Radiation Production by Axion in Space between Two Flat Conductors

We have shown a new production mechanism of radiations produced by dark matter axion $a(t)$ under strong magnetic field $B$. The axion generates oscillating electric current in the surface of conductor. The current is extremely enhanced such as $J_c=(m_a\delta_e)^{-2}J_a$ compared with vacuum current $J_a\equiv g_{a\gamma\gamma}\partial_t a(t)B$; $\delta_e$ is skin depth and axion mass $m_a$. We have shown that sufficiently strong radiation is emitted by cylindrical super ( normal ) conductor to be easily detected. Then, we naively expect that such strong radiation also arises in resonant cavity experiment. But we show that the expectation is wrong. The radiation generated in the cavity is just the one given in the standard estimation, even if we consider the enhanced current in the conductor of the cavity. This is because the radiation in the cavity is standing wave, while the radiation emitted from the cylindrical conductor is outgoing wave. For simplicity we consider radiation arising in the space between two parallel flat conductors.