Page 7 - Transport studies in high-performance field reversed configuration plasmas

shape. A marked reduction of laser intensity that Esirkepov et al.[35] required may be accomplished if the ponderomotive acceleration of electrons by the laser pulse is smoother and more adiabatic when compared to linearly polarized laser irradiation with otherwise like parameters of laser and target even if the laser intensity is far less than that of Esirkepov [35]. This is because the ponderomotive acceleration of CP removes a component of electron acceleration at 2ω frequency, which is present in the LP pulse case. Recall that the longitudinal acceleration of electrons is exerted by the Lorentz term v x B, in which v is proportional to E, the laser field. In these experiments some evidence of semi-isolated or quasi-monoenergetic energy spectrum begins to manifest. However, their spectrum remains to be improved to become a beam of isolated single energy. There is some circumstantial evidence of ions trapped behind the electron charge sheet.
To increase the adiabaticity of ion acceleration, additional possibilities include making the group velocity of the laser to gradually increase from small (near zero) at the beginning of interaction to a high value at the end. This may be done by setting the plasma density at the entrance to the critical density and to reduce it gradually so that the group velocity of the laser tends to increase [40]. A possibly related method of controlling the accelerating velocity to be more adiabatic may be done by adopting nanoclusters distributed appropriately [41]. An enhanced energy production with nanoclusters in [42] may be attributable to such an effect.
(a)
(b)
FIGURE 4. (a) Cartoon versions of non-adiabatic ion acceleration in which the accelerating structure does not stop and then accelerate. (b) That of the adiabatic smooth acceleration of ions in which the accelerating structure first stops and then adiabatically picks up the speed.
BEAM-DRIVEN PLASMA FUSION REACTORS
It is central to have an intense beam drive in an FRC plasma in the C-2U program at TAE [9], as discussed in Introduction, for the beam injection to stabilize macro-instabilities such as the tilt mode [7] and drift instabilities [46] as suggested by Norman’s conjecture. In addition, we now observe in C-2U that (i) the beam drives robust kinetic bump-on-the-tail beam-plasma micro-instabilities; (ii) nonetheless, these instabilities incur no global plasma destruction; and (iii) even enhance the deuteron-deuteron (D-D) fusion reactivity. We are now led to a new hypothesis beyond Norman’s Conjecture: waves with a high phase velocity can retain robustness and keep plasma from its total destruction over a substantial period of their evolution, i.e. the hypothesis of waves with a high phase velocity. Below we briefly review this phenomenon and we compare this with our own simulation that shows beam driven micro-instabilities that are non-destructive, but transfer energy from fast ions to the plasma, causing phase space bunching. This hypothesis shares the same philosophy with the wakefield excitation [10]. Such a mechanism may explain an experimentally observed anomalous neutron signal (10-100× the predicted thermonuclear fusion
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