Long-pulse stability limits of the ITER baseline scenario

Abstract

DIII-D has made significant progress in developing the techniques required to operate ITER, and in understanding their impact on performance when integrated into operational scenarios at ITER-relevant parameters. Long duration plasmas, stable to m/n = 2/1 tearing modes, with an ITER-similar shape and Ip/aBT, have been demonstrated in DIII-D, that evolve to stationary conditions. The operating region most likely to reach stable conditions has normalized pressure, βN ≈ 1.9–2.1 (compared to the ITER baseline design of 1.6–1.8), and a Greenwald normalized density fraction, fGW 0.42–0.70 (the ITER design is fGW ≈ 0.8). The evolution of the current profile, using internal inductance (li) as an indicator, is found to produce a smaller fraction of stable pulses when li is increased above ≈1.1 at the beginning of βN flattop. Stable discharges with co-neutral beam injection are generally accompanied with a benign n = 2 magnetohydrodynamic mode. However if this mode exceeds ≈10 G, the onset of a m/n = 2/1 tearing mode occurs with a loss of confinement. In addition, stable operation with low applied external torque, at or below the extrapolated value expected for ITER has also been demonstrated. With electron cyclotron injection, the operating region of stable discharges has been further extended at ITER equivalent levels of torque and to edge-localized mode (ELM) free discharges at higher torque but with the addition of an n = 3 magnetic perturbation from the DIII-D internal coil set. The characterization of the ITER baseline scenario evolution for long pulse duration, extension to more ITER-relevant values of torque and electron heating, and suppression of ELMs have significantly advanced the physics basis of this scenario, although significant effort remains in the simultaneous integration of all these requirements.

Development of the Q = 10 scenario for ITER on ASDEX Upgrade (AUG)

“…Based on results from tokamaks with a carbon wall, a high triangularity shape (δ = δ average ∼ 0.4) has been identified to be best suited in ITER to combine high density operation using continuous deuterium gas puffing with good H-mode confinement ( [2] and references therein). In recent years experimental demonstration of the ITER BL scenario has been studied on devices like Alcator C-Mod, DIII-D and JET [3][4][5][6].…”

Multi-species impurity granule injection and mass deposition projections in NSTX-U discharges

“…A comparison of the ablation times for similar sized granules injected into roughly equivalent discharges showed an ablation rate that was accelerated by approximately a factor of 1.7 in these low torque discharges. This factor is the result of the IGI granule flight path being located geometrically close and roughly perpend icular to the trajectory of the counter propagating neutral beam, which was utilized to heat the ITER baseline discharge [27]. The ability of an incident energy source to accelerate the ablation process of injected pellets has been documented in the literature [28], and was observed in these experiments by noting that the lithium granules began to evaporate as soon as they had traversed the tile shadow, prior to any contact with the last closed flux surface (LCFS) [29].…”

Resolving ECRH deposition broadening due to edge turbulence in DIII-D by heat deposition measurement

“…However, it must be noted that fusion gain is impacted by both unsuppressed islands and by always-on EC power use. ITER is expected to use 50 MW of power in its baseline configuration, and thus with an expected fusion power of 500 MW, a gain of Q=10 can be achieved [37].…”