Bulletin of the American Physical Society
2009 APS April Meeting
Volume 54, Number 4
Saturday–Tuesday, May 2–5, 2009; Denver, Colorado
Session J15: Windows to Burning Plasmas |
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Sponsoring Units: DPP Chair: Vincent Chan, General Atomics Room: Governor's Square 14 |
Sunday, May 3, 2009 1:30PM - 2:06PM |
J15.00001: Energetic Particle Diagnostics for Magnetic Fusion Experiments Invited Speaker: In magnetic confinement experiments, energetic ions are produced in fusion reactions, through acceleration by RF waves, and by ionization of injected neutral beams. The distribution function $f$ that describes the energetic ion population is shaped by orbital effects, Coulomb collisions, atomic processes, and interactions with waves, resulting in a distribution function that has a complicated dependence on velocity $\vec v$, spatial position $\vec r$, and time $t$. The diagnostic challenge is to measure $f(\vec v,\vec r,t)$ in the harsh plasma environment. Many diagnostic techniques rely on emission from fusion reactions or from interaction with a probe neutral beam; unconfined energetic particles are also measured. In all cases, the measurement effectively averages over the variables that describe the distribution function. To understand these complicated averages, it is convenient to define an instrument function $W$ that describes the diagnostic weighting in phase space; the measured signal is then the convolution of $W$ and $f$ over the phase space variables. In practice, measured signals from the various energetic-particle diagnostics often differ dramatically but qualitative differences are readily explained by differences in instrument function $W$. Owing to the complexity of $W$, quantitative comparisons with a theoretically predicted $f$ require forward modeling. A relatively new spectroscopic technique dubbed fast-ion D-alpha (FIDA) provides valuable data at the DIII-D tokamak and the National Spherical Torus Experiment. In plasmas with weak MHD activity, FIDA measurements often compare well with theoretical predictions. Simulations employing the calculated distribution function during RF heating also match many features of the FIDA measurements. On the other hand, flattened fast-ion profiles observed during strong energetic-particle-driven instabilities are harder to explain theoretically. [Preview Abstract] |
Sunday, May 3, 2009 2:06PM - 2:42PM |
J15.00002: The Importance of Turbulence Measurements to Burning Fusion Plasmas Invited Speaker: The fusion science community is actively preparing for the ``burning plasma era'' epitomized by ITER -- an international collaboration to construct, operate and study the ``next-step'' fusion device. Performance projections for the device currently rely on empirical scaling of the confinement properties of existing fusion devices. This is not entirely satisfactory, and advances in computational power have resulted in the ability to predict transport/confinement properties based on first-principles nonlinear gyrokinetic turbulence models. This talk will describe the role of turbulence measurements in validating such predictions and, thereby, enhancing confidence in the ability to project fusion performance. Since the predicted transport is determined by the turbulence physics inherent in the code, performing comparison and obtaining agreement with the measured turbulence properties is essential to establishing confidence in extrapolating to ``next-step'' devices. Measurements have advanced considerably and are able to locally monitor turbulence at all relevant spatial scales and in multiple fields. Such measurements will be described, together with comparison with code predictions in existing fusion plasmas. Burning plasmas will provide some unique challenges (e.g. role of alphas, low collisionality, high neutron and thermal fluxes) which will potentially modify the range of validity of code predictions while also constraining measurement capabilities. There is, therefore, an urgent need to develop diagnostic techniques suitable for the burning plasma environment, since measurement of the turbulence properties will be essential to provide the necessary information to guide future modifications to the simulations. Some of the challenges and possible solutions will be described. *Supported by the US DOE under DE-FG03-01ER54615 and DE-FG02-08ER54984. [Preview Abstract] |
Sunday, May 3, 2009 2:42PM - 3:18PM |
J15.00003: Scientific and Technological Challenges of Diagnosing Burning Plasmas Invited Speaker: Research in magnetically confined fusion is now approaching a major milestone which is in evaluating and controlling burning plasma conditions. This milestone will be first met in the ITER experiment, presently being built in Cadarache, France through an international partnership, which includes China, the European Union, India, Japan, South Korea, Russia and the United States. In order to achieve its mission of achieving burning plasma conditions, and possibly ignition, a comprehensive set of scientific instruments (diagnostics) is being planned. That set represents the culmination of more than 50 years of development and research. More than 40 plasma parameters will be measured, including many which will be directly controlled. Some of these measurements will be done for the first time, such as probing the production, distribution and behavior of fusion produced, i.e. alpha particles, a key element in sustaining the fusion reaction process. These measurements will need to be done in a hostile environment, where a large nuclear radiation field, substantial direct particle flux, long pulse length and lack of direct access will bring severe constraints. Furthermore, the needs of the experiment will demand high reliability, low maintenance and the ability to retain a good calibration over a long period of time. We will review the challenges of the task and the opportunities for scientific breakthroughs from these state-of-the-art diagnostics instruments, as they pertain to the specific context of burning plasma conditions, together with examples of where these measurements will directly impact our scientific understanding and ability to control these conditions. [Preview Abstract] |
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