![The Langmuir probes array (LP) was moved parallel to the torus midplane (z = 1 cm) from
9.4 cm (-0.6 cm inside LCMS, edge plasma) to 12.0 cm (2 cm outside the LCMS, SOL).
As a recording facility, a 12 bit ADC with 1.6 µs sampling rate/channel was used.
Electrical probes setup
• radial turbulent particle flux
• wavenumber-frequency spectrum
• mean poloidal phase velocity
• skewness, kurtosis
3 2 1( ) ( )[ ( ) ( )]υΓ = ∝ − −
r s f ft n I t V t V t
( , )stat locP kθ ω
phθυ
E.J. Powers, Nucl. Fusion, 1974, 14, P. 749-752
S.J. Levinson, J.M. Beall, E.J. Powers and R. D., Nucl. Fusion 24, 527 (1984)](https://image.slidesharecdn.com/43b9d670-b14c-4cb7-8e2a-90679393cf57-161203142029/85/Electrostatic-Edge-Plasma-Turbulence-in-the-Uragan-3M-torsatron-6-320.jpg)
Electrostatic Edge Plasma Turbulence in the Uragan-3M torsatron
- 1. Aleksey Beletskii Electrostatic edge plasma turbulence in the Uragan-3M torsatron
- 2. Outline Introduction Electrical probes setup. General discharge conditions Plasma density fluctuations in SOL and divertor Er shear formation. Its influence on edge turbulent transport Contribution to International Stellarator/Heliotron Edge Turbulence Data Base Future plans Conclusion
- 3. Introduction FUSION PHYSICS. Edited by M. Kikuchi, K. lackner, M. Quangtran Vienna : International Atomic Energy Agency, 2012, p. 368 • Edge plasmas play an important role and often even dominate central plasma processes • The understanding of the plasma edge and the control of the edge conditions critically depend on measurements of the local plasma parameters • Electrical probe measurements are one of the earliest approaches in plasma diagnostics. In plasmas in which probes can survive, this diagnostic remains the easiest and most accurate way to measure the local plasma parameters: Te, Ti, ne, Vfl, Vpl • Electrostatic turbulence driven transport, as well as local particle fluxes can only be fully evaluated with electrical probes • Electrical probes in general include the variety of diagnostics with one or several electrodes contacting with a plasma and using an electrical measurement technique. Ion temperature, ion and electron energy distribution and impurity ions content can be obtained with more complicated and sophisticated kinds of electrical probes
- 4. G R Tynan, A Fujisawa and G McKee, Plasma Phys. Control. Fusion 51 (2009) 113001, 77pp FUSION PHYSICS. M. Kikuchi, et al. Vienna : International Atomic Energy Agency, 2012, p. 368 H-mode (1982) Edge plasma play an important role and often even dominate central plasma processes Electrostatic turbulence driven transport, as well as local particle fluxes can be fully evaluated with electrical probes X. Garbet / C. R. Physique 7 (2006) 573–583 Introduction
- 5. • Torsatron: • A large vacuum chamber, 70 m3 • Open natural helical divertor • Magnetic islands • Continuous hydrogen admission, 10-5÷10-4 Torr • РRF ≲ 150 kW, tpulse ~ 50 ms A7 D7 VG8 03, 9, 100 ( ) / 2 0.3, 12 , 0.72ϕ = = = ι π ≈ ≈ = m R cm a a cm B T Electrical probes setup III II I I II III I II III movable probes (VG8, VG7) ion energy anlyzers (A8, D7) divertor probes (D7, A7) ion energy anlyzers (D5,A6,D6) RF antenna G. G. Lesnyakov, E. D. Volkov, A. V. Georgievskij, et al., Nucl. Fusion 32, 2157 (1992); V. N. Kalyuzhnyj and V. V. Nemov, Fusion Sci. Technol. 46, 248 (2004). U-3M Magnetic system Magnetic field Poincaré cross-sections where probes were disposed
- 6. The Langmuir probes array (LP) was moved parallel to the torus midplane (z = 1 cm) from 9.4 cm (-0.6 cm inside LCMS, edge plasma) to 12.0 cm (2 cm outside the LCMS, SOL). As a recording facility, a 12 bit ADC with 1.6 µs sampling rate/channel was used. Electrical probes setup • radial turbulent particle flux • wavenumber-frequency spectrum • mean poloidal phase velocity • skewness, kurtosis 3 2 1( ) ( )[ ( ) ( )]υΓ = ∝ − − r s f ft n I t V t V t ( , )stat locP kθ ω phθυ E.J. Powers, Nucl. Fusion, 1974, 14, P. 749-752 S.J. Levinson, J.M. Beall, E.J. Powers and R. D., Nucl. Fusion 24, 527 (1984)
