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Book Configuration and Heating Power Dependence of Edge Parameters and H mode Dynamics in National Spherical Torus Experiment NSTX

Download or read book Configuration and Heating Power Dependence of Edge Parameters and H mode Dynamics in National Spherical Torus Experiment NSTX written by C. E. Bush and published by . This book was released on 2003 with total page 34 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Book Configuration and Heating Power Dependence of Edge Parameters and H mode Dynamics in National Spherical Torus Experiment NSTX

Download or read book Configuration and Heating Power Dependence of Edge Parameters and H mode Dynamics in National Spherical Torus Experiment NSTX written by C. E. Bush and published by . This book was released on 2003 with total page 34 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Book The National Spherical Torus Experiment NSTX Research Program and Progress Towards High Beta Long PulseOperating Scenarios

Download or read book The National Spherical Torus Experiment NSTX Research Program and Progress Towards High Beta Long PulseOperating Scenarios written by E. J. Synakowski and published by . This book was released on 2002 with total page 12 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Book H Mode Turbulence Power Threshold ELM and Pedestal Studies in NSTX

Download or read book H Mode Turbulence Power Threshold ELM and Pedestal Studies in NSTX written by and published by . This book was released on 2005 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: High-confinement mode (H-mode) operation plays a crucial role in NSTX [National Spherical Torus Experiment] research, allowing higher beta limits due to reduced plasma pressure peaking, and long-pulse operation due to high bootstrap current fraction. Here, new results are presented in the areas of edge localized modes (ELMs), H-mode pedestal physics, L-H turbulence, and power threshold studies. ELMs of several other types (as observed in conventional aspect ratio tokamaks) are often observed: (1) large, Type I ELMs, (2) ''medium'' Type II/III ELMs, and (3) giant ELMs which can reduce stored energy by up to 30% in certain conditions. In addition, many high-performance discharges in NSTX have tiny ELMs (newly termed Type V), which have some differences as compared with ELM types in the published literature. The H-mode pedestal typically contains between 25-33% of the total stored energy, and the NSTX pedestal energy agrees reasonably well with a recent international multi-machine scaling. We find that the L-H transition occurs on a [approx]100 [micro]sec timescale as viewed by a gas puff imaging diagnostic, and that intermittent quiescent periods precede the final transition. A power threshold identity experiment between NSTX and MAST shows comparable loss power at the L-H transition in balanced double-null discharges. Both machines require more power for the L-H transition as the balance is shifted toward lower single null. High field side gas fueling enables more reliable H-mode access, but does not always lead to a lower power threshold e.g., with a reduction of the duration of early heating. Finally the edge plasma parameters just before the L-H transition were compared with theories of the transition. It was found that while some theories can separate well-developed L- and H-mode data, they have little predictive value.

Book Results of NSTX Heating Experiments

Download or read book Results of NSTX Heating Experiments written by D. Mueller and published by . This book was released on 2002 with total page 8 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Book Profile Modifications Resulting from Early High harmonic Fast Wave Heating in NSTX

Download or read book Profile Modifications Resulting from Early High harmonic Fast Wave Heating in NSTX written by and published by . This book was released on 2001 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Experiments have been performed in the National Spherical Torus Experiment (NSTX) to inject high harmonic fast wave (HHFW) power early during the plasma current ramp-up in an attempt to reduce the current penetration rate to raise the central safety factor during the flattop phase of the discharge. To date, up to 2 MW of HHFW power has been coupled to deuterium plasmas as early as t= 50 ms using the slowest interstrap phasing of k approximately equals 14 m(superscript)-1 (nf= 24). Antenna-plasma gap scans have been performed and find that for small gaps (5-8 cm), electron heating is observed with relatively small density rises and modest reductions in current penetration rate. For somewhat larger gaps (10-12 cm), weak electron heating is observed but with a spontaneous density rise at the plasma edge similar to that observed in NSTX H-modes. In the larger gap configuration, EFIT code reconstructions (without MSE[motional Stark effect]) find that resistive flux consumption is reduced as much as 30%, the internal inductance is maintained below 0.6 at 1 MA into the flattop, q(0) is increased significantly, and the MHD stability character of the discharges is strongly modified.

Book Characterization of H mode Discharges in NSTX

Download or read book Characterization of H mode Discharges in NSTX written by and published by . This book was released on 2001 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: We report the observation of the first H-mode transitions in the National Spherical Torus Experiment (NSTX). Energy confinement time transiently increased by more than a factor of 2, to order 100 ms. The heating power requirement for accessing the H-mode regime (power threshold) was significantly higher than predicted by a multi-machine database compiled from conventional aspect ratio tokamaks. Our power threshold results are similar to other STs, such as the START and MAST machines. These H-mode observations in STs challenge and extend the existing international power threshold and energy confinement time scalings based on conventional aspect ratio tokamaks. The remainder of this paper discusses characteristics of the H-modes in NSTX.

Book The Dependence of H mode Energy Confinement and Transport on Collisionality in NSTX

Download or read book The Dependence of H mode Energy Confinement and Transport on Collisionality in NSTX written by and published by . This book was released on 2012 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Understanding the dependence of confi nement on collisionality in tokamaks is important for the design of next-step devices, which will operate at collisionalities at least one order of magnitude lower than in present generation. A wide range of collisionality has been obtained in the National Spherical Torus Experiment (NSTX) by employing two different wall conditioning techniques, one with boronization and between-shot helium glow discharge conditioning (HeGDC+B), and one using lithium evaporation (Li EVAP). Previous studies of HeGDC+B plasmas indicated a strong and favorable dependence of normalized con nement on collisionality. Discharges with lithium conditioning discussed in the present study gen- erally achieved lower collisionality, extending the accessible range of collisionality by almost an order of unity. While the confinement dependences on dimensional, engineering variables of the HeGDC+B and Li EVAP datasets differed, collisionality was found to unify the trends, with the lower collisionality lithium conditioned discharges extending the trend of increasing normalized confi nement time with decreasing collisionality when other dimension less variables were held as fi xed as possible. This increase of confi nement with decreasing collisionality was driven by a large reduction in electron transport in the outer region of the plasma. This result is consistent with gyrokinetic calculations that show microtearing and Electron Temperature Gradient modes to be more stable for the lower collisionality discharges. Ion transport, near neoclassical at high collisionality, became more anomalous at lower collisionality, possibly due to the growth of hybrid TEM/KBM modes in the outer regions of the plasma.

Book Operational Regimes of the National Spherical Torus Experiment

Download or read book Operational Regimes of the National Spherical Torus Experiment written by and published by . This book was released on 2002 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Book Engineering Overview of the National Spherical Torus Experiment NSTX

Download or read book Engineering Overview of the National Spherical Torus Experiment NSTX written by and published by . This book was released on 1997 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The National Spherical Torus Experiment (NSTX) Project will provide a national facility for the study of plasma confinement, heating, and current drive in a low-aspect-ratio, spherical torus (ST) configuration. The ST configuration is an alternate confinement concept which is characterized by high beta, high elongation, high bootstrap fraction, and low toroidal magnetic field compared to conventional tokamaks. The NSTX is the next-step ST experiment following smaller experiments such as the Princeton Plasma Physics Laboratory CDX-U (Current Drive Experiment-Upgrade), the START (Small Tight Aspect Ratio Tokamak) at Culham Laboratory, UK, and the HIT (Helicity Injected Tokamak) at the University of Washington, and it is smaller in scale to the MAST (Meg-Amp Spherical Tokamak) machine now under construction at Culham. This paper provides a description of the NSTX mission and gives an overview of the main engineering features of the design of the machine and facility and discusses some of the key design solutions.