RADIOISOTOPIC THERMOINIC CONVERTER

• US 3,843,896 A
• Filed: 02/04/1972
• Issued: 10/22/1974
• Est. Priority Date: 01/29/1969
• Status: Expired due to Term

• Current Assignee: John G De Steese, Kenneth A. Gasper, Ned S. Rason
• Original Assignee: John G De Steese, Kenneth A. Gasper, Ned S. Rason
• Inventors: De Steese, John G., Gasper, Kenneth A., Rason, Ned S.
• Primary Examiner(s): Duggan, D. F.
• Application Number:
  US05/223,691
• Time in Patent Office: 991 Days
• Field of Search: 310/4
• US Class Current: 310/306
• CPC Class Codes: G21H 1/106 Cells provided with thermionic generators

Abstract

Atomic diode battery or thermionic converter including a radioisotopic fuel pellet enclosed in a capsule having an emitter surface extending over substantially the entire capsule external area, a housing enclosing the emitter capsule and having an internal collector surface extending over substantially the entire housing internal area and maintained at a predetermined spacing from the emitter surface, a cesium vapor source communicating with the interelectrode space under such low vapor pressure as to effect nominally vacuum mode operation, and emitter and collector connections providing an electrical output from the battery. An optimum relationship established among battery parameters provides maximum energy conversion efficiency at practical electrode temperatures and spacings using available materials.

Claims

1. A radioisotopic thermionic converter comprising:

an emitter capsule including a radioisotope fuel mass source of thermal power, at least one layer of material encapsulating and shielding said fuel mass, and an external emitter surface on said layer of material energized by said fuel mass;

an outer housing including an internal collector surface, said housing enclosing said emitter capsule and providing further shielding for said encapsulated fuel mass, said housing providing a vacuum envelope and maintaining a low pressure condition therein to effect a nominally vacuum mode of operation of said converter;

means for mounting said emitter capsule in said housing and maintaining said emitter surface normally at a substantially predetermined spacing from said collector surface, said mounting means including elastic means connecting respective ends of said emitter capsule to corresponding ends of said housing whereby said emitter capsule is supported substantially at its ends; and

output means adapted to connect respectively with said emitter and collector surfaces, for providing an electrical output from said converter, at least one of said elastic means simultaneously serving as the one of said output means connecting with said emitter surface, whereby direct containment of fuel within said emitter capsule effects the most efficient thermal coupling of heat source and diode conversion portion of said converter and the maximum temperature of any portion of said fuel mass does not differ significantly from the temperature of said emitter surface.

2. In a radioisotopic thermionic converter including an emitter capsule containing a spontaneously and naturally decaying radioisotope fuel and having an external emitter surface, an outer housing enclosing said emitter capsule and having an internal collector surface, said housing maintaining a low pressure condition therein to effect a nominally vacuum mode of operation of said converter, and output means adapted to connect respectively with said emitter and collector surfaces for providing an electrical output from said converter, mounting means comprising:

first elastic means connecting a first end of said emitter capsule to a corresponding first end of said housing; and

second elastic means connecting a second end of said emitter capsule to a corresponding second end of said housing whereby said emitter capsule is supported substantially at its ends in said housing and said emitter surface is maintained normally at a substantially predetermined distance from said collector surface, at least one of said first and second elastic means simultaneously serving as the one of said output means connecting with said emitter surface.

3. In a radioisotopic thermionic converter including an emitter capsule containing a radioisotope fuel and having an external emitter surface, and an outer housing enclosing said emitter capsule and having an internal collector surface, said housing maintaining a low pressure condition therein to effect a nominally vacuum mode of operation of said converter, mounting means comprising:

first elastic means connecting a first end of said emitter capsule to a corresponding first end of said housing; and

second elastic means connecting a second end of said emitter capsule to a corresponding second end of sAid housing whereby said emitter capsule is supported substantially at its ends in said housing and said emitter surface is maintained normally at a substantially predetermined distance from said collector surface, said first and second elastic means including first and second thin-walled tubes longitudinally connected to support said emitter capsule axially at its ends.

