Small plasma probe using tungsten wire collector in tubular shiel

Beck, A. F.

English

NASA Technical Reports Server

REPLY TO 
ATTNOF GP 
NATIONAL AERONAUTICS A N D  S P A C E  ADMINISTRATION 
WASHINGTON, D.C. 20546 
March 27, 1971 
TO : USI/Scientific & Technical Information Division 
Attention: Miss Winnie M. Morgan 
FROM r GP/Office of Assistant General 
Counsel for Patent Matters 
SUBJECT: Announcement of NASA-Owned 
U . S .  Patents in STAR 
In accordance with the procedures contained in the Code GP 
to Code US1 memorandum on this subject, dated June 8 ,  1970, 
the attached NASA-owned U . S .  patent is being forwarded for 
abstracting and announcement in NASA STAR. 
The following information is provided: 
U . S .  Patent No. : 3,356,885 
Corporate Source : Lewis Research Center 
Supplementary 
Corporate Source 
NASA Patent Case No.: =E-02578 
Gayle Parker 
Enclosure : 
Copy of Patent 
NASA-HQ 
https://ntrs.nasa.gov/search.jsp?R=19710011272 2020-03-17T02:53:32+00:00Z
Dec. 5, 1967 
ALBERT F. BECK 
BY 
3,356,885 United States Patent Office patented 5, 1967 
1 
3 , 3 5 6 , 8 8 5 
SMALL PLASMA PROBE 
Albert F. Beck, Independed6eY Ohio, as&gnor to the 
United States of America as represented by the Ad. 
ministrator of the National Aeronautics and Space 
Administration 
Filed Jury 1, 1965,’Ser. No. 469,012 
5 Cldms. (Cl. 313-271) 
ABSTRACT OF THE DISCLOSURE 
A very small plasma probe in the form of a tungsten 
wire collector supported in a tubular shield by a hypo- 
dermic tubing liner. Both ends of the liner are symmetrical- 
ly pinched onto the wire to center the collector in the 
shield. 
The invention described herein may be manufactured 
and used by or for the Government of the Uhited States 
of America for governmental purposes without the pay- 
ment of any royalties thereon or therefor. 
This invention is concerned with sensors for studying 
various properties of ionized gases and, more particularly, 
is directed to small plasma probes. The invention further 
relates to plasma probes having improved structures 
which maintain the probe components in their proper 
positions relative to each other. 
Various devices have been used in the past to measure 
the properties of ionized gases. The operation of such 
devices relies on the fact that any object of device in 
contact with a plasma or neutral ionized gas accumu- 
lates a negative charge. This potential difference between 
the plasma and the contacting object develops because 
electrons in the plasma have much greater velocities than 
ions therein. 
A probe can be placed in a plasma and connected 
through a variable potential, with appropriate instru- 
mentation, to another electrical entry into the plasma, 
such as one of the electrodes used to generate the plasma 
or another probe. The probe potential can be varied from 
negative to positive relative to  the plasma, and charac- 
teristic positive to negative currents, respectively, can 
be measured. When the shapes and areas of these probes 
are known, values for plasma properties can be obtained 
from the voltage-current functions. Because the general 
principles of plasma probes have been publicized in the 
literature, a knowledge of such .general principles will 
be assumed in what follows. Reference is made to the 
General Electric Review No. 27. 
Because of the size, conventional probes cause local 
perturbations of the plasma being measured which effect 
the accuracy of the data obtained. Also, certain shield- 
ing is required to prevent the deposition of a conductive 
coating on certain portions of the probe. Such coatings 
add to the collecting area and make it difficult to deter- 
mine the actual area of the collecting surface. This shield- 
ing gives rise to several problems because it not only 
increases the physical size of the probe, but also fails to 
function properly if the various components of the probe 
are not properly positioned. As the size of the probe is 
decreased the problem of fabrication increases because 
of the close tolerances involved and the difficulty of ob- 
taining reliable electrical connections. 
These problems have been solved by probes constructed 
in accordance with the present invention which are very 
small in size to reduce local perturbations in the plasma. 
Also, these probes have portions of their collectors 
shielded by a tubular member. Each collector is sup- 
ported inside its tubular shield in such a manner as to 
reduce the possibility of the collector contacting the 
shield. 
2 
It is, therefore, an object of the present invention ‘to 
provide a device for measuring the propdies of a plasma 
which is small in siz the effect of its presence 
on the plasma being 
the collecting surface. 
A further object of the invention is to’provide a small 
aP- 
parent from the specification which follows the 
drawings wherein like numerals are used throwghobt ‘to 
identifir like Darts. 
lo plasma probe which is easily fabricated. 
These and other objects of the invention 
In <he drawings. 
FIG. 1 is a partial sectional view of a plasma probe 
constructed in accordance with the invention, and 
FIG. 2 is an enlarged sectional view taken along the 
line 2-2 in FIG. 1. 
Referring now to the drawings, there is shown in FIG. 
1 a very small plasma probe constructed in accordance 
with the invention. This probe includes a collector 10 
in the form of a wire that is connected to a suitable vari- 
25 able potential source 12 through a lead 14. The collector 
10 is carried by a support 16 of an insulating material 
which is used to position the collector in the ionized gas 
to be studied. A ceramic rod having a diameter of VS 
