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Journal Articles

Investigation of collective fast ion instability-induced redistribution or loss in the National Spherical Torus Experiment

Medley, S. S.*; Andre, R.*; Bell, R. E.*; Darrow, D. S.*; Fredrickson, E. D.*; LeBlanc, B. P.*; Levinton, F. M.*; Menard, J. E.*; Stutman, D.*; Roquemore, A. L.*; et al.

Proceedings of 21st IAEA Fusion Energy Conference (FEC 2006) (CD-ROM), 8 Pages, 2007/03

The National Spherical Torus Experiment (NSTX) is particularly well suited to investigate fast-ion driven instabilities. These instabilities are observed in the wide range of frequency from 0 kHz to the ion cyclotron frequency. Two recently implemented diagnostics on NSTX, the Motional Stark Effect (MSE) and scintillator Fast Lost Ion Probe (sFLIP), facilitate separation of redistribution and loss effects. Outward redistribution of the core-peaked energetic beam ions modifies the beam-driven current profile and hence the core q-profile. For certain H-mode discharges where NPA measurements of the NB energetic ion spectra exhibit MHD-induced fast-ion depletion, the sFLIP data confirm the existence of an ion loss that occurs primarily for passing particles near the NB full injection energy. Observations and TRANSP simulations representing fast ion instability-induced redistribution/loss phenomena in NSTX are presented.

Oral presentation

Effects of heat waves on photosynthetic performance in Douglas-fir

Andre, D.*; Nadine, R.*; Katata, Genki

no journal, , 

The frequency and intensity of climate extremes, such as heat waves, are predicted to increase in the future. Temperature could rise beyond the threshold that allows trees to function optimally, and have severe implications on plant growth and productivity. In this context, the present study aims to assess how photosynthetic traits in Douglas-fir, a tree of worldwide economic and environmental importance, is affected by exposure to three heat waves with temperatures about 10 degree above ambient. A combined set of parameters was assessed, including maximum photosynthetic capacity (A$$_{rm max}$$), maximal rate of carboxylation ($$V_{cmax}$$) and electron transport ($$J_{max}$$), minimum stomatal conductance (g$$_{rm min}$$), needle carbon and nitrogen content. The temporary increase in growth temperature caused A$$_{rm max}$$, $$V_{cmax}$$, $$J_{max}$$ and g$$_{rm min}$$ to decrease, indicating high-temperature limitations on photochemistry. The observed decline in electron transport rates, carboxylation activity, and stomatal conductance reflected the increase in photorespiration and concomitant decrease in photosynthetic rates. Moreover, even one month after the last heat wave, the photosynthetic apparatus was still impaired. These results can offer new insights into the physiological response of Douglas-fir to consecutive episodes of increased temperatures, and help further our understanding of the limitations that heat waves could impose on the development and functioning of Douglas-fir in future climatic scenarios.

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