4. A radioisotopic thermionic converter assembly comprising:

a plurality of emitter capsules each including a spontaneously and naturally decaying radioisotope fuel source of relatively low predetermined thermal power density not greater than the order of 10 watts/cm3, at least one layer of material fully encapsulating and shielding said radioisotope fuel, and an external emitter surface of predetermined work function on said layer of material energized by said radioisotope fuel;

a plurality of outer housings each including an internal collector surface of predetermined work function, said housings respectively enclosing said emitter capsules and providing further shielding for said encapsulated radioisotope fuel;

means for mounting said emitter capsules respectively in said housings and maintaining said emitter surfaces normally at a substantially predetermined spacing respectively from said collector surfaces, said mounting means including electrically insulating spheres positioned between said emitter and collector surfaces, a plurality of converters being thereby formed;

a predetermined charge of an additive vapor loaded in said predetermined spacings between said emitter and collector surfaces, said additive vapor being provided at a predetermined low pressure and used essentially only as a surface adsorbate to modify said predetermined work functions of said emitter and collector surfaces without generating plasma contributing electron scattering effects therebetween;

output means adapted to connect respectively with said emitter and collector surfaces, for providing a plurality of electrical outputs from said converters; and

a casing enveloping said converters in a unit and maintaining said predetermined low pressure in the approximate range from 10 3 to 0.1 torr, said converters characterized by operating at low emitter current densities established by said thermal power density of said radioisotope fuels and said predetermined work function of said emitter surfaces in the approximate range of 0.1 to 400 ma/cm2 in a nominally vacuum mode of operation established by the operating temperature of said emitter and collector surfaces, said predetermined spacings and said predetermined low pressure, with negligible ion neutralization of space charge and negligible plasma contributing electron scattering effects, said emitter and collector surfaces having relatively low oeprating temperatures in the approximate ranges of 600* to 1,400*K and 300* to 800*K, respectively, and each of said converters operating thermionically as a space charge limited device having an electron motive diagram wherein a motive maximum is located intermediate to said emitter and collector surfaces thereof whereby an output voltage higher than the difference of said predetermined work functions of said emitter and collector surfaces is obtained from each of said converters, said output means of said converters being interconnected to provide an output for said unit at useful efficiency.

5. The invention as defined in claim 4 further comprising an additive source communicating with said predetermined spacings between said emitter and collector surfaces of said converters, said source providing supplemental additive vapor which can be used to supplement said predetermined charge of additive vapor and functions essentially only as a surface adsorbate to modify said predetermined work functions of said emitter and collector surfaces with negligible ion neutralization of space charge and without generating pLasma contributing electron scattering effects therebetween, and each of said converters operating thermionically as said space charge limited device to provide an output voltage higher than the difference of said predetermined work functions of said emitter and collector surfaces thereof.

6. A radioisotopic thermionic converter comprising:

an emitter capsule including a spontaneously and naturally decaying radioisotope fuel source of relatively low predetermined thermal power density not greater than the order of 10 watts/cm3, at least one layer of material fully encapsulating and shielding said radioisotope fuel, and an external emitter surface of predetermined work function on said layer of material energized by said radioisotope fuel;

an outer conductive housing including an internal collector surface of predetermined work function, said housing enclosing said emitter capsule and providing further shielding for said encapsulated radioisotope fuel;

means for mounting said emitter capsule in said housing and maintaining said emitter surface normally at a substantially predetermined spacing from said collector surface, said mounting means including elements installed between said emitter and collector surfaces and transmitting lost heat energy very much smaller compared to useful heat energy transmitted by said emitter and collector surfaces;

