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Author: Publisher: ISBN: Category : Languages : en Pages : 12
Book Description
Fusion power gain has been increased by a factor of 3 in DIII-D plasmas through the use of strong discharge shaping and tailoring of the pressure and current density profiles. H-mode plasmas with weak or negative central magnetic shear are found to have neoclassical ion confinement throughout most of the plasma volume. Improved MHD stability is achieved by controlling the plasma pressure profile width. The highest fusion power gain Q (ratio of fusion power to input power) in deuterium plasmas was 0.0015, which extrapolates to an equivalent Q of 0.32 in a deuterium-tritium plasma and is similar to values achieved in tokamaks of larger size and magnetic fields.
Author: Publisher: ISBN: Category : Languages : en Pages : 12
Book Description
Fusion power gain has been increased by a factor of 3 in DIII-D plasmas through the use of strong discharge shaping and tailoring of the pressure and current density profiles. H-mode plasmas with weak or negative central magnetic shear are found to have neoclassical ion confinement throughout most of the plasma volume. Improved MHD stability is achieved by controlling the plasma pressure profile width. The highest fusion power gain Q (ratio of fusion power to input power) in deuterium plasmas was 0.0015, which extrapolates to an equivalent Q of 0.32 in a deuterium-tritium plasma and is similar to values achieved in tokamaks of larger size and magnetic fields.
Author: John Wesson Publisher: Oxford University Press ISBN: 0199592233 Category : Science Languages : en Pages : 828
Book Description
The tokamak is the principal tool in controlled fusion research. This book acts as an introduction to the subject and a basic reference for theory, definitions, equations, and experimental results. The fourth edition has been completely revised, describing their development of tokamaks to the point of producing significant fusion power.
Author: Publisher: ISBN: Category : Languages : en Pages :
Book Description
Plasma configurations with reversed magnetic shear have been proposed for steady-state tokamak operation since the plasma profiles can be made consistent with good confinement, high bootstrap current fraction, and stability at very high beta. The stability of reversed magnetic shear discharges with beta up to 11% has previously been demonstrated in DIII-D. Reversed magnetic shear (RMS) refers to a safety factor profile, q([rho]), which is a non-monotonic function of minor radius, [rho]. The magnetic shear S[equivalent-to] ([rho]/q) dq/d[rho] is negative within the plasma core and positive at the edge. When S
Author: Publisher: ISBN: Category : Languages : en Pages : 8
Book Description
OAK A271 DEMONSTRATION IN THE DIII-D TOKAMAK OF AN ALTERNATE BASELINE SCENARIO FOR ITER AND OTHER BURNING PLASMA EXPERIMENTS. Discharges which can satisfy the high gain goals of burning plasma experiments have been demonstrated in the DIII-D tokamak in stationary conditions with relatively low plasma current (q95> 4). A figure of merit for fusion gain [Beta]{sub N}H9/q952 has been maintained at values corresponding to Q = 10 operation in a burning plasma for> 6 s or 36 [tau]{sub E} and 2 [tau]{sub R}. The key element is the relaxation of the current profile to a stationary state with q{sub min}> 1, which allows stable operation up to the no-wall ideal [beta] limit. These plasmas maintain particle balance by active pumping rather than transient wall conditions. The reduced current lessens significantly the potential for structural damage in the event of a major disruption.
Author: Publisher: ISBN: Category : Languages : en Pages :
Book Description
Wall stabilization of the ideal n= 1 external kink mode is shown to be possible in high[beta], rotating DII-D plasmas for times much longer than the resistive wall penetration time. The gain in[ss] can be more than 30% above the calculated stability limit with no wall stabilization. Stabilization from the resistive wall is found to require plasma rotation speeds of several kHz; otherwise, unstable locked or slowly rotating modes appear, with growth times of the order of the wall penetration time, which ultimately lead to termination of the discharge. The slowly rotating modes have the characteristics expected of the theoretically predicted resistive wall mode in an ideal plasma.
Author: Publisher: ISBN: Category : Languages : en Pages : 29
Book Description
Detailed analysis of recent high beta discharges in the DIII-D tokamak demonstrates that the resistive vacuum vessel can provide stabilization of low n magnetohydrodynamic (MHD) modes. The experimental beta values reaching up to [beta]{sub T} = 12.6% are more than 30% larger than the maximum stable beta calculated with no wall stabilization. Plasma rotation is essential for stabilization. When the plasma rotation slows sufficiently, unstable modes with the characteristics of the predicted {open_quotes}resistive wall{close_quotes} mode are observed. Through slowing of the plasma rotation between the q = 2 and q = 3 surfaces with the application of a non-axisymmetric field, the authors have determined that the rotation at the outer rational surfaces is most important, and that the critical rotation frequency is of the order of [Omega]/2[pi] = 1 kHz.
Author: Publisher: ISBN: Category : Languages : en Pages : 11
Book Description
OAK A271 RESISTIVE WALL STABILIZATION OF HIGH BETA PLASMAS IN DIII-D. Recent DIII-D experiments show that ideal kink modes can be stabilized at high beta by a resistive wall, with sufficient plasma rotation. However, the resonant response by a marginally stable resistive wall mode to static magnetic field asymmetries can lead to strong damping of the rotation. Careful reduction of such asymmetries has allowed plasmas with beta well above the ideal MHD no-wall limit, and approaching the ideal-wall limit, to be sustained for durations exceeding one second. Feedback control can improve plasma stability by direct stabilization of the resistive wall mode or by reducing magnetic field asymmetry. Assisted by plasma rotation, direct feedback control of resistive wall modes with growth rates more than 5 times faster than the characteristic wall time has been observed. These results open a new regime of tokamak operation above the free-boundary stability limit, accessible by a combination of plasma rotation and feedback control.
Author: Publisher: ISBN: Category : Aeronautics Languages : en Pages : 652
Book Description
Lists citations with abstracts for aerospace related reports obtained from world wide sources and announces documents that have recently been entered into the NASA Scientific and Technical Information Database.
Author: Publisher: ISBN: Category : Languages : en Pages : 7
Book Description
One of the major goals of advanced tokamak research is to develop plasma configurations with good confinement and improved stability at high [beta]. In DIII-D, various high performance configurations with H- and VH-mode edges have been produced. These include discharges with poloidal cross sections in the forms of dee and crecent shapes, single- and double-null divertors, and with various central magnetic shear profiles and current profile peakedness. All these discharges exhibit confinement in the outer plasma region which leads to a large edge pressure gradient and a large edge bootstrap current driven by this steep pressure gradient. These edge conditions often drive an instability near the edge region which can severely degrade the discharge performance. An understanding of this edge instability is essential to sustain an enhance discharge performance.
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