Rapid change of the neutral hydrogen energy distribution at theL/Htransition in the JFT-2M tokamak

Abstract

Rapid changes of the main ion energy distribution at transitions from L to //, H to L, and during edge localized modes (ELMs) are studied with the time-of-flight neutral measurement on the JFT-2M tokamak. At the L to H transition, 200-400 /us prior to the start of the H a drop, an increase of the high-energy outflux above an energy of 200 eV is observed. An energy of more than 200 eV for hydrogen corresponds to the collisionless condition v*, < 1 just inside the separatrix. A change of the energy distribution preceding that of the H c signal is also found for ELMs.

Ion heat pulse after a sawtooth crash in the JAERI Fusion Torus-2M tokamak

“…Almost all H-mode transitions are triggered by a sawtooth in JFT-2M experiments and our previous report 12 shows the important role of ions at the L/Htransition. The change of the energy distribution by a sawtooth crash during a steady L-mode is the same as that at an L/H-transition.…”

“…The observation of the ion heat pulse could also provide a basic understanding of broader phenomena. For instance, the increase of hot ions near the edge after a crash is known to have a strong influence on the low-confinement mode ͑L-mode͒ to a high confinement mode ͑H-mode͒ transition 12 ͑L/H transition͒. The understanding of solar flares 13 and magnetospheric substorms requires a knowledge of the reconstruction of the ion energy and momentum after the fast reconnection.…”

Experimental studies of the physical mechanism determining the radial electric field and its radial structure in a toroidal plasma

“…Even if the normalized ion collisionality, v * i , for the L-to H-mode transition is much larger than unity, a high-energy tail of ions near the plasma edge may play an important role at the L-to H-mode transition. Rapid changes in the ion energy distribution at the transition of L to H, H to L and during edge-localized modes (ELMs) are observed with the time-of-flight neutral measurement at the top of the plasma (near separatrix) on the JFT-2M tokamak [120]. As seen in figure 21(a), high-energy particles with energies greater than 200 eV (v * i ∼ 1) increase in number at and after the L-to H-mode transition.…”

“…As discussed in section 5.3, the orbit losses of ions which are toroidally ripple-trapped or have banana orbits are sensitive to the edge radial electric field in tokamaks [120][121][122][123][124][125][126][127]. In stellarator or heliotron/torsatron devices, the loss cone due to the helical ripple extends to well inside the plasma and the loss cone structure is sensitive to the radial electric field profiles.…”

Direction of ion ∇B drift and power threshold in high confinement mode in diverted tokamaks

“…The results of this model are in good agreement with those of the experiments over a wide range of ion collisionality. 7,8 Thus, the issue of collisionality had already been addressed, resolved, and understood before the later experiments 9,10 were carried out. Note that the non-Maxwellian nature of the ion distribution in the edge region of a tokamak does not depend on the heating methods, contrary to the popular misconception.…”