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IAEA – 1 st RCM – 2004

IAEA – 1 st RCM – 2004. Plasma edge studies in the ETE spherical tokamak G.O. Ludwig , E. Del Bosco, L.A. Berni, J.G. Ferreira, R.M. Oliveira, M.C.R. Andrade, J.J. Barroso, P.J. Castro , C.S. Shibata. Laboratório Associado de Plasma Instituto Nacional de Pesquisas Espaciais

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IAEA – 1 st RCM – 2004

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  1. IAEA – 1st RCM – 2004 Plasma edge studies in the ETE spherical tokamak G.O. Ludwig, E. Del Bosco, L.A. Berni,J.G. Ferreira, R.M. Oliveira, M.C.R. Andrade, J.J. Barroso, P.J. Castro, C.S. Shibata. Laboratório Associado de Plasma Instituto Nacional de Pesquisas Espaciais 12227-010 São José dos Campos, SP, Brazil CRP – Joint research using small tokamaks 7-10 November, 2004 - Lisbon, Portugal Instituto Nacional de Pesquisas Espaciais - Laboratório Associado de Plasma

  2. ETE Spherical Torus General view of the Spherical Tokamak Experiment – October 2004. Instituto Nacional de Pesquisas Espaciais - Laboratório Associado de Plasma

  3. ETE main parameters and objectives • Explore the physics of low aspect ratio. • Investigate plasma edge conditions. • Undertake diagnostics development. • Follow worldwide spherical tokamak advancements. Instituto Nacional de Pesquisas Espaciais - Laboratório Associado de Plasma

  4. Axisymmetric configurations The spherical torus presents both the strong toroidicity effects of compact tori (notably magnetic shear) and the good stability properties provided by the external toroidal field of conventional tokamaks. Instituto Nacional de Pesquisas Espaciais - Laboratório Associado de Plasma

  5. Plasma current evolution Instituto Nacional de Pesquisas Espaciais - Laboratório Associado de Plasma

  6. Present plasma parameters • Current  60 kA – Pulse duration  12 ms. • Density  0.351020 m3 – Temperature  160 eV. • Peaks at R0  26 cm with A  2.2 (design values R0 = 30 cm and A = 1.5). Instituto Nacional de Pesquisas Espaciais - Laboratório Associado de Plasma

  7. Plasma pictures • High-speed CCD camera (frame speed 1/500 to 1/20,000 s) – • 30 to 500 FPS (upgrade to 10,000 FPS). • Pictures, as well as (ne, Te) profiles, show plasma displaced to the inner side. • Need position and shape control taking into account eddy current effects. Instituto Nacional de Pesquisas Espaciais - Laboratório Associado de Plasma

  8. Typical shot (#5401) • Plasma current = 40~60 kA, Pulse duration = 8~5 ms (>12 ms with glow discharge). • Loop voltage at Z = 0 in gap between OH solenoid and vacuum vessel. • Evidence of runaway discharge (hard X-rays, Iplasma≠ 0, Vloop 0). • Current induced in vacuum chamber = 60 kA. Instituto Nacional de Pesquisas Espaciais - Laboratório Associado de Plasma

  9. Coils currents and power supplies • Parameters at ~1/3 of first phase, compatible with installed capacitor banks (~1/4). • TF coil current 50 kA  B = 0.4 T. • OH solenoid current 20 kA  Ip ~ 200 kA. • Next: increase installed energy (2x). Instituto Nacional de Pesquisas Espaciais - Laboratório Associado de Plasma

  10. Baking and glow discharge cleaning • Vacuum vessel covered by hot tapes (11 kW) and thermal insulation blanket. • Baking up to 120C so far (limited by viton seals) but can go up to 200C. • Glow discharge (500 V/0.5 A, refrigerated anode) with He at 2.410-3 mbar. • Base pressure < 810-8 mbar after baking (2-3 days) and glow (~48 hours). Instituto Nacional de Pesquisas Espaciais - Laboratório Associado de Plasma

  11. Vacuum conditioning and breakdown • Glow discharge and biased hot filament. • Next: Conditioning improvement needed for removal of O2 – overcome the radiation barrier. Instituto Nacional de Pesquisas Espaciais - Laboratório Associado de Plasma

  12. Thomson scattering system • 10 J, 30 ns pulse duration, Q-switched ruby laser. • f/6.3 lens images the scattered light on 4.5 mm  1.5 mm optical fiber bundles. • 5-channels filter polychromator with avalanche photodiodes. • Up to 22 plasma positions (15 mm) along 50 cm of the laser beam trajectory. Instituto Nacional de Pesquisas Espaciais - Laboratório Associado de Plasma

  13. Thomson scattering system upgrade Measured attenuation of time-delayed signals in channels 1 and 8: loss = 84%, dispersion = 73%, total = 61%. • Multipoint diagnostic based on time-delay technique using fibers of different lengths. • Simultaneous temperature and density profiles – ten spatial points per polychromator. Instituto Nacional de Pesquisas Espaciais - Laboratório Associado de Plasma

