Multipactor in Low Pressure Gas and in ... - of Richard Udiljak

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creasing ratio Ri/Ro was observed. It was also found that the first multipactor zone became narrower for decreasing Ri/Ro. This behaviour was seen in the analytical analysis and it is evident also in the PICsimulations. Figure 5.16 shows the result of a simulation for Z = 174 Ω (Ro/Ri = 18.26). The agreement between simulations and experiments is good. The multipactor zone becomes narrower and the threshold increases. The position of the zone is slightly shifted compared with the experimental data and the reason for this deviation may partly be explained by an inaccuracy of the dimensions of the copper electrodes. The main reason, however, seems to be related to the SEY-model and the description of the initial velocity of the secondary electrons, but a more detailed study will be necessary to settle this matter. log 10 (Amplitude) [V] 3.2 3 2.8 2.6 2.4 2.2 2 1.8 −1.6 −1.4 −1.2 −1 −0.8 −0.6 log (Frequency) [GHz] 10 Figure 5.16: Ratio of power deposited on the inner and outer conductors due to electron impacts (log-scale) for the same parameters and SEY-formula as in Fig. 5.15 except that Ro/Ri = 18.26. In the section summarizing the main findings of the analytical part, it was mentioned that no single-sided multipactor was noted in the experiments. This is in agreement with the PIC-simulations and shows that no measurements were made at high enough voltage and frequency, where single sided multipactor would be the main phenomenon (the dark blue regions in Fig. 5.16). 90 0 −0.5 −1 −1.5 −2 −2.5 −3 −3.5 −4 −4.5
5.2.4 Main conclusions The analytically obtained results are confirmed by the PIC-simulations. In addition, the significance of initial velocity spread as well as different maximum secondary electron emission have been highlighted. The results have shown that the behaviour with respect to these conditions, in both the single-sided and the double-sided cases, is qualitatively the same as for the parallel plate multipactor. The results are in good agreement with available experimental data, but the commonly used model for SEY seems to be inadequate for large Ro/Ri-ratios, since a small, but not negligible, deviation from the experiments was noticed. 91
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Thesis for the degree of Doctor of
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Multipactor in Low Pressure Gas and
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Conference contributions by the aut
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viii
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3.2.4 Key findings . . . . . . . .
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xii
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xiv
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addition, it is difficult to make c
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numerical study of the phenomenon i
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to physically damage microwave comp
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odd positive integer (N = 1,3,5...)
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σ se [−] 2.5 2 1.5 1 0.5 W 1 W m
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Voltage [V] 10 4 10 3 10 2 10 0 N=1
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even though it may be sufficient fr
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where φL and φR are the left and
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(cf. Fig. 2.7). When taking the env
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2.1.4 Methods of suppression Many o
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Noise (dBm) Power #1 (dBm) Match #1
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andom spread in emission velocities
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Figure 2.12: Multipactor experiment
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where kn is a factor determining th
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allows for another design margin, w
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Boundary function Method One of the
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carriers, because the NLSQ method r
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multipactor discharge. Using a Mont
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the assumption of a constant ratio
Page 54 and 55: Voltage (V) 10 3 10 2 10 1 10 −2
Page 56 and 57: 3.1.3 Main results The main result
Page 58 and 59: lytical model is obviously needed.
Page 60 and 61: where 〈vt 2 〉 represents the av
Page 62 and 63: these quantities in the range from
Page 64 and 65: analytical. Attempts were made to f
Page 66 and 67: only model, the inclusion of ionisa
Page 68 and 69: Normalised Voltage 1.1 1.05 1 0.95
Page 70 and 71: Voltage [V] 10 3 10 0 µ=0 µ=0.75
Page 73 and 74: Chapter 4 Multipactor in irises A c
Page 75 and 76: h l Figure 4.1: The geometry used i
Page 77 and 78: N e /N 0 [−] 3 2.5 2 1.5 1 Multip
Page 79 and 80: to compensate for electron losses i
Page 81: 4.4 Main results This analysis has
Page 84 and 85: support for the qualitative analyti
Page 86 and 87: where R(t) is the average position,
Page 88 and 89: where d stands for the gap width, V
Page 90 and 91: there are different oscillatory vel
Page 92 and 93: Phase [degrees] 60 50 40 30 20 10
Page 94 and 95: G 100 90 80 70 60 50 40 30 20 10 0
Page 96 and 97: possible for quite large Ro/Ri-valu
Page 98 and 99: upper right region of the figures,
Page 100 and 101: σse,max the zones become wider and
Page 102 and 103: G 50 45 40 35 30 25 20 15 10 5 0.2
Page 107 and 108: Chapter 6 Detection of multipactor
Page 109 and 110: Amplitude of acceleration [Gm/s 2 ]
Page 111 and 112: tipactor events that are short-live
Page 113 and 114: software and the time evolution of
Page 115 and 116: ditional test sample, a resonant ca
Page 117 and 118: the FFT. It was concluded that ther
Page 119 and 120: 6.2.1 Single carrier When using the
Page 121 and 122: Reference signal generator Phase co
Page 123 and 124: Amplitude [A.U.] 2.5 2 1.5 1 0.5 De
Page 125 and 126: Chapter 7 Conclusions and outlook T
Page 127 and 128: tioned there were multipactor in no
Page 129 and 130: References [1] W. Henneberg, R. Ort
Page 131 and 132: [27] A. Ruiz et al, “Ti, V, and C
Page 133 and 134: [51] D. Wolk, D. Schmitt, and T. Sc
Page 135 and 136: [75] R. Udiljak, Multipactor in low
Page 137: Included papers A-F 123
Page 141: Paper B R. Udiljak, D. Anderson, M.
Page 145: Paper D R. Udiljak, D. Anderson, M.
Page 149: Paper F V. E. Semenov, N. Zharova,
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Multipactor in Low Pressure Gas and in ... - of Richard Udiljak

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