Development of a non-ideal plasma target for non-linear beam–plasma interaction experiments

A shock-driven plasma target was developed to examine non-linear interactions between low-energy heavy ions and cold-dense plasmas. MD calculations predicted that beam–plasma coupling constant γ∼0.1γ∼0.1 must be achieved to observe the non-linearity, which corresponds to the plasma coupling constant Γ≈0.2Γ≈0.2 for projectiles of vproj≈10keV/u and q≈2q≈2. One-dimensional numerical estimations using SESAME equation of state showed that a shock wave propagating in 5-Torr H2H2 gas with 47 km/s must be produced to satisfy Γ≈0.2Γ≈0.2. Utilizing an electromagnetic shock tube with a peak current of 50 kA and a current rise time of 800 ns, we achieved a shock speed of 45 km/s. The electron density distribution of the shock-produced plasma along the beam axis was measured by a Mach–Zehnder interferometer. From this measurement we confirmed that the electron density was over 1017cm-3 and the homogeneity was acceptable during several hundred nanoseconds. The electron temperature was also determined by optical spectroscopic measurements. The Coulomb coupling constant was evaluated using these experimental data to investigate feasibility of the beam–plasma interaction experiments.