  14. Test of the multipoint Thomson scattering system • Radial profile of the electron temperature obtained with the four-channels • multiplexed Thomson scattering system (4 fibers, Ø 0.8 mm, 14 m steps). • Three curves obtained in three different shots. • Next: upgrade to ten channels. Instituto Nacional de Pesquisas Espaciais - Laboratório Associado de Plasma

  15. Lithium beam probe development • 10 keV neutral lithium beam probe for measurements of the edge plasma density • and its fluctuations. • Current density up to 1 mA/cm2 (glassy b–eucryptite source) – 80% neutralization. • Plasma density measured in He glow discharge at 2.010-3 mbar  ne=21017 m-3. Instituto Nacional de Pesquisas Espaciais - Laboratório Associado de Plasma

  16. First results of the lithium beam probe • Gas injection by fast puff valve and pump out. • Radial profile of plasma density measured with Thomson scattering, fast neutral Li beam probe and Langmuir probe. • Fluctuation of the plasma density at the edge. Instituto Nacional de Pesquisas Espaciais - Laboratório Associado de Plasma

  17. Lithium beam probe upgrade • Objective lens, fiber optics (Ø 1.5 mm). • Interference filters – 1 nm. • Multichannel (8 x 8) photomultiplier. • Next: 8 radial positions (< 17 cm) – gain factor 8. Instituto Nacional de Pesquisas Espaciais - Laboratório Associado de Plasma

  18. Monotron for plasma heating experiments f = 6.7 GHz, V0 = 10 kV,I0 = 10 A. • Transit-time microwave tube – cylindrical cavity excited by a hollow electron beam. • Single-cavity monotron with RF electric field tail pre-modulating the electron beam – 25% conversion efficiency. Instituto Nacional de Pesquisas Espaciais - Laboratório Associado de Plasma

  19. Monotron electron gun • Optimized design collimates electron beam – uses improved filament support. • Annular strip of nickel coated with a (Ba,Sr,Ca)O film  3 A/cm2 (800 K, 10 A). • Next: Tests of pulsed HV power supply (20 kV, 30 A, 50 µs), gun, and monotron. Instituto Nacional de Pesquisas Espaciais - Laboratório Associado de Plasma

  20. Foucault currents in the central column Study of the currents induced by the OH solenoid in the 12 trapezoidal bars of the TF coil central column (cross section shown at left). Bode plot of the OH solenoid impedance comparing theoretical results with experimental values obtained before the central stack was assembled in ETE. Instituto Nacional de Pesquisas Espaciais - Laboratório Associado de Plasma

  21. Foucault currents in the vacuum vessel Distribution of eddy currents induced by the poloidal field coils on the vacuum vessel was determined experimentally and compared with theoretical results. Instituto Nacional de Pesquisas Espaciais - Laboratório Associado de Plasma

  22. Foucault currents and plasma start-up simulation • Currents in capacitor banks and external coils calculated self-consistently with eddy currents. • Current distributions in the vacuum vessel will be used in zero-dimensional simulations of the plasma discharge. • Use distributions to eliminate error-fields in the magnetic reconstruction of the plasma equilibrium. Instituto Nacional de Pesquisas Espaciais - Laboratório Associado de Plasma

  23. Further theoretical development • Bootstrap current dependence on plasma profiles in self-consistent equilibrium calculations. • Effects of viscosity on plasma instabilities (simple edge plasma models). • First attempts of magnetic reconstruction using a variant of the moments method (possibility of including edge resistivity). • Monotrons using a novel twin-cavities concept with a bisecting grid should attain 40% electronic efficiency – comparable to gyrotrons, but simpler design (no magnetic field, large power handling capability). • Two coupled cavities with stepped electric field profile: monotrons with up to 45% electronic efficiency. Instituto Nacional de Pesquisas Espaciais - Laboratório Associado de Plasma

  24. Budget and planning – 2005 • Main scientific staff (9 researchers) – US$ 250,000.00 (Institute) • Four part time technicians (Institute) – Researchers & engineers urgently needed • Maintenance of the laboratory – US$ 85,000.00 (Institute) • Materials, services, travel/transportation – US$ 25,000.00 • Additional capacitor bank chargers – US$ 48,000.00 • Fast CCD camera upgrade (10,000 FPS) – US$ 12,000.00 (?) • Diagnostics – US$ 85,000.00 (Energy research fund – under analysis) • Upgrade of the Thomson scattering (10 x) and lithium beam (8 x) diagnostics – US$ 5,000.00 • Magnetic pickup coils (reconstruction) and electrostatic probes (natural divertor) – US$ 15,000.00 • Bolometers, soft X-ray arrays – US$ 15,000.00 • VME data acquisition modules – US$ 20,000.00 • Microwave interferometer (1 mm) – US$ 30,000.00 • Pre-ionization, preheating – US$ 82,000 (Energy research fund – under analysis) • EC heating system (9.5 GHz, 40 kW, 500 μs) – US$ 82,000.00 • Fusion activities in Brazil presently under discussion at the government level Instituto Nacional de Pesquisas Espaciais - Laboratório Associado de Plasma

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