| We have experimentally and theoretically investigated the spatial and temporal evolution of ultra-soft x-ray radiation in the Princeton Large Torus tokamak. The ultra-soft x-ray emission (USX; 100 eV < h(nu) < 1 keV) is often a significant energy loss mechanism, and is an excellent tool for monitoring particle transport and magnetic field evolution.;The broadband USX emission was measured with arrays of silicon surface-barrier detectors to obtain good spatial and temporal resolution. In some discharges heated with ion cyclotron waves there was an increased influx of iron. The iron particle confinement time was determined to be about 40 ms with and without the ion cyclotron heating, and the influx of iron and deuterium both increased by a factor of 2.5 when the heating was introduced.;When discharges with tungsten limiters were heated by neutral beams injected opposite to the plasma current, there was evidence that the tungsten influx not only increased, but also concentrated at the center. Just before these discharges disrupted the USX power emission density was about 2 W/cm('3) at the center, and n(,W)/n(,e) was four times larger at the center than at half the minor radius.;During some discharges with auxiliary heating the USX radiation exhibited an "inverse" sawtooth behavior, increasing at the center while the soft x-rays decreased. It appeared that outer regions, which were cool, became loaded with iron which suffused the region inside q = 1 during the internal disruption. The fractional fluctuation of the USX radiation at q = 1 reached 25%, and a previously observed hot spot, which did not reconnect entirely, is here identified as a hole in the USX emission.;A rotating crystal spectrometer with (lamda)/(DELTA)(lamda) = 400 was constructed and used to measure the USX spectrum every 100 ms. Oxygen-K and iron-L spectra were prominent constituents, and radial emission profiles of charge states Fe XVII to Fe XXIV were obtained. The experimentally deduced radial locations of the peaks for each charge state were radially shifted outward for the lower charge states when compared with theoretical predictions based on coronal equilibrium.;Disruptions were classified on the basis of the spatial evolution of the USX radiation as asymmetric, explosive, or implosive. During asymmetric disruptions the USX increased primarily at one edge, perhaps due to interaction with the limiter. In the explosive disruption the USX evolved similarly to the soft x-rays, decreasing at the center and increasing at larger radii. The major events during the implosive disruption were an asymmetric soft x-ray flash which lasted for 10-20 (mu)s (conjectured to be caused by the conversion of magnetic into kinetic energy), and, simultaneously, a doubling of the USX emission over the cross-section in 10 (mu)s (which may have resulted from enhanced oxygen radiation). |
