Existing and new applications of micropellet injection (MPI) in magnetic fusion

Abstract

The intense heat and energetic particle fluxes expected in ITER and future magnetic fusion reactors pose prohibitive problems to the design, selection and maintenance of the first wall and divertor. Micropellet injection (MPI) technologies can offer some innovative solutions to the material and extreme heat challenges. Basic physics of micropellet motion, ablation and interactions with high-temperature plasmas and energetic particles are presented first. We then discuss MPI technology options and applications. In addition to plasma diagnostic applications, controlled injection of micropellets of different sizes, velocities and injection frequencies will offer several possibilities: (1) better assessment of the core plasma cooling due to dust produced in situ; (2) better understanding of the plasma–material interaction physics near the wall; (3) new methods for plasma fuelling and impurity control; and (4) techniques for edge cooling with minimal impact on the plasma core. Dedicated small-scale laboratory experiments will complement major fusion experiments in development and applications of MPI.

Micro-particle injection experiments in ADITYA-U tokamak using an inductively driven pellet injector

“…Presently the device allows a diverse range of experiments to be performed and controlled with relative ease to explore the mass, material, and velocity of pellets to be used for heat and energetic particle mitigation during disruption. Its usage and utility can be extended to carry out fundamental investigations of micro-dust motion, ablation, and interaction with high-temperature plasmas thereby helping us with a better understanding of plasma-material interaction physics, especially near the reactor walls, better assessment of impurity control and plasma core cooling (due to dust produced in-situ), explore techniques for edge cooling, etc [32].…”

Hollow pellet injection for magnetic fusion

“…A number of existing impurity launchers may be used to achieve the injection speeds as required in figures 4 and 5 [7]. Different launchers may be distinguished by their different forces of acceleration.…”

“…where we assume that the residue radius is (r p − T h ) T 0 (which is referred to as the residue thickness here) in both equations (7) and (8). The pellet density n p is 4.44 × 10 22 for Li and 1.39 × 10 23 for B.…”

“…The amount of energy released by ELMs is proportional to the stored plasma energy and can exceed 10% in extreme cases. Natural ELMs in ITER and similar can potentially accelerate the plasma facing wall deterioration, and ELM control is therefore necessary for ITER and future fusion reactors [1][2][3][4][5][6][7]. Cryogenic hydrogen pellets [8] and impurity pellets have experimentally shown to be feasible in inducing ELMs at a frequency higher than the natural ELM frequency of a few Hz and can reduce the peak energy flux onto the divertor and other plasma-facing surfaces.…”

Measurement of incandescent microparticle acceleration using stereoscopic imaging

“…In comparison, mega-frame cameras can now capture movies continueously for seconds at a time 1 . A growing number of mass injection techniques are used in magnetic fusion 7 , allowing controlled mass injection and therefore quantitative analysis of microparticle dynamics. Additionally, the broad uses of imaging techniques, including applications in machine vision, have led to rather sophisticated tool kits that are availability for three-dimensional (3D) particle tracking from multiple camera views 8,9 .…”