OHTE: A Helical Pinch with Pitch Reversal

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Abstract
The OHTE configuration is obtained by surrounding a reversed field pinch (RFP) with a stellarator-like helical winding whose pitch is chosen to enhance field line pitch reversal. The helical coil current needed to form a separatrix boundary is calculated analytically for a simple plasma model, which gives results in close agreement with a numerical two-dimensional (2-D) MHD equilibrium code. Basic properties of the field line transform, which is predominantly in the axial or toroidal direction, are investigated. The 2-D equilibrium code is used to investigate the effects of current profiles and high beta, and the OHTE is compared with the RFP. These calculations show that the helical winding can significantly enlarge the parameter space for interchangestable finite-ß equilibria with pitch reversal while avoiding axial current reversal.