Plasma Profiles And Flows In The High Field Side Scrape Off Layer In Alcator C Mod
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| Author | : Noah M. Smick |
| Publisher | : |
| Total Pages | : 28 |
| Release | : 2004 |
| Genre | : |
| ISBN | : |
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.
| Author | : Christopher James Boswell |
| Publisher | : |
| Total Pages | : 26 |
| Release | : 2004 |
| Genre | : |
| ISBN | : |
Measurements from an inner wall mounted scanning Langmuir probe and modelling of D[alpha] emission show a sharp fall-off of plasma density in the inboard private flux region. D[alpha] emission is modelled using a one dimensional space, two dimensional velocity kinetic neutral code in order to track the changes in the density profile while the magnetic topology is changed from single to double null. A sharp density decay is observed to track with the location of the secondary separatrix. The presented data is consistent with a lower level of cross-field transport on field lines in the private flux region restricted to the high-field side when compared to cross-field transport on field lines in the low-field side scrape-off layer.
| Author | : James L. Terry |
| Publisher | : |
| Total Pages | : 68 |
| Release | : 2005 |
| Genre | : |
| ISBN | : |
(cont.) Evidence that this turbulent transport may play an important role in the core-plasma density limit is presented. Much lower levels of turbulence and no blobs are observed in the high-field-side scrape-off-layer. For single-null magnetic configurations, plasma in the inboard scrape-off-layer appears to be almost entirely a result of plasma flow along field lines from the low-field side. Strong parallel flows with sensitivity to magnetic topology are found, along with strong evidence for momentum coupling between these scrape-off-layer flows and core toroidal rotation
| Author | : Noah M. Smick |
| Publisher | : |
| Total Pages | : 234 |
| Release | : 2009 |
| Genre | : |
| ISBN | : |
(Cont.) Toroidal rotation, Pfirsch-Schlilter and transport-driven contributions are unambiguously identified. Parallel flows are found to dominate the high-field particle fluxes; the total poloidally-directed flow carries one half of the particle flux arriving on the inner divertor. As a result, convection is also found to be an important player in high-field side heat transport. In contrast, E_r x B plus parallel flows yield a mostly-toroidal flow component in the low-field SOL. The magnitude of the transport-driven flow component is found to be quantitatively consistent with radial fluctuation-induced particle fluxes measured on the low-field side, identifying this as the primary driver. In contrast, fluctuation-induced flux measurements on the high-field side midplane are found to be essentially zero, thereby excluding an 'inward pinch' effect as the mechanism that closes the mass-flow loop in this region.
| Author | : John Rice |
| Publisher | : Springer Nature |
| Total Pages | : 158 |
| Release | : 2022-01-13 |
| Genre | : Science |
| ISBN | : 3030922669 |
This book provides a comprehensive look at the state of the art of externally driven and self-generated rotation as well as momentum transport in tokamak plasmas. In addition to recent developments, the book includes a review of rotation measurement techniques, measurements of directly and indirectly driven rotation, momentum sinks, self-generated flow, and momentum transport. These results are presented alongside summaries of prevailing theory and are compared to predictions, bringing together both experimental and theoretical perspectives for a broad look at the field. Both researchers and graduate students in the field of plasma physics will find this book to be a useful reference. Although there is an emphasis on tokamaks, a number of the concepts are also relevant to other configurations.
| Author | : Brian LaBombard |
| Publisher | : |
| Total Pages | : 62 |
| Release | : 2004 |
| Genre | : |
| ISBN | : |
Factor of ~2 higher power thresholds for low- to high-confinement mode transitions (LH) with unfavorable x-point topologies in Alcator C-Mod [Phys. Plasmas 1, 1511 (1994)] are linked to flow boundary conditions imposed by the scrape-off layer (SOL). Ballooning-like transport drives flow along magnetic field lines from low- to high-field regions with toroidal direction dependent on upper/lower x-point balance; the toroidal rotation of the confined plasma responds, exhibiting a strong counter-current rotation when Bx B points away from the x-point. Increased auxiliary heating power (rf, no momentum input) leads to an L-H transition at approximately twice the edge electron pressure gradient when Bx B points away. As gradients rise prior to the transition, toroidal rotation ramps toward the co-current direction; the H-mode is seen when the counter-current rotation imposed by the SOL flow becomes compensated. Remarkably, L-H thresholds in lower-limited discharges are identical to lower x-point discharges; SOL flows are also found similar, suggesting a connection.
| Author | : Sanjay Gangadhara |
| Publisher | : |
| Total Pages | : 20 |
| Release | : 2002 |
| Genre | : |
| ISBN | : |
Accurate measurements of plasma flows in the scrape-off layer (SOL) are a necessary requirement for understanding the physics of tokamak edge plasmas. A system is being developed on Alcator C-Mod for inferring flows parallel (v) and perpendicular (vE x B) to local magnetic field lines from impurity emission patterns ("plumes") generated by local gas injection. Carbon plumes are generated at variable location in the SOL by puffing deuterated ethylene gas (C2D4) through the end of a reciprocating fast-scanning probe. Two intensified CCD cameras are used to record C+1 and C+2 emission patterns simultaneously from near-perpendicular views. Plumes are modeled using a Monte Carlo impurity transport code, from which values for the background flows may be extracted. The sensitivity of the plume structure is investigated for a number of code inputs, including radial electric field (Er) and the neutral launch dynamics. Initial modeling results indicate discrepancies between values of v and Er extracted from the plumes and measurements obtained from probe data. Key words: Alcator C-Mod; Scrape-Off Layer Flows; Plumes.
| Author | : |
| Publisher | : |
| Total Pages | : 652 |
| Release | : 2005 |
| Genre | : Electronic journals |
| ISBN | : |
| Author | : Brian LaBombard |
| Publisher | : |
| Total Pages | : 20 |
| Release | : 2002 |
| Genre | : |
| ISBN | : |
Parallel and ExB plasma flows near the separatrix on the outside midplane of Alcator C-Mod are investigated with a scanning probe for a range plasma densities, currents, and magnetic fields. Strong parallel flows (up to Mach 0.6) are found to peak 2 mm into the scrape-off layer (SOL), reverse nearly symmetrically with magnetic field reversal, and decrease in magnitude with increasing line-averaged density normalized to the Greenwald density. ExB flows in the SOL inferred from the poloidal propagation velocity of plasma fluctuations appear to compensate these parallel flows and scale similarly, i.e., the dominant flow pattern is a pure toroidal rotation. ExB flows inferred by probe-sheath potentials are generally smaller, exhibit more scatter, and do not scale the same, perhaps indicating a less reliable measurement. These measurements suggest a residual poloidal flow (along field lines) of 0.2 to 1 times the electron diamagnetic velocity, depending on plasma conditions.
| Author | : |
| Publisher | : |
| Total Pages | : 890 |
| Release | : 2007 |
| Genre | : Fusion reactors |
| ISBN | : |
