Abstract
This paper reports a fishnet hyperbolic metamaterial that mimics the electromagnetic properties of magnetically confined plasma. These electromagnetic properties are strongly anisotropic and different from any conventional material, therefore cannot be mimicked by bulk materials. The structure is made of a stack of thin copper grids spaced by Rohacell foam. We numerically and experimentally show that this kind of structuration matches well the properties of a homogeneous plasma. This solution breaks a long-lasting bottleneck and will accelerate the development of high-frequency heating systems to be used in nuclear fusion.
Highlights
Design and FabricationThe coupling of Lower Hybrid Range of Frequencies (LHRF, 1–8 GHz) waves to strongly magnetized plasmas is a critical issue for tokamaks as it often limits the RF power, which can be transferred from the antenna to the plasma
The problem is to transfer power from the antenna to the plasma, and test these antennas under relevant conditions
We present here a metamaterial load that is close to optimal coupling conditions (ε// = −3) for LHRF waves
Summary
The coupling of Lower Hybrid Range of Frequencies (LHRF, 1–8 GHz) waves to strongly magnetized plasmas is a critical issue for tokamaks as it often limits the RF power, which can be transferred from the antenna to the plasma. It is shown in ref.[9] that these wire metamaterials have a strong spatial dispersion, i.e. ωp (and ε// and the response of the medium) depends on the wavevector component along the wire direction Since the phased waveguide antenna launches waves with n// = kz/k0 ≈ 2, we retained the parameters associated with the green dispersion curve (Fig. 2b) This is a good compromise between a curve close to the hyperbola and one that gives for kz/k0 ≈ 2 the same energy propagation direction as the homogeneous plasma (magenta arrows).
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