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Fusion neutron research in Novosibirsk including experiments

“ Piero Caldirola ” International Centre for the Promotion of Science and International School of Plasma Physics. Fusion neutron research in Novosibirsk including experiments. A. Ivanov Budker Institute, Novosibirsk. Layout of the talk. Brief description of the approach

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Fusion neutron research in Novosibirsk including experiments

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  1. “Piero Caldirola” International Centre for the Promotion of Science and International School of Plasma Physics Fusion neutron research in Novosibirsk including experiments A. Ivanov Budker Institute, Novosibirsk

  2. Layout of the talk • Brief description of the approach • GDT as a Neutron Source formaterialstestingand Hybrid • Experiments: • Electron temperature measurements with extended NBs • MHD andmicrostability of high- plasma • Observation of AIC instability • axialconfinementambipolarplugs • Conclusions 2 WORKSHOP ON FUSION FOR NEUTRONS AND SUB-CRITICAL NUCLEAR FISSION Villa Monastero, Varenna, Italy, September 12 - 15, 2011

  3. Gas Dynamic trap – general layout • The Gas-Dynamic Trap is a version of a standard simple mirror whose characteristic features are – a very high mirror ratio, R , in the range of a few tens; – a relatively large length, L , exceeding an effective mean free path, ii lnR /R, with respect to scattering into the loss cone. • The warm target plasma is almost Maxwellian – behaves like an ideal gas in a container with a pinhole leak • MHD-stable even though system is fully axially symmetric – non-negligible amount of plasma in the regions beyond the mirror throats, where magnetic field has favorable curvature – MHD ballooning/interchange modes limit stability at  40-60% • The electron neat flux to the end walls is suppressed by potential drop in expanders which develops if H mirror / H wall exceeds ~ 40 3 WORKSHOP ON FUSION FOR NEUTRONS AND SUB-CRITICAL NUCLEAR FISSION Villa Monastero, Varenna, Italy, September 12 - 15, 2011

  4. Requirements to VNS for fusion materials testing • Fusion neutron spectrum • About 2MW/m2 neutron flux or higher for accelerated tests • Small enough gradient of neutron flux density • Continuous operation • More than 70% availability • Reasonably small tritium consumption 4 WORKSHOP ON FUSION FOR NEUTRONS AND SUB-CRITICAL NUCLEAR FISSION Villa Monastero, Varenna, Italy, September 12 - 15, 2011

  5. Layout of GDT-based neutron source Neutron flux density as a function of electron temperature for injection energy 65 keV 5 WORKSHOP ON FUSION FOR NEUTRONS AND SUB-CRITICAL NUCLEAR FISSION Villa Monastero, Varenna, Italy, September 12 - 15, 2011

  6. Neutron shield & Testing zone arrangement 6 WORKSHOP ON FUSION FOR NEUTRONS AND SUB-CRITICAL NUCLEAR FISSION Villa Monastero, Varenna, Italy, September 12 - 15, 2011

  7. Status of GDT-NS development • Conceptual design is completed for a version of GDT-NS with 1.8MW/m2 neutron flux, 60MW power consumption (BINP, Efremov, Snejinsk) • Plasma physical model based on Monte-Carlo approach is developed (BINP, FZR) • Feasibility of neutron shield is proven by numerical calculation (FZR, ENEA, Snejinsk) • 26T, 90mm bore mirror coil design is developed (Efremov) • Small specimen test technology is proposed (KFK, BINP) • Application of GDT-NS for MA burner is considered (FZR, BINP) 7 WORKSHOP ON FUSION FOR NEUTRONS AND SUB-CRITICAL NUCLEAR FISSION Villa Monastero, Varenna, Italy, September 12 - 15, 2011

  8. Conceptual parameters for GDT-based applications

  9. Experimental model of GDT View before and after upgrade of neutral beams 9 WORKSHOP ON FUSION FOR NEUTRONS AND SUB-CRITICAL NUCLEAR FISSION Villa Monastero, Varenna, Italy, September 12 - 15, 2011

  10. U ~ Te a b Potential profile Plasma decay a) with vortex, b) no vortex VORTEX plasma CONFINEMENT IN GDT Plasma flow lines for m=1 mode with vortex. Steep potential gradient at periphery causes differential plasma rotation The limiter biasing considerably improved plasma confinement M=1 mode nonlinearly saturates Limiter biasing produces radial electric field and plasma rotation at periphery WORKSHOP ON FUSION FOR NEUTRONS AND SUB-CRITICAL NUCLEAR FISSION Villa Monastero, Varenna, Italy, September 12 - 15, 2011

  11. STEADY STATE IS ACHIEVED WITH PLASMA REFUELING No gas puff Gas puff with 5mc, 3.5 MW beams 11 WORKSHOP ON FUSION FOR NEUTRONS AND SUB-CRITICAL NUCLEAR FISSION Villa Monastero, Varenna, Italy, September 12 - 15, 2011

  12. AXIAL RE-DESTRIBUTION OF HIGH-PLASMA PRESSURE Loop dataPlasma diamagnetism 12 WORKSHOP ON FUSION FOR NEUTRONS AND SUB-CRITICAL NUCLEAR FISSION Villa Monastero, Varenna, Italy, September 12 - 15, 2011

