High voltage insulator for electron bombardment ion thruster has electric field directed through dielectric material and electrons emitted by field emission are constrained in negative junction region. Surface flashover and unstable operation are eliminated, and maximum voltage is limited only by dielectric strength of material, aluminum oxide in this case

Byers, D. C.

Margosian, P. M.

Mealy, G. E.

English

NASA Technical Reports Server

December 1972	 B72-10181 
•	
NASA TECH BRIEF 
Lewis Research Center 
NASA Tech Briefs announcenew 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. 
Improved High Voltage Insulator for Use in Vacuum 
.
Accelerator 
Support 
Negative	 Cylindrical 
Junction	 Depression	 Pin	 Insulator 
Recessed	 Screen 
Portion	 GridMounting  
Plate	 Support 
An improved high voltage insulator for use in a vacu-
um has been devised for an electron bombardment ion 
thruster. With conventional spherical insulators in vacu-
um, electrical breakdown across the insulator usually 
commences with electrons drawn from the negative 
electrode striking the positive electrode and releasing 
moie electrons. With an electrostatic thruster, where 
strong electron fields are prevalent, the electric field at 
a point on the negative electrode wire extracts electrons 
by field emission. With this improved insulator, the 
electric field is directed through the dielectric material 
and electrons emitted by field emission are constrained 
in the region of the negative junction. Also, there is 
probably some reduction in the electric field strength 
at this junction. In this manner, surface flashover and 
unstable operation at high voltages have been eliminated, 
and the maximum voltage the improved insulators can 
support is limited only by the dielectric strength of the 
insulator material.
The improved insulators are mounted between the 
screen grid support and the mounting plate as shown in 
the figure. Each insulator is made of a dielectric material, 
such as aluminum oxide, and has a flat face which engages 
either the screen grid support or the mounting plate. At 
the opposite end of the insulator is a recess which 
receives a pin. The pin should extend into the recess of 
the insulator at a distance greater than the width of the 
recess opening. 
As shown, the recess is provided with a cylindrical 
depression at the bottom. This depression serves to de-
crease the local electric field strength at the junction 
between the pin and the insulator. The ratio of the pene-
tration of the pin in the depression to the gap between 
the pin and the surface of the depression should be 
about 4 to I. 
The accelerator support which is attached to the pin 
is highly negative, relative to the screen grid support and 
mounting plate. Consequently, the pin is a negative 
electrode. The recess of each insulator serves to shield 
this negative electrode to prevent electrical breakdown 
at high voltages. 
Conventional spherical insulators 5 cm in diameter 
(such as utilized in low voltage thrusters) were found to 
break down at 22 kV. The improved insulator design 
eliminated insulator flashover breakdown up to voltages 
of 250 kV, at which point the insulator failed due to 
puncture through the dielectric. 
Reference: 
Byers, D.C.: An Experimental Investigation of a High-
Voltage Electron-Bombardment Ion Thruster, J. Electro-
chemical Society, Vol. 116, No. 1, January 1969. 
Notes: 
1. This insulator design may be of interest for other 
applications requiring high voltage insulation in a 
vacuum.
(continued overleaf) 
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 Slates 	 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=19720000181 2020-03-17T03:32:49+00:00Z
Technical questions may be directed to: Patent status: 
Technology Utilization Officer This invention has been patented by NASA (U. S. 
Lewis Research Center Patent No. 3,324,659). Inquiries concerning non-exclu-
21000 Brookpark Road sive or exclusive license for its commercial development 
Cleveland, Ohio 44135 should be addressed to: 
Reference: B72-10181 Patent Counsel 
Lewis Research Center 
Mail Stop 500-311 
21000 Brookpark Road 
Cleveland, Ohio 44135
Source: D. C. Byers, P. M. Margosian, and

G. E. Mealy

Lewis Research Center

(LEW-1 1401)
. 
B72-10181	 Category 01 


Improved high voltage insulator for use in vacuum

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server