Bifurcation-Like Behavior of Electrostatic Potential in LHD

Abstract

The temporal evolution of the potential is measured with the heavy ion beam probe (HIBP) in the Large Helical Device (LHD). A rapid change in the potential is observed early in the tangential neutral beam injection (NBI) phase, just after the switch from tangential to perpendicular NBI, and in a low-power electron cyclotron heated (ECH) discharge in the LHD. The radial profile of the potential is measured before and after the potential change. This rapid potential change is considered to indicate the bifurcation of the radial electric field in the edge region of the LHD plasma.

A review of impurity transport characteristics in the LHD

“…Here, it should be noted that the absolute potential of the core plasma is usually negative in the case of a plasma with a negative electric field, and it increases gradually in the radial direction, as shown in figure 29 (see case D) [78]. In contrast to this, the absolute potential of the core plasma is positive, as shown in figure 28(e), so the potential decreases (namely the positive electric field) somewhere at the plasma edge and should become about zero (to be precise, at the wall of the vacuum chamber).…”

Observation of MHD Instabilities Driven by Energetic Electrons in the Large Helical Device

“…Note that the CsI(Tl) detectors can be applied to LHD plasmas under the condition of very low background hard Xrays generated by intense runaway electrons, because the net current-free LHD plasmas are produced without any externally applied toroidal electric field. The heavy ion beam probe (HIBP) [27] also plays an important role in measuring potential changes due to the MHD mode activities excited by energetic electrons in an interior region of plasma in this work.…”