Design and Control of Long-Pulse High-Power Klystron Modulators

Max Collins

Forskningsoutput: AvhandlingDoktorsavhandling (monografi)

107 Nedladdningar (Pure)


The European Spallation Source (ESS) is an under-construction material science research facility in Lund, Sweden, and will upon completion host the most powerful superconducting linear accelerator (linac) in the world. The ESS linac is powered by klystron modulators required to deliver long high-power pulses (pulse amplitude 115 kV/100 A, pulse length 3.5 ms, pulse repetition rate 14 Hz) of very high quality (combined flat top ripple and droop < 0.15% of the pulse amplitude, pulse-to-pulse variability < 0.15% of the pulse amplitude, 0-99% pulse rise time < 150 μs) while maintaining excellent AC grid power quality (low flicker operation < 0.2%, line current THD < 3%, unitary power factor). Conventionally, solid-state modulators are based on pulse transformers due to their high performance, robustness, simplicity and straightforward design. However, pulse transformer size is fundamentally linked to application pulse length, pulse power and pulse rise time, i.e., considering this modulator topology for the unprecedented and extremely demanding pulse power requirements posed by the ESS linac results in very large and unpractical modulator systems. As an alternative, this dissertation presents the novel Stacked Multi-Level (SML) modulator topology based on a modular power converter chain including an active constant-power capacitor charger (eliminating flicker, line current harmonics and reactive power) and a switched pulse generation stage utilizing a pulse modulation-demodulation technique in effectively eliminating the direct size - pulse length dependency. This dissertation develops models and design optimization frameworks for both the conventional pulse transformer-based modulator topology, serving as benchmark, as well as the novel SML modulator topology. The developed models are validated through both simulations and experiments, and the use of the optimization frameworks are exemplified through the design and implementation of modulator systems for, e.g., the Facility for Antiproton and Ion Research (FAIR) in Germany and the ESS in Sweden. The developed optimization frameworks are also used to directly compare the two modulator topologies in view of high-power applications (115 kV/100 A) through parametric studies, sweeping the pulse length from 1-10 ms and the pulse repetition rate from 1-50 Hz. The dissertation ends with a complete description and experimental validation of both a reduced-scale technology demonstrator as well as the full-scale klystron modulators developed for and implemented at the ESS.
Tilldelningsdatum2024 feb. 9
ISBN (tryckt)978-91-985109-6-6
ISBN (elektroniskt)978-91-985109-7-3
StatusPublished - 2024

Bibliografisk information

Defence details
Date: 2024-02-09
Time: 09:00
Place: Lecture Hall MA2, Centre of Mathematical Sciences, Sölvegatan 20, Faculty of Engineering LTH, Lund University, Lund.
External reviewer(s)
Name: Burkhart, Craig
Title: Dr.
Affiliation: SLAC National Accelerator Laboratory Stanford, USA.

Ämnesklassifikation (UKÄ)

  • Annan elektroteknik och elektronik


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