Local and fast density pump-out by ECRH in the LHD

A decrease in the electron density is observed during high-power heating, particularly in electron cyclotron resonance heating (ECRH). One possible mechanism is the increase in the number of trapped particles, which can enhance the radial particle flux, because ECRH accelerates electrons in a direction perpendicular to the magnetic field lines. To observe the effects of the production of trapped particles, high-power (1 MW) ECRH was applied at the ripple bottom of the magnetic field strength, where trapped particles are readily produced. A rapid local outward flux of electrons was first observed near the heating position shortly after ECRH injection. The outward flux is proportional to the electron density in the density range of 0.4 × 10¹⁹ to 0.8 × 10¹⁹ m^-3. The inward electron flux was subsequently enhanced in the core region. (author)