Experimental vertical stability studies for ITER performance and design guidance

Abstract

Abstract. Operating experimental devices have provided key inputs to the design process for ITER axisymmetric control. In particular, experiments have quantified controllability and robustness requirements in the presence of realistic noise and disturbance environments, which are difficult or impossible to characterize with modeling and simulation alone. This kind of information is particularly critical for ITER vertical control, which poses the highest demands on poloidal field system performance, since the consequences of loss of vertical control can be

Disruptions, Disruptivity, and Safer Operating Windows in the High-β Spherical Torus NSTX

“…The current quench can also lead to the generation of runaway electrons [6,7,[16][17][18][19][20][21], which can result in catastrophic vessel and PFC damage [33]. Finally, if the control of the plasma vertical position [23][24][25][26][27] is lost, the plasma can drift up or down and come in contact with the vessel and PFCs; the "halo currents" [28][29][30][31][32][33][34] that are shared between those components and the plasma can lead to destructive forces [15]. Clearly, it is necessary to avoid these events.…”

“…The most basic example of this control is the regulation of the plasma vertical position with radial field feedback [25][26][27]; when this control is lost, the plasma can drift upwards or downwards, leading to a disruption known as a Vertical Displacement Event (VDE). More recently, active control has been demonstrated for both the slowly varying n=1 error field [77,78] and the rapidly growing n=1 the resistive wall mode [51,52,[79][80][81].…”

Detection of Disruptions in the High-β Spherical Torus NSTX

“…For instance, a quantity like ΔZ max [52] indicative of the maximum controllable vertical displacement, could be calculated based on equilibrium quantities determined in realtime. These could then be compared to measurements or estimates of the disturbance spectrum, in order to determine when vertical control has become marginal and the likelihood of a VDE has significantly increased.…”

“…Examples of equilibrium control techniques include control of the strongly shaped plasma boundary [37,38], the global β N [39][40][41], the internal profiles [42][43][44][45], or error fields [46,47]. The vertical position instability [48][49][50][51][52] is controlled [50][51][52] as a matter of routine in all shaped tokamaks. Active control of the resistive wall mode (RWM) [53,54] has been demonstrated using magnetic mode detection and applied 3D fields [55][56][57][58][59][60].…”

Dynamics of the Disruption Halo Current Toroidal Asymmetry in NSTX

“…These were quite rapid VDEs, where radial field feedback was deliberately frozen [63] at t= 0.3 s; the plasma was then actively pushed down by applying a positive bias to the upper radial field coil and a negative bias to the lower radial field coil. The vertical motion under these scenarios begins to clearly grow at ~310 ms, with, as shown in Fig 12a), disruption following at ~340 ms.…”