Abrupt in time and wide in space variations of heat diffusivity during ITB formation in JT-60U reverse shear discharges

Abstract

New features of the space-time evolution of the internal transport barrier (ITB) were highlighted during recent JT-60U reverse shear (RS) experiments. An ITB evolution in RS plasmas is often a combination of the fast time-scale processes and the gradual ones. Fast time-scale processes are the common intrinsic features of JT-60U RS plasmas and are seen as the simultaneous (within a few milliseconds) rise and decay of electron temperature (T e ) on two zones separated by a region without variation of T e . The region without variation of T e is located near the position of the minimum safety factor profile (q min ) for many fast processes. The present robust result is that the region of fast-time-scale improvements of electron heat diffusivity is wide in space (around 0.3 of the minor radius) and well extended to the zone of T e decay.

Profile and Shape Control of the Plasmas with Transport Barriers towards the Sustainment of High Integrated Performance in JT-60U.

“…The reason or condition of such a double jump has not yet been clarified, but this observation suggests the existence of multiple stages (or structures) of transport in the box type ITB regime. In JT-60U we have observed a so called 'ITB event' [38] which is characterized by abrupt and spatially wide (covers 30% The to big circles at n e /n GW~0 .7 corresponds to a pellet injected discharge and a reference gas fuelled discharge shown later in Fig. 15.…”

Internal transport barriers in tokamak plasmas*

“…One possible explanation is based on the reduction of the turbulent viscosity due to E × B velocity shear, resulting in a localized jet of E × B flow (Staebler 2000). Staebler (2000) no special role is attributed to rational q values, many experiments suggest, that, in the presence of an evolving current profile, ITB transitions are triggered, when low order rational q values emerge as q 0 or q min decrease (Koide et al 1994, Bell et al 1996, Greenfield et al 1999, Neudatchin et al 1999, Joffrin et al 2001, Günter et al 2001a, Joffrin et al 2002a. Although different in its appearance, further evidence for a link between transport and rational q values is given by the RTP results (figure 12 in section 2.3.1), which describe the electron heat transport by the coexistence of a multitude of transport barriers in the proximity of rational q-surfaces (Hogeweij et al 1998).…”

Systems determined by nonlinear operator valued measures and controlled by vector measures: Existence of optimal controls and necessary conditions of optimality

“…where Φ : Σ × R n −→ R n , c : Σ × Ω −→ R, b : I × Ω −→ R n , and u : Σ × Ω −→ R. The function Φ satisfies the following properties: There exist two countably additive bounded nonnegative measures γ (·), β(·) ∈ M + c (Σ) (not necessarily nonatomic) and nonnegative constants c 1 , c 2 such that (1) …”

“…First is theoretical; the author has studied evolution equations determined by linear operator valued measures and this is an attempt to generalize such studies to nonlinear operator valued measures. The second is physical; in the study of plasma [1] dynamics, thermodynamics and material sciences, it has been observed by scientists that under certain physical situations diffusion coefficient (or conductivity) may exhibit dramatic change in an extremely short period of time. Similarly, in population studies [2] abrupt change of diffusion coefficient including drift may occur due to shock leading to sudden and possibly chaotic dispersal of $ WCNA-2008, Orlando, July 2-9, 2008.…”