Download or read book Pressure Profile Control of Internal Transport Barrier Plasmas in Alcator C Mod written by John E. Rice and published by . This book was released on 2003 with total page 32 pages. Available in PDF, EPUB and Kindle. Book excerpt: Internal transport barrier (ITB) plasmas with peak pressures of 0.25 MPa and pressure gradients as large as 2.5 MPa/m have been produced in Alcator C-Mod using off-axis ICRF heating. The onset of the ITBs is apparent when the pressure gradient exceeds 1.0 MPa/m, which is similar to the JET criterion of [rho]* s/L [equal to or greater than] 0.014. Concomitant with the peaking of the core pressure as the ITB develops is a drop of the toroidal rotation velocity profile inside of the barrier foot; the maximum of the velocity gradient coincides with the peak in the pressure gradient. The quasi-coherent (QC) mode, associated with the enhanced D[alpha] (EDA) H-mode plasmas which evolve the ITBs, breaks up and disappears as the barriers develop, even though the measured edge pedestal parameters remain fixed. The position of the ITB foot has been moved over a range of 1/3 of the plasma minor radius by varying the toroidal magnetic field. The peak in the calculated bootstrap current density profile has correspondingly been regulated over a similar range in plasma minor radius. The location of the density profile foot is found to expand as the toroidal magnetic field is reduced and the ICRF frequency is lowered. The density foot radius is relatively independent of q95, however, in a scan of the plasma current at fixed BT and wave frequency.
Download or read book Internal Transport Barriers in Alcator C Mod written by Catherine L. Fiore and published by . This book was released on 2005 with total page 90 pages. Available in PDF, EPUB and Kindle. Book excerpt: Internal transport barriers, marked by steep density and pressure profiles and reduction of core transport are obtained in Alcator C-Mod. Transient single barriers are observed at the back transition from H- to L- mode, and also when pellet injection is accompanied by ICRF power. Double barriers are induced with injection of off-axis ICRF power deposition. These also arise spontaneously in Ohmic H-mode plasmas when the H-mode lasts for several energy confinement times. C-Mod provides a unique platform for studying such discharges: the ions and electrons are tightly coupled by collisions with Ti/Te=1, and the plasma has no internal particle or momentum sources. ITB plasmas with average pressure greater than 1 atmosphere have been obtained. To form an ITB, particle and thermal flux are reduced in the barrier region, allowing the neoclassical pinch to peak the density while maintaining the central temperature. Gyrokinetic simulation suggests that long wavelength drift wave turbulence in the core is marginally stable at the ITB onset, but steepening of the density profile destabilizes trapped electron (TEM) modes inside the barrier. The TEM ultimately drives sufficient outgoing particle flux to balance the inward pinch and halt further density rise, which allows control of particle and impurity peaking.
Download or read book Control of Internal Transport Barriers on Alcator C Mod written by Catherine L. Fiore and published by . This book was released on 2003 with total page 58 pages. Available in PDF, EPUB and Kindle. Book excerpt: Recent studies of internal transport and double transport barrier regimes in Alcator C-Mod [I.H. Hutchinson, et al., Phys. Plasmas 1, 1511 (1994)] have explored the limits for forming, maintaining, and controlling these plasmas. C-Mod provides a unique platform for studying such discharges: the ions and electrons are tightly coupled by collisions and the plasma has no internal particle or momentum sources. The double-barrier mode comprised of an edge barrier with an internal transport barrier (ITB) can be induced at will using off-axis ion cyclotron range of frequency (ICRF) injection on either the low or high field side of the plasma with either of the available ICRF frequencies (70 or 80 MHz). When enhanced D [alpha] high confinement mode (EDA H-mode) is accessed in Ohmic plasmas, the double barrier ITB forms spontaneously if the Hmode is sustained for [approx.] high confinement times. The ITBs formed in both Ohmic and ICRF heated plasmas are quite similar regardless of the trigger method. They are characterized by strong central peaking of the electron density, and reduction of the core particle and energy ...
Download or read book Double Transport Barrier Plasmas in Alcator C Mod written by John E. Rice and published by . This book was released on 2001 with total page 38 pages. Available in PDF, EPUB and Kindle. Book excerpt: Double transport barrier plasmas comprised of an edge enhanced Da (EDA) H-mode pedestal and an internal transport barrier (ITB) have been observed in Alcator C-Mod. The ITB can be routinely produced in ICRF heated plasmas by locating the wave resonance off-axis near r/a [approx.] 0.5, provided the target plasma average density is above [approx.] 1.4 1020/m3, and can develop spontaneously in some Ohmic H-mode discharges. The formation of the barrier appears in conjunction with a decrease or reversal in the central (impurity) toroidal rotation velocity. The ITB foot is located near r/a = 0.5, regardless of how the barrier was produced. The ITBs can persist for [approx.] 15 energy confinement times (tE), but exhibit a continuous increase of the central electron density, up to values near 11021/m3 (in the absence of an internal particle source), followed by collapse of the barrier. This barrier is also evident in the ion temperature profiles, and a significant drop of the core thermal conductivity, ceff, when the barrier forms is confirmed by modeling. Application of additional on-axis ICRF heating arrests the density and impurity peaking, which occurs along with an increase (co-current) in the core rotation velocity. Steady state double barrier plasmas have been maintained for 10 tE or longer, with n/nGW [approx.] 0.75 and with a bootstrap fraction of 0.13 near the ITB foot. The trigger mechanism for the ITB formation is presently not understood.
