Author: Brian LaBombardPublisher:
ISBN:
Category :
Languages : en
Pages : 18
Book Description
Scaling of Plasma Parameters in the SOL and Divertor for Alcator C-Mod
Author: Brian LaBombardComparison of Particle Transport in the Scrapeoff Layer Plasmas of Alcator C-Mod and DIII-D
Author: B. LipschultzPublisher:
ISBN:
Category :
Languages : en
Pages : 50
Book Description
Scrapeoff Layer (SOL) data from DIII--D and C--Mod have been acquired and analyzed for radial particle transport based on a particle balance model. This has allowed a detailed comparison for L--mode plasmas. The inferred radial particle flux, ... , is parameterized in terms of diffusive [ ... ] and convective particle transport [ ... ]. The magnitude of the inferred Deff or veff increases across the SOL for both tokamaks. The inferred Deff or veff in the 'far' SOL (one density e-folding length from the separatrix and beyond) are essentially unchanged by changes in core density by factors of 2-3. This corresponds to changes in the far SOL density, collisionality (v*), and radial fluxes of a factor of 10 or more. Thus v* does not appear to be an important parameter in determining the radial particle transport in that region. The dimensionlessly-scaled SOL plasma profiles from the two tokamaks overlay for similar dimensionless plasma parameters. The SOL density profile near the separatrix is steeper than in the 'far' SOL. The scaled Deff and veff are slightly larger on DIII-D than C-Mod. This difference appears to be within experimental uncertainties. Neutral ionization in the SOL does not appear to affect radial transport but may be related to the observed flattening of the density profiles with increasing ... .
Analysis of Separatrix Plasma Parameters Using Local and Multi-machine Databases
Author: Publisher:
ISBN:
Category :
Languages : en
Pages : 8
Book Description
The ITER divertor modeling and database expert groups have assembled a scalar database of the edge plasma parameters for existing diverted tokamak devices as a means of enabling scaling studies of the SOL plasma. Data exist from ASDEX, ASDEX-Upgrade, C-MOD, COMPASS-D, DIII-D, JET, JFT-2M, and JT-6OU. We describe the scaling of plasma parameters at the outer midplane obtained from examination of this multi-machine database in this paper. The plasma parameters at the outer rnidplane are used as a boundary condition for all simulations of the SOL plasma, and hence understanding of the expected value of these parameters is crucial for the successful design of the ITER divertor.
Power Balance and Scaling of the Radiated Power in the Divertor and Main Plasma of Alcator C-Mod
Author: John Anthony GoetzDensity Limit and Cross-field Edge Transport Scaling in Alcator C-Mod
Author: Brian LaBombardPublisher:
ISBN:
Category :
Languages : en
Pages : 16
Book Description
Recent experiments in Alcator C-Mod have uncovered a direct link between the character and scaling of cross-field particle transport in the edge plasma and the density limit, nG. As ne/nG is increased from low values to values approaching [approx.] 1, an ordered progression in the cross-field edge transport physics occurs: first benign cross-field heat convection, then cross-field heat convection impacting the scrape-off layer (SOL) power loss channels and reducing the separatrix electron temperature, and finally 1bursty2 transport (normally associated with the far SOL) invading into closed flux surface regions and carrying a convective power loss that impacts the power balance of the discharge. These observations suggest that SOL transport and its scaling with plasma conditions plays a key role in setting the empirically observed density limit scaling law.
Local Plasma Parameters and H-mode Threshold in Alcator C-mod
Author: Amanda E. HubbardMetals Abstracts
Author: Observations and Empirical Scalings of the High-confinement Mode Pedestal on Alcator C-Mod
Author: J. W. HughesPublisher:
ISBN:
Category :
Languages : en
Pages : 50
Book Description
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.
Cross-field Transport in the SOL
Author: Brian LaBombardPublisher:
ISBN:
Category :
Languages : en
Pages : 11
Book Description
The sources of neutrals at the outer midplane of the plasma are discussed. We find that both the flux of neutrals escaping the divertor through leaks and ion recycling at main chamber surfaces appear to contribute. The ion flux to the walls is larger than the flux entering the divertor and comparable to recycling at the divertor plate. The cause of these high wall ion fluxes is an enhancement of cross-field particle transport which gives rise to substantial convective heat transport at higher densities. We have further explored main chamber recycling and impurity transport utilizing a novel divertor 'bypass', which connects the outer divertor plenum to the main chamber. We find that leakage of neutrals (fuel and recycling impurities) from the divertor appears to be determined primarily by the conductance through the divertor structure, thus indicating that tight baffling would be desirable in a reactor for fuel and helium ash compression.
Observations of Cold, High Density Plasma in the Private Flux Region of the Alcator C-Mod Divertor
Author: Christopher James BoswellPublisher:
ISBN:
Category :
Languages : en
Pages : 10
Book Description
Significant plasma density has been observed in the private flux zone of the Alcator C-Mod tokamak. The behavior of the Dg emission profiles is consistent with the source of the plasma being due to an E x B drift generated by a poloidal temperature gradient. The plasma flux due to this drift is derived and evaluated. A plasma flux into the private flux zone is inferred by measurements of volumetric recombination using a tangentially viewing CCD camera and several spectroscopic views observing the high n-lines of the Do Balmer series. For the case of an attached divertor the inferred plasma flux to the PFZ has a linear scaling with respect to plasma pressure, as is expected from the temperature-gradient-induced, E x B drift.