Electron beam deflection devices for measuring electric field

Shelton, R. D.

English

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REPLY TO 
ATTpdOF GP 
QNAUTICS AND SPACE AD 
WASHINGTON, D.C. 205.46 
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Pn accordance h the  procedures eo ned in t h e  Code e p  
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the  a t t ached  -owned U , S ,  p a t e n t  
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ng information is provided: 
U , S .  Patent  No. 
Corporate Sou 
Supplementa 
Corporate Source 
NASA Pa ten t  C a s e  
Gayfe Parker 
Enclosure : 
Copy. of Pa ten t  - -  
(ACC€SSlOod NUMBER) 
7 
(NASA CR OR YMX OR AD NUMBER) 
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ELECTRON BEAM INSTRUMENT FOR MEASURING ELECTRTC FIELI)? 
Filed Oct. 10, 1967 2 Sheets-Sheet ? 
FIG. 3 
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S f G M f f d l  3 5  
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SEGMENT 37 
SEGMENT 39 
SEGMENT 3 3  
SEGMENT 35 
SEGMENT 37 
5 EG MENT 39 
FlG.4 
INVENTOR (S) 
RUSSELL D SHELTON 
B Y  & f Z /  
c+d--.. 5 
ATTORNEYS 
atente 
3,470,466 
2 Claims 
A CT OF 
An apparatus for determining electric field strength in- 
cluding an electron discharge device for directing an elec- 
tron beam in a circular sweep so as to normally impinge 
for an equal time period each segment of a target having 
four segments arranged in diametrically opposite pairs, 
said beam being deflectable by an electric field to vary 
the time each segment is impinged. Control deflection 
plates are provided to act upon the electron 'beam in 
opposition to the applied electric field and the deflection 
plates are energized in accordance with variations in the 
time diametrically opposite segments are impinged so as 
to establish a state of equilibrium between the deflection 
caused by the applied electric field and the deflection 
caused by the control deflection plates. The energy re- 
quired to effect this state of equilibrium is proportional 
to the applied electric field. 
IBackground of the invention 
The invention described herein was made by an em- 
ployee of the United Statest Government and may be 
manufactured and used by or for the Government for 
governmental purposes without the payment of any royal- 
ties thereon or therefor. 
This invention relates to electron discharge devices and 
more particularly to electron beam deflection devices for 
measuring electric fields. 
The recent advent of space flight has placed a greater 
demand on instruments originally designed to operate 
within the earth's atmosphere because of the hostile en- 
vironment of interplanetary space. For example, in the 
area of measurement of electric fields of the order of one 
volt per meter, the use of conventional field meters of 
the induction type have proved to be difficult in inter- 
planetary space because of the interaction of energetic 
photons, energetic charged particles, or plasma with the 
metallic surfaces of the field meters. Also, problems with 
bearings and lubricants in the vacuum of space diminish 
the reliability of conventional field meters. 
According to the present invention these disadvantages 
may be overcome by employing an electron beam device 
in which use is made of the direct relationship between 
the strength of an electric field and the deflection of an 
electron beam. Instruments in which use is made of this 
relationship are known in the art, but previous applica- 
tions are believed to be too complex and to require exces- 
sively difficult manufacturing techniques. 
It is therefore an object of this invention to provide an 
electrical field meter suitable for use in interplanetary 
space. 
Another object of this invention is to provide an im- 
proved electron beam deflection device for providing out- 
put signals indicative of the deflection of the electron 
beam. 
Still another object of this invention is to provide a 
simpler and more dependable electron beam deflection 
device. 
Summary of the invention 
According to the invention an electric field meter utiliz- 
ing an electron beam device is constructed around the 
use of a segmented electron receiving means. The use of 
5 a segmented electron receiving means is made possible 
by the novel technique of directing the electron beam in 
a circular sweep so that the time impinged and the num- 
ber of electrons intercepted by a given segment is de- 
pendent on the deflection of the electron beam caused by 
lo the electric field. This technique coupled with the unique 
use of control deflecting means energized in accordance 
with the time each segment is impinged allows the elec- 
tron beam to be placed in a state of equilibrium with the 
15 energy required to effect this state being proportional to 
the electric field. 
Description of the drawings 
These and other objects of this invention will be appar- 
ent from the following description taken in accordance 
