Heavy ion beam probing—diagnostics to study potential and turbulence in toroidal plasmas

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Heavy ion beam probing (HIBP) is a unique diagnostics to study the core plasma potential and turbulence.Advanced HIBPs operate in the T-10 tokamak and TJ-II flexible heliac with fine focused (<1 cm) and intense (100 µA) beams.They provide measurements in the wide density interval n e = (0.3-5) × 10 19 m -3 , in a wide range of Ohmic and electron cyclotron resonance heated (ECRH) discharges with various currents at T-10, and in the wide range of magnetic configurations with ECR and neutral beam injection (NBI) heating at TJ-II.Time evolution of the radial profiles and/or local values of plasma parameters from high field side (HFS) to low field side (LFS), -1 < ρ < 1, is observed in TJ-II by 125 keV Cs + ions in a single shot, while LFS (+0.2 < ρ < 1) is observed in T-10 by 300 keV Tl + ions.Multi-slit energy analyzers provide simultaneously data on the plasma potential ϕ (by the beam extra energy), plasma density n e (by the beam current), poloidal magnetic field B pol (by the beam toroidal shift), poloidal electric filed E pol that allows one to derive the electrostatic turbulent particle flux Γ E×B .The cross-phase of density oscillations produces the phase velocity of their poloidal propagation or rotation; also it gives the poloidal mode number.Dual HIBP, consisting of two identical HIBPs located ¼ torus apart provide the long-range correlations of core plasma parameters.Low-noise high-gain electronics allows us to study broadband turbulence and quasi-coherent modes like geodesic acoustic modes and Alfvén eigenmodes.