Chapter 2: Plasma confinement and transport

Abstract

The understanding and predictive capability of transport physics and plasma confinement is reviewed from the perspective of achieving reactor-scale burning plasmas in the ITER tokamak, for both core and edge plasma regions. Very considerable progress has been made in understanding, controlling and predicting tokamak transport across a wide variety of plasma conditions and regimes since the publication of the ITER Physics Basis (IPB) document (1999 Nucl. Fusion 39 2137–2664). Major areas of progress considered here follow. (1) Substantial improvement in the physics content, capability and reliability of transport simulation and modelling codes, leading to much increased theory/experiment interaction as these codes are increasingly used to interpret and predict experiment. (2) Remarkable progress has been made in developing and understanding regimes of improved core confinement. Internal transport barriers and other forms of reduced core transport are now routinely obtained in all the leading tokamak devices worldwide. (3) The importance of controlling the H-mode edge pedestal is now generally recognized. Substantial progress has been made in extending high confinement H-mode operation to the Greenwald density, the demonstration of Type I ELM mitigation and control techniques and systematic explanation of Type I ELM stability. Theory-based predictive capability has also shown progress by integrating the plasma and neutral transport with MHD stability. (4) Transport projections to ITER are now made using three complementary approaches: empirical or global scaling, theory-based transport modelling and dimensionless parameter scaling (previously, empirical scaling was the dominant approach). For the ITER base case or the reference scenario of conventional ELMy H-mode operation, all three techniques predict that ITER will have sufficient confinement to meet its design target of Q = 10 operation, within similar uncertainties.

Observation of Critical-Gradient Behavior in Alfvén-Eigenmode-Induced Fast-Ion Transport

“…Transport near a critical gradient is of great interest in understanding, for example, substorms in Earth's magnetosphere [1] or the equilibrium profile limits in fusion plasmas associated with temperature or density gradient driven turbulence [2]. Energetic particle transport studies are particularly relevant for reaching the burning plasma state in a fusion reactor, where a large number of fast ions must be confined for sufficiently long times so that their energy is transferred through collisions to the colder, background plasma.…”

Chaotic transport in Hamiltonian systems perturbed by a weak turbulent wave field

“…The perturbation Hamiltonian of such systems contains an infinite number of modes with the regular phases χ mn and the amplitudes H mn ∼ |m| −α , (α 2) [51] (see also [40]). The transport barrier formation near the low-order rational tori found numerically in Hamiltonian systems perturbed by a weak turbulent field at the large Kubo numbers, probably, may have some sort of relation to the transport barriers in fusion experiments (see, e.g., a review [4]). As was mentioned above there is a possible relation between the density of rational magnetic surfaces (or tori) and the transport of particles and energy, particularly, the transport barrier formation in fusion experiments, which has been already discussed in a number of papers [12][13][14][15][16][17][18][19][20][21][22][23][24][25].…”

“…The study of transport of charged particles in turbulent magnetic and electric fields is of a great interest in laboratory and astrophysical plasmas (see, e.g., [1][2][3][4][5][6][7] and references therein). Particularly, in magnetically confined fusion devices one of the great challenges is to reduce the enhanced transport of particles known as anomalous transport which is induced by small-scale turbulent fields generated by instabilities [1,4].…”

“…Particularly, in magnetically confined fusion devices one of the great challenges is to reduce the enhanced transport of particles known as anomalous transport which is induced by small-scale turbulent fields generated by instabilities [1,4]. Such improved confinement regimes of plasmas has been experimentally found by heating plasma [8,9].…”

“…Such improved confinement regimes of plasmas has been experimentally found by heating plasma [8,9]. They are achieved due to a creation of radially localized zones with the reduced transport, known as transport barriers (see, e.g., reviews [2,4,10,11]). …”