- 7. Plasma density fluctuations below torus midplane 0 20 40 60 80 100 kHz 0 0.2 0.4 0.6 0.8 1 power,a.u. 0 20 40 60 80 100 kHz 0 0.2 0.4 0.6 0.8 1 power,a.u. above torus midplane cross-section A cross-section D 0 20 40 60 80 100 kHz 0 0.2 0.4 0.6 0.8 1 power,a.u. 0 20 40 60 80 100 kHz 0 0.2 0.4 0.6 0.8 1 power,a.u. close to the LCMS VG7 VG8 more distant from LCMS SOL divertor V. Chechkin et al., Nucl. Fusion, 2002, V. 42, P. 192; T. Mizuuchi et al., J. Nucl. Mater. 313–316 (2003) 947. A. A. Beletskii et al. Plasma Phys. Reports 2009, 35, 10, p. 818-823 In the SOL to more (less) distantly located points relative to the LCMS, higher- (lower-) frequency fluctuations are inherent. A similar spectral splitting in two subranges occurs in the diverted plasma flows (DPF) too, depending on flow disposition relative to the torus midplane. A manifestation of the up-down asymmetry of diverted plasma flows in U-3M
- 8. Er shear formation The fast ion content passes over a maximum and a short-time burst of fast ion outflow to the divertor takes place. Simultaneously a hard bifurcation of the floating potential and, correspondingly, radial electric field shear increase are observed I. M. Pankratov et al. Contrib. Plasma Phys. 2010, 50, 6-7, p. 520–528 0.9 1.0 1.1 -20 0 20 40 60 80 100 120 140 0.9 1.0 1.1 -20 0 20 40 60 80 100 120 140 ∇Er weak Er ,Volt/cm -0.005 mc -0.004 mc -0.003 mc -0.002 mc -0.001 mc 0.0 mc Vfl , Volt ∇Er strong 0.001 mc 0.002 mc 0.003 mc 0.004 mc 0.005 mc ρ -300 -200 -100 0 100 200 300 400 -300 -200 -100 0 100 200 300 400
- 9. ∇Eh weaker ∇Eh stronger wavenumber-frequency power spectrum Fluctuations poloidal phase velocity Turbulent particle flux Er shear formation 9.0 9.5 10.0 10.5 11.0 -4 -3 -2 -1 0 1 2 3 4 5 6 LCFS υph,105 cm/c h, cm 9.0 9.5 10.0 10.5 11.0 -4 -3 -2 -1 0 1 2 3 4 5 6 υph,105 cm/c h, cm LCFS A strong radial electric field shear and, consequently, a higher E×B velocity shear result in decrease of turbulence-induced anomalous transport in the URAGAN-3M torsatron Density fluctuations statistics changes from Levy to Gaussian after ∇Eh increase Temperature fluctuation yet have to be taken into account B.Nold, New J. Phys. 14 (2012) 063022
- 10. International Edge Turbulence Data Base The U-3M electrical probes measurements are included in the International Stellarator/Heliotron Edge Turbulence Data Base. A universal parabolic relation between S and K occurs in the case of non-diffusive transport when non-Gaussian distribution of turbulent fluctuations take place (F. Sattin et al., Phys. Scr. 79 (2009) 045006). The relation is true for edge plasma fluctuations in U-3M. Scaling and transport analyses based on the international edge turbulence database have been carried out by P.Simon Nold B. et al., 37th EPS Conference on Plasma Physics (Dublin, Ireland 2010); 7th Coordinated Working Group Meeting (Greifswald 2010); P Simon, M Ramisch, A Beletskii et al., Plasma Phys. Control. Fusion 56 (2014) 095015 (8pp) https://ishpdb.ipp-hgw.mpg.de
- 11. Future plans 0 2 4 6 8 10 12 14 16 0 2 4 6 8 10 12 14 16 Is Bϕ V+ Is VflVfl 84 12 8 6 BPP Bθ BPP mm BN W A new combined probe will be utilized in future experiments in order to: • Direct measurements of edge plasma potential • Electron temperature fluctuations • Radial turbulent particle flux • The parallel heat flux R. Schrittwieser, J. Ad´amek et al., Czech. J. Phys. 56 (2006) C. Silva et al., Plasma Phys. Control. Fusion 57 (2015) 025003 (9pp) J. Adamek et al., Nucl. Fusion 57 (2017) 022010 (9pp)
- 12. Conclusion Asymmetric loss of particles with higher energies results in spectral splitting of plasma density fluctuations The radial electric field shear strongly affects edge turbulent transport in the URAGAN-3M torsatron Fast ion loss is the cause of the strong Er shear formation In U-3M, the edge transport is strongly non-diffusive. Universal statistical relation K=1.54S2 + 2.68 is satisfied Electron temperature fluctuations should be included to the International Stellarator/Heliotron Edge Turbulence Data Base Investigations of electrostatic turbulence in U-3M will be continued with use of the combined probe