output means for providing an electrical output from said converter, said output means including a conductive collector contact electrically connected to said collector surface and a conductive emitter contact electrically connected to said emitter surface, said collector contact being a contact portion of said housing and said emitter contact being an insulated contact portion thereof, whereby said capsule is supported and spaced from said collector surface by said mounting means and said housing provides a vacuum envelope for said converter, a quasi-vacuum condition being provided in, and maintained by, said housing of a predetermined low pressure and said converter is characterized by operating at low emitter current densities established by said thermal power density of said radioisotope fuel and said predetermined work function of said emitter surface in the approximate range of 0.1 to 400 ma/cm2 in a nominally vacuum mode of operation established by the operating temperatures of said emitter and collector surfaces, said predetermined spacing and said predetermined low pressure, with negligible ion neutralization of space charge and negligible plasma contributing electron scattering effects together with practically large spacings and low work function materials for said emitter and collector surfaces, said emitter and collector surfaces having relatively low operating temperatures in the approximate ranges of 600* to 1400*K and 300* to 800*K, respectively, providing a converter module with useful efficiency and which operates thermionically as a space charge limited device having an electron motive diagram wherein a motive maximum is located intermediate to said emitter and collector surfaces whereby an output voltage higher than the difference of said predetermined work functions of said emitter and collector surfaces is obtained from said converter; and

an additive material loaded in said predetermined spacing between said emitter and collector surfaces, said additive material including a predetermined charge of additive vapor used essentially only as a surface adsorbate to modify said predetermined work functions of said emitter and collector surfaces without generating significant plasma contributing electron scattering effects therebetween at said operating temperatures of said emitter and collector surfaces, said predetermined spacing between said emitter and collector surfaces and said predetermined low pressure maintained within said housing, said pressure being in the approximate range from 10 3 to 0.1 torr and said converter operating thermionically as said space charge limited device.

7. The invention as defined in claim 6 further comprising an additive source communicating with said predetermined spacing between said emitter and collector surfaces, said source providing supplemental additive vapor which can be used to supplement said predetermined charge of additive vapor and functions essentially only as a surface adsorbate to modify said predetermined work functions of said emitter and collector surfaces with negligible ion neutralization of space charge and without generating plasma contributing electron scattering effects therebetween, and said converter module operating as said space charge limited device to provide an output voltage higher than the difference of said predetermined work functions of said emitter and collector surfaces thereof.

8. The invention as defined in claim 7 wherein said emitter surface extends substantially over the entire external surface of said emitter capsule and said collector surface extends substantially over the internal surface of said housing which fully encloses said emitter capsule, said emitter capsule having a significant lateral dimension relative to its axial dimension whereby said emitter surface also provides a significant amount of emission in a generally axial direction to correspondingly opposite portions of said collector surface, and said mounting includes electrically insulating elements installed in respective pairs of opposing recesses in said emitter and collector surfaces, said insulating elements comprising first and second spheres which axially and centrally support respective ends of said emitter capsule and maintain said emitter surface normally at said substantially predetermined spacing from said collector surface.

9. The invention as defined in claim 6 wherein said emitter surface extends substantially over the entire external surface of said emitter capsule and said collector surface extends substantially over the internal surface of said housing which fully encloses said emitter capsule, said emitter capsule having a significant lateral dimension relative to its axial dimension whereby said emitter surface also provides a significant amount of emission in a generally axial direction to correspondingly opposite portions of said collector surface, and said mounting means includes electrically insulating elements installed in respective pairs of opposing recesses in said emitter and collector surfaces, said insulating elements comprising first and second spheres which axially and centrally support respective ends of said emitter capsule and maintain said emitter surface normally at said substantially predetermined spacing from said collector surface.

10. A radioisotopic thermionic converter comprising:

an emitter capsule including a spontaneously and naturally decaying radioisotope fuel source of thermal power, at least one layer of material encapsulating and shielding said radioisotope fuel, and an external emitter surface on said layer of material energized by said radioisotope fuel;

an outer housing including an internal collector surface, said housing enclosing said emitter capsule and providing further shielding for said encapsulated radioisotope fuel;

means for mounting said emitter capsule in said housing and maintaining said emitter surface normally at a substantially predetermined spacing from said collector surface, said mounting means including means connecting respective ends of said emitter capsule to corresponding ends of said housing whereby said emitter capsule is supported substantially at its ends, said connecting means comprising coiled spring elastic means; and

