Predictive modeling of plasmas for gaseous plasmonics

Abstract

The electromagnetic response of a resonant cavity in the presence of plasma discharges is studied, and a model to predict the formation of microwave pulses is developed using fluid plasma simulations and analytic microwave theory. Results for a 14 GHz rectangular cavity partially filled with plasma are then presented from both the model and from experiment as validation. Experimental results are shown to have good agreement with predicted values. It is seen that microwave pulses are generated with widths and delays as short as 1 μs during the plasma discharge decay and pulses with widths and delays as short as hundreds of ns during the plasma discharge ionization. Lastly, comparison is made with a simplified analysis by assuming a uniform plasma cylinder, which is shown to have reasonable agreement given enough fitting parameters.

Millimeter wave control using a plasma filled photonic crystal resonator

“…The plasma ignition causes the transmission to drop 20 dB within 1 µs then recover within 75 µs. Compared to our previous work using a simple two copper post resonator in a WR62 waveguide [12], the initial transmission drop occurs in approximately the same time due to a similar voltage pulse waveform, while the recovery is faster by a factor of 5 due to the higher pressure (10 Torr versus 2 Torr). However, it should not be concluded that the WR62 resonator experiments should also be ran at 10 Torr, as such an increase in the pressure would result in a excessively high electron collision frequency, and hence increase in losses within the cavity.…”

“…The lowpower microwave pulse data from figure 5 can be also used as a diagnostic of the plasma density resident inside the microwave cavity. There are several ways to do this including electromagnetic simulations [7,11] and analytic methods [12,15,16], with the latter being sufficient for most estimation purposes. We have previously described a theory of plasma density estimation [12], and for convenience to the reader, we repeat the equation for the nondimensional frequency shift ∆ω res = (ω res − ω 0 )/ω 0 , where the subscript 0 denotes the unperturbed properties,…”

“…The chamber was fab ricated using additive manufacturing methods with plastics followed by an electroplating process to coat the surface with a conducting layer of 10 µm of copper. We used this same technique on our previous device that consisted of a micro wave resonant cavity in a WR62 waveguide [11,12]. In the hexagonal photonic crystal device we create a resonant cavity by introducing a point defect at the center of the cavity and maintain the same lattice constant at the defect, which results in a resonance frequency of 27 GHz.…”

“…It also results in the formation of microwave pulses with delays and widths ranging from tens of microseconds to submicroseconds. The formation of these tunable microwave pulses has been the motivation of our research in these devices [11,12], where previously we had achieved in creating microwave pulses at 14 GHz with pulse delays and widths as small as 1 µs and 3 µs, respectively. The microwave pulses are formed when the plasma density changes in time within the resonator, causing a changing plasmacavity resonance frequency, and hence a CW microwave signal will change from being reflected to transmitted and back to being reflected.…”

“…Recently, we presented results of studies of a Kuband microwave resonant cavity that was partially filled with a plasma [11,12]. The resonant cavity was situated inside a rectangular waveguide section and consisted of two metallic posts that created a volume within which electromagnetic fields were amplified.…”