Formation of dee-shaped plasmas with single-null poloidal divertor in Doublet III

Abstract

As a result of the vertical elongation of dee-shaped plasmas, natural single-null poloidal-divertor equilibria have been stably obtained in the upper half of the Doublet III vacuum chamber with a plasma current of 320 kA, a major radius of 140 cm, an average minor radius of ∼45 cm, and a vertical elongation of 1.3–1.4 in the plasma cross-section. Without employing any particular divertor chamber, this simple divertor reduces the influx of metallic impurities to the main plasma and the re-cycling of charged particles in the periphery of the main plasma. The divertor reduces the radiation loss power and improves the energy confinement time.

High magnetic field tokamaks

“…3.2 this enhancement is shown for FT: during the discharge evolution the H a (or D ft ) emission increases by a factor 10 to 100, without any corresponding variations of macroscopic parameters such as plasma current, loop voltage or horizontal position. Similar effects have also been observed in low field tokamaks, only at the extremes of their operating range [60,61]; they resemble strongly the high recycling conditions created in adivertor chamber [62,63].…”

Impurity reduction and remote radiative cooling with single-null poloidal divertor in Doublet-III

“…The strong accumulation of particles and re-cycling in the divertor region in high-density operation can be explained by radiative cooling of the divertor plasma, which will be discussed in the next section, and a reduction of the attenuation length of neutral hydrogen particles produced at the wall with the increase of plasma density in the divertor region: \ ~ 10 cm at n e =lX10 1 3 cm" 3 a n d X < 3 c m a t n e > 5 X 1 0 1 3 cm" 3 with T e ~several eV. This phenomenon observed in Doublet III, which is a relatively large device (a ~ 40 cm), is significantly different from that observed in a small device, such as DIVA (a~ 10 cm), where a linear relation between n e and n eDIV was observed.…”

“…divertor coils outside the vacuum chamber [2]. In diverted discharges, a significant, non-linear increase is observed in the plasma density and particle re-cycling in the divertor with the increase of the main plasma density [3].…”

“…divertor coils outside the vacuum chamber [2]. In diverted discharges, a significant, non-linear increase is observed in the plasma density and particle re-cycling in the divertor with the increase of the main plasma density [3]. This results in a high radiation power density in the divertor region [4] and a large increase in the helium pressure in the divertor region [5].…”

“…This work presents the experimental results of impurity reduction and the remote radiative cooling in the divertor with the single-null poloidal divertor in Doublet-Ill. Doublet-Ill is a tokamak device capable of producing circular and non-circular equilibria with a major radius of 143 cm and a horizontal minor radius of 45 cm. Divertor experiments are performed with Ohmically heated hydrogen discharges, toroidal field BT of 24 kG, plasma current I p of 350-500 kA, lineaverage electron density n e of (1.5-5) X 10 13 cm" 3 . Section 2 discusses the formation of divertor equilibrium and impurity control with this simplified divertor.…”