Transport studies in high-performance field reversed configuration plasmas

Robustness of Waves with a High Phase Velocity
T. Tajima1,2,a) and A. Necas2,b)
1Department of Physics and Astronomy, University of California at Irvine, Irvine, CA, 92697 USA 2Tri Alpha Energy, Inc., P.O. Box 7010, Rancho Santa Margarita, CA 92688, USA
a)Corresponding author: ttajima@uci.edu b)anecas@trialphaenergy.com
Abstract. Norman Rostoker pioneered research of (1) plasma-driven accelerators and (2) beam-driven fusion reactors. The collective acceleration, coined by Veksler, advocates to drive above-ionization plasma waves by an electron beam to accelerate ions. The research on this, among others, by the Rostoker group incubated the idea that eventually led to the birth of the laser wakefield acceleration (LWFA), by which a large and robust accelerating collective fields may be generated in plasma in which plasma remains robust and undisrupted. Besides the emergence of LWFA, the Rostoker research spawned our lessons learned on the importance of adiabatic acceleration of ions in collective accelerators, including the recent rebirth in laser-driven ion acceleration efforts in a smooth adiabatic fashion by a variety of ingenious methods. Following Rostoker’s research in (2), the beam-driven Field Reversed Configuration (FRC) has accomplished breakthroughs in recent years. The beam-driven kinetic plasma instabilities have been found to drive the reactivity of deuteron-deuteron fusion beyond the thermonuclear yield in C-2U plasma that Rostoker started. This remarkable result in FRCs as well as the above mentioned LWFA may be understood with the aid of the newly introduced idea of the “robustness hypothesis of waves with a high phase velocity”. It posits that when the wave driven by a particle beam (or laser pulse) has a high phase velocity, its amplitude is high without disrupting the supporting bulk plasma. This hypothesis may guide us into more robust and efficient fusion reactors and more compact accelerators.
INTRODUCTION
The word plasma arose from the blood plasma that is an amorphous and liquid organic material, as ionized gas is also as amorphous and fluid as the blood plasma. Over many years of research the plasma physicist has discovered that plasma is so unstable that large volumes of literatures have been written such as [1]. Often plasma instabilities either destroy the intended magnetic bottle that tries to contain plasma or enhance the plasma escape path (often called the plasma anomalous confinement). Because of this plasma penchant for instabilities, it is often believed that the utility of plasma for useful functions such as fusion reactors or as an accelerator medium is limited. Sometimes it would be said that if there is free energy available, the plasma would go unstable. So it is of great merit to advance research in either confirming the above point or perhaps to find methods by which the plasma’s inclination to go unstable may be curbed or avoided.
Norman Rostoker was a pioneer in pushing the frontier of beam-driven plasma fusion reactor research (accelerator-driven plasma) as well as leading the collective plasma acceleration in which plasma is marshaled as a central driving component of an accelerator (plasma-driven accelerator). He was one of rare species of scientists who bridged over two distinct fields of plasma fusion research and accelerator physics (Incidentally, he was not only one of the greatest integrators of the accelerator science and fusion plasma science, but he brought fields such as exploratory geophysics, solid state physics (see Professor Kohn’s article [2] in this proceedings), and a broad genre of scientists (see Professor Mackey’s article [3] in this proceedings). In the occasion of the Norman Rostoker Memorial Symposium, commemorating the visions and accomplishments of Norman, we would like to make an attempt to carve out unique properties of beam-plasma interactions in which we can expect robust behavior of the plasma, rather than the fragile and chaotic outcome of plasma. Our working hypothesis here is what we term as the robustness of waves with a high phase velocity. This is in addition to the now famous “Norman’s Conjecture”,
The Physics of Plasma-Driven Accelerators and Accelerator-Driven Fusion
AIP Conf. Proc. 1721, 020006-1–020006-13; doi: 10.1063/1.4944015 © 2016 AIP Publishing LLC 978-0-7354-1368-9/$30.00
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