Scaling laws of potential formation and associated effects are theoretically and experimentally investigated in the GAMMA 10 tandem mirror. In GAMMA 10, the main tandem-mirror operations from 1979 to 2003 are characterized in terms of (i) a high-potential mode having kV-order plasma-confining potentials, and (ii) a hot-ion mode yielding fusion neutrons with 10-20 keV bulk-ion temperatures. In this paper, the externally controllable parameter scaling including electron cyclotron heating (ECH) powers for potential formation covering over these two representative operational modes is investigated; that is, the construction of "the central-cell plasma-confining potentials" c formation scaling with plug ECH is studied on the basis of the electron energy-balance equation and Cohen's strong electron cyclotron heating (ECH) theory for investigating the formation physics of plasma confining potentials.

It is found that our proposed scaling formulae are in good agreement with the experimental data in the two representative operational modes of the high-potential and hot-ion modes in the GAMMA 10 tandem mirror.

This scaling shows a favorable increase in confining potentials with installing more powerful ECH sources by the use of ECH powers over the present 250 kW. On the basis of the scaling prediction, we also report the design of a newly developed 500 kW gyrotron for an application to investigate the validity of the abovedescribed c formation scaling with plug ECH aiming at achieving higher plasma parameters.