| 41. |
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| 42. |
- Rasch, Joel, 1982, et al.
(författare)
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Microwave Corona Breakdown in rf Devices
- 2009
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Ingår i: Progress in Electromagnetics Research Symposium (PIERS), August 18-21, 2009, Moscow, Russia, PIERS Proceedings, Moscow Russia, The Electromagnetics Academy, Cambridge, MA, USA. ; , s. 1228-1231
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Konferensbidrag (refereegranskat)
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| 43. |
- Rasch, Joel, 1982, et al.
(författare)
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Microwave Corona Breakdown in Strongly Inhomogeneous Fields
- 2009
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Ingår i: 36th European Physical Society Conference on Plasma Physics 2009, EPS 2009; Sofia; Bulgaria; 29 June 2009 through 3 July 2009. - 9781622763368 ; 33E, s. 657-660
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Konferensbidrag (refereegranskat)abstract
- We investigate the main physical properties of microwave corona breakdown in strongly inhomogeneous electric fields. The focus is put on numerical and approximate analytical calculations of the breakdown threshold in an exponential ionization profile, which is the basic form of the ionization profile caused by the field enhancement around irregular and curved conducting objects. The breakdown threshold is a value associated with a certain plasma density profile. We explain the major characteristics of the density profile, its dependance on pressure and the interplay of diffusion and attachment. For lower pressures the diffusion distributes the electrons from regions of high ionization frequency to regions of weak ionization, where the attachment acts as a sink. For high pressures the diffusion becomes negligible and the breakdown threshold is set by the equality of the ionization and attachment frequencies in the high field region.
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| 44. |
- Rasch, Joel, 1982, et al.
(författare)
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Microwave multipactor breakdown between two cylinders
- 2010
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Ingår i: IEEE Transactions on Plasma Science. - 0093-3813 .- 1939-9375. ; 38:8, s. 1997 - 2005
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Tidskriftsartikel (refereegranskat)abstract
- An analysis has been made of the microwave breakdownthreshold for multipactor in an open structure comprisingtwo parallel cylinders, approximating, e.g., parts of a helix antenna. The electron motion in the corresponding electromagnetic field is analyzed by separating the motion into a slowly varying drift velocity (driven by the ponderomotive force due to the electric field inhomogeneity) and a rapidly oscillating part (driven bythe oscillating electric field). Furthermore, the curvature of the cylindrical surfaces of emission is shown to give rise to a new effect that implies a loss of electrons. This leads to a more stringent multipactor breakdown condition for the two-wire structure thanfor the classical situation corresponding to the case of two plane parallel infinite plates. The importance of this effect is determined by the ratio of the cylinder radii and the distance between the cylinders, and it is shown that when this ratio is small, multipactor can only occur for surfaces having very large secondary emissioncoefficients. A detailed analysis is also made to determine the lowest voltage between the cylinders at which multipactor becomes possible.
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| 45. |
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| 46. |
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| 47. |
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| 48. |
- Rasch, Joel, 1982, et al.
(författare)
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Multipactor breakdown in microwave pulses
- 2013
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Ingår i: Journal of Physics D: Applied Physics. - : IOP Publishing. - 1361-6463 .- 0022-3727. ; 46:50
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Tidskriftsartikel (refereegranskat)abstract
- A theoretical investigation is made of the effect of finite pulse length on the multipactor breakdown condition for microwave signals. The analysis considers the case of multipactor between two parallel metallic plates, using the classical resonance theory. It is found that decreasing pulse length tends to successively eliminate higher order resonance zones and lead to a 'pulse hardening' of lower order modes where the multipactor-prone resonance zones shrink and the lower boundary breakdown field of the zones smoothly increases as the pulse becomes shorter, eventually to completely eliminate the multipactor effect for sufficiently short pulses.
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| 49. |
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| 50. |
- Rasch, Joel, 1982, et al.
(författare)
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On the microwave breakdown stability of a spherical hot spot in air
- 2010
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Ingår i: Journal of Physics D: Applied Physics. - : IOP Publishing. - 1361-6463 .- 0022-3727. ; 43:32
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Tidskriftsartikel (refereegranskat)abstract
- An analysis is made of the basic physical conditions under which a small local microwave-induced breakdown region in a gas may develop to extended 'global' breakdown. The analysis describes the different nonlinear stages of the microwave breakdown process. In the first stage, the increasing breakdown plasma density suppresses the electric field in the breakdown region to reach a quasi-stationary state with constant electron density. The subsequent heating of the gas due to absorption of microwave power in the breakdown plasma is then analysed and the corresponding steady state for the thermal evolution is found including the temperature dependence of the breakdown electric field. The stability properties of the stationary state are examined and it is found that there exists a critical (unstable) radius of the initial breakdown plasma region such that initial regions smaller than this critical dimension will shrink to ultimately vanish whereas plasma regions larger than the critical dimension will grow indefinitely and transform the local breakdown region into full scale 'global' breakdown. The practical implication of this model is to give an order of magnitude estimate for the critical size of hot spots, regions of enhanced field and intensified heating in rf systems.
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