Negative-permittivity plasma generation in negative-permeability metamaterial space

Negative-permittivity plasma is generated in negative-permeability metamaterial space. Unlike cases of positive permeability, which is quite usual in almost all materials available so far, negative-permeability space realized in metamaterial structure [1] allows microwaves to propagate in negative-permittivity media. Our previous study [2, 3] verified that microwaves can propagate in a negative-permittivity plasma immersed in a negative-permeability metamaterial space, which indicates that a dynamic state of negative refractive index was successfully generated. In this study, negative-permeability space was prepared using metamaterial structure as well, and we investigated plasma generation by high-power microwaves in such a metamaterial structure. Langmuir probe measurement revealed that electron density is higher than the cutoff density, which means that permittivity is negative [4, 5]. We also confirmed in both model predictions [6] and experimental results [4, 5, 7] that nonlinear phenomena are key issues to understand underlying physics; they include bifurcations of permittivity or electron density in nonlinear dynamics and harmonic wave generation similar to that reported in nonlinear optics, and both phenomena are observed in experiments. \\[4pt] [1] J. B. Pendry et al., IEEE Trans. Microw. Theory Techniq. \textbf{47}, 2075 (1999).\\[0pt] [2] O. Sakai and K. Tachibana, Plasma Sources Sci. Technol. \textbf{21}, 013001 (2013).\\[0pt] [3] O. Sakai et al., Phys. Plasmas \textbf{20}, 073506 (2013).\\[0pt] [4] Y. Nakamura and O. Sakai, Jpn. J. Appl. Phys. \textbf{53}, 03DB04 (2014).\\[0pt] [5] Y. Nakamura, A. Iwai and O. Sakai, Plasma Sources Sci. Technol. \textbf{23}, 064009 (2014). \\[0pt] [6] O. Sakai, J. Appl. Phys. \textbf{109}, 084914 (2011).\\[0pt] [7] A. Iwai, N. Nakamura, A. Bambina and O. Sakai, Appl. Phys. Express \textbf{8}, 056201 (2015).