An electric propulsion system which relies on the formation of cesium ions in contact with a porous wall made of a metal with a high work function when the wall is heated to 1500 K was described. The manufacture of porous walls on the mountings was considered. Erosion of the electrodes by slow ions was examined, and the life times of the ionizers was estimated by means of experimental studies. The purpose of the electric propulsion system was to bring about minor corrections in the orbits of geostationary satellites; the main advantage of this system was that it weighs less than currently used hydrazine systems

Hivert, A.

Labbe, J.

English

NASA Technical Reports Server

General Disclaimer 
One or more of the Following Statements may affect this Document 
 
 This document has been reproduced from the best copy furnished by the 
organizational source. It is being released in the interest of making available as 
much information as possible. 
 
 This document may contain data, which exceeds the sheet parameters. It was 
furnished in this condition by the organizational source and is the best copy 
available. 
 
 This document may contain tone-on-tone or color graphs, charts and/or pictures, 
which have been reproduced in black and white. 
 
 This document is paginated as submitted by the original source. 
 
 Portions of this document are not fully legible due to the historical nature of some 
of the material. However, it is the best reproduction available from the original 
submission. 
 
 
 
 
 
 
 
Produced by the NASA Center for Aerospace Information (CASI) 
https://ntrs.nasa.gov/search.jsp?R=19780011254 2020-03-22T06:03:59+00:00Z
NASA TECHNICAL jfE2,j0RANDUP.1 NASA TM-75280
a ^^a- .k
MANUFACTURE OY IONIZERS INTENDED FOR ELECTRIC PRCPULSION
Andre Hivert and Jean Labbe
(NAS1-T"-75280)	 MA1,113FACTT3FF OF IONIZERS	
N78-19197
IN:ENDF.D FOR ELECTRIC PROP TILSIO N' (4,ational
Aeronautics and Space hdministratiOTI)CSC L15210	 tlnclasIiC A02/MF A01	 G3/20 08659
i
i
J
Translation of "Fabrication D'ioniseurs Destines a la
Propulsion Electridue," Office National D'Etudes et de Recherche:
Aerospatiales, Chatillon-sous-Bagneux ONERA TP Ile. 1977-36 ? 1977, 11
pages. iSeminaire Plansee De Re Metallica, 9th, Reutte, Austria, May
23-26, 1977•)
MAR 278
RECEIVED
K^^! "I F,!CVTT
1.
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
WASHINGTON, D.C. 20546
	 MARCH 1978
iSTANDARD TITLE PAGE
1.	 Report No.
NASA TY-75280
2	 Gove r nment Accession No	 — T	 Recipient's Catalog No
4	 Title and Subtitle
_
S	 Report Dote
7ANUFACTURE OF IONIZERS INTENDED FOR ^'arh
6.	 Performing Organisation CodaELECTRIC PROPULSION
7	 Authot(s)
Hivert, Andre and J(-an Labbe
6	 Performing Organ,satron Report No
National Center of Aerospace Studies 10	 Worw Unit No.
and Research, Chatillon, France _	
1{pI I	 Co	 r N or 4{vat, li
""''^^ —•	
`lI
— -
a .	 Performing Organisation Nome and Address
L:eo Kanner As socia tes U	 Type of Report and Period Covered
Fedwood City,
	
California 91:063
Translation
12	 Sponsoring Agency Nome and Address
National Aeronautics and Space Adminis-
tration, Washinrton,	 D.C.	 20946 1'	 Sponsoring "o•^^y cad.
IS	 Supplementary Notes
Translation of "Fabrication D'ioniseurs Destines a la
Fronulsion Electrique, ft
 Office National D'Etudes et de Recherches
Aerospatiales, Chatillon-sous-Bagneux ONERA TF No. 1977-36, 1911,
11 pages. (Seminaire Plansee De Re Metallica, 9th, Beutte, Austria,
1077•)	 (A 77-50,-)78)
16	 Absrroct
The paper describes an electric propulsion system which
relies on the formation of cesium ions in contact with a
porous wall made of a metal with a high work function when
