Observations of ramped current operation in ZT-40M

A new mode of reversed-field pinch (RFP) startup has been tested in the RFP experiment ZT-40M. Instead of increasing the toroidal current almost sinusoidally to its maximum, as is normally done, the current is initially raised to approx. 70 kA in 0.8 ms and subsequently slowly ramped up to approx. 170 kA in 14 ms. The behaviors of toroidal flux, particle density, temperature, and radiated power for the ramped discharges are compared with fast current rise, flat-topped operation. The successful demonstration of ramped toroidal discharges has an important impact on future large RFP experiments since the voltage necessary to drive the toroidal current for slow (approx. 10 to approx. 20 ms) startup is reduced