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Time Domain Characterization of High Power Solid State Amplifiers for the Next Generation Linear Accelerators
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, FREIA. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
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, FREIA.
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.
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2018 (English)In: Microwave and optical technology letters (Print), ISSN 0895-2477, E-ISSN 1098-2760, Vol. 60, no 1, p. 163-171Article in journal (Refereed) Published
Abstract [en]

This paper presents the time domain characterization of high power pulsed solid state amplifiers to be used forlinear accelerator applications. The study comprises nonlinear circuit envelope simulations and time domainenvelope measurements. Measurements and simulations are performed under the pulsed conditions (3.5 mspulse width, 5% duty cycle) specific to the European Spallation Source (ESS) high intensity proton accelerator.We measure the characteristics of pulsed LDMOS based power amplifiers such as: pulse droop along the pulse,efficiency, average envelope pulse amplitude and phase, pulse drain current waveform, pulse drain voltagewaveform, etc. A comparison between the measured results and the simulated results is also presented. Inaddition to the pulse profile characterization, the pulse to pulse (P2P) stability of the presented solid state poweramplifier (SSPA) is investigated as variations of amplitude and phase. The P2P stability simulations areintroduced as a combination of the Monte-Carlo simulations and the nonlinear circuit envelope simulations. Thesimulated results are used for fitting the P2P measurements to give an early insight of causes of instabilities ofthe nonlinear LDMOS models.

Place, publisher, year, edition, pages
2018. Vol. 60, no 1, p. 163-171
Keywords [en]
accelerator, solid state amplifiers, LDMOS, nonlinear circuit envelope, time domain envelope measurements, pulse profile
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
URN: urn:nbn:se:uu:diva-334910DOI: 10.1002/mop.30926ISI: 000416937700028OAI: oai:DiVA.org:uu-334910DiVA, id: diva2:1161125
Projects
ESSAvailable from: 2017-11-29 Created: 2017-11-29 Last updated: 2019-11-21Bibliographically 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
Keywords
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
2. High Power Radio Frequency Solid-State Amplifiers and Combiners for Particle Accelerators: From module to system design approach
Open this publication in new window or tab >>High Power Radio Frequency Solid-State Amplifiers and Combiners for Particle Accelerators: From module to system design approach
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The rise of Big Science projects brings issues related to the energy consumption and the associated environmental impacts of such large-scale facilities. Therefore, environmentally-sustainable developments are undertaken towards the adoption of energy savings and improved energy-efficient approaches. The advent of the superconducting (SC) radio frequency (RF) accelerating cavity is bringing answers to these issues. Such superconducting RF (SRF) cavity is made of niobium that allows much higher accelerating gradients with a minimization of the energy consumption. The SC RF technology is increasingly used in many modern particle accelerators, including: 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 innovation of solid state PA technology pushes limits regarding packaging, efficiency, frequency capability, thermal stability, making them more attractive than other well-established alternative technologies, such as vacuum tube technology in mid-range power applications. Through the investigations of designs and techniques, this research goal of the thesis allows to improve solid-state based power generation systems from module to the overall system design. This thesis introduces the single-ended PA design approach in planar technology and at kilowatt level. The design solution unlocks different possibilities including: improved integration, layout flexibility for tuning, and suitably for mass productions that are demanded in future high peak power generation systems. The novel amplifier design is followed by time domain characterization to fully evaluate the pulse profiles of such amplifiers when delivering kilowatt output power level for operation in conjunction with SRF accelerating cavities. Amplitude and phase stability of those amplifiers are also investigated in time-domain. The extracted data can then be used as measurement-based model for predicting factors which could degrade the overall stability of the associated PA.

Future RF power generation systems built around solid state PAs need also efficient combining strategies. Two engineering design solutions are investigated in this thesis aiming for mid- and high- range power combination. One solution is based on a combination of the Gysel structure using suspended strip-line technology for improved power handling capability. Another solution is implementing a radial combiner, which uses re-entrant cavity resonator at 352 MHz and door-nob geometry for coupling at inputs and at the output. These solutions facilitate the scaling up 400 kW for powering ESS spoke cavities while maintaining a high degree of efficiency in RF power generation. This thesis gives insights of system integration and tuning procedures with a demonstration of combining 8 modules, delivering a total of 10 kW output power. Along with the proposed combining solutions at higher power levels, the nominal power block of 10 kW is used as an elementary block to propose scaling up in power till the 400 kW nominal power required by ESS.

Finally, this thesis focuses on implementing an optimal charging scheme for SRF cavities, which helps reducing the wasted energy and improves the overall efficiency operation at future accelerating facilities. Therefore, these results contribute further to the larger adoption of solid state technologies in the future power generation systems for particle accelerators.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2019. p. 98
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1881
Keywords
solid state technology, power amplifier, superconducting cavities, optimal charging, high efficiency, particle accelerators
National Category
Engineering and Technology
Research subject
Engineering Science with specialization in Microwave Technology
Identifiers
urn:nbn:se:uu:diva-397500 (URN)978-91-513-0818-0 (ISBN)
Public defence
2020-01-15, Häggsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 09:15 (English)
Opponent
Supervisors
Available from: 2019-12-20 Created: 2019-11-21 Last updated: 2020-01-13

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Hoang Duc, LongBhattacharyya, AnirbanGoryashko, VitaliyRuber, RogerOlsson, JörgenDancila, Dragos

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