SRX-precursor to large scale high beta plasma devices

Access to an operation in the second regime, using a large aspect ratio range (R/a=6-9) device, is discussed. The large aspect ratio was chosen to reduce required heating power for second regime studies and to permit large aspect ratio confinement experiments under ohmic, NBI, and ECH heating conditions. In addition, it leads to a simplified machine geometry based on reduced stresses from relatively low values of plasma current and magnetic field strength. Design features include an inside null divertor to test divertor physics at high beta and to provide added flexibility to control the plasma boundary. A close-fitting, adjustable conducting shell providing stabilization against external modes allows study of wall-plasma separation effects and permit R/a variation. The size and field of the SRX conceptual design were selected to minimize cost while maintaining sufficient beam-ion confinement for neutral beam current drive and sufficient bulk-ion thermal confinement for meaningful measurements of tokamak energy confinement scaling at high beta.<>