Debye length and plasma skin depth: two length scales of interest in the creation and diagnosis of laboratory pair plasmas

In traditional electron/ion laboratory plasmas, the system size L is much larger than both the plasma skin depth ls and the Debye length gimel(D). In current and planned efforts to create electron/positron plasmas in the laboratory, this is not necessarily the case. A low-temperature, low-density system may have.gimel(D) < L < l(s); a high-density, thermally relativistic system may have l(s) < L <.gimel(D). Here we consider the question of what plasma physics phenomena are accessible (and/or diagnostically exploitable) in these different regimes and how this depends on magnetization. While particularly relevant to ongoing pair plasma creation experiments, the transition from single-particle behaviour to collective, 'plasma' effects -and how the criterion for that threshold is different for different phenomena -is an important but often neglected topic in electron/ion systems as well.