FIGURE 1 is a diagrammatic view showing the essen- 
tial component parts of the electron beam deflection de- 
vice and the relationship of such parts to one another. 
FIGURE 2 illustrates the collector electrode and a 
FIGURES 3 and 4 are graphs illustrating various wave- 
forms appearing on the target electrode of the electron 
beam of deflection device. 
Referring now to FIGURE 1, the electron beam de- 
2o with the accompanying drawings in which: 
25 normal and deflected path of the electron beam. 
30 flecting device includes a filament 1 
able source of current, for heating 
emission of electrons therefrom. 
accelerated and focused into a beam 16 by a concentrat- 
ing and accelerating electrode 15 which is maintained at 
35 ground potential and the cathode I3 is held at a negative 
potential with respect to ground by means of battery 17. 
The electron beam 1 emitted by the cathode I3 is 
deflected in a circular sweep by a primary deflecting cir- 
4o cuit 19 consisting of vertical control deflection plates 
and 22, horizontal control deflecting plates 23 and 
sinusoidal generator 25 and phase shifting network 27. 
In operation, the sinusoidal generator 25 energizes the 
phase shifting network 27 for obtaining two equal AC 
45 output signals that are 90" out of phase. In the well 
known manner one output of the phase shifting network 
is applied to charge the horizontal deflecting plates 23 
while the other output is applied to charge the vertical 
deflecting plates 26. SO that a circular sweep of the elec- 
tron beam is obtained. 
The electron beam 16 is directed to pass through con- 
trol deflecting plates 29 g of horizontal control 
deflecting plates 59 and vertical control deflect- 
ing plates 67 and 68 so a inge on target electrode 
55 31. As shown in FIGURES 1 and 2, the target electrode 
31 includes a plurality of segments 33, 35, 37 and 39 of 
equal size and triangular in shape with segments 33 and 
37 and segments 35 and 39 forming horizontal and verti- 
cal symmetrical pairs respectively. Each of the segments 
60 is made of a conductive material having a relatively 
resistance and are separated by an insulting material 
The segments 33, 35, 37 and 39 are mounted in coplanar 
relation on a back plate 38 and positioned so that the im- 
pingement of the beam in its normal sweep impinges each 
65 segment an equal time, as indicated by circle 43 in FIG- 
URE 2. 
The electron beam impinging on the segments 33,35,37 
and 39 is converted into suitable voltage levels by low pass 
filters or averaging circuit ,49 and 5B which couple 
70 the respective segments to ground. The output terminals 
53 and 55 of low pass fil and 49 are connected in 
opposition to an output device 57, such as a meter, and 
3,470,466 
in opposition to the horizontal deflecting plates 59 and 
60 of the con@ol deflecting plates 29 by leads 56 and 58 
respectively. Likewise the output terminals 61 and 63 of 
low Dass filters 47 and 51 are connected in omosition to 
ing plates may be provided for deflecting the electron beam 
in accordance with an input signal. 
It will be obvious to those skilled in the art that many 
other variations and modifications mav be made without 
A *  
an iutput device 65, such as a meter, and in opposition 
to the vertical deflecting plates 67 and 68 of the control 
deflecting plates 29 by leads 62 and 64. It will be under- 
stood that the electron beam 16 will be deflected by the 
control defletcing plates 29 in accordance with the dif- 
ference in voltage applied to the horizontal deflecting 
10 and the vertical deflecting plates 67 
ration, when the electron beam sweep is aligned 
as indicated at  43 in FIGURE 2 and no electric field is 
present, the waveform of the signals from target segments 
33, 35, 37 and 39 applied to low pass filters 45, 47, 49 
and 51 will be square waves of equal amplitude and width 
as shown in FIGURE 3.  As the beam sweeps the segments 
33, 35, 37‘and 39 the current provided by the incident 
beam of electrons charges in s spective ca- 
pacitors of the low pass filters 4 1 in accord- 
ance with their respective time will readily 
be seen the voltage apeparing on the output terminals 53, 
55,61 and 63 is directly related to the time period that the 
electron beam impinges any one segment of the target 31. 
Thus, under normal conditions the average potential ap- 
pearing on the output terminals 53, 55, 61 and 63 will be 
equal since each segment of the target 31 is impinged an 
equal time so that the voltages applied to the control de- 
flection plates 29 and load device 5’7 and 65 will neutralize 
each other. 
HQWeVer, when an electric field is present, the beam will 
be deflected from its normal sweep in accordance with the 
strength and direction of the electric field as indicated by 
way of example at 71 in FIGURE 2. The signal waveform 
obtained from each segment of the target will thereby 
change as shown in FIGURE 4. Under these conditions, 
the signal waveforms applied to the low pass filters 45 
