Reassessment of steady-state operation in ITER with NBI and EC heating and current drive

Abstract

One of the three goals of the ITER project is to demonstrate fusion gain Q ≥ 5 in steady-state operation (SSO). A reassessment of the necessary conditions for Q ≥ 5 SSO in ITER has been carried out for steady-state scenarios assuming no internal transport barrier in the core plasma and with the sole use of neutral beam injection (NBI) and electron cyclotron heating and current drive (EC H&CD) as heating and current drive sources in these scenarios. The parametric operational space for SSO in ITER has been reassessed utilizing an inverse evaluation approach that takes into account the baseline design of the NBI and EC H&CD systems with P NBI = 33 MW, P EC = 20 MW and their possible upgrade capabilities included in their design, P NBI ≤ 49.5 MW, and P EC ≤ 30 MW. The optimal operational points from this evaluation approach have been chosen for detailed 1.5-D transport modelling by ASTRA and followed-up by magnetohydrodynamic (MHD) stability analysis to demonstrate the conditions in which the Q = 5 SS goal can be achieved in ITER where the plasma current is fully accounted for by the driven current by NBI and EC H&CD and the self-driven bootstrap current. The ideal MHD stability of plasma configurations with self-consistently simulated plasma profiles and equilibrium for the chosen OPs has been analysed by the KINX code. Using this analysis, the possibility to control the MHD stability of these steady-state plasmas by tailoring the current profile with the flexibility provided by design of the systems for electron cyclotron current drive and neutral beam current drive in ITER has been demonstrated. Issues related to the realization of such scenarios from the point of view of plasma physics, experimental demonstration and design limits of the ITER systems and components is discussed.

Constructing a new predictive scaling formula for ITER's divertor heat-load width informed by a simulation-anchored machine learning

“…The new ML-found formula is tested on three different ITER model plasmas: i) the first H-mode plasma to be explored in the initial phases of ITER operation at 5MA [25], ii) an H-mode hybrid plasma at 12.5MA providing long pulse operation with fusion yield Q = 5 [26], and iii) an H-mode steady-state plasma at 10 MA providing steady-state operation with Q = 5 [27]. These three ITER model plasmas have distinctively different values of the kinetic parameter a/ρi,pol at outboard midplane edge.…”

Plasma Stability in a Tokamak with Reactor Technologies Taking into Account the Pressure Pedestal

“…Figure 2 shows the stability limits in units of normalized beta for the modes with toroidal wave numbers ; , , , where , , a are the pressure averaged over the volume of the plasma, the vacuum toroidal field at the geometric center, and the small radius of the plasma, respectively. We note that at higher values of n, diamagnetic stabilization may be significant [5]. Thus, equilibrium with (Fig.…”

“…This factor turns out to be less for TRT plasma with an aspect ratio of = 2.15/0.56 = 3.8, an elongation of κ = 2 and a triangularity of δ = 0.2: = 3.7-3.9 compared to = 4.4-5 for ITER (A = 6.2/2 = 3.1, κ = 1.8, δ = 0.4). Most likely, a lower shape factor is the reason for lowering the Troyon limit compared to in similar ITER scenarios [5]. The limiting beta can be increased with a larger triangularity, as well as by optimizing the current and pressure profiles.…”

“…where the coefficient for a plasma with a cross-sectional geometry similar to the ITER. Together with (2), for the depth of the pedestal D close to Δ for the EPED1 profiles [7], this gives , which, taking into account the geometry of the plasma in the ITER ( = 18.2/2) and with the approximate replacement of , leads to a convenient expression for the limiting pressure on the pedestal (4) For the value of the normalized beta on the pedestal , this is equivalent to (5) for the width of the pedestal in units of the normalized poloidal flux (6) To obtain equilibria consistent with the pedestal model for a given width Δ, which determines in accordance with (2), it is sufficient to set the plasma density at the top of the pedestal and at the separatrix, and to select the temperature according to , provided that the temperature at the plasma boundary is low: the standard value = 75 eV. The consistent equilibrium is determined iteratively for a given vacuum magnetic field and the value , which varies due to the current density in the pedestal.…”

“…The thick dashed lines correspond to the level lines of the growth rate normalized to the diamagnetic frequency =0.5, 1.0, 1.5. * approaches the region of a small shear and a large pressure gradient (infernal modes [5]), as well as their resistive analogues, including double tearing modes. Thus, the achievement of current density in the pedestal, which leads to reversal of the shear even before destabilization of the peeling-ballooning modes, can be interpreted as another limit of the pedestal stability.…”