Ion engine with magnetic circuit for optimal discharg

Kaufman, H. R.

Reader, P. D.

English

NASA Technical Reports Server

REPLY TO 
ATTN OF: GP 
TO: 
FROM: 
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION 
WASHINGTON. D.C. 20546 
October 15, 1970 
~ ~ ~ / ~ c i e n t i f i c  & Technical Information Division 
Attention: Miss Winnie M. Morgan 
~P/~ffice 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 forwareed for 
abstracting and announcement in NASA STAR. 
The following information is provided: 
U. S. Patent No. 
Corporate Source 
Supplementary 
Corporate Source 
Lewis Research Center 
NASA Patent CaseNo.: XLE-01124 
Gayle Parker 
Enclosure : 
Copy of Patent (ACCESSIONiUMBER) 
(PAGES) 
od 
(CODE) 
A 1 4  
u (NASA CR OR TMX OR AD NUMBER) (CATEGORY) 
4 ,  
NASA-HQ 
1 
https://ntrs.nasa.gov/search.jsp?R=19710004568 2020-03-17T02:33:34+00:00Z
March 8, 1966 P. D. READER ETAL 
4 0 
5 
FIG. 3 
INVENTORS 
PAUL D. READER 
March 8, 1966 P. D. READER ETAL 3,238,";B 5 
ELECTROSTATIC ION ENGINE HAVING A PERMANENT MAGNETIC CIRCUIT 
Filed Sept . 27, 1963 2 Sheets-Sheet 2 
FIG. 2 
I Oa 
/32 \.\ , , ,, -, , ,, , , ,  
FIG. 6 
INVENTORS 
PAUL D. READER 
ATTORNEYS 
3,238,715 United States Patent O6ce ,,,, Mare , ,, 
J , L J 0 9  I I3 
ELEC'HlfPOSTATIC ION ENGINE N A V m G  A 
P E W A N E N T  MAGNETIC CPWCUPT 
Paul D. Reader, Parma Heights, and Harold R. Kaufman, 
Berea, Ohio, assignors to the United States o f  America 
as reloresented bv the Administrator ef the Nalu'onal 
 erab ban tics and space Administration 
Filed Sept. 27,1963, Ser. No. 312,269 
10 Claims. (Cl. 60-35.5) 
(Granted under Title 35, U.S. Code (1952), see. 266) 
The invention described herein may be manufactured 
and used by or for the Government of the United States 
of America for governmental purposes without the pay- 
ment of any royalties thereon or therefor. 
This invention is concerned with electrostatic engines 
and, more particularly, with an electron bombardment 
ion engine having an improved structure for providing a 
magnetic field that has the shape and strength required 
for optimum efficiency of operation of the discharge. 
Electron bombardment ion engines of the type shown 
in copending application Ser. No. 139,007, now Patent 
No. 3,156,090, utilize wrappings of high conductivity wire 
about their ion chambers to produce the required mag- 
netic field as current is passed through the wire. This 
wire coil or electromagnet requires an electrical power 
supply which adds weight to the system, and to obtain 
a high electrical efficiency a heavy coil is needed. The 
reduction of the overall weight of the engine system is 
an important consideration in designing electrostatic en- 
gines. 
These disadvantages have been overcome by the pres- 
ent invention wherein a permanent magnet circuit is pro- 
vided by a group of permanent magnets arranged with 
permeable paths to conduct and properly distribute the 
magnetic lines o i  flux through the ion chamber. The 
permeable paths are incorporated in the engine as struc- 
tural members, and because many of these members are 
normally required in an engine utiiizing an electromagnet 
the ovcrail weight of the present engine is approximately 
equal to that of an engine with an electromagnet. 
The electrical power supply required by the electro- 
magnet is eliminated by the present structure thereby re- 
ducing the total weight of the system. The required mag- 
netic field is produced by apparatus which is passive be- 
cause after the magnets have been initially magnetized 
and placed in the circuit no further activation, control, 
or power supply is required for proper operation. 
It is, therefore, an object of the present invention to 
produce an improved electron bombardment ion engine 
having a permanent magnetic circuit which is reliable, 
mechanically strong, and efficient with a reduced total 
system weight because of the omission of the weight of 
the power supply required by an electromagnet. 
Another object of the invention is to provide an im- 
proved electron bombardment ion engine utilizing per- 
manent magnets which serve as a return path for the 
magnetic fiux of the engine thereby enabling engine 
modules in a multi-engine array to be positioned closer 
together without magnetic field interaction whereby the 
total engine area is reduced by the elimination of dead 
space which produces higher thrust per unit area. 
Other objects and advantages of the invention will be 
apparent from the specification which follows and from 
the drawings wherein like numerals are used throughout 
to identify like parts. 
In the drawings: 