9 from segments 33 and 37 respectively will still be of 
equal amplitude but will be of unequal width. In the 
example shown the signal applied to low pass filter 45 
would be of shorter duration than the signal applied to low 
pass filter 49. Accordingly, the average potential level of 
output terminal 55 will be higher than the average po- 
tential level of output terminal 53 so that a potential dif- 
ference will be applied across horizontal control deflecting 
plates 59 and 60 and load device 57. In the same manner 
low pass filter 47 will be energized a longer time period 
than low pass filter 51. Accordingly, the average potential 
level of output terminal 61 will be higher than the average 
potential level of output terminal 63 so that a potential 
difference will be applied across vertical control deflecting 
plates 67 and 68 and load device 45. 
The potential differences applied to the vertical and hori- 
zontal control deflecting plates act in opposition to the de- 
flection caused by the electric field and the electron beam 
will assume a position of equilibrium where the effects of 
the two deflecting forces are balanced. Under this condi- 
tion, the voltage supplied to load devices 57 and 65 have a 
definite relation to the value of the applied electric field. 
The proportion or ratio between the electric field and the 
signal supplied to load devices 57 and 65 may be adjusted 
or controlled by adjustment of the time constant of the low 
pass filters 45, 47, 49 and 51. 
In the arrangement described herein an increasing deflec- 
tion of the beam from a normal sweep pattern results in 
the establishment of increasing energy in the output circuit. 
In this arragement the deflection is accomplished by plac- 
ing the device at the location in outer space where it is 
desired to measure the electric field. It will be understood 
however that for operation on earth the device may be pro- 
vided with an evacuated chamber and additional deflect- 
departing from the spirit and scope of t i e  invention. There- 
fore, this invention is to be considered as limited only in 
accordance with the teachings thereof as set forth in the 
claims appended hereto. 
I claim: 
1. An electron beam electric field measuring instrument 
means for producing an electron beam; 
a target assembly comprising first and second pairs of 
electrically conductive segments, said first pair of 
segments disposed in opposed relationship along a 
first axis and said second pair of segments disposed 
in opposed relationship along a second axis normal 
to said first axis; 
means for deflecting said electron beam in a circular 
sweep so as to normally impinge upon each of said 
segments an equal time; 
said beam being deflectable in response to an external 
electrical field to be measured to vary the path of im- 
pingement of said beam of electrons thereby varying 
the time each segment is impinged; 
a detecting circuit electrically connected to each of said 
segments, each of said detecting circuits including 
means for establishing an output voltage whose 
magnitude is dependent on the time each segment is 
a first pair of deflection plates disposed on opposite sides 
of said beam path for deflecting said beam along said 
first axis; 
a second pair of deflection plates disposed on opposite 
sides of said beam path for deflecting said beam along 
said seoond axis; 
means connecting the outputs of said detecting circuits 
associated with said first pair of segments to the 
input of said first deflection plates in a direction tend- 
ing to deflect said beam opposite to the direction of 
deflection caused by said electric field; 
means connecting the outputs of said detecting circuits 
associated with said second pair of segments to the 
input of said second deflection plates in a direction 
tending to deflect said beam opposite to the direction 
of deflection caused by said electric field; 
means to compare the output voltages of said detecting 
circuits associated with said first pair of segments for 
deriving a signal indicative of the electric field along 
means to compare the output voltages of said detecting 
circuits associated with said second pair of segments 
for deriving a signal indicative of the electric field 
along said second axis. 
2. The apparatus of claim 1 wherein said means for es- 
tablishing an output voltage dependent on the time each 
segment is impinged comprises a low pass filter. 
References Cited 
UNITED STATES PATENTS 
1,960,333 511934 Du Mont _--_____ 324-109 XR 
2,368,328 1/1945 Rosencrans _ _ _ _ _ _ _  313-89 XR 
2,534,372 12/1950 Ring _ _ _ _ _ _ _ _ _ _ _ _  324-88 XR 
65 3,090,240 5/1963 Nashman et al. _ _ _ _ _ _ _  73-517 
10 
comprising: 
15 
20 
25 
30 impinged; 
33 
*O 
45 
50 said first axis; and 
60 
RUDOLPH V. ROLINEC, Primary Examiner 
E. F. KARLSEN, Assistant Examiner 
70 U.S. C1. X.R. 
324-109, 121 


Electron beam instrument for measuring electric fields Patent

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