Electron density control using fast gas puffing in reversed-field pinch device, TPE-RX

Electron density is scanned using fast gas puffing in the reversed-field pinch (RFP) device, TPE-RX. The gas puffing technique extends the operating range of IP/N from 12 to 2x10-14 Am (IP and N denote the plasma current and line density, respectively). It is estimated that the poloidal beta, βP, increases as IP/N decreases. This βP scaling with IP/N in TPE-RX confirms a similar tendency previously obtained in other RFP plasmas. The radiation fraction increases from ∼20% in the low-density regime to ∼35% in the highest-density regime. This result indicates that the lowest IP/N limit in RFP is similar to the density limit in tokamak plasmas. (author)