FIG. 1 is an axial quarter section of an electron bom- 
bardment ion engine shown in perspective utilizing an 
improved magnetic circuit constructed in accordance with 
the invention; 
FIG. 2 is an axial quarter section of an electron bom- 
bardment ion engine shown in perspective utilizing an 
alternate embodiment of a magnetic circuit constructed 
in accordance with the invention; 
FIG. 3 is a schematic view illustrating tbe ~ ~ ~ a g n e t i c  
5 circuit of the electron bombardment Icn ci:ginc sliown In 
FIG. 1; 
FIG. 4 is a schematic view of an electron bombard- 
ment ion engine having a modified magnetic circuit; 
FIG. 5 is a schematic view of the maznciic c:icuit of 
10 the electron bombardment ion engine shown in FIG 2; 
and 
FIG. 6 is a schematic view of an ajtc~na'.r embodinlent 
of a magnetic circuit for an electron bombardment ion 
engine. 
15 Referring now to the drawings, thcre is shown sevcral 
electrostatic ion engines which utilize electi-or!-bombard- 
ment ion sources. In each of thesc engines, neutral par- 
ticles in the form of a gaseous propellant entcr the up- 
stream end of an ion chamber in which high-velocity 
20 electrons thermionically emitted by a cxihode in the 
form of a hot filament in this chamber ionize thesc par- 
ticles to form a plasma. A screen grid and accc;eralor 
grid at the downstream end of the ion chamber focus 
and accelerate ions that reach that end. T!lc thrust pio- 
25 ducing mechanism of this device is thc momentum chanze 
of the ions as they are accelerated by t13c elccirost-;:ic 
field which is applied between the screen and accclerztor 
grids. 
Both FIGS. 1 and 2 show c!ectron bombardment ion 
30 engines 10 and 10a having a propellant supply campris- 
ing a source 12 in the form of a cylindrical container 
or boiler which furnishes the propelIant, such as mercury 
vapor, to a manifold 13. An ion cbambcr 14 wiih~n a 
tubular casing 16 is in communication with the manii'old 
35 13 in a manner which will be dcscvibed later in detail. 
A tubular anode 18 is concentrically supported within the 
casing 16 and insulated therefrom. A ci?ihode 20. such 
as a tungsten filament, is centrally supported in the center 
of the chamber 14 by a pair of arms 22 and %I carried 
40 by an insulator 26 mounted on the caqing PL6. A pair of 
electrical leads 28 and 35 extending from the cutwa:dly 
directed surface of the insulator 26 are in cl~ciricnl com- 
munication with the cathode 283 thl-ouglr tFe arms 22 anis 
24. 
45 A grid 32 in the form of a plate innving a plurality of 
apertures 34 is positioned at the downstre:im 0:. exhaust 
end of the chaniber 14 to accelerate the ions in the plasn?a 
that move to this end of the engine. Thc grid 33 is se- 
cured to and in electrical contact wit11 ap annuirrs plate 
50 33. Both the anode IS and the cathode 20 2s we11 as the 
accelerator grid 32 and its annulus plntc 33 are con- 
nected to suitable sources of power in the manner shown 
in the aforementioned copending applicalion Scr No. 
139,007, now Patent No. 3,156,090, and the propelPant 
'' is ionized in the chamber 14 in the manner dascribcd in 
this copending application. 
The particle densities of the plasma En the chamber 14 
are sufficiently small that the mean free pat11 for ioniza- 
tion is quite long thereby necessitating the containment 
of the high velocity ionizing electrons wiih~n the ion 
chamber 14. A magnetic field is utilized ;s lengthen the 
path of these high-velocit~~ electrons that  aic ei-lilted from 
the cathode 20. According to the prescclf rn\,ent:on, srich 
a magnetic field is provided by a group of permanent m1g- 
65 nets arranged with permeable paths tc conduct and prop- 
erly distribute magnetic lines of Bus. 
Referring to the embodiment of the i n v e n t ~ ~ n  shown in 
FIG. 1 and illustrated sc].ematically in PIG. 3, a plurality 
of permanent magnets 40 in the form of eiong?ted cylirm- 
70 ders are arranged concentrically about the periphery of 
the casing 16 with the nor~nal axis of each of the cylin- 
ders being substantially parallel with the a x s  of the casing 
3,238,715 
- 
k:, 4 
16. The magrlets 40 are equally spaced and supported 72 extends around the periphery of the central portion 70 
by a pair of spaced plates 42 and 44 of a magnetic per- and engages the downstream ends of the magnets 4Oa. 
meable material. such as soft iron, which form not only Insulators 47 and 48 are utilized to mount the annulus 
strzrcburai components of the ion engine 10 but also pole plate 33 and accelerator grid 32 on the plate 64 as previ- 
pleccs which provide permeable paths for magnetic lines 5 ously described. The magnetic field illustrated by the 