Download or read book 107 2 Hearings Energy and Water Development Appropriations For 2003 Part 4 2002 written by and published by . This book was released on 2002 with total page 1512 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Energy and Water Development Appropriations for 2003 written by United States. Congress. House. Committee on Appropriations. Subcommittee on Energy and Water Development and published by . This book was released on 2002 with total page 1440 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Radio Frequency Power in Plasmas written by Tak K. Mau and published by American Institute of Physics. This book was released on 2001-11-09 with total page 568 pages. Available in PDF, EPUB and Kindle. Book excerpt: This proceedings volume includes the most recent research advances in the application of RF power in plasmas, mainly in fusion science. Most papers deal with plasma heating and current drive, profile control, and stabilization using RF techniques, with some on RF sources and launchers. New and exciting results from all major tokamak experiments, and from theory and modeling are included. There is also a paper on RFplasma application in space propulsion by an active NASA astronaut. This book is a valuable reference for the RF researchers in fusion and other disciplines.
Download or read book Energy and Water Development Appropriations for 2003 Department of Energy National Nuclear Security Administration Power Marketing Administrations written by United States. Congress. House. Committee on Appropriations. Subcommittee on Energy and Water Development and published by . This book was released on 2002 with total page 2986 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Fusion Science and Technology written by and published by . This book was released on 2007 with total page 890 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Internal Transport Barrier Driven by Redistribution of Energetic Ions written by K. L. Wong and published by . This book was released on 2004 with total page 14 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Observations and Empirical Scalings of the High confinement Mode Pedestal on Alcator C Mod written by J. W. Hughes and published by . This book was released on 2002 with total page 50 pages. Available in PDF, EPUB and Kindle. Book excerpt: On the Alcator C-Mod tokamak [Phys. Plasmas 1, 1511, (1994)], radial profiles of electron temperature (Te) and density (ne) are measured at the plasma edge with millimeter resolution Thomson scattering [Rev. Sci. Instrum. 72, 1107 (2001)]. Edge transport barriers in the high confinement regime (H-mode) exhibit Te, ne pedestals with typical widths of 2-6 mm, with the Te pedestal on average slightly wider than and inside the ne pedestal. Measurements at both the top and the base of the pedestal are consistent with profiles obtained using other diagnostics. The two primary H-mode regimes on C-Mod, enhanced Da (EDA) and edge-localized mode free (ELM-free), have been examined for differences in pedestals. EDA operation is favored by high edge collisionality n*, in addition to high edge safety factor q95. Scaling studies at fixed shape yield little systematic variation of pedestal widths with plasma parameters, though higher triangularity is seen to increase the ne pedestal width dramatically. Pedestal heights and gradients show the clearest dependencies on plasma control parameters. Pedestal ne and Te both scale linearly with plasma current IP, while pedestal Te depends strongly on power flowing from the core plasma into the scrape-off layer PSOL. The electron pressure (pe) pedestal and pe gradient both scale with IP2 PSOL1/2. Plasma stored energy WP scales with pedestal pe, implying that pedestal scalings may in large part determine global confinement scalings.
Download or read book Impurity Transport in Alcator C mod Plasmas written by John E. Rice and published by . This book was released on 1996 with total page 19 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Plasma Profiles and Flows in the High field Side Scrape off Layer in Alcator C Mod written by Noah M. Smick and published by . This book was released on 2004 with total page 28 pages. Available in PDF, EPUB and Kindle. Book excerpt: A novel, magnetically-driven swing probe was recently installed near the midplane on the high-field side SOL in Alcator C-Mod. The probe collects plasma from co- and counter-current directions during its respective 0-90 and 90-180 degrees of motion, thus providing profiles of density, electron temperature and plasma flow parallel to magnetic field lines (Mach number ... ) up to the separatrix. Results are reported from discharges with different magnetic topologies: lower single-null, upper single-null, and double-null. In single-null, a strong parallel flow ( ... M ...~ 1) is detected, which is always directed from the low- to high-field SOL. In double-null discharges, e-folding lengths in the high-field SOL are a factor of ~4 shorter than the low-field SOL. Thus, plasma appears to 'fill-in' the high-field SOL in single-null plasmas, not by cross-field transport but by parallel flow from the low-field SOL -- a picture consistent with a very strong ballooning-like component to the cross-field transport.
Download or read book 108 1 Hearings Energy and Water Development Appropriations For 2004 Part 4 2003 written by and published by . This book was released on 2003 with total page 3122 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Proceedings of the Fifth Carolus Magnus Euro Summer School on Plasma and Fusion Energy Physics written by and published by . This book was released on 2002 with total page 502 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Nuclear Fusion written by and published by . This book was released on 2009 with total page 324 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Impurity Transport in Alcator C Mod Plasmas written by John E. Rice and published by . This book was released on 2005 with total page 86 pages. Available in PDF, EPUB and Kindle. Book excerpt: (cont.) These edge values of the transport coefficients during EDA H-mode are qualitatively similar to the neoclassical values. In ELM-free H-mode discharges, impurity accumulation occurs, dominated by large inward impurity convection in the pedestal region. A scaling of the impurity confinement time with H-factor reveals a very strong exponential dependence. In ITB discharges, there is significant impurity accumulation inside of the barrier foot, typically at r/a = 0.5. Steady state impurity density profiles in L-mode plasmas have a large up-down asymmetry near the last closed flux surface. The impurity density enhancement, in the direction opposite to the ion BxB drift, is consistent with modeling of neo-classical parallel impurity transport.
