Energetics of a long-implosion-time, 12-cm-diameter argon-gas-puff Z pinch at 6.5 MA

We carry out an energy-inventory analysis for a 12-cm-diameter, argon gas-puff shot on the Saturn generator. From the measured pinch inductance time history, we infer the average radius of the pinch current, r
ind
, and the total work done on the pinch, E
coupled
, both as functions of time. The kinetic energy as a function of time, E
KE
, is inferred from r
ind
and the measured initial mass distribution, assuming all of the mass is accreted as in a snowplow. The results show that early in the implosion, E
coupled
≈ E
KE
. However, when the pinch begins to radiate significantly, E
KE
begins to decrease while E
coupled
continues to increase. The increase in coupled energy goes into plasma internal energy, E
int
, i.e., ionization and thermal energies of the z-pinch plasma, and total radiation, E
rad
. During the time of K-shell emission, the significant (∼ 150-kJ) increase in E
coupled
is reflected in approximately the same increase in E
rad
. There is agreement between E
int
at the time of peak K-shell emission inferred from E
coupled
and measurements of E
rad
, and E
int
inferred from independent spectroscopic measurements combined with an atomic-physics model.