Pulsed electron beam scattering and heating by electrostatic beam-plasma turbulence
A dense electron beam (t[sub r] [approximately] 20ns, V[sub b] = 200V, I[sub b] < 1A, n[sub b]/n[sub e] < 10%) is injected into a uniform plasma (n[sub e] =1-4[times]10[sup 10]cm[sup [minus]3], kT[sub e] < 0.53V, B[sub o] = 90G) to study the interactions at the front of the beam on short time scales, where background ions are immobile and ion dynamics can be ignored. Using novel optical diagnostics to measure the beam electrons and radiofrequency antenna diagnostics for the electrostatic waves, it is found that above a threshold injected beam density (n[sub b]/N[sub e] = 5 - 10%), the beam propagation into the plasma is slowed down by beam scattering, energetic tail production and plasma heating that develop rapidly at the beam front from beam-generated broadband electrostatic turbulence. The turbulent electric fields are found to have evolved from coherent high frequency beam mode waves (f[sub HF] [approx] f[sub pe]) excited by the streaming beam-plasma instability. In addition, a new low frequency electrostatic wave mode (f[sub pi] < f[sub LF] < f[sub pe]) and the formation of a weak negative potential well ([phi][sub p] [approximately] [minus]10V) have also been detected that are important for the turbulence mechanism. These results should be relevant and important for the propagation of short electron beams into plasmas. Futhermore, they reveal the rich phenomena that exists in this particular beam-plasma regime, which present plasma theory cannot fully explain.
- Research Organization:
- California Univ., Los Angeles, CA (United States)
- OSTI ID:
- 7270696
- Country of Publication:
- United States
- Language:
- English
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