output means adapted to connect respectively with said emitter and collector surfaces, for providing an electrical output from said converter, said housing including a conductive collector contact electrically connected to said collector surface, and said output means includinG said collector contact and a conductive emitter contact electrically connected to said emitter surface, whereby said capsule is supported and spaced from said collector surface by said mounting means, said housing provides a vacuum envelope for said converter, and said emitter contact provides an electrical connection to said emitter surface, a quasi-vacuum condition being provided in, and maintained by, said housing of such low pressure that said converter is characterized by operating at low emitter current densities in the nominal range of 0.1 to 400 ma/cm2 in a nominally vacuum mode of operation with negligible contributing electron scattering effects together with practically large spacings and low work function materials for said emitter and collector surfaces, said emitter and collector surfaces having relatively low operating temperatures in the nominal ranges of 600* to 1, 400*K and 300* to 800*K, respectively, providing a converter module with useful efficiency.

11. A radioisotopic thermionic converter comprising:

an emitter capsule including a radioisotope fuel mass source of thermal power, at least one layer of materal encapsulating and shielding said fuel mass, and an external emitter surface on said layer of material energized by said fuel mass;

an outer housing including an internal collector surface, said housing enclosing said emitter capsule and providing further shielding for said encapsulated fuel mass, said housing providing a vacuum envelope and maintaining a low pressure condition therein to effect a nominally vacuum mode of operation of said converter;

means for mounting said emitter capsule in said housing and maintaining said emitter surface normally at a substantially predetermined spacing from said collector surface, said mounting means including means connecting respective ends of said emitter capsule to corresponding ends of said housing whereby said emitter capsule is supported substantially at its ends and said connecting means includes thin-walled tubes; and

output means adapted to connect respectively with said emitter and collector surfaces, for providing an electrical output from said converter, whereby direct containment of fuel within said emitter capsule effects the most efficient thermal coupling of heat source and diode conversion portion of said converter and the maximum temperature of any portion of said fuel mass does not differ significantly from the temperature of said emitter surface.

12. A radioisotopic thermionic converter comprising:

an emitter capsule including a spontaneously and naturally decaying radioisotope fuel source of relatively low predetermined thermal power density not greater than the order of 10 watts/cm3, at least one layer of material fully encapsulating and shielding said radioisotope fuel, and an external emitter surface of predetermined work function on said layer of material energized by said radioisotope fuel;

an outer housing including an internal collector surface of predetermined work function, said housing being fabricated of a conductive material electrically connected to said collector surface and enclosing said emitter capsule and providing further shielding for said encapsulated radioisotope fuel, and said emitter surface extends at least over the major portion of the external surface of said emitter capsule and said collector surface extends at least over the corresponding major portion of the internal surface of said housing;

means for mounting said emitter capsule in said housing and maintaining said emitter surface normally at a substantially predetermined spacing from said collector surface, said mounting means including first and second electrically insulating spheres installed in respective pairs of opposing recesses located axially and centrally in said emitter capsule and collector housing surfaces to support said emitter capsule axially and centrally at its eNds;

output means adapted to connect respectively with said emitter and collector surfaces, for providing an electrical output from said converter, said output means including a collector contact portion of said housing, and an emitter contact portion thereof electrically connected to said emitter surface and located externally of the main part of said housing and insulated therefrom, whereby said capsule is supported and spaced from said collector surface by said mounting means and said housing provides a vacuum envelope for said converter, a quasi-vacuum condition being provided in, and maintained by, said housing of a predetermined low pressure and said converter is characeterized by operating at low emitter current densities established by said thermal power density of said radioisotope fuel and said predetermined work function of said emitter surface in the approximate range of 0.1 to 400 ma/cm2 in a nominally vacuum mode of operation established by the operating temperatures of said emitter and collector surfaces, said predetermined spacing and said predetermined low pressure, with negligible ion neutralization of space charge and negligible plasma contributing electron scattering effects together with practically large spacings and low work function materials for said emitter and collector surfaces, said emitter and collector surfaces having relatively low operating temperatures in the approximate ranges of 600* to 1400*K and 300* to 800*K, respectively, providing a converter module with useful efficiency which operates thermionically as a space charge limited device having an electron motive diagram wherein a motive maximum is located intermediate to said emitter and collector surfaces whereby an output voltage higher than the difference of said predetermined work functions of said emitter and collector surfaces is obtained from said converter;

