Measurement of Correlation-Enhanced Collision Rates in the Mildly Correlated Regime (Γ≈1)

We have measured correlation-enhanced perpendicular-to-parallel collision rates ν_perp-par in cryogenic, strongly magnetized mildly correlated ion plasmas. The enhancement of ν_perp-par is directly analogous [1] to the correlation-enhancement of fusion collisions in hot dense stellar plasma, as first analyzed by Salpeter [2]. The enhancement occurs because plasma screening reduces the repulsive Coulomb potential between charges, allowing closer collisions for a given relative energy.Correlations are parameterized by Γ=e²/aT which is the ratio of the nearest neighbor potential energy to the ion thermal energy. Our prior measurements [3] over the range 0 < Γ < 15 observed enhancement up to 10⁷x, in broad agreement with Salpeter “equilibrium screening” theory. However recent “dynamical screening” theories [4] predict negligible enhancement for Γ≈1.
In our magnesium ion plasmas, we obtain Γ≈1 at densities n=2x10⁷cm^-3 and temperatures T≈5x10^-5eV. After improving lasers stability, we can rule out dynamical screening theories.
[1] D.H.E. Dubin, Phys. Plas. 15, 055705, (2008); [2] E.E. Salpeter, Austr. J. Phys., 7, 373, (1954); [3] F. Anderegg et.al., PRL, 102, 185001, (2009); [4] W. Däppen and K. Mussack Contr. Plas. Phys. 52, 149, (2012).