Experimental study of a 200--300 GHz megawatt gyrotron oscillator
An experimental study is presented of a pulsed megawatt gyrotron oscillator operating in the 200-300 GHz range whose design is consistent with continuous operation for ECRH of fusion plasmas. A cylindrical waveguide cavity over 20 free space wavelengths in diameter was designed to limit ohmic wall losses in the copper cavity to < 2 kW/cm[sup 2]. The frequency spacing between TE waveguide modes in this highly overmoded cavity is < 2%. The cavity is positioned at the peak magnetic field of a 14 T Bitter magnet. Two different radii beams produced by magnetron injection guns (MIGs) were used to excite the cavity. The large and small MIG guns produced annual beams of 0.75 cm and 0.45 cm radius. The guns operate with beam currents approaching 60 A and voltages as high as 100 kV. The voltage is produced by a line-type modulator with a pulse length of 3 [mu]s at a repetition rate of up to 4 Hz. Megawatt power levels can be generated in CW gyrotron oscillators at 200-300 GHz with efficiencies approaching 20%. The emission is single mode, single frequency with a single rotation which can easily be mode converted for transmission. No multimoding was observed at the high powers and efficiencies. The highest power reached with the large MIG gun was 0.97 MW at 230 GHz in the TE[sub 34,6] mode with an efficiency of 18% and beam parameters of 59 A and 90kV. This was the peak efficiency which was also obtained at 290 GHz in the TE[sub 41,8] mode with a power of 0.89 MW and beam parameters of 54 A and 93 kV. The highest power with the small MIG gun was 0.78 MW at 280 GHz in the TE[sub 25,13] mode with an efficiency of 17% and beam parameters of 51 A and 92 kV. The small MIG gun peak efficiency was 18% at 0.72 MW, 290 GHz in the TE[sub 25,14] mode. Efficiencies are about half of less highly overmoded gyrotrons. Mode competition is the main cause of the low efficiency, with voltage depression, beam thickness and velocity spread contributing only a fraction to the decrease.
- Research Organization:
- Massachusetts Inst. of Tech., Cambridge, MA (United States)
- OSTI ID:
- 6969957
- Resource Relation:
- Other Information: Thesis (Ph.D.)
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
Fu
42 ENGINEERING
ECR HEATING
HIGH-FREQUENCY DISCHARGES
MICROWAVE AMPLIFIERS
DESIGN
EFFICIENCY
EXPERIMENTAL DATA
GHZ RANGE 100-1000
THERMONUCLEAR REACTIONS
AMPLIFIERS
DATA
ELECTRIC DISCHARGES
ELECTRONIC EQUIPMENT
EQUIPMENT
FREQUENCY RANGE
GHZ RANGE
HEATING
HIGH-FREQUENCY HEATING
INFORMATION
MICROWAVE EQUIPMENT
NUCLEAR REACTIONS
NUCLEOSYNTHESIS
NUMERICAL DATA
PLASMA HEATING
SYNTHESIS
700460* - Fusion Technology- Heating & Fueling Systems
Fuels- (1992)
426000 - Engineering- Components
Electron Devices & Circuits- (1990-)