Effect of convective loss on the parametric decay of cold electron plasma waves

The resonant decay of cold electron plasma waves was investigated in the Princeton L‐3 device in an argon plasma with n∼10¹⁰–10¹¹ cm⁻³, B∼700 G–2 kG, f₀∼50–80 MHz (ω₀⩾10 ω_lh). The decay waves were identified to be ion‐acoustic waves and cold electron plasma waves. Because of convective losses in the finite extent pump field, the threshold for parametric decay is considerably higher than the collisional threshold for the dominant E_0⊥×B coupling. Coupling due to E_0∥ can be important in low density, high magnetic field plasmas. At high densities (n≳3×10¹⁰ cm⁻³), E_0⊥×B coupling becomes dominant. The E_0⊥×B decay convective threshold was measured at various antenna lengths, magnetic field strengths, and plasma densities. The experimental results are in good agreement with theory. Indication of pump depletion and enchanced Landau heating of electrons were observed in the parametric decay process.