Microwave Gas and Multipactor Breakdown in Inhomogeneous Fields
Doktorsavhandling, 2012

Microwave gas and multipactor breakdown remains to be one of the limiting factors for the maximum power in microwave devices. Above a certain electric field strength, the so-called breakdown threshold, free electrons can multiply by making ionizing impacts with neutral gas molecules, or causing secondary emission upon impact with system surfaces. The free electron number will rise exponentially, and a number of problems may arise, ranging from noise and changes in the device impedance, to the melting of metal parts and possible destruction of the system. In this thesis we focus our attention at certain aspects of microwave breakdown in satellites and space related systems. This entails air breakdown during testing on ground and ascent, as well as multipactor breakdown in the vacuum of orbit. Our approach to the breakdown problem is a purely theoretical one. Starting from well known physical laws and empirical approximations we apply them to novel systems in an effort to determine the breakdown characteristics. For the case of gas breakdown, our main concern in this thesis has been on analyzing the effect of there being small regions of field enhancement or gas heating inside the microwave system. We try to answer the questions: under what circumstances can small regions of breakdown plasma expand and cause full scale breakdown, and what might be the effect of having local heating of the gas? In the case of multipactor, all our research have sprung from the analysis of a complicated quadri-filar helix antenna. The open geometry, curved surfaces, and large wire separation has lead us to explore an approximate model for the electron dynamics: where the trajectories are dictated by the geometry of the emitting surface, and the action of the ponderomotive force; and the electron impacts can be treated using statistical methods.


inhomogeneous fields


Microwave breakdown

Sal EE, EDIT-huset, Hörsalsvägen 11, Chalmers
Opponent: Igor Kossyi, General Physics Insititute, RAS, Moskva, Ryssland


Joel Rasch

Chalmers, Rymd- och geovetenskap, Icke-linjär elektrodynamik

On the microwave breakdown stability of a spherical hot spot in air

Journal of Physics D: Applied Physics,; Vol. 43(2010)

Artikel i vetenskaplig tidskrift

Microwave multipactor breakdown in helix antennas, theory and simulations

Mulcopim, September 21 - 23, 2011, Valencia, Spain,; (2011)

Konferensbidrag (offentliggjort, men ej förlagsutgivet)

Gas breakdown in inhomogenous microwave electric fields

Journal of Physics D: Applied Physics,; Vol. 42(2009)p. 205203-

Artikel i vetenskaplig tidskrift

Microwave breakdown in a gas-filled rectangular resonator cavity

Journal of Physics D: Applied Physics,; Vol. 42(2009)p. 055210-

Artikel i vetenskaplig tidskrift

Microwave multipactor breakdown between two cylinders

IEEE Transactions on Plasma Science,; Vol. 38(2010)p. 1997 - 2005

Artikel i vetenskaplig tidskrift

Mikrovågsöverslag är ett skadligt fenomen som kan uppstå i mikrovågsutrustning som arbetar vid hög effekt. Fenomenet uppstår när det elektriska fältet går över den såkallade överslagströskeln, vilket leder till att populationen av fria elektroner i systemet kan öka exponentiellt, antingen på grund av jonisering av luft i systemet, eller på grund av sekundäremission av elektroner från ytor i systemet. Fokuset i denna avhandling ligger på överslagsfenomenet i utrusting avsedd för rymdtillämpningar, specifikt antenner och vågledare. Detta innebär jonisering av luft, så kallat korona-överslag, vid testning på marken och under uppskjutning. Väl i omloppsbana arbetar systemet i vakuum, och löper risk för multipaktoröverslag. Båda formerna av överslag leder till störningar och upphettning av utrustningen, med risk för totalhaveri. I syfte att undvika både korona och multipaktoröverslag har vi arbetat med att ta fram teoretiska modeller för att förstå överslagsdynamiken, samt kunna räkna ut den faktiska överslagströskeln för olika komplicerade system.

Microwave breakdown is a harmful phenomenon which can arise in high power microwave systems. The phenomenon occurs when the electric field exceeds the so called breakdown threshold, which leads to an exponential growth of the population of free electrons in the system, either because of ionization of air in the system, or secondary emission of electrons from surfaces in the system. The focus in this thesis is on the breakdown phenomenon in equipment meant for space applications, specifically antennas and waveguides. This entails ionization of air, so called corona breakdown, during testing on ground and ascent. In orbit, the system is operating in vacuum, and runs the risk of multipactor breakdown. Both forms of breakdown leads to disturbances and heating of the equipment, and the risk of total failure. In order to avoid both corona and multipactor breakdown we have tried to develop theoretical models to understand the dynamics of the breakdown phenomena, and to be able to calculate the actual breakdown threshold in different complicated systems.


Fusion, plasma och rymdfysik



Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 3438

Sal EE, EDIT-huset, Hörsalsvägen 11, Chalmers

Opponent: Igor Kossyi, General Physics Insititute, RAS, Moskva, Ryssland