Benjamin Wang

Plasma modification of spoof plasmon propagation along metamaterial-air interfaces

We report on measurements of the shift in resonance frequency of “spoof” surface plasmon polariton propagation along a 2-D metamaterial slow-wave structure induced by a gaseous plasma near the metamaterial/air interface. A transmission line circuit model for the metamaterial structure interprets the introduction of a plasma as a decrease in unit cell capacitance, causing a shift in the plasmon dispersion to higher frequency. We show through simulations and experiments that the effects of this shift at the resonance frequency and attenuation below and above resonance depend on the plasma density. The shifts recorded experimentally are small owing to the low plasma densities generated near the structure, ∼ 10 11 cm − 3, but simulations show that a shift of ∼ 3 % of the resonance frequency can be generated at plasma densities of ∼ 10 12 cm − 3.

A tunable microstrip photonic crystal bandgap device with plasma elements

Summary form only given. A tunable microstrip bandgap device with plasma elements is designed and experimentally characterized. A straight microstrip waveguide with patterned holes in the copper ground plane form a photonic bandgap structure, with an operating frequency of 2 GHz-10 GHz. ANSYS HFSS simulations were performed to characterize the transmission characteristics of the device. A switchable plasma element is integrated into one of the holes in the ground plane using a pulsed laser generated plasma. Atmospheric and argon gas conditions were used for the generation of the laser plasma. The plasma element in the ground plane bandgap structure allows the transmission in the bandgap frequencies to be tuned as a function of plasma density.

Plasma photonic crystals with tunable bandgap and configurable transmission modes

Summary form only given. A fully tunable plasma photonic crystal is used to control the propagation of free space electromagnetic waves in the S to X band of the microwave spectrum. A structured array of discharge plasma tubes are arranged in a square crystal lattice with the individual plasma dielectric constant tuned through variation in the plasma density. We show through simulations and experiments that transverse electric (TE) mode bandgaps exist, arising from both positive and negative dielectric constant regimes of the plasma. We experimentally demonstrate that the bandgap frequencies can be shifted through changing the dielectric constant by varying discharge current density, allowing for an actively tunable device with a controllable bandgap. Additional transmission modes, including waveguiding and bending modes, are simulated and experimentally demonstrated by changing the structure of the plasma discharges within the crystal lattice structure.

Characterization of a plasma deflagration accelerator as an ELM replicator for PFC testing

Transient events in fusion power plants such as DEMO and ITER are known to pose a severe threat to plasma facing components (PFCs) due to melting and erosion after repeated edge localized mode (ELM) loads. Experimental testing in situ of potential PFC materials at fusion relevant conditions is difficult and expensive, and no facility currently in operation accurately replicates the salient plasma environment. At Stanford University, an experimental facility designed to mimic the heat flux, particle fluence, and other key characteristics of ELMs and disruption events in a controlled setting is under development. A pulsed plasma accelerator operating in the deflagration mode is used to generate high velocity (40-100 km/s) directed plasma jets that are stagnated on target material samples. In this work, we present probe data characterizing the plasma parameters of the accelerated plume using hydrogen as the working gas, as well as preliminary target studies of copper tokens exposed to pulses at various total and peak shot energies. Results from the probe analysis indicate achieved energy fluxes and heat flux parameters that are ELM-like, and the observed damage morphologies on the witness plates indicate that initial surface roughness plays a significant role in the growth and characteristics of surface melt patterns.