Update of ZTH physics and design issues and physics goals of ZTH and role in the Fusion Program

The ZTH construction program is scheduled for completion in December of 1992. Some design features are still amenable to changes directed by new physics or computational information. Numerical results for the ZTH tapered poloidal field gap show that a relatively simple linear taper results in substantial reduction in field error. This design is simpler to manufacture compared with the compound curve predicted by analytical calculations. Also, ongoing analysis of ZT-40M data indicates that the fluctuation levels of magnetic fields and x-rays at high θ (1.7), can be reduced to the fluctuation levels at ''standard'' operational θ (1.4) by changing the winding configuration of the toroidal field (TF) coils. The effect is thought to depend on the shell-like action of the TF coils when they consist of many turns in parallel. Magnetic-field effects, such as field errors, at the unshielded toroidal-field butt-joint gap in the shell can be reduced by this effective external shell. Design implications for installing a second low-current TF coil on ZTH are presented. ZTH has the capability of operating at 4 MA with the addition of power supplies. The projected parameters of ZTH are discussed in the context of various conceptual design. The sensitivity of the conceptual design to the physics results from machines like RFX and ZTH is reviewed. It is shown that the 4 MA ZTH physics results will make a significant advance for the RFP program toward the programmatic RFP fusion goals. Finally, the influence of RFP and tokamak physics on the conceptual design of high mass-power-density (MPD) fusion reactors is investigated through the TITAN and ARIES studies. The confinement characteristics required of these conceptual designs are compared; physics issues are identified that are required to bring the MPD and fusion-power-core of the tokamak designs into coincidence with the RFP designs