Review of recent laboratory double layer experiments

Recent laboratory measurements of double layers are reviewed. Most experiments that are considered employed triple plasma devices or Q-machines. It is shown that a variety of both one and three dimensional phenomena have been achieved. Stationary one and three dimensional structures consist of monotonic double layers, very weak, weak, strong and very strong double layers with potential steps e(phi)/T(e) equal to about 1, less than, greater than, and much greater than 10, respectively. Multiple double layers consist of structures with large potential dips on the low potential side and stairstep double layers. Two and three dimensional structures include multiple double layers, which resemble U shaped double layers, and ionization produced strong double layers. Moving double layers include ion acoustic double layers and double layers which are the result of drifting species and mismatches at plasma boundaries. It appears that double layers can be BGK solutions or related to turbulence. Double layer creation can occur in a variety of different ways. Ionization can sometimes be important and sometimes play no role at all.