an additive material loaded in said predetermined spacing between said emitter and collector surfaces, said additive material including a predetermined charge of additive vapor; and

an additive source communicating with said predetermined spacing between said emitter and collector surfaces, said source providing supplemental additive vapor which can be used to supplement said predetermined charge of additive vapor, said supplemental and predetermined charge of additive vapors functioning essentially only as a surface adsorbate to modify said predetermined work functions of said emitter and collector surfaces without generating significant plasma contributing electron scattering effects therebetween at said operating temperatures of said emitter and collector surfaces, said predetermined spacing between said emitter and collector surfaces and said predetermined low pressure maintained within said housing, said pressure being in the approximate range from 10 3 to 0.1 torr and said converter operating thermionically as said space charge limited device.

13. A plurality of radioisotopic thermionic converters;

series-forming means for positioning said converters in separate series stacks; and

parallel-forming means for connecting said stacks together in parallel whereby a power supply system of a desired total output power can be obtained, said series-forming means comprising a plurality of insulating tubular casings each mounting a plurality of converters in a series stack therein and passing a coolant therethrough, and said parallel-forming means comprising lower and upper hollow bus bars respectively engaging lower and upper ends of each of said converter series stacks and conveying said coolant to and from said casings, each of said converters comprising an emitter capsule including a spontaneously and naturally decaying radioisotope fuel source of thermal power, at least one layer of material encapsulating and shielding said radioisotope fuel, and an external emitter surface on said layer of material eneRgized by said radioisotope fuel, an outer housing including an internal collector surface, said housing being fabricated of a conductive material electrically connected to said collector surface and fully enclosing said emitter capsule and providing further shielding for said encapsulated radioisotope fuel, and said emitter surface extends at least over the major portion of the external surface of said emitter capsule and said collector surface extends at least over the major portion of the internal surface of said housing, means for mounting said emitter capsule in said housing and maintaining said emitter surface normally at a substantially predetermined spacing from said collector surface, said mounting means including small insulating spheres positioned between said emitter and collector surfaces, output means adapted to connect respectively with said emitter and collector surfaces, for providing an electrical output from said converter, said output means including a contact portion of said housing, and an emitter contact electrically connected to said emitter surface and located externally of said housing and insulated therefrom, whereby said capsule is supported and spaced from said collector surface by said mounting means and said housing provides a vacuum envelope for said converter, a quasi-vacuum condition being provided in, and maintained by, said housing of such low pressure that said converter is characterized by operating at low emitter current densities in the nominal range of 0.1 to 400 ma/cm2 in a nominally vacuum mode of operation with negligible contributing electron scattering effects together with practically large spacings and low work function materials for said emitter and collector surfaces, and an additive source communicating with the spacing between said emitter and collector surfaces, said source providing an additive vapor used as a surface adsorbate to modify surface properties of said emitter and collector surfaces without generating significant plasma contributing electron scattering effects therebetween at said low pressure maintained within said housing, said pressure being substantially less than 1 torr.

14. In a radioiostopic thermionic converter including an emitter capsule containing a spontaneously and naturally decaying radioisotope fuel and having an external emitter surface, an outer housing enclosing said emitter capsule and having an internal collector surface, said housing maintaining a low pressure condition therein to effect a nominally vacuum mode of operation of said converter, and output means adapted to connect respectively with said emitter and collector surfaces for providing an electrical output from said converter, mounting means comprising:

first elastic means connecting a first end of said emitter capsule to a corresponding first end of said housing; and

second elastic means connecting a second end of said emitter capsule to a corresponding second end of said housing whereby said emitter capsule is supported substantially at its ends in said housing and said emitter surface is maintained normally at a substantially predetermined distance from said collector surface.