Neutron Generation by Laser-Driven Spherically Convergent Plasma Fusion

Abstract

We investigate a new laser-driven spherically convergent plasma fusion scheme (SCPF) that can produce thermonuclear neutrons stably and efficiently. In the SCPF scheme, laser beams of nanosecond pulse duration and 10^{14}-10^{15} W/cm^{2} intensity uniformly irradiate the fuel layer lined inside a spherical hohlraum. The fuel layer is ablated and heated to expand inwards. Eventually, the hot fuel plasmas converge, collide, merge, and stagnate at the central region, converting most of their kinetic energy to internal energy, forming a thermonuclear fusion fireball. With the assumptions of steady ablation and adiabatic expansion, we theoretically predict the neutron yield Y_{n} to be related to the laser energy E_{L}, the hohlraum radius R_{h}, and the pulse duration τ through a scaling law of Y_{n}∝(E_{L}/R_{h}^{1.2}τ^{0.2})^{2.5}. We have done experiments at the ShengGuangIII-prototype facility to demonstrate the principle of the SCPF scheme. Some important implications are discussed.

Ladder climbing and autoresonant acceleration of the spherical plasma density wave

“…The theoretical predictions given by equations (20)- (22) can be confirmed by numerical simulation of the slow evolution equation (12) with the initial condition B m (τ=τ 0 )=δ m,1 . For a given set of (P 1 , P 2 ), we define the resonant capture probability…”

“…Therefore, we only present the points of (P 1 , P 2 ) that satisfying P=0.85 as the form of the blue full circles in figure 2. In addition, figure 2 also shows the different regimes of phase-locking transition of the system obtained by theoretical results of equations (20)- (22). The blue solid and red dash lines are approximate analytic thresholds of the spherical and one-dimensional plasma, respectively.…”

“…For our system (15), when it is expressed in terms of the parameters P 1 and P 2 , we can obtain the theoretical threshold of the classical AR transition P P 14.44 . (22) but the driving parameter P 1 should be replaced with P 1.66 1 . So, the coupling strength in the spherical plasma is weaker than that in the one-dimensional plasma (the former is 0.5/ 0.83≈0.6 times that of the latter).…”

“…However, the asymptotic analytical thresholds (i.e. equations (20)- (22)) are obtained according to the simplified constant coefficient equation (15) (it is only an approximate result of equation (12)), thus, obviously, there will be the deviation between the numerical simulation results and the asymptotic analytical thresholds. Furthermore, because the system belongs to the mixing of LC and AR when 1<P 2 <10 and the classical AR also can be achieved when a stronger inequality, P 1 2  , is satisfied for P 1 ?1 [14].…”

“…The spherical plasma is an interesting subject of studying and it is significant for the injection and acceleration of the electrons [20,21]. In addition, the most of the laboratory facilities about the inertial confinement fusion are spherically symmetric [22,23]. Clearly, the existence of the LC and AR in the spherically symmetric plasma has important impact on the electrons acceleration and inertial confinement fusion.…”