of J'iux F as iilustsated in FIG. 3. Both the upstream plate flux lines Fa in FIG. 5 has a tapered configuration. 
42 and the downstlearn plate 44 are substantially planar Another ion engine 1Qc having a permanent magnetic 
2nd ~ o r m a l  to the longitudinal axis of the engine 10, and field with a tapered configuration is illustrated in FIG. 6. 
the central portio? of each plate forms an end wall of In this embodiment, a plurality of permanent magnets 80 
the ion chaniijer 14. The ul~stream plate 42 contains a 10 having a length that is longer than the ion chamber l 4 c  
pfurai:ty of apertures 45 which serve to distribute the flow are mounted in spaced relationship about the casing 16. 
of the gascous propellant from the manifold 13 into the These magnets 80 are mounted between an upstream plate 
ion chili~lber 14. The downstream plate 44 contains a 82 and a downstream plate 44 which is substantially iden- 
plutaiilji of apertures 46 in substantial alignment with the tical with the corresponding plate of the embodiment 
apertures 34 in the grid 32 to reduce the impingement of 15 shown in FIGS. 1 and 3. The upstream plate 82 includes 
the ions on the accelerator grid 32 thereby reducing ero- a central portion 86 which forms the upstream end wall of 
sion. Both the plates 42 and 44 are in electrical contact the ion chamber l 4 c  and has a plurality of apertures in 
with thc casing 16 while the accelerator grid 32 and an- communication with the propellant manifold as in the 
nulus plate 33 are insulated from and maintained in a case of the previous embodiments. A circumferential 
fixed spaced relationship relative to the plate 44 by insula- 20 flange 88 encircles the central portion $6 and extends 
tors 47 and 43. The plates 42 and 44 as well as the angularly upstream away from the ion chamber 14c. A 
casing 43 are coilnected to a suitable power source in a radially extending annulus 90 encircles the upstrem end 
manner described in copending application Ser. No. 139,- of the flange 88 and engages the upstream end of each of 
007, now Patcnt No. 3,156,090, and are operated at the the magnets 80. The configuration of the plate 82 dis- 
same potential. 25 tributes the magnetic lines of flux Fc to form the tapered 
Referring to FIG. 4, there is shown an electron bom- configuration shown in FIG. 6. 
bardrnent ion engine 10b having an accelerator grid 32 While several embodiments of the present invention 
and a screen grid 49 mounted at the downstream end of have been illustrated and described, various structural 
an ion chamber P4b within a casing 16 in the manner de- modifications may be made to these embodiments without 
scribed in the aforementioned application Ser. No. 139,- 30 departing from the spirit of the invention or the scope of 
007, now Patent No. 3,156,090. Pn this embodiment, a the subjoined claims. By way of example, the various per- 
plurality of permanent magnets 50 in the form of cylin- manent magnets have been described as being elongated 
ders each having a shorter Length than that of the ion cylinders. It is contemplated that permanent magnets 
chamber P4b are arranged concentrically about the casing having other shapes and configurations may be utilized. 
16. The ugstl-eam plate 42 or pole piece is substantially 35 For example, the magnets may be shorter than those 
planar as in the case of the embodiment shown in FIG. 1, illustrated with the remaining length being supplied by 
and a marginal peripheral portion of this plate engages outwardly extending pole pieces which contact the spaced 
the upsdrcarn end of each of the magnets 50. An oppo- mounting plates. Also, a single permanent magnet which 
sits pole piecs is formed by a radially extending annulus encircles the casing may be used. 
52 which engages the downstream ends of the magnets 40 What is claimed is: 
50 and a sleeve 54 which engages a portion of the casing 1. An electrostatic ion engine comprising 
16 between the annulus 52 and exhaust end of the cham- a casing forming the peripheral wall of a chamber for 
ber 14h. It  is contemplated that the sleeve 54 may be containing an ionizable propellant, 
eliminated by malting this downstream portion of the a source of said propellant positioned at one end of 
casing 14 of a magnetically permeable material while the 45 said casing, 
upstream poltion between the annulus 52 and the plate a thermionic emitting cathode within said casing for 
42 is of anolhcr material that is not magnetically perme- bombarding said propellant with high velocity elec- 
able. As illtistrated by the flux lines Fb in FIG. 4 this trons to form ions, 
