Response to the anti-Catholic writings of José Maria Blanco y Crespo, later known as Blanco White (Joseph), addressed to the editor of the Mexican Gazett

Gemisic-Adamov, M.

Kurzan, B.

Scarabosio, A.

"El verdadero Defensor de nuestra constitucion"

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Large scale inter-ELM fluctuations in the pedestal and the density limit in ASDEX Upgrade

Large scale inter-ELM fluctuations in the pedestal and the density limit inASDEX UpgradeB. Kurzan, A. Scarabosio, M. Gemišić-Adamov and ASDEX Upgrade teamMax-Planck-Institut für Plasmaphysik, EURATOM Association, Boltzmannstr. 2, 85748Garching, GermanyIntroductionIn H mode plasmas in-between type-I edge localised modes (ELMs) [1] large scale fluctu-ations of the electron density and temperature were found recently in the pedestal of ASDEXUpgrade [2]. They appear in 2D poloidal snapshots of the electron density and temperature,measured by Thomson scattering, as ‘blobs’ and ‘dips’. For the type of plasma investigated in[2] the typical relative fluctuation amplitude of the electron density was around 21%.In this paper a set of type-I ELMy H mode plasmas with parameters covering a broad rangeare analysed: It is found that the relative fluctuation amplitudes in the pedestal increase with theplasma density normalised to the Greenwald density nGW [3]. There are experimental hints thatthe perpendicular transport of particles and heat in the pedestal increases with rising relativefluctuation amplitudes of electron density and temperature. This is similar to the findings onAlcator C-Mod, where increased convective transport in the scrape-off layer was found forohmic L mode plasmas when approaching the density limit [4].Experimental Setup ICRHantennascatteringvolumesseparatrix1.40.70.0-0.7-1.40.8 1.7 2.6z [m]R [m]H5F14Figure 1: Poloidal cross section.The vertical Thomson scattering diagnostic [5] consists ofa bundle of up to six vertically launched, radially staggeredNd-YAG laser beams. The scattered light is observed fromthe low-field side in 16 spatial channels. The whole systemwas shifted radially to measure low field side edge electrondensity and temperature profiles (Fig. 1).The Thomson scattering data are compared to the signalsof other diagnostics: The line-averaged electron density atthe plasma edge including the pedestal shoulder, ne  H5, ismeasured by the DCN interferometer-signal H5. The neu-tral particle flux at the outer midplane, fmpl , is measured bythe ionisation gauge F14. These diagnostics are all located atdifferent toroidal positions.35th EPS Conference on Plasma Phys. Hersonissos, 9 - 13 June 2008 ECA Vol.32D, P-2.001  (2008)ResultsH mode plasmas from 49 discharges heated by neutral beam co-injection (NBI) and ioncyclotron resonance heating (ICRH) with powers between 2  5 MW  PNBI  PICRH  16 MW ,with upper and lower triangularities of  0  07  δu  0  50, 0  31  δl  0  55, elongations 1  34 κ  1  84, line averaged electron densities, 4  6  n̄e  1019m  3   9  3, toroidal magnetic fields 3 T  Bt 	 1  9 T and plasma currents Ipl MA  0  8  1  0  were investigated.#18395, t = 1.6 s - 6.0 s-0.3 cm ≤ R-R       ≤ -0.1 cmouta bFigure 2: The large scale fluctuations of ne and Te are correlatedin amplitude (a) and have the same radial shifts (b).The probability distribu-tion functions (PDFs) ofthe large scale fluctua-tions in the poloidally av-eraged radial profiles ofelectron density and tem-perature in-between ELMswere investigated in [2]:in the middle of the steepgradient region the PDFsare symmetric and asym-metric both further inwards (more minima), and further outwards (more maxima).To compare the amplitudes of the large scale fluctuations for different discharge parametersthe variance of the normalised electron density, Var  ne    ne  , with   ne  as the mean value overthe time interval of the evaluation, was determined at the radial position in the steep gradientregion where its PDF is symmetric.a bP        [MW] ∈ [2.5, 7.5)    , ∈ [7.5, 11.5)    , ∈ [11.5, 16.0]heatFigure 3: Relative amplitudes of the large scale fluctuations ver-sus normalised edge density for Ipl MA  0  8  1  0  (a), andIpl  1  0 MA (b), and different total heating powers Pheat .The large scale fluc-tuations of electron den-sity and temperature are inphase, which is seen whenplotting the relative fluctu-ations of electron densityversus those of the electrontemperature for one dis-charge (fig. 2a). The rela-tive amplitudes of the elec-tron temperature fluctua-tions are larger than for the35th EPS 2008; B.Kurzan et al. : Large scale inter-ELM fluctuations in the pedestal and the density limit in... 2 of 4electron density (fig. 2a). This correlates with the usual finding that the gradient length ofthe electron