A limitation to the analogy between pure electron plasmas and two‐dimensional inviscid fluids

Thermal corrections to E×B drifts cause small structures in pure electron plasmas to smear. This smearing breaks the strict analogy between the behavior of pure electron plasmas and the behavior of two‐dimensional inviscid fluids. The causes and consequences of this smearing are discussed, a criterion for the validity of the plasma/fluid analogy is constructed, and experimental examples of the failure of the analogy are presented. The criterion indicates that fluid‐like behavior can persist to scale lengths far smaller than the normal ‘‘collective’’ behavior limit.