  The dense plasma focus is a plasma discharge powered by a capacitor bank.
Standard diagnostics include measurement of the time derivative of the current
through and the voltage across its connections with the capacitor bank.
Interpretation of this diagnostic data often involves some assumptions
regarding the representation of the dense plasma focus as a time varying
inductance. One of the characteristic features of the current derivative
waveform is a relatively sharp dip and an associated sharp voltage spike. This
has often been interpreted as a result of a rapid rise in the time varying
inductance of the plasma. Sometimes, an anomalous plasma impedance is invoked.
This Letter discusses instances where such interpretation creates conceptual
difficulties. A first principles approach to the representation of the dense
plasma focus as a circuit element reveals some fundamental problems with the
traditional representation of plasma focus as a time varying inductance. The
anomalous impedance is shown to be necessary to account for the difference in
the motional impedance implied by a time-varying inductance in the circuit
element representation and a first principles description based on Poynting's
Theorem. Dynamo effects that convert post-stagnation local motion of plasma
into 3-dimensional magnetic fields are shown to contribute to the effective
inductance of the plasma focus and resolve the observed conceptual difficulties
