Sustained reversed magnetic shear mode of operation in the HL-2A tokamak

Abstract

Realistic reversed magnetic shear (RS) discharges for the HL-2A tokamak are simulated with the TRANSP code. Early NBI heating achieves reversed shear (RS) configurations characterized by highly peaked pressure profiles and a narrow shear reversal region. To avoid excessive peaks in the pressure, and to sustain RS operation towards steady state, LHCD is used to control the current profile. The combined LH and bootstrap current create a quasi-stationary RS discharge with rmin/a ≈ 0.6 and qmin ≈ 2.8. A self-consistent internal transport barrier is produced, and the RS configuration is established with a wider shear reversal region and broader pressure profile that is favourable to achieving the high beta limit.

Temperature oscillating regimes in Tore Supra diagnosed by MHD activity

“…Oscillating regimes have been described as an incomplete ITB transition [1], during which the heat diffusivity, owing to its dependence on the q-profile, oscillates between low values (corresponding to an ITB) and usual values (which implies no ITB). The improved confinement is often related to a negative central magnetic shear (see for example [34][35][36][37][38]). But the analysis of MHD modes during the oscillating regimes points towards the additional role of low order rational value of the safety factor, not only its gradient.…”

Predictive study of high performance scenarios in HL-2A

“…In order to sustain the RS Table 1. Main equilibrium parameters of the two shaped plasmas 1 . 1 k 95 and δ 95 are the elongation and triangularity of the 95% flux surface, respectively; n e0 / n e and p 0 / p indicate the profile peaking of the plasma density and pressure, respectively (where denotes volume averaging).…”

“…The elevated heat diffusivity between the two minima separates the two barriers. The transport barriers are also shown on the ion temperature profile ( figure 7), where the shaded regions are the transport barrier layers defined by |∇T i | > 1 2 max |∇T i |. Comparing with the RS dicharge shown in figure 5, the RS discharge with DB has the following features: (1) a lower minimum q (q min ≈ 1.64, q ψ ≈ 4.7) is obtained, which is consistent with experimental evidence that the combined Hmode edge and ITB results in broadened profiles and improved stability [9][10][11]; and (2) taking into account the fact that the triangularity of plasmas improves the edge pressure limit as evidenced by many experiments [2][3][4][5], the transport barrier located near the edge will enhance the plasma confinement, so that higher plasma parameters (T e0 ∼ 1.7 keV, T i0 ∼ 3.6 keV, H 98(y,2) = 1.17-1.34, β N = 1.45-1.58), compred to those in figure 5, are obtained during the stationary RS phase ( figure 8).…”

Modelling of Profile Control with Lower Hybrid Wave Injection in the HL-2A Single-Null Divertor Plasma

“…In order to raise the plasma parameters and achieve more interesting operation scenarios in HL-2A [1], a campaign to carry out plasma heating using the available auxiliary heating schemes is essential. Now the auxiliary heating scheme of lower hybrid (LH) wave (2 klystrons with power up to 2.0 MW at frequency f = 2.45GHz) is available, and it had been successfully used in the HL-1M tokamak for current drive [2].…”