Upgrade possibilities for the central solenoid in CIT

Upgrade possibilities for the central OH (ohmic heating) solenoid in the CIT (Compact Ignition Tokamak) are discussed. A higher performance solenoid could be designed for either higher flux capability or longer pulse length. A solenoid that provides larger flux linkage while still satisfying the engineering and the physics constraints is described. The optimization scheme consists of grading the turns of the pancakes of the central solenoid, either radially (in a given pancake), axially (using different pancake geometry), or both. Increases between 10 and 20% in the flux-swing from the PF (poloidal field) system can thus be obtained, corresponding to 6-12 V-s. Detailed calculations of the plasma equilibrium and the power/energy requirements of these cases are presented. A comparison with the baseline case is made