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High Power Radio Frequency Solid-State Amplifiers and Combiners for Particle Accelerators: From module to system design approach
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.
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 [en]
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: urn:nbn:se:uu:diva-397500ISBN: 978-91-513-0818-0 (print)OAI: oai:DiVA.org:uu-397500DiVA, id: diva2:1371852
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
List of papers
1. Kilowatt-level power amplifier in a single-ended architecture at 352 MHz
Open this publication in new window or tab >>Kilowatt-level power amplifier in a single-ended architecture at 352 MHz
2016 (English)In: Electronics Letters, ISSN 0013-5194, E-ISSN 1350-911X, Vol. 52, no 18, p. 1552-1553Article in journal (Refereed) Published
Abstract [en]

This paper demonstrates the feasibility and very good performance of a kilowatt-level power amplifier in a single-ended architecture, intended for energy systems. The prototype is designed at 352 MHz for the ESS LINAC and delivers 1250 W with 71% efficiency in pulsed operation with a duty cycle of 5%, 3.5 ms pulse at 14 Hz repetition.

Keywords
RF power amplifiers, RF energy, 352 MHz, ESS, FREIA
National Category
Accelerator Physics and Instrumentation Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-300237 (URN)10.1049/el.2016.2117 (DOI)000383378500025 ()
Available from: 2016-08-08 Created: 2016-08-08 Last updated: 2019-11-21Bibliographically approved
2. Time Domain Characterization of High Power Solid State Amplifiers for the Next Generation Linear Accelerators
Open this publication in new window or tab >>Time Domain Characterization of High Power Solid State Amplifiers for the Next Generation Linear Accelerators
Show others...
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.

Keywords
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:nbn:se:uu:diva-334910 (URN)10.1002/mop.30926 (DOI)000416937700028 ()
Projects
ESS
Available from: 2017-11-29 Created: 2017-11-29 Last updated: 2019-11-21Bibliographically approved
3. A new high-power low-loss air-dielectric stripline Gysel divider/combiner for particle accelerator applications at 352 MHz
Open this publication in new window or tab >>A new high-power low-loss air-dielectric stripline Gysel divider/combiner for particle accelerator applications at 352 MHz
Show others...
2018 (English)In: IET Control Theory & Applications, ISSN 1751-8644, E-ISSN 1751-8652, no 5, p. 264-267Article in journal (Refereed) Published
Abstract [en]

This study presents a new two-way Gysel combiner based on an air-dielectric stripline which allows to handle very high radio-frequency power levels with low-loss suitable for power combination in accelerator applications. The insertion loss of the combiner is 0.1 dB (2%). A thick stripline implementation allows improving the power capability in both continuous wave (CW) and pulsed operation. In addition, a mechanical tuner allows compensating for assembly and fabrication discrepancies. A methodology of designing the Gysel combiner as well as high-power measurements up to 22 kW in pulsed mode are presented. Simulations and measurements are in very good agreement.

National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:uu:diva-334913 (URN)10.1049/joe.2017.0793 (DOI)000436345200003 ()
Projects
ESS
Available from: 2017-11-29 Created: 2017-11-29 Last updated: 2019-11-21Bibliographically approved
4. 12-Way 100 kW Reentrant Cavity-Based Power Combiner With Doorknob Couplers
Open this publication in new window or tab >>12-Way 100 kW Reentrant Cavity-Based Power Combiner With Doorknob Couplers
Show others...
2018 (English)In: IEEE Microwave and Wireless Components Letters, ISSN 1531-1309, E-ISSN 1558-1764, Vol. 28, no 2, p. 111-113Article in journal (Refereed) Published
Abstract [en]

We present radio frequency (RF) and thermal characterization of a compact 12-way power combiner designed for operation at 352 MHz at a power level of 100 kW with 5% duty factor. The combiner is based on a reentrant cavity with 12 input doorknob couplers and one output coupler that is integrated with the post of the cavity and forms doorknob type geometry. We introduce convenient design formulas that allow easy identification of a suitable parameter space, which is then refined with numerical simulations. Low-power RF measurements of a prototype show 0.2% insertion loss and a relative rms amplitude imbalance between the ports of 0.1% and phase imbalance of 0.036 degrees rms. The matching is better than -25 dB over a 3-dB bandwidth around the design frequency. We also tested the combiner up to 200 kW and found the RF loss to be comparable to that of the low-power measurement. In a long test run at 100 kW with 5% duty factor, the combiner temperature stabilized at 10 degrees above ambient.

Place, publisher, year, edition, pages
IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2018
Keywords
High-power handling capability, high-power radio frequency (RF) measurements, power combiner, thermal study
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:uu:diva-349845 (URN)10.1109/LMWC.2017.2780619 (DOI)000425173500007 ()
Available from: 2018-05-03 Created: 2018-05-03 Last updated: 2019-11-21Bibliographically approved
5. Feedback compensated 10 kW solid-state pulsed power amplifier at 352 MHz for particle accelerators
Open this publication in new window or tab >>Feedback compensated 10 kW solid-state pulsed power amplifier at 352 MHz for particle accelerators
2019 (English)In: Review of Scientific Instruments, ISSN 0034-6748, E-ISSN 1089-7623, Vol. 90, no 10, p. 104707-1-104707-10, article id 4707Article in journal (Refereed) Published
National Category
Engineering and Technology
Research subject
Engineering Science with specialization in Microwave Technology
Identifiers
urn:nbn:se:uu:diva-397226 (URN)
Available from: 2019-11-18 Created: 2019-11-18 Last updated: 2019-11-21
6. A design of a Highly Efficient Solid State RF Power Source for Optimal Power Consumption during the Charging of Superconducting Cavities
Open this publication in new window or tab >>A design of a Highly Efficient Solid State RF Power Source for Optimal Power Consumption during the Charging of Superconducting Cavities
(English)Manuscript (preprint) (Other academic)
Abstract [en]

This paper demonstrates supply modulation of a kilo-watt single-ended amplifier using optimal charging shaping function, which allows to charge European Spallation Source (ESS) superconducting cavities with minimal reflection power at 352~MHz with 5\% duty cycle (3.5~ms pulse width). A 400-kW power source to be used for those cavities is based on the proof-of-concept supply modulated amplifiers following the optimal filling scheme. Theoretically, the 400-kW power system exhibits 70\% in average efficiency, and 24% of energy drawn from wall plug can be saved using the optimal charging scheme with the beam injection time of 300 us.  

Keywords
envelope tracking, optimal charging, power amplifier, superconducting cavities
National Category
Engineering and Technology
Research subject
Engineering Science with specialization in Microwave Technology
Identifiers
urn:nbn:se:uu:diva-397497 (URN)
Available from: 2019-11-21 Created: 2019-11-21 Last updated: 2019-11-21

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