  13. Oscillations NB attenuation data –spontaneous excitation of m=2 mode in high- plasma

  14. Findings in GDT experiments Issues addressed Some important results Te is determined by balance between fast ion drag power and collisional end losses Fast ion relaxation is classical Skew NBI provide fast ion density peaks at turning points High-β (>0.5) MHD – stable plasma in axisymmetric field Suppression of axial electron heat conduction to the end wall by decreasing magnetic field Plasma is sustained during several characteristic times with extended neutral beams • Factors controlling electron temperature • Equilibrium and stability of anisotropic fast ions • Steady state operation • Ballooning instability threshold • Effect of ambipolar fields on confinement • Effect of plasma rotation/vortex barrier formation • Non-paraxial effects due to high β 14 WORKSHOP ON FUSION FOR NEUTRONS AND SUB-CRITICAL NUCLEAR FISSION Villa Monastero, Varenna, Italy, September 12 - 15, 2011

  15. Injected (Pinj) and trapped (Ptr) NBI power Fast ion energy content Linear DD yield near fast ion the mirror point. PLASMA PARAMETERS IN GDT EXPERIMENT DD reaction yield: axial profile radial profile

  16. PLASMA PARAMETERS IN GDT EXPERIMENT- ELECTRON TEMPERATURE

  17. PLASMA PARAMETERS IN GDT EXPERIMENT- PLASMA BETA On-axis magnetic field depression in turning point region vsenergy accumulated in fast ions B/B variation across plasma at the turning point 2<i Magneticfielddepressionandlocaldiamagnetismvs time WORKSHOP ON FUSION FOR NEUTRONS AND SUB-CRITICAL NUCLEAR FISSION Villa Monastero, Varenna, Italy, September 12 - 15, 2011

  18. “Saw teeth” relaxations “Saw teeth” relaxations Spectrum of RF noise Axial broadening of fast ion reflection region WORKSHOP ON FUSION FOR NEUTRONS AND SUB-CRITICAL NUCLEAR FISSION Villa Monastero, Varenna, Italy, September 12 - 15, 2011

  19. Compact mirror cell GDT central cell Experiment with additional mirror cell Internal cell: Magnetic field: Background plasma: L=30 cm, d =70 cm. B0=2.4 T, Bm=5.2 T hydrogen, n0 ≈ 1019 m-3,Te ≈ 70 eV, a=9 cm. NBI: H0 or D0 , E0=20 keV, θ=90º, Pinj ≈ 1 MW, τinj=4 ms 19 WORKSHOP ON FUSION FOR NEUTRONS AND SUB-CRITICAL NUCLEAR FISSION Villa Monastero, Varenna, Italy, September 12 - 15, 2011

  20. Fast ion density in mirror cell 20 WORKSHOP ON FUSION FOR NEUTRONS AND SUB-CRITICAL NUCLEAR FISSION Villa Monastero, Varenna, Italy, September 12 - 15, 2011

  21. — anisotropy in velocity space Polarization Bφ, arb. u. Br, arb. u. Experimental observation of aic instability in mirror cell HF oscillations threshold: n > 2.5·1019m-3,A ≈ 35,β┴=0.02, сi/аp ≈ 0.23. Main frequency f0 < fci The magnetic field vector of the wave rotates in the direction of ion gyration. Azimuthal mode number m = 1-2 AIC instability WORKSHOP ON FUSION FOR NEUTRONS AND SUB-CRITICAL NUCLEAR FISSION Villa Monastero, Varenna, Italy, September 12 - 15, 2011

  22. Axialconfinementwithambipolarendplugs WORKSHOP ON FUSION FOR NEUTRONS AND SUB-CRITICAL NUCLEAR FISSION Villa Monastero, Varenna, Italy, September 12 - 15, 2011

  23. NBI Plasma dump Magnetic coils Plasma dump Central cell Expander Limiter Fas ions Plasma source Plug cell with plugging with plugging with plugging one side plugging w/o plugging w/o plugging difference w/o plugging difference Ambipolar plugging experiment at GDT. x 2 on axis Radial profile of the plasma potential. Radial profile of the plasma density. Linear plasma density time evolution

  24. The probe measured potential fluctuations show the presence of waves having small azimuthal mode numbers m=1,2. The oscillation frequency is below local ion-cyclotron frequency. Magnetic fluctuation probes show that the mode is nearly left-circularly (direction of ion gyration) polarized. These properties are all consistent with an Alfven-like wave generated by AIC instability. The AIC instability threshold is observed Observation of AIC instabilityin local cell 24 WORKSHOP ON FUSION FOR NEUTRONS AND SUB-CRITICAL NUCLEAR FISSION Villa Monastero, Varenna, Italy, September 12 - 15, 2011

  25. Conclusions • Electron temperature achieved already at the GDT experiment corresponds to ~0.4MW/m2 neutron flux for GDT-NS • Belowsomelimitinpressureplasmabehaviorisclassical. No critical issues were found preventing from further improvement of plasma parameters • Reductionofaxiallosseswithambipolarplugsisdemonstrated • Plasma steady state conditions are planned to be achieved at the next step device at higher electron temperature • Conceptual design of GDT-NS for fusion materials and sub-components development is completed • Possible application of GDT-NS as a driver for fission/fusion hybrids is underconsideration

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