Chapter 5: Physics of energetic ions

Abstract

Physics knowledge (theory and experiment) in energetic particles relevant to design of a reactor scale tokamak is reviewed, and projections for ITER are provided in this Chapter of the ITER Physics Basis. The review includes single particle effects such as classical alpha particle heating and toroidal field ripple loss, as well as collective instabilities that might be generated in ITER plasmas by energetic alpha particles. The overall conclusion is that fusion alpha particles are expected to provide an efficient plasma heating for ignition and sustained burn in the next step device. The major concern is localized heat loads on the plasma facing components produced by alpha particle loss, which might affect their lifetime in a tokamak reactor. Contents 1. Introduction 2471 2. Classical physics of energetic particle confinement and plasma heating 2473 2.1. Classical interaction with the main plasma . . . . . . . . . . . . 2473 2.2. Alpha particle density and beta profiles2474 2.3. Neoclassical diffusion of alpha particles 2475 3. Toroidal field ripple loss and other single particle effects 2475 3.1. Mechanisms and loss channels of toroidal field ripple loss . . . . . . . 2475 3.2. Experimental results on fast ion ripple loss .

Chapter 5: Physics of energetic ions

“…Although these sources were already well understood and extensively tested [2] at the time of writing of the previous ITER Physics Basis [3,4], the intervening years have seen further demonstrations and applications of each of them.…”

“…the parallel wave number [22][23][24]. When the energetic tail ions are 3 He or 4 He, gamma ray tomography is a powerful new technique to measure the fast ion profile [25]. Experiments involving ICRF acceleration of helium could be employed to test alpha particle diagnostics prior to the introduction of tritium in ITER.…”

“…The resulting heat load on the first wall limits the allowable TF ripple amplitude in a tokamak fusion reactor, thereby setting a lower limit on the number of coils. The major points that were understood on ripple losses at the time of the publication of the ITER Physics Basis were: (1) ripple losses are numerically predictable as indicated by experiments in JET [53], JT-60U [54] and TFTR [10]; (2) ripple losses of α-particles in ITER are anticipated to be negligible in discharges with monotonic, positive magnetic shear [3]; (3) on the other hand, the losses can be a concern in advanced operation scenarios based on reversed shear. Since the writing of the ITER Physics Basis, publications on ripple loss experiments have appeared for TFTR [6,10,55,56], JFT-2M [57][58][59] and Tore Supra [60,61].…”

Lévy walk description of suprathermal ion transport

“…They can be generated by turbulent acceleration, 1 external sources, [2][3][4][5][6][7] or, as in the case of fusion devices, nuclear reactions. 4,8,9 The dynamics of those ions results from the complex interplay between drifts related to the magnetic field configuration and interactions with the plasma turbulence. 10 Finding an effective way to describe and characterize suprathermal ion dynamics is a key challenge for basic plasma physics and is of significant importance for the success of tokamaks.…”

“…10 Finding an effective way to describe and characterize suprathermal ion dynamics is a key challenge for basic plasma physics and is of significant importance for the success of tokamaks. [3][4][5]8 From a macroscale perspective, transport of suprathermal ions is often described with a diffusion equation. On the other hand, a microscale view of the transport process can provide insights, especially when the transport process does not obey the diffusion equation.…”