inch has provided a satisfactory support for a one-mil 
A hollow shield 18 of an insulating material is utilized 
to prevent the conductive coating which is deposited on 
the collector 10 during normal use of the probe from 
extending onto the support 16 which would increase the 
35 collecting area of the probe. The width of the hollow 
shield 18 is kept as small as possible to reduce perturba- 
tions in the plasma being studied. Clearance between 
the collector 10 and the bore of the hollow shield 18 is 
required to prevent the conductive coating from bridging 
4o the space at the end of the shield which is shown in FIG. 
2. A quartz tube having an inside diameter of 0.015 inch 
and a wall thickness of 0.0015 inch has been satisfactorily 
used to shield the aforementioned one-mil tungsten wire 
collector. The collector wire 10 must be rigidly supported 
45 and properly centered within the bore of the shielding 
tube 18 to prevent the collector wire from being dis- 
placed laterally toward the surface of the bore. 
According to the present invention, the collector wire 
10 is mounted in the shielding tube 18 by a deformable 
5o metal liner 20. Both ends of the liner 20 are symmetrically 
pinched or swaged at 22 and 24 onto the collector wire 
10 as shown in FIG. 2. Electrically conducting tubing 
of the hypodermic type having an outside diameter of 
0.010 inch has been satisfactory when used with the above- 
55 mentioned tubular quartz shield and tungsten wire col- 
lector. 
The probe is assembled in accordance with the inven- 
tion by first passing the collector wire 10 through the 
metal liner 20 while permitting one end of the wire to 
60 extend a proper distance from the end 22 of liner. The 
ends of the tubular liner 20 are pinched at 22 and 24 
onto the wire 10 to center it along the axis of liner which 
is inserted into the quartz shielding tube 18 so that the 
protruding end of the wire 10 extends a proper distance 
65 from the end of the shield as shown in FIG. 2. The lead 
14 is then soldered to the pinched end 24 which eliminates 
any fragile electrical connection directly between the wire 
10 and the lead 14. The liner 20 is then inserted into the 
7o shielding tube 18, and the pinched end 22 of the liner 
should be positioned well inside the shielding tube to 
prevent any brkiging bv the collective film. 
2o 
3o tungsten wire collector. 
3,356,885 
3 
By way of example, 1% inch length of hypodermic 
tubing 20 was pinched to a length of one-mil tungsten wire 
10 so that one end of the wire extended approximately 
% inch from a pinched end 22 of the tubing. After con- 
necting the lead 14 to the pinched end 24, the wire 10 
and hypodermic tubing 20 were inserted in a quartz shield- 
ing tube 18 until the opposite pinched end 22 was approxi- 
mately 0.1 inch from the outermost end of the shielding 
tube, and the outermost end of the collector wire pro- 
truded approximately 0.15 inch beyond the end of the 
shielding tube. 
After the tubing 20 which carries the wire 10 has been 
secured to  the bore of the shielding tube 18, the assembly 
is mounted on the end of the support rod 16 as shown 
in FIG. 1. This is accomplished by inserting the quartz 
tubing 18 with the hypodermic tubing 26 contained there- 
in approximately % inch into a suitable hole of the sup- 
port rod 16. 
While only one embodiment of the invention has been 
shown and described, it will be appreciated that various 
structural modifications may be made to the disclosed 
plasma probe without departing from the spirit of the in- 
vention or the scope of the subjoined claims. 
What is claimed is: 
1. A probe for measuring the properties of ionized 
gases comprising, 
an elongated collector adapted to be electrically con- 
nected to a variable potential source, 
a support mounting said collector for insertion into 
the ionized gases, 
a hollow shield extending outward from said support 
for preventing the deposition of a conductive coating 
on said support adjacent said collector, 
a liner in engagement with the inner surface of said 
5 
10 
15 
20 
25 
30 
4 
shield for mounting said collector therein, one end 
of said collector extending outward from said liner 
away from said support through said shield so that 
a portion of said one end of said collector extends 
outward from said shield into said ionized gases, said 
one end of said collector being spaced from said 
inner ,surface of said shield. 
2. A probe as claimed in claim 1 wherein the collector 
comprises a length of one-mil tungsten wire. 
3. A probe as claimed in claim 1 wherein the shield 
comprises a length of quartz tubing. 
4. A probe as claimed in claim 1 wherein the liner 
comprises a length of deformable tubing having at least 
one end thmmf pinched on the collector and adapted to be 
electrically connected to the variable potential source. 
5. In a probe for measuring the properties of ionized 
gases of the type having a collector wire connected to a 
variable potential source and a support for mounting the 
collector wire for insertion of an end thereof into the 
ionized gases, the improvement comprising 
a tubular shield surrounding a portion of the end of 
the collector wire in the ionized gases, and 
a length of deformable tubing rigidly mounted in said 
'shield, a portion of said deformable tubing being 
pinched onto said collector wire for maintaining the 
same concentric with the bore of said tubular shield. 
References Cited 
UNITED STATES PATENTS 
2,653,199 9/1953 Brown et al. _ _ _ _ _ _  313-152 X 
JAMES D. KALLAM, Primary Examiner. 
A. J. JAMES, Assistant Examiner. 


Small plasma probe Patent

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