High ion energies in Z pinches: Potential for 3he fusion?

Summary form only given. Doppler-broadened lines with large widths, indicative of ion energies much higher than the thermal electron energies, are sometimes observed in Z pinches. In some Z-pinch experiments, these large energies are likely due to a high ion temperature, but turbulence may dominate in others. The rate of the aneutronic fusion reaction ³He+D→⁴He+H+18.4 MeV, is near its maximum at ion temperatures of 200 keV, similar to those measured on the Z facility in experiments described in Ref. 3. Viscous heating of the ions due to the dynamics of the m=0 instability is an attractive candidate to generate high ion temperatures. The important parameters at stagnation determining whether ion viscous heating is dominant are the ratio of the ion-electron equilibration time to the radial Alfven transit time, and the magnetic Prandtl number. Both should be larger than one. Importantly, for Z pinches in which this viscous process is not expected to be significant, ion heating was not observed. When integrated over the pinch volume, the viscous heating can be expressed in terms of an effective additional nonlinear resistance, as in the magnetic bubble model proposed in. Employing a 1D Lagrangian RMHD model with ion viscous heating, we investigate the scaling of ³He-bearing Z-pinch parameters up to currents of 60 MA, and evaluate their favorability for the ³He+D reaction.