IPP Annual Report 2007 - Max-Planck-Institut für Plasmaphysik ...

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Plasmagenerator PSI-2 Performing plasma diagnostic measurements with Langmuir probes one has to take into consideration possible disturbances of the plasma by the probe itself. Apart from the probe tip, there is especially the probe shaft that could influence the results of a measurement. To resolve this question, measurements were made of the electron temperature and density using two Langmuir probes. The probes were arranged in two positions: In the first case, they were aligned in azimuthal direction of the PSI-2 plasma column. In the second case, they were placed in the same axial plane but tilted to each other in azimuthal direction. Data was acquired keeping one probe at fixed position while the second one was scanning the plasma radially. We have found that, irrespective of the geometry, the electron temperature is not affected by the probe, however the electron density is. This result can be explained within a theoretical transport model in which the probe shaft acts as an additional particle sink (figure 1). It is interesting to note that the disturbance of the plasma by the probe takes place on a global scale. n e and T e [normalized] 1.1 1 0.9 0.8 0.7 T e n e Model The flow behaviour of plasmas in contact with a target surface was investigated. The ion velocity distribution function (ivdf) of Ar + ions was measured at different displacements from the target using LIF techniques (see Annual Report 2006). In addition to the ivdf, the electron temperature was measured by means of a Langmuir probe. Assuming T e =T i and combining the results from the ivdf and Langmuir probe measurements the Mach number M=u/c s was evaluated (u streaming velocity, c s =[(T e +T i )/m i ] 1/2 speed of sound). Figure 2 shows M and the electron density at different axial positions z (spatial resolution Δz~0.5 mm). Close to the target (z=0) the Mach number approaches unity in agreement with the prediction by Bohm. Humboldt-University of Berlin Arbeitsgruppe Plasmaphysik Head: Prof. Dr. Gerd Fußmann -40 -20 0 20 40 Radial Position x [mm] of Disturbing Probe Figure 1: Normalized electron density (red) and temperature (blue) measured at fixed position while a second probe was radially driven. The calculated density distribution is plotted in black. The plasma physics group at the Humboldt University operates the plasma generator PSI-2 and the electron beam ion trap (EBIT). Research activities comprise basic plasma physics, plasmamaterial interactions and highly charged ion processes relevant to fusion experiments. Further effort is dedicated to the study of plasmoids produced on water surfaces at atmospheric pressure. 111 Our measurement is thus the first confirmation of Bohm’s criterion for conditions relevant to fusion experiments. An unexpected result is the short distance (Δz~5 mm) over which the final acceleration of the ions to M=1 takes place. Using a theoretical presheath model the measured profiles can be reproduced by relying on D=20 m 2 s -1 for the perpendicular diffusion coefficient. However, this D value is unrealistically large to explain the profiles solely by diffusion. A more refined analysis of our results suggests that radial electric fields build up in front of the target causing strong particle transport onto the target surface. M LIF M n LIF n -50 -40 -30 -20 -10 0 0 z [mm] Figure 2: Mach number and electron density as a function of axial position Electron Beam Ion Trap (EBIT) To complement earlier work on the line emission from highly charged tungsten ions (see Annual Reports 1999 and 2000), x-ray spectra from Si-like W 60+ to Ne-like W 64+ were measured in the 1-2 Å wavelength region. Our study includes the directly excited L-shell spectra as well as the associated satellite emission originating from dielectronically excited W ions. Precise knowledge of such data is essential owing to the increasing use of tungsten as wall material in nuclear fusion devices. The tungsten ions in the EBIT were produced by directing a continuous flow of W(CO) 6 gas towards the trap and ionizing the injected carbonyl compound by the monoenergetic electron beam. Spectra were obtained for a number of beam energies between 10 and 20 keV and analyzed using high resolution x-ray spectroscopy. As an example, in figure 3(a) we present a 15 keV electron beam energy spectrum showing lines from W 60+ to W 64+ recorded between 1.18 and 1.57 Å. To support our identification of the lines, wavelengths and intensities were calculated for the ions under investigation using an atomic structure computer package combined with a collisional-radiative model (in cooperation with the division Tokamak Edge and Divertor Physics in Garching). n 0 M 0 1 0.8 0.6 0.4 0.2 M or n/n 0
Intensity [cph] I [10-16 3 Ph/s cm /Å] cs [10 -20 cm 2 ] 100 50 0 5 0 a) 3p - 2s 10 W 64+ 5 4 3 2 1 0 b) W 63+ W 62+ W 64+ The results (figure 3b) show that atomic structure calculations can reproduce the general pattern of the observed spectra. The predictions for the wavelengths agree with the experimental values to within about 2-3 %. In a further experiment, measurements were made of the LMn (n=3-6) dielectronic-recombination (DR) resonances using a scanning technique described earlier (see Annual Report 1997). The DR process proceeds by capture of a free electron to a target ion forming an autoionizing doubly excited state followed by a stabilizing photon emission. Figure 3c shows the DR spectrum for the LMM resonance of tungsten ions with charge q
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Annual Report 2007 Max-Planck-Insti
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Annual Report 2007 The Max-Planck-I
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control but also because of the nov
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Tokamak Research
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use of generator power consumption
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an admixture of 10 % D 2 ) were per
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power in the range of 80-90 % of IC
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the future, a new safety interlock
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Field line excursion [cm] 1 0.75 0.
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as r/a≈0.75, depending on the q p
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It measures back-scattered radiatio
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oscillations) keeps the profiles in
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the peak ion flux by more than one
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flux across the separatrix due to c
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Tokamak Edge and Divertor Physics (
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From bolometer (KB5) studies in 200
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1 Introduction In 2007 the organisa
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The manufacture of the 20 planar co
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assembled between the plasma vessel
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mechanical supports on the plasma v
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will be later supplied from outside
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eing created quite detailed in one
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4.1.1.2.4 Central support elements
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Figure 18: Framed outer vessel uppe
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led to the establishment of the dep
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5.2.3 Torus Hall Layout The main mi
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of plasma vessels difficulties aros
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speedily as planned. Additional res
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Page 95 and 96: Introduction The Rechenzentrum Garc
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Page 99 and 100: SERF Euro-Asian electricity model C
Page 101 and 102: Charged Water Clusters Many aspects
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Page 105 and 106: Since evaporation of cesium and the
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Page 121 and 122: Hacquin, S., S. E. Sharapov, B. Alp
Page 123 and 124: Kobayashi, M., N. Ohyabu, T. Mutoh,
Page 125 and 126: P. Monier-Garbet, R. Neu, H. Pacher
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Page 137 and 138: Groth, M., N. H. Brooks, D. P. Cost
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Page 143 and 144: Wigger, C.: Entwicklung eines Codes
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Page 157 and 158: ments at the WEGA Stellarator. (34
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Marushchenko, N. B., H. Maaßberg a
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Otte, M., D. Andruczyk, A. Komarov,
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Sangines, R., D. Andruczyk, R. N. T
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Suttrop, W.: Tokamak equilibrium, t
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Wagner, F.: Energiepolitik für Deu
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You, J. H.: Integrated modelling ap
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P. Kornejev, R. Krampitz, R. Krause
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Stuttgart A8 Appendix How to reach
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Appendix Organisational structure o
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