High Gradient Multilayer Vacuum Insulator

• US 20100078198A1
• Filed: 08/07/2009
• Published: 04/01/2010
• Est. Priority Date: 08/13/2008
• Status: Abandoned Application

• Current Assignee: Lawrence Livermore National Security LLC (Government of the United States of America)
• Original Assignee: Lawrence Livermore National Security LLC (Government of the United States of America)
• Inventors: Sandes, David M., Harris, John Richardson, Hawkins, Steven A., Falabella, Steven
• Application Number:
  US12/537,897
• Publication Number:
  US 20100078198A1
• Time in Patent Office: Days
• US Class Current: 174/140.R
• CPC Class Codes: H05H 7/22 Details of linear accelerators, e.g. drift tubes H05H7/02 - H05H7/20 take precedence

Abstract

A high gradient multilayer vacuum insulator (HGI) with increased resistance to vacuum arcing to improve electrical strength. In an exemplary embodiment, the HGI includes a plurality of conductive and dielectric layers stacked in alternating arrangement so that the edges of the layers together form a vacuum-insulator interface and the stack has an overall length L_S. The dielectric layers each have a thickness I that is less than I_t

$I_t={\left(\frac{E_M}{E_{\mathrm{BD}}}\right)}^2L_S$

where I_t is the transitional dielectric layer thickness below which failure of the vacuum insulator is by vacuum arcing, E_BD is the breakdown field required to initiate vacuum arcing across one of said dielectric layers, and E_M is the breakdown field required to initiate surface flashover across a monolithic dielectric material of length L_S.

Claims

1. A high gradient multilayer vacuum insulator comprising:

a plurality of conductive and dielectric layers stacked in alternating arrangement so that the edges of said layers together form a vacuum-insulator interface and the stack has an overall length L_S, wherein said dielectric layers each have a thickness I that is less than I_t

$I_t={\left(\frac{E_M}{E_{\mathrm{BD}}}\right)}^2<br><br>L_S$

where I_t is the transitional dielectric layer thickness below which failure of the vacuum insulator is by vacuum arcing, E_BD is the breakdown field required to initiate vacuum arcing across one of said dielectric layers, and E_M is the breakdown field required to initiate surface flashover across a monolithic dielectric material of length L_S.

2. The high gradient multilayer vacuum insulator of claim 1,

wherein said conductive layers are of a type having a high E_BD breakdown field that enables thinner dielectric layers of thickness I that is resistant to vacuum arcing at the vacuum-insulator interface.

3. The high gradient multilayer vacuum insulator of claim 2,

wherein said conductive layers of the type having a high E_BD breakdown field and selected from a group consisting of tungsten, molybdenum, nickel, zirconium, aluminum, titanium, tantalum, cadmium, platinum, and alloys thereof.

4. The high gradient multilayer vacuum insulator of claim 1,

wherein said conductive layers are electropolished prior to assembly to reduce the number of field enhancement sites and thereby increase resistance to vacuum arcing at the vacuum-insulator interface.

5. The high gradient multilayer vacuum insulator of claim 1,

wherein said conductive layers are of a type having a high work function greater than about 4.0 eV to increase resistance to vacuum arcing at the vacuum-insulator interface.

6. The high gradient multilayer vacuum insulator of claim 5,

wherein said conductive layers of the type having a high work function greater than about 4.0 eV are selected from a group consisting of tungsten, selenium, platinum, nickel, iridium, germanium, cobalt, and alloys thereof.

7. The high gradient multilayer vacuum insulator of claim 1,

wherein said conductive layers are coated with a second material prior to assembly, said second material chosen from a group consisting of conductor, dielectric, and semiconductor of a type having a high E_BD breakdown field that enables thinner dielectric layers of thickness I that is resistant to vacuum arcing at the vacuum-insulator interface.

8. The high gradient multilayer vacuum insulator of claim 1,

wherein outer edge surfaces of said conductive layers are recessed from outer edge surfaces of said dielectric layers.

9. A high gradient multilayer vacuum insulator comprising:

a plurality of conductive-material-coated dielectric layers stacked in alternating conductive-dielectric arrangement so that the edges of said layers together form a vacuum-insulator interface and the stack has an overall length L_S, wherein the dielectric sections of said conductive-material-coated dielectric layers each have a thickness I that is less than I_t

$I_t={\left(\frac{E_M}{E_{\mathrm{BD}}}\right)}^2<br><br>L_S$

where I_t is the transitional dielectric layer thickness below which failure of the vacuum insulator is by vacuum arcing, E_BD is the breakdown field required to initiate vacuum arcing across one of said dielectric layers, and E_M, is the breakdown field required to initiate surface flashover across a monolithic dielectric material of length L_S.

10. The high gradient multilayer vacuum insulator of claim 9,

wherein said conductive-material coating is selected from a group consisting of tungsten, selenium, platinum, nickel, iridium, germanium, cobalt, molybdenum, zirconium, aluminum, titanium, tantalum, cadmium, and alloys thereof.

11. A high gradient multilayer vacuum insulator comprising:

a plurality of semi-conductor and dielectric layers characterized by a lower relative permittivity and a higher relative permittivity, respectively, and stacked in alternating arrangement so that the edges of said layers together form a vacuum-insulator interface and the stack has an overall length L_S, wherein the dielectric layers each have a thickness I that is less than I_t

$I_t={\left(\frac{E_M}{E_{\mathrm{BD}}}\right)}^2<br><br>L_S$

where I_t is the transitional dielectric layer thickness below which failure of the vacuum insulator is by vacuum arcing, E_BD is the breakdown field required to initiate vacuum arcing across one of said dielectric layers, and E_M is the breakdown field required to initiate surface flashover across a monolithic dielectric material of length L_S.

12. A high gradient multilayer vacuum insulator comprising:

a plurality of dielectric layers characterized by one of a lower relative permittivity and a higher relative permittivity and stacked in alternating arrangement so that the edges of said layers together form a vacuum-insulator interface.

13. A high gradient multi layer vacuum insulator comprising:

a dielectric cylinder having a curvilinear side surface which is a vacuum-insulator interface with grooves formed thereon in a direction substantially parallel to the cylinder ends to produce alternating grooves and lands with the lands having a higher relative permittivity than the space within the grooves.

14. The high gradient multilayer vacuum insulator of claim 13,

wherein the grooves and the lands have a 1:

1 packing factor.

15. The high gradient multilayer vacuum insulator of claim 13,

wherein the grooves are formed continuously on the curvilinear side surface.

16. A high gradient multilayer vacuum insulator comprising:

a plurality of dielectric layers in stacked arrangement so that the edges of said layers together form a vacuum-insulator interface and outer edge surfaces of a first set of alternating layers are recessed from outer edge surfaces of a second set of alternating layers.