High density experiments with gas puffing and ECRH in T-10

Abstract

High density experiments were carried out in T-10 with gas puffing and electron cyclotron resonance heating (with absorbed power value up to 1.4 MW) with oblique and perpendicular power launch. Densities exceeding the Greenwald limit (n Gw ) by up to a factor of 1.8 were achieved in a regime with a high value of the edge safety factor at the current flat-top, q(a) ∼ = 8.2. The decrease of q(a) to a value of 3 led to the reduction of the ratio ( ne ) lim /n Gw to 1. Confinement degradation with density increase was not significant up to the density limit. However, the typical T-10 linear increase of energy confinement time with density saturates at ne 0.6n Gw . This saturation is the result of the development of an additional transport in the electron heat channel. However, the saturated τ E values exceeded the ITER L-mode scaling predictions by up to a factor of 1.2 and were close to the value predicted by the ITER H-mode scaling. Effect of the strong gas puffing on the plasma confinement and experiments with neon seeding are also discussed in this paper.

Analysis of the highest energy confinement in tokamaks based on thermodynamic approach

“…These two regimes of energy confinement are called linear ohmic confinement and saturated ohmic confinement (SOC). The same dependence of τ E on the plasma density is observed in the Lmode with additional heating [2]. Since this dependence exists both in the ohmic heating and additional heating plasmas, we will use the terminology linear energy confinement (LEC) and saturated energy confinement (SEC ) for all types of heating.…”

Explanation of Experimentally Observed Phenomena in Hot Tokamak Plasmas from the Nonequilibrium Thermodynamics Position

“…Among the many unexplained phenomena is the dependence of the energy confinement time τ E = W d /P in on the plasma density observed experimentally ( Figure 3) [11]. At low densities, τ E ∝ n e , then it saturates.…”

The 2008 Public Release of the International Multi-tokamak Confinement Profile Database

“…where the energy confinement time, τ E , increases linearly with density for n e /n G < 0.6 and saturates for n e /n G > 0.6 [102].…”

“…T-10 experiments with ECRH have demonstrated regimes where the energy confinement time, τ E , increases linearly with density for n e /n G < 0.6, and saturates for n e /n G > 0.6 [102]. The T-10 contribution to PR08 consists of three discharges from a plasma density scan in such a regime, where the density spanned the range 0.25 ≤ n/n G ≤ 1: in #33957 (low density) τ E was in the linear regime; in #33970 (high density) the τ E density dependence had saturated; and in #33965 the density was close to the intermediate transition point between these states [102,103].…”

“…The T-10 contribution to PR08 consists of three discharges from a plasma density scan in such a regime, where the density spanned the range 0.25 ≤ n/n G ≤ 1: in #33957 (low density) τ E was in the linear regime; in #33970 (high density) the τ E density dependence had saturated; and in #33965 the density was close to the intermediate transition point between these states [102,103]. On-axis 2nd harmonic ECRH (140GHz, X-mode) provided auxiliary plasma heating, and these waves were launched along the major radius from the low field side to give an absorbed ECRH power of 0.9MW during this scan.…”