Sausage instabilities in the electron current layer and its role in the concept of fast ignition

Das, Amita ; Jain, Neeraj ; Kaw, Predhiman ; Sengupta, Sudip (2004) Sausage instabilities in the electron current layer and its role in the concept of fast ignition Nuclear Fusion, 44 (1). pp. 98-105. ISSN 0029-5515

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The fast ignition concept of laser fusion utilizes hot electrons produced at the surface of the target by an incident intense laser pulse for the creation of the hot spot for ignition. As the hot electrons move inwards to the core of the precompressed target, the electrons from the background plasma provide a return shielding current. Three-dimensional PIC simulations have shown that intense Weibel, tearing and coalescence instabilities take place which organize the current distribution into a few current filaments. In each of these filaments the central core region constitutes a current due to the fast electrons propagating inwards towards the pellet core, while the outer cylindrical shell region carries the return shielding current. The presence of instabilities and their subsequent nonlinear development can hinder the propagation of fast electrons towards the core influencing the location of the hot spot for ignition. Earlier studies showing the existence of sausage-like modes were carried out in the non-relativistic limit and under the assumption of equal electron densities of the fast and the cold electrons. The fast electron density, in general, differs considerably from the background plasma density as it is dependent on the incident laser intensity. This paper incorporates relativistic effects and also studies the dependence of the growth rate on the fast electron density. Finally, nonlinear saturation of the instability and its impact on the stopping of the fast electron motion towards the core have also been investigated using numerical simulations. The simulations have, however, currently been carried out for non-relativistic dynamics. The results show that the sheared velocity profile of the channel gets flattened, causing an effective drop in the inward moving current.

Item Type:Article
Source:Copyright of this article belongs to Institute of Physics.
ID Code:70463
Deposited On:21 Nov 2011 10:09
Last Modified:21 Nov 2011 10:09

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