Measurement of Correlation-Enhanced Collision Rates in the Mildly Correlated Regime ($\Gamma \quad \sim $\textbf{1)}

We have recently measured correlation-enhanced perpendicular-to-parallel collision rates $\nu_{\bot //} $ in cryogenic, strongly magnetized ion plasmas in the mildly correlated regime. The enhancement of $\nu_{\bot //} $ 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. The correlations are parameterized by $\Gamma =e^{2}/aT$which is the ratio of the nearest neighbor potential energy to the ion thermal energy. Our prior measurements [3] over the range $0<\Gamma <15$ observed enhancement up to 10$^{\mathrm{7}}$x, in broad agreement with Salpeter ``equilibrium screening'' theory. However recent ``dynamical screening'' theories [4] predict negligible enhancement for $\Gamma \sim 1$. In our magnesium ion plasmas, we obtain $\Gamma \sim 1$ at densities $n=2\times 10^{7}\mbox{cm}^{-3}$and temperatures$T\cong 5\times 10^{-5}\mbox{eV}$. Recent improvements in our cooling and diagnostic lasers provide better long-term stability in $T$, enabling more accurate measurements of the enhancements. Our new results rule out the dynamical screening theories. [1] D.H.E. Dubin, Phys. Plasmas \textbf{15}, 055705, (2008) [2] E.E. Salpeter, Austr. J. Phys., 7, 373, (1954) [3] F. Anderegg et.al., Phys. Rev. Lett. \textbf{102}, 185001, (2009) [4] W. D\"{a}ppen and K. Mussack Contrib. Plasma Phys. 52, 149, (2012).