Experimental tests of transport models using modulated ECH

Both the dynamic and equilibrium thermal responses of an L-mode plasma to repetitive ECH heat pulses were measured and compared to predictions from several thermal transport models. While no model consistently agreed with all observations, the GLF23 model was most consistent with the perturbated electron and ion temperature responses for one of the cases studied which may indicate a key role played by electron modes in the core of these discharges. Generally, the IIF and MM models performed well for the perturbed electron response while the GLF23 and IFS/PPPL models agreed with the perturbed ion response for all three cases studied. No single model agreed well with the equilibrium temperature profiles measured

A System for Simulating Fluctuation Diagnostics for Application to Turbulence Computations

Present-day nonlinear microstability codes are able to compute the saturated fluctuations of a turbulent fluid versus space and time, whether the fluid be liquid, gas, or plasma. They are therefore able to determine turbulence-induced fluid (or particle) and energy fluxes. These codes, however, must be tested against experimental data, not only with respect to transport, but also characteristics of the fluctuations. The latter is challenging because of limitations in the diagnostics (e.g., finite spatial resolution) and the fact that the diagnostics typically do not measure exactly the quantities the codes compute. In this work, we present a system based on IDL{reg_sign} analysis and visualization software in which user-supplied ''diagnostic filters'' are applied to the code outputs to generate simulated diagnostic signals. The same analysis techniques as applied to the measurements, e.g., digital time-series analysis, may then be applied to the synthesized signals. Their statistical properties, such as rms fluctuation level, mean wave numbers, phase and group velocities, correlation lengths and times, and in some cases full S(k,{omega}) spectra can then be compared directly to those of the measurements

The evidence for non-local transport in TEXT

The electron temperature response of a tokamak to rapid edge cooling has characteristics difficult to reconcile with local transport analysis. The initial observations in TEXT have been extended to a wider range of plasma and perturbation parameters, including auxiliary heating, and the associated turbulence changes have been measured across the plasma radius. The fast edge temperature drops and core temperature increases are quantified by more extensive analysis. A perturbation complementary to edge cooling, edge heating by a fast current ramp, evokes a completely complementary plasma response

Optimization of a mega-ampere spherical tokamak for beta-limit and confinement studies

Recent favorable results on the START experiment have caused renewed interest in the potential of low aspect ratio tokamaks. To aid in designing a next-step spherical tokamak to study confinement scaling, high beta, and high normalized beta plasmas for minimal cost, the authors have developed a transport scaling and device optimization code. This code STOP, benchmarked against START, includes 10 empirical confinement scaling laws and essential tokamak physics such as stability limits. Parameters are optimized separately for each scaling law and physical goal. Using STOP the authors find for R/a = 1.2 to 2.0 one can achieve {beta}{sub N} = 5, ({beta}) = 31--44%, and easily study predicted confinement degradation with auxiliary heating with just two neutral beams (P{sub NB} < 3.5 MW) for I{sub p} {ge} 0.75 MA, and R{sub 0} {ge} 0.6 m. In contrast, if one insists on using the nominal device parameters, i.e. I{sub p} = 1 MA and R{sub 0} = 0.8 m, with each scaling law, achieving {beta}{sub N} = 5 requires typically P{sub NB} {approx} 7.5 MW. They also conclude that while running D{sup 0} {yields} D{sup +} increases {tau}{sub E} {approx} 25%, with {tau}{sub E} already uncertain by 2--3{times}, one incurs restricted machine access and compromised physics operation

Tierra Grande: Journal of the Real Estate Center at Texas A&M University

This is a quarterly journal provided to real estate licensees covering information related to various aspects of real estate buying and ownership in Texas. Articles in this issue covers real estate and investment post Enron, real estate auctions, housing counseling agencies, tax-deferred exchanges, conserving natural landscapes and real estate, office redesign for improved productivity, real estate market watch, property tax increases, and Farm Credit System

Tierra Grande: Journal of the Real Estate Center at Texas A&M University

This is a quarterly journal provided to real estate licensees covering information related to various aspects of real estate buying and ownership in Texas. Articles in this issue covers the deregulation of electric utilities, wind power, rural property developers water supply options, FHA Loans, Texas' economy slowing, rural subdivisions in countrified atmosphere, novice home buyers, Texas Veterans Land Board uses, changing demographics in Texas, and ownership and uses of surface water

Gyrokinetic study of turbulence suppression in a JET-ILW power scan

For exploring tokamak operation regimes that deliver both high beta and good energy confinement, power scans at JET with ITER-like wall have been performed. Relatively weak degradation of the confinement time coincides with increased core temperature of the ions at high power. The changes in core turbulence characteristics during a power scan with an optimized (broad) q profile are analyzed by means of nonlinear gyrokinetic simulations. The increase in beta is crucial for stabilizing ion temperature gradient driven turbulence, accompanied by increased ion to electron temperature ratio, the presence of a dynamic fast ion species, as well as the geometric stabilization by increased thermal and suprathermal pressure. A sensitivity study with respect to the q profile reveals that electromagnetic effects are more pronounced at larger values of q. Further, it is confirmed that turbulence suppression due to rotation becomes less effective in such strongly electromagnetic systems. Electrostatic simplified models may thus perform well in present-day devices, in which high beta is often correlated with high rotation, but provide poor extrapolation towards low rotation devices. Implications for ITER and reactor plasmas are discussed.</p