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Parametric Decay Instability accompanying Electron Bernstein Wave Heating in Spherical Tokamaks

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This presentation by E.Z. Gusakov and A.V. Surkov at the 12th International Workshop on Spherical Tokamaks explores parametric decay instabilities (PDI) in laboratory plasmas and their consequences in tokamak heating experiments. It discusses nonlinear wave coupling and the unique challenges of electron Bernstein wave heating in dense plasma environments. Additionally, it highlights observations from the MAST EBWH experiment, analyzing the amplification effects and risks posed by nonlinear phenomena, particularly in the context of upper hybrid resonance excitation.

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Parametric Decay Instability accompanying Electron Bernstein Wave Heating in Spherical Tokamaks

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  1. Parametric Decay Instability accompanying Electron Bernstein Wave Heating in Spherical Tokamaks E.Z.Gusakov, A.V. Surkov Ioffe Institute St.Petersburg, Russia Presentation at the 12th International Workshop on Spherical Tokamaks Chengdu PRC, 12.10.06

  2. OUTLINE • Introduction. Observations of the UHR parametric decay instabilities (PDI) in laboratory plasmas and in tokamak heating experiments. • Nonlinear coupling and equations for UH and LH waves. • PDI in inhomogeneous plasmas. Amplification and absolute instability. • Anomalous reflection threshold. • Interpretation of observations performed in the MAST EBWH experiment. • Summary

  3. EBW heating scheme and risks of nonlinear phenomena excitation • The only way of electron cyclotron heating of dense spherical tokamak plasma in relatively low magnetic field is to use EBW excitation via linear wave conversion in the upper hybrid resonance (UHR) • Conversion of electromagnetic waves into slow plasma waves (EBW) is accompanied by a substantial growth of the microwave field in the UHR zone • High risk of nonlinear effects manifestation among which parametric decay instabilities possess the lowest thresholds and thus are the most dangerous

  4. Observation of PDI atFT-1 tokamak in XB heating experiment at 100 kWpower level FT-1 parameters R=62 cm; a=16cm; Ip=30 kA; B=1 T; PRF=150 kW FRF=30.6 GHz 1 – ECR; 2,3 – UHR for different plasma densities; 4,5 – microwave power launchers; 6 – microwave diagnostic horns

  5. Observation of the PDI spectra atFT-1 tokamak GHz M.M. Larionov et al. Sov. Journ. Plasma Physics 1986

  6. Observation of fast ion tails generation atFT-1 tokamak 60kW LHH 90kW EBWH E, keV

  7. Observation of the PDI threshold atFT-1 tokamak Pbs pLH Nnpa kW

  8. Experimental observations of anomalousreflection in the UHR in linear devices at 10 mW power level. Electron plasma wave dispersion: The pump frequency 2.2 GHz < F0 < 2.8 GHz The pump power 10 mW < P < 10 kW

  9. Backscattering decay instability observation V.I. Arkhipenko et al. Sov. JETPh Lett.1987

  10. Strong anomalous reflection Temporal correlation of microwave reflection bursts and depressions of fast electron generation.

  11. MAST EBW heating system

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