Unstable Whistler-Wave Propagation along the Resonance Cone in a Large Beam-Plasma System

A very-large-diameter (∼½m) uniform electron beam is injected along a magnetic field ($B_0\simeq 75$ G) into a dense background plasma ($n_e\simeq {10}^{10}$ ${\mathrm{cm}}^{-3\mathrm{}}$). The beam drives oblique whistler waves ($\omega <{\omega }_c<{\omega }_p$) unstable which are in resonance with the beam ($\frac{\omega }{k_{\parallel }}\simeq v_b$) and propagate nearly along the resonance cone angle ($cos\theta =\frac{k_{\parallel }}{k}\simeq \frac{\omega }{{\omega }_c}$). Growth of test waves as well as spontaneous broad-band emission reminiscent of very-low-frequency hiss are observed.