected waves, one finds the cavity coupling. Then, performing a time-decay measurement and finding the total quality factor, one gets Q0. However, this approach suffers from a deficiency originating from a single data-point measurement of the reflection coefficient. In our method by varying the loop phase shift, one obtains amplitudes of the reflection coefficient of the cavity as a function of its phases. The complex reflection coefficient describes a perfect circle in polar coordinates. Fitting the overdetermined set of data to that circle allows more accurate calculation of Q0 via the least-squares procedure. The method has been tested at the FREIA Laboratory on two cavities from IPN Orsay: a single spoke and a prototype ESS double spoke.

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