One cathode includes array of square-shaped conductor columns. Columns are electrically interconnected by conducting plate on bottom. Each column provides field-emission current. Another cathode includes array of rodlike conductors. Layer is covered by control film made of conducting material. Film is isolated from each conductor

Lees, W. L.

English

NASA Technical Reports Server

Projectior 
(a)
Pnsltjve 
Itage 
ctric Field 
voltage 
Conductor 
Columns 
(b) 
January 1975	 B74-10253 
•	
.
 
NASA TECH BRIEF 
NASA Pasadena Office 
NASA Tech Briefs announce new technology derived from the U.S. space program. They are issued to encourage 
commercial application. Tech Briefs are available on a subscription basis from the National Technical Information 
Service, Springfield, Virginia 22151. Requests for individual copies or questions relating to the Tech Brief program may 
be directed to the Technology Utilization Office, NASA, Code KT, Washington, D.C. 20546. 
Self-Protected Electrodes Limit Field-Emission Current 
.
The problem: 
Electric breakdown, or arcing, in vacuum tubes 
and similar devices can occur at minute projections on 
the electrode surfaces. When an electric field is 
applied, these projections carry larger charge 
lnsul
Projection 
Cond 
Figure 1. Cathode Design Using Square-Shaped 
Conductor Columns: (a) Electrode Configuration; 
(b) Field Distribution During Arcing 
(Note: Field-Emission Current Is Directed 
Opposite to the Electric-Field Lines)
concentrations than the remaining areas. In opera-
tion, whenever field-emission current is increased 
between two electrodes, arcing occurs at the 
projections. The process is progressively destructive. 
Arcing causes more projection on the metal surface. 
The projections in turn attract further breakdown 
until much of the electrode surface is destroyed. 
The solution: 
New self-protected cathodes have been developed 
which limit field-emission current to a safe value. 
How it's done: 
One cathode includes an array of square-shaped 
conductor columns, as shown in Figure 1. The 
columns are electrically interconnected by a con-
ducting plate on the bottom. Above this plate the 
columns are insulated from each other. Each column 
provides field-emission current. 
If any one conductor patch contains a projection, 
charge distribution becomes uneven. The projection 
will accumulate a high negative charge, leaving the 
remaining patch area more positive with the 
surrounding patches. This potential difference re-
duces the applied field at the affected patch. As a 
result, the field-emission current is limited during 
arcing. Arcing lasts only until the projection is 
removed, after which normal operation is restored. 
Another cathode includes an array of rodlike 
conductors, as shown in Figure 2. These ,
 are also 
electrically interconnected on the bottom by a 
conducting plate and provide the sources of field-
emission current. A layer of insulation above the plate 
separates the conductors. The layer is covered by a 
control film made of conducting material. The film is 
isolated from each conductor.
(continued overleaf) 
onauctor 
columns 
Patches) 
This document was prepared under the sponsorship of the National
	
Government assumes any liability resulting from the use of the 
Aeronautics and Space Administration. Neither the United States
	
information contained in this document, or warrants that such use 
Government nor any person acting on behalf of the United States
	
will be free from privately owned rights.
https://ntrs.nasa.gov/search.jsp?R=19740000253 2020-03-17T13:58:51+00:00Z
Insulation 
Con 
Electric Field
(a) 
(Positive 
Voltage)
Control 
Film 
Electric Field
(Positive 
Voltage) 
Conductor Conductor 
,I
Conductors 
Before Arcing	 During Arcing
(b) 
Figure 2. Cathode Design Using Rodlike Conductors: 
(a) Cathode Section: (b) Field Distributions Before and During Arcing 
(Note: Field-Emission Current Is Directed Opposite to the Electric-Field Lines) 
Note:	 Patent status: 
Requests for further information may be directed 	 This invention has been patented by NASA (U.S. 
to:	 Patent No. 3,671,798). Inquiries concerning nonex-
Technology Utilization Officer	 elusive or exclusive license for its commercial develop-
NASA Pasadena Office
	
ment should be addressed to:. 
4800 Oak Grove Drive	 Patent Counsel 
Pasadena, California 91103	 NASA Pasadena Office 
Reference: TSP74-10253	 4800 Oak Grove Drive 
Pasadena, California 91103 
Source: Wayne L. Lees

Electronics Research Center
(ERC-10015) 
Categories: 01 (Electronics - Components and 
Circuitry) 
02 (Electronics Systems) 
B74-10253	 03 (Physical Sciences) 


Self-protected electrodes limit field-emission current

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