Figure 1

The poloidal cross section of the Proto-RT chamber, the magnetic surfaces of dipole field, and the typical electron orbit after being injected from the electron gun. A pair of vertical field coils (not seen) is located outside of the chamber.Reuse & Permissions

Figure 2

Potential profiles of an electron plasma in a poloidal cross section of the Proto-RT (a) when the potential is not controlled: IC electrode bias $V_{\mathrm{IC}}=0$ and (b) when the IC electrode is negatively biased: $V_{\mathrm{IC}}=-300\mathrm{V}$. The profile images are reconstructed from 284 data points measured shot by shot. The thin lines show the magnetic surfaces. Base pressure $P_{\mathrm{base}}=8\times {10}^{-5}\mathrm{Pa}$ and typical magnetic field strength $B_{\mathrm{typ}}=1.3\times {10}^{-2}\mathrm{T}$.Reuse & Permissions

Figure 3

(a) Waveform of the wall probe signal. (b) Decay of the charge on the wall probe. The IC electrode was biased to $-300\mathrm{V}$. The gun was terminated at $t=0$. $P_{\mathrm{base}}=8\times {10}^{-5}\mathrm{Pa}$ and $B_{\mathrm{typ}}=1.3\times {10}^{-2}\mathrm{T}$.Reuse & Permissions

Figure 4

The dominant frequency of electrostatic fluctuations (just before the quiescent phase) as functions of (a) the typical strength of dipole magnetic field $B$ (at $r=40\mathrm{cm}$) and (b) potential of the IC electrode $V_{\mathrm{IC}}$. $P_{\mathrm{base}}=8\times {10}^{-5}\mathrm{Pa}$, (a) $V_{\mathrm{IC}}=-250\mathrm{V}$, and (b) $B_{\mathrm{typ}}=6.0\times {10}^{-3}\mathrm{T}$.Reuse & Permissions

Figure 5

The lifetime $t^{*}$ as functions of (a) the back pressure of hydrogen gas and (b) typical magnetic field strength $B$. $P_{\mathrm{base}}=8\times {10}^{-5}\mathrm{Pa}$, (a) $B_{\mathrm{typ}}=1.3\times {10}^{-2}\mathrm{T}$, and (b) $V_{\mathrm{IC}}=-300\mathrm{V}$.Reuse & Permissions