A study of particle confinement properties in ohmically and neutral beam heated hydrogen plasmas in the JT-60 tokamak

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Abstract
The characteristics of particle confinement and recycling of ohmically and neutral beam (NB) heated hydrogen plasmas in the JT-60 tokamak are investigated by using the global particle balance equation. The total number of ionization events is estimated by employing a simple formula for the Hα radiation profile, and the gas fuelling efficiency is determined from the time derivatives of the electron density before and after gas feed termination. The global particle confinement time in the Ohmic heating divertor plasma decreases nearly inversely proportionally to the electron density, because of the enhancement of recycling in the plasma periphery. NB injection deteriorates the particle confinement time by a factor of about two. The effective particle confinement time closely related to the density control increases proportionally to the electron density in the Ohmic plasma. In contrast, the effective particle confinement time of the NB heated plasma is independent of the electron density although it decreases with the NB injection power. These results show that the plasma density can be controlled by the gas puff in both ohmically and NB heated hydrogen discharges.

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