809-Forecast-TEXT.pdf

Forecast of TEXT Plasma Disruptions Using SoftX-Rays as Input Signal in a workA. i,?. Oliveira,?and T. TajimaInstitute for Fusion Studies, The University of Texas at AustinAustin, Texas 78712 USAMarch 3, 1998AbstractAfeed-forward work with two hidden layers is used in this work to forecastmajor and minor disruptive instabilities in TEXT discharges. Using soft X-ray signalsas input data, the is trained with one disruptive plasma pulse, and a di?erentdisruptive discharge is used for validation. After being properly trained works,with the same set of weights, is then used to forecast disruptions in two others di?erentplasma pulses. It is observed that the is able to predict the ing ofa disruption more than 3 ms in advance. This time interval is almost three timeslonger than the one already obtained previously when ic signal from a Mirnovcoil was used to feed the works with. To our own eye we fail to see anyindication of an ing disruption from the experimental data this far back fromthe time of disruption. Finally, from what we observe in the predictive behavior of work, speculations are made whether the disruption triggering mechanism would beassociated to an increase of them= 2 ic island, that disturbs the central partof the plasma column afterwards or, in face of the results from this work, the initialperturbation would have occurred ?rst in the central part of the plasma column, withintheq= 1 ic surface, and then them= 2 MHD mode would be destabilizedafterwards.?Instituto de Fisica, Universidade de Sao Paulo, . 66318, Sao Paulo, 05315-970, SP, Brazil11 IntroductionDisruptive instabilities in tokamaks are still a major concern and considered a great obstaclein achieving thermonuclear fusion using a tokamak reactor. The next large fusion devices,because of the large current values and high plasma temperature to be achieved [1], will haveto be very carefully projected and properly constructed in order to support the occurrenceof a large number of such instabil