Progress in Low-Aspect-Ratio RFP Research in RELAX

RELAX is a low-aspect-ratio RFP experiment with R=0.51m/a=0.25m (A=2). Initial results have shown the advantages of low-A RFP configuration with Ip of up to 100kA and Vl of down to ~30V; the configuration tends to relax to a quasi-single helicity (QSH) state. A high-speed camera diagnostic has revealed simple helix structure. In the extreme case, rotating Helical Ohmic equilibrium state has been realized. The pressure driven bootstrap current fraction is shown to be less than 5% of the total current in the present RELAX plasmas. Recent progress includes a test of field error compensation; the control system will also be used in feedback control of RWM. The electron density measurements with a 104 GHz microwave interferometer show that the density lies in the range from ~5 ×1018m-3 to ~1019m-3. Design study of Thomson scattering system is also in progress.