The US Home Team has investigated the physics and engineering issues for two alternate poloidal field coil configurations for ITER. The first is called the Segmented CS configuration, where all of the solenoid modules are pancake-wound. The second option, termed the Hybrid CS configuration, utilizes a layer-wound central module and pancake-wound end modules.

The reference configuration of the poloidal field coils for ITER features a 12 m long monolithic central solenoid, which is layer-wound and consists of three regions of varying superconductor grades. The stray field from the ends of this long coil inhibit plasma shaping flexibility and shape conformity of the plasma over the reference 21 MA ignited scenario. The plasma performance can be improved by vertically segmenting the solenoid. The Segmented CS configuration offers superior plasma performance but suffers from the necessity to invoke high field (~13 T) joints in the superconductor. Development of such high field joints is beyond the scope of the ITER Engineering Design Activity, and therefore this concept was abandoned. The difficulties of the Segmented CS design prompted the US Home Team to develop the so-called Hybrid CS option, where the central portion of the solenoid is of the same design as the reference design--only shorter. In this configuration, independently controlled end-coils are located beyond the central module (separated by vertical gaps of about 1.5 m) to allow space for the leads of the 9.5 m layer-wound central module. The Hybrid CS design suffers from excessive insulation shear stress, but it is thought that a modest R&D effort can resolve the problem.

Performance comparisons are presented for the three PF configurations, characterizing the per-formance for the reference scenario and its required operational flexibility range (in b_p and l_i) and alternate operating modes such as reverse-shear operation and a 17 MA driven mode.

*Work performed under the auspices of the US Department of Energy by Lawrence Livermore National Laboratory under contract number W-7405-ENG-48

**Work performed under the auspices of the US Department of Energy by Princeton Plasma Physics Laboratory under contract number DE-AC02-76CH03073