temperature, lTe, is smaller than for the electron density, lne. The effective radialshifts of the electron density fluctuations, ∆Rne  2 Var1  2  ne  ne  lne, are correlated withthe analogously defined radial shifts ∆RTe of the electron temperature fluctuations and bothare of the same size (fig. 2b). These radial shifts have the same size as the radial widths ofthe fluctuations in electron density and temperature, seen in the 2D poloidal snapshots [2].These fluctuations apparently move macroscopic plasma volumes radially with respect to theirpositions in the unperturbed profile.P         [MW] ∈ [2.5, 7.5)    , ∈ [7.5, 11.5)    , ∈ [11.5, 16.0]heata bFigure 4: Var1  2  ne   ne  versus λei   πq95R  for Ipl MA  0  8  1  0  (a), and Ipl  1  0 MA (b) and different Pheat .The relative amplitudesof the large scale fluctu-ations increase with theline-averaged edge den-sity ne  H5, normalised tothe Greenwald density [3]nGW  Ipl   πa2  with a 0  5 m as the minor radiusof the ASDEX Upgradeplasma (fig. 3a). For a sin-gle plasma current and thusa single Greenwald density a near linear increase of Var0  5  ne    ne  with the normalised den-sity ne  H5  nGW is found (fig. 3b), especially for low total heating powers Pheat .A decrease of the relative fluctuation amplitudes of the electron density in the pedestal isfound with increasing local electron-ion mean free path, λei  T 2e  ne, over connection length,πq95R, between the inboard and outboard midplane (fig. 4).In general heat is transported by radiation, conduction and convection. For investigatingthe influence of the large scale fluctuations on the perpendicular heat-flux, however, here asimplified ansatz is used by estimating an effective perpendicular heat diffusivity χ  in thepedestal from Pheat  Prad  A ne χ  dTe  dR with Pheat as the total heating power, Prad as thepower lost by radiation, and ne and dTe  dR of the background profiles, averaged over the largescale fluctuations. The local heat flux is assumed to extent over an area of A  10 m2 of theplasma surface on the low field side. With increasing electron temperature the perpendicularheat diffusivity χ  decreases, which is opposite to Bohm diffusivity, χB  Te   16eBt  (fig. 5a).The relative amplitudes of the electron density fluctuations decrease also with rising Te (fig. 5b).Thus the perpendicular heat diffusivity increases slightly with the electron density fluctuations35th EPS 2008; B.Kurzan et al. : Large scale inter-ELM fluctuations in the pedestal and the density limit in... 3 of 4(fig. 5c), indicating that already on the closed magnetic surfaces in the pedestal the fluctuationscontribute to the perpendicular heat transport.a bc dFigure 5: χ  (red squares) decreases with Te, which is opposite toχB (green triangles) (a). Var1  2  ne    ne  decreases with increas-ing Te (b). χ  increases slightly with Var1  2  ne    ne  as shown bya fit to the data (c). fmpl increases with Var1  2  ne    ne  (d).A clear increase of theneutral particle flux in theouter midplane, fmpl , withrelative amplitudes of thefluctuations of the electrondensity,Var1  2  ne    ne  , isfound (fig. 5d). The num-ber of data points here issmaller than in the previ-ous plots, because fmpl isnot available for each in-vestigated discharge.DiscussionIt is now tried to inter-pret the experimental find-ings: Since the fluctuationamplitudes of electron den-sity and temperature in thepedestal are correlated (fig. 2a) and the radial shifts ∆Rne and ∆RTe of these fluctuations arethe same (fig. 2b), the fluctuations can be seen as macroscopic volumes confining plasmas ofeither higher, or lower electron density and temperature, than the background plasma, as wasalready found in [2]. The perpendicular heat diffusivity and particle transport increase with theamplitudes of these large scale fluctuations (fig. 5) acting as convection cells. The amplitudesof these fluctuations increase with increasing density normalised to the Greenwald density (fig.3), with decreasing temperature (fig. 5b), or with decreasing mean free path over connectionlength (fig. 4), i. e. with increasing collisionality.References[1] W. Suttrop, Plasma Phys. Control. Fusion 42, A1 (2000)[2] B. Kurzan et al., Plasma Phys. Control. Fusion 49, 825 (2007)[3] M. Greenwald, Plasma Phys. Control. Fusion 44, R27 (2002)[4] B. LaBombard et al., Phys. Plasmas 8, 2107 (2001)[5] H. Murmann et al., Rev. Sci. Instrum. 63, 4941 (1992)35th EPS 2008; B.Kurzan et al. : Large scale inter-ELM fluctuations in the pedestal and the density limit in... 4 of 4

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http://hdl.handle.net/21.11116/0000-000A-38D0-C

Atencion! que los apóstatas quieren variar nuestra religion

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