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Minimization of power consumption during charging of superconducting accelerating cavities
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy. (FREIA)
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, High Energy Physics. (FREIA)
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, High Energy Physics. (FREIA)
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy. (FREIA)
2015 (English)In: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, ISSN 0168-9002, E-ISSN 1872-9576, Vol. 801, p. 78-85Article in journal (Refereed) Published
Abstract [en]

The radio frequency cavities, used to accelerate charged particle beams, need to be charged to their nominal voltage after which the beam can be injected into them. The standard procedure for such cavity filling is to use a step charging profile. However, during initial stages of such a filling process a substantial amount of the total energy is wasted in reflection for superconducting cavities because of their extremely narrow bandwidth. The paper presents a novel strategy to charge cavities, which reduces total energy reflection. We use variational calculus to obtain analytical expression for the optimal charging profile. Enemies, reflected and required, and generator peak power are also compared between the charging schemes and practical aspects (saturation, efficiency and gain characteristics) of power sources (tetrodes, IOTs and solid state power amplifiers) are also considered and analysed. The paper presents a methodology to successfully identify the optimal charging scheme for different power sources to minimize total energy requirement.

Place, publisher, year, edition, pages
2015. Vol. 801, p. 78-85
Keyword [en]
Superconducting cavity, Optimization, IOT, Tetrode, Doherty architecture, Solid-state
National Category
Accelerator Physics and Instrumentation
Identifiers
URN: urn:nbn:se:uu:diva-265660DOI: 10.1016/j.nima.2015.07.056ISI: 000362282200012OAI: oai:DiVA.org:uu-265660DiVA, id: diva2:867486
Available from: 2015-11-05 Created: 2015-11-02 Last updated: 2018-02-28Bibliographically approved
In thesis
1. From Macroscopic to Microscopic Dynamics of Superconducting Cavities
Open this publication in new window or tab >>From Macroscopic to Microscopic Dynamics of Superconducting Cavities
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Superconducting (SC) radio frequency (RF) cavities are at the heart of many large-scale particle accelerators such as the European Spallation Source (ESS), the X-ray Free Electron Laser (XFEL), the Linac Coherent Light Source (LCLS)-II and the proposed International Linear Collider (ILC). The SC cavities are essentially resonant structures with very high intrinsic quality factors (Q0) of the order of 1010. The high Q0 of the cavities leads to increased reflection during charging of the cavities to nominal voltage because the bandwidth of the signal exceeding that of the cavity. This results in high energy losses in case of pulsed machines. In this thesis I explore and present a novel technique to optimally charge the superconducting cavities with the particular example of the spoke cavities to be used for the ESS project in Lund, Sweden. The analysis reveals that slow charging with hyperbolic sine cavity voltage profile matches the signal bandwidth to that of the cavity which leads to energy efficient filling.

However, a filling rate lower than some particular value is counter-productive. The energy expended in cryogenic cooling to evacuate the heat due to ohmic losses in the cavity starts to dominate the lost energy. Such cryogenic losses are dependent on cavity Q0 through the residual resistance. The residual resistance changes with the applied electromagnetic field due to the pair-breaking mechanism of Cooper-pairs. Hence, methods for accurate measurement of the cavity Q0 are essential for accurate characterization and operation of the superconducting cavities. In this thesis I propose a novel method to accurately measure Q0 as a function of the applied electromagnetic field and present experimental results from the prototype spoke cavity in the Facility for Research Instrumentation and Accelerator Development (FREIA), at Uppsala University.

The cavity quality factor (Q0) is also dependent on the material’s purity and the trapped magnetic flux in the superconducting material. Recent studies have revealed that the rate of cooling of materials through the critical temperature has an effect on the residual flux trapped in the material. In this thesis I use the time-dependent Ginzburg-Landau equations to model the process of state transition from a normal to a superconducting state. This theoretical study may allow an explanation of the experimentally observed results from the basic principles of the general theory of state transitions as proposed by Ginzburg and Landau.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2018. p. 75
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1638
Keyword
superconducting cavity, superconductivity, self-excited loop, Ginzburg-landau, vortex, optimization, quality factor, microwave
National Category
Accelerator Physics and Instrumentation
Research subject
Physics with specialization in Elementary Particle Physics
Identifiers
urn:nbn:se:uu:diva-343704 (URN)978-91-513-0253-9 (ISBN)
Public defence
2018-04-20, Polhemsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 09:30 (English)
Opponent
Supervisors
Available from: 2018-03-27 Created: 2018-02-28 Last updated: 2018-04-24

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Bhattacharyya, Anirban KrishnaZiemann, VolkerRuber, RogerGoryashko, Vitaliy

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Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment
Accelerator Physics and Instrumentation

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