Microwave production from a plasma driven by a high power relativistic electron beam
Microwave emission from an unmagnetized plasma (T = 1 eV, n/sub e/ = 1.5 x 10/sup 11/ cm/sup -3/) driven by an electron beam (2.7 < I/sub b/ < 60 kA, 1.2 < V/sub b/ < 1.4 MV, t/sub rise/ = 15 ns, t/sub pulse/ = 60 ns) emitted from a 93 cm/sup 2/ velvet cathode with anode cathode gaps of 3.5 and 6.0 cm has been measured. A 90 ..mu..s, 80 A current pulse, emitted from a thermionic lanthanum hexaboride electron source, preionizes a 1.4 mT argon fill in a 1-m-long, 15-cm-diameter Lucite tube. A 6 ..cap omega.. water dielectric accelerator injects the electron current, 50 ..mu..s into the afterglow, into the tube through an aluminized Mylar anode. A Microwave spectrometer measures the radio frequency output in 2 to 18, 18 to 26, and 26 to 47 GHz bands that filters separate into narrower subbands. Digitizers record beam voltage, current, and microwave power obtained from diode detectors. The intrinsic electrical noise of the system is 15 mV p-p. A 3.36 cm-gap diode, delivering a 1.2 MeV, 90 kA beam into the tube, produces an intense pinch beyond the aluminized Mylar anode with little microwave output. A diode with a 6 cm gap, fills the aperture of the tube with 200 A/cm/sup 2/ (35 kA) of 1.4 MeV electrons that result in intense microwave radiation. The emission takes place in two distinct phases. The 2 to 6 GHz output, that includes ..omega../sub p/, rises promptly with the current pulse and then decays. For 6 GHz and above, there appears a low level microwave prepulse simultaneous with the 2 to 6 GHz output. This output raises sharply 25 ns after the current pulse begins, and includes frequencies out to and beyond 40 GHz. The radio frequency output falls off before the current pulse ends. The microwave intensity decays monotonically with frequency.
- Research Organization:
- Lawrence Livermore National Lab., CA (USA); California Univ., Davis (USA). Dept. of Applied Science
- DOE Contract Number:
- W-7405-ENG-48
- OSTI ID:
- 6569716
- Report Number(s):
- UCRL-94882; CONF-8606300-1; ON: DE87008482
- Country of Publication:
- United States
- Language:
- English
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Molecular & Chemical Physics-- Beams & their Reactions
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
BEAM INJECTION HEATING
BEAMS
ELECTROMAGNETIC RADIATION
ELECTRON BEAMS
FREQUENCY DEPENDENCE
FREQUENCY MEASUREMENT
HEATING
LEPTON BEAMS
MICROWAVE RADIATION
MICROWAVE SPECTRA
PARTICLE BEAMS
PLASMA
PLASMA HEATING
PRODUCTION
RADIATIONS
SPECTRA