structural arrmgement produces a tapered magnetic field an apertured grid having a relatively high negative po- 
having ilu~ lines which diverge or become less dense 50 tential relative to said cathode positioned at the op- 
from the upstream end towards the downstream end for posite end of said casing remote from said propellant 
improved efficiency. supply to accelerate said ions away from said engine, 
Bn the embodiment shown in FIG. 2 and illustrated a plurality of permanent magnets positioned around 
schematically in FIG. 5, a plurality of permanent magnets said casing to form a magnetic field about said pro- 
40a in the foim of elongated cylinders are mounted cir- 55 pellant and said cathode whereby the paths of said 
curnferentially around the casing 16 as in the previous high velocity electrons are lengthened to increase the 
embodiments, but the normal axis of each cylinder is rate of .collision of said electrons with particles of 
angularly dfsposed to the axis of the ion engine 10a. The said propellant, 
permanent magnets 40a are equally spaced about the cas- a pair of spaced members for mounting said magnets, 
ing 16 and are mounted by spaced plates 6E and 64 which 60 said members being of a magnetic permeable mate- 
likewise function as both structural elements and per- rial and in contact with said casing to form the end 
meable paths for the magnetic lines of flux illustrated by walls of said chamber, and means for maintaining 
the arrows Fa in FIG. 5. The upstream plate has a cen- said members and said casing at the same electrical 
trally disposed planar portion 66 which contacts the up- potential. 
stream end oF the casing 16 and forms an end wall of the 65 2.  An electrostatic ion engine as claimed in claim ion chamber 140. A plurality of apertures 45a in the 
cenlrdY 65 comnlunicates with the interior of the wherein one of said membcrs is positioned between said 
propellapt rnanifold 13. The upstream plate 62 further One end of said casing and said propellant source, said 
includes an afignlarly extending flange 68 around the member having a plurality of openings therein for con- 
central portion $6 which mounts the upstream end of 70 veying said propellant from said source to said chamber 
each of the permanent magnets 40a. and distributing the same therein. 
The downstream plate 64 likewise includes a central 3. An electrostatic ion engine as claimed in claim 1 
portion 70 containing a plurality of apertures 46a which wherein one of said members is positioned between said 
are in stihstantial alignment with the apertures 34 to re- opposite end of said casing and said grid, said member 
cluce erosion of the accelerator grid 32. An angular flange 75 having a plurality of apertures therein in substantial align- 
3,238,715 
5 6 
ment with the apertures in said grid for shielding the same 9. An electrostatic ion engine as claimeci in claim 4 
from said ions to reduce erosion. wherein each of said magnets has a length substantially 
4. An electrostatic ion engine as claimed in claim 1 shorter than said casing, and one of said members corn- 
wherein said casing is tubular and said magnets are cylin- prises a flange extending radially outward from said cas- 
drical and equally spaced about said casing. 5 ing. 
5. An electrostatic ion engine as claimed in claim 4 10. An electrostatic ion engine as clain~ed in claim 9 
wherein the normal axis of each of said magnets is sub- including 
stantially parallel to the axis of said casing. a sleeve mounted concentric with said casing and in 
6.  An electrostatic ion engine as claimed in claim 4 engagement with said flange. 
wherein the normal axis of each of said magnets is an- 10 
gularly disposed to the axis of said casing. References Cited b y  the Examiner 
7. An electrostatic ion engine as claimed in claim 4 UNITED STATES PATENTS 
wherein each of said magnets and said casing are sub- Re. 25,440 9/1963 Engelman ---- 313-157 
stantially equal in length. 2,681,421 6/1954 Gethmann ---------- 313-84 8. An electrostatic ion engine as claimed in claim 4 15 2,919,370 12/1959 Giannini et al. 
whei-cin each of said magnets has a length substantialIy 
longer thaz said casing and one of said members includes 2,997,013 8/1961 Rice --------------- 60-35.5 
a circumferential flange extending angularly outward 39156,090 ICaufman -------- --- 50-35S 
from said casing, and 
a radially extending annulus adjacent said flange in en- 20 MARK NEWMAW, Prin7ary Examiner. 
gagement with an end of each of said magnets. C. R. CRQYLE, Assistant Examiner. 


Electrostatic ion engine having a permanent magnetic circuit Patent

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