Princeton Plasma Physics Laboratory (PPPL) annual site environmental report for calendar year 1990

Non-neoclassical up/down asymmetry of impurity emission on Alcator C-Mod

“…Measurements consistent with neoclassical theory have been observed for carbon, with ñz / n z scaling like n e B t /I 2 p [5,6]. In other cases where the up/down asymmetry of low ionization states of impurities did not exhibit behaviours consistent with neoclassical predictions, the explanation was that strong poloidally localized impurity sources were likely the cause [20,28]. Recent measurements of up/down asymmetries of molybdenum density in the core, r/a < 0.8, of C-Mod plasmas also showed disagreement with neoclassical theory [29], although only small asymmetries, | ñz / n z | < 0.1, were observed.…”

“…If the parallel equilibration time of the impurities, τ , becomes close to τ ⊥ , then anomalous radial transport can influence the parallel force balance. If this radial transport is not uniform on a flux surface then it will result in a poloidal asymmetry, qualitatively similar to how a poloidally varying limiter source has been shown to influence the up/down asymmetry in low-Z emission [5,20]. While measurements of such an up/down asymmetry of turbulence are currently not possible at Alcator C-Mod, observations have been made previously on TEXT [21] and Tore-Supra [22] that show not only an up/down asymmetry in n e fluctuations at large minor radii, but also show this phenomenon reverses sign, up/down goes to down/up, with the reversal of the direction of the current with respect to the toroidal field.…”

“…Up/down asymmetries of impurity emission have been observed in many tokamaks using conventional soft x-ray tomography [24][25][26] and bolometry tools [6], or employing poloidally scanning spectrometers [13,20,27]. The impurity emission above the midplane is measured and compared to that below the midplane, where, assuming n e and T e are flux functions, the emission ratio will be equivalent to the ratio of impurity density, n z (π/2)/n z (3π/2).…”

A fusion-driven subcritical system concept based on viable technologies

“…Fusion-fission hybrid systems have the potential attractiveness of providing rich neutrons for applications of nuclear waste transmutation and fissile fuel breeding while easing the requirement of fusion plasma technology (with a low fusion gain Q) and plasmafacing material technology (with a low neutron wall loading), which represent a possible use of fusion power to build a power reactor with the current understanding of plasma physics and technologies. A lot of research activity has been done to evaluate the possibility of the hybrid systems in China and other countries in the world [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20]; however, most of these were based on advanced fusion and fission technologies.…”