In the production of high temperature by electron bombardment the cathode is held at ground potential while the hot anode is raised to a high negative potential. An annealing chamber using the inverted grounding is constructed around a commerically available stainless steel cross

Jirberg, R. J.

English

NASA Technical Reports Server

December 1968	 Brief 68-10411 
NASA TECH BRIEF	 1 
NASA Tech Briefs are issued to summarize specific innovations derived from the U.S. space program, 
to encourage their commercial application. Copies are available to the public at 15 cents each 
from the Clearinghouse for Federal Scientific and Technical Information Springfield, Virginia 22151. 
Inverted Grounding Technique for Electron Beam Heating 
High Voltage	 Plastic Tubing Electrode	 +
Tap Water 
fl4
J11WaterCooled / 
k (:	 Electrode	 Drain 
Sample 
(Anode) 
Port
To Vacuum Pump 
- 
Cathode
Low Voltage Supply

Electrode 
Conventionally, in the production of high tempera-
tures by electron bombardment the anode is held at 
ground potential while the hot cathode is raised to a 
high negative potential. This practice is employed pri-
marily to eliminate cold cathode discharge around 
grounded surfaces inside the vacuum chamber. It also 
provides a convenient means of heat-sinking the anode 
supporting structure through conduction directly to 
the normally massive chamber walls. 
There is a distinct advantageto be realized, how-
ever, if the cathode can instead be grounded. In an
all-metal chamber, the electron beam from a grounded 
cathode is effectively focused electrostatically by 
the chamber walls. In the conventional arrangement, 
an additional element is required to contain the beam. 
This element ordinarily encloses both the cathode and 
anode, and is electrically connected to the highly neg-
ative cathode. The elimination of this shielding allows 
a substantial reduction in the size of the vacuum 
chamber, since the allowance of sufficient space be-
tween the chamber walls and internal members at 
cathode potential to prevent electrical breakdown is 
(continued overleaf) 
This document was prepared under the sponsorship of the National 
Aeronautics and Space Administration. Neither the United States 
Government nor any person acting on behalf of the United States
Government assumes any liability resulting from the use of the 
information contained in this document, or warrants that such use 
will be free from privately owned rights.
https://ntrs.nasa.gov/search.jsp?R=19680000411 2020-03-12T05:55:54+00:00Z
no longer a factor. In addition, its elimination re-
moves a potential source of contamination in the vac-
uum system. This is particularly important in the an-
nealing of high purity refractory metals 8near their 
melting points in vacua in excess of 10 torr. The 
high vacua required in these applications to attain ac-
ceptable impurity levels within the chamber makes 
possible the operation of a grounded cathode system 
without an attendant cold cathode discharge. 
Shown in the accompanying figure is an annealing 
chamber using the inverted grounding. It is con-
structed around a commercially available stainless steel 
"cross." Single insulated-electrode high-temperature 
flanges provide the necessary electrical feed-throughs: 
one to the sample holder anode, the other to one side 
of the wire cathode. The 'cathode return is made by 
connection directly to the grounded flange. Heat con-
ducted along the sample holder is satisfactorily re-
moved at the flange by a water cooled electrode at-
tachment. The length of the plastic lines carrying the 
cooling water is dictated by the conductivity of the 
locally available water and by the cross-sectional area
of the tubing so as to keep the leakage currents 
through the water within tolerable limits. 
Such a system is successfully being employed in the 
annealing of high purity single crystals of niobium and 
similar metals. 
Notes: 
I. No additional documentation is available for this 
invention. 
2. Technical questions concerning this invention may 
be directed to: 
Technology Utilization Officer 
Lewis Research Center 
21000 Brookpark Road 
Cleveland, Ohio 44135 
Reference: B68-10411 
Patent status: 
Inquiries about obtaining rights for the commercial 
use of this invention may be made to NASA, Code 
GP, Washington, D.C. 20546. 
Source: Russell J. Jirberg 
(LEW- 10543) 
Brief 68-10411	 Category 01


Inverted grounding technique for electron beam heating

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