Page 12 - Transport studies in high-performance field reversed configuration plasmas

Another impact that the Rostoker lab launched was for us to consider the electron acceleration with the collective method in order to avoid the difficulty of trapping and accelerating heavier particles to relativistic energies. This prepared the way to invent the idea of plasma acceleration by a relativistically fast wave to trap and accelerate electrons, as electrons are more tolerant of the nonadiabatic nature of acceleration due to their light mass. This endeavor led to the creation of the LWFA concept. In addition, it was realized that the fast phase velocity of the laser-driven plasma wave is capable of sustaining robust plasma waves without disrupting the plasma medium that supports the wave. Although this claim may have encountered suspicion that plasma may be too unstable and thus unable to keep its structure intact, the principle and the subsequent experiments proved instability to not be a concern, as the robustness of waves with a high phase velocity was instrumental in preserving the plasma integrity.
In more recent developments the beam-driven FRC plasma shows that in spite of strong kinetic beam-plasma instabilities the plasma remains intact. The excited plasma waves in this magnetized plasma exhibit a large enough amplitude that we observe wave-induced anomalous heating, leading to enhanced fusion reactivity in the deuteron FRC plasma . In this phenomenon, once again the hypothesis of robustness of waves with a high phase velocity helps us to understand why such beam-injection leads to a remarkable fusion reactivity enhancement. Here we have found that the beam-instability causes robust wave excitation in the range of ion Bernstein frequency. The wave amplitude is high, because the phase velocity of this ion-beam driven instability has a phase velocity much higher the thermal velocity of the bulk ions. Consistent with our hypothesis, such instability is capable of exciting robust ion waves that can draw sufficient amount of the tail plasma ion distribution toward the fusion enhancement. It is important to consider this phenomenon and mechanism in the proton-boron 11 fusion condition and to evaluate if and how this physics manifests in p-B11 fusion reactors.
In conclusion we have seen a broad applicability of the introduced hypothesis of the robustness of waves with a high phase velocity, including the improvement of the recent progress in laser-driven ion acceleration and the interpretation and possible extrapolation of the observed beam-driven fusion reactivity enhancement.
ACKNOWLEDGMENTS
We gratefully thank G. Mourou, M. L. Zhou, X. Q. Yan, F. Mako, J. A. Wheeler, K. Nakajima, M. Binderbauer, R. Magee, T. Roche, M. Thompson, S. Nicks, H. Gota, J. Douglas, H. Berk, T. O’Neil, B. Coppi, R. Davidson, R. Kulsrud, M. Yamada, and B. Richter for illuminating discussions and encouragements. We dedicate this paper to the memory of Professor Norman Rostoker, whose tutelage of us was so fundamental. The work was in part supported by the Norman Rostoker Fund at UCI.
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