THE ENERGY DISTRIBUTION FOR ELECTRONS IN A THERMIONIC DIODE PLASMA CANNOT BE TRULY MAXWELLIAN

Journal Article · Sun Jul 01 04:00:00 EDT 1962 · Advan. Energy Conversion

OSTI ID:4695343

Nottingham, W B

For the refractory emitters such as tungsten, tantalum, and molybdenum operated in an energy conversion diode, the ratio of the emitter temperature to the cesium temperature strongly influences the operating properties. If this ratio exceeds 3.2 an ion-rich sheath usually forms at the emitter surface. Electrons are accelerated in the plasma space by this injection potential. The analysis given here shows that at the open circuit condition, the energy distribution of the electrons at the plasma edge of the emitter sheath cannot be a true Maxwellian over the entire range in electron energy. Instead, it is thought to be made up of two quasi-Maxwellians. The low energy electrons are trapped and may have a high average energy close to that of the injection potential. The untrapped electrons will have an electron temperature equal to that of the emitter and their density will be that associated with an apparent or fictitious density many times that of the actual density. The theory is developed to describe quantitatively the relations that must be satisfied for the above description to apply. Typical numerical results applicable to specific diode configurations are presented. It is concluded that if the emitter to cesium temperature ratio exceeds 3.6, volume ionization is not required for a stable sheath. In the range 3.2-3.6 surface ionization is usually insufficient and it is necessary to have volume ionization to sustain the sheath. Further studies will be required to establish the mechanism. It may be direct ionization by high energy electrons or ionization from excited states of the cesium atoms. (auth)

• Research Organization: Massachusetts Inst. of Tech., Cambridge
• NSA Number: NSA-17-020617
• OSTI ID: 4695343
• Journal Information: Advan. Energy Conversion, Journal Name: Advan. Energy Conversion Vol. Vol: 2
• Country of Publication: Country unknown/Code not available
• Language: English

Related Subjects

ATOMS
CESIUM
CIRCUITS
CONFIGURATION
CONVERSION
DENSITY
DIODES
ELECTRIC POTENTIAL
ELECTRON TEMPERATURE
ELECTRON TUBES
ELECTRONS
EMISSION
ENERGY
EXCITATION
INJECTION
IONIZATION
IONS
LAYERS
MAXWELL DISTRIBUTION
MOLYBDENUM
NUMERICALS
PHYSICS
PLASMA
REFRACTORIES
SPECTRA
STABILITY
SURFACES
TANTALUM
TEMPERATURE
THERMIONICS
TRAPS
TUNGSTEN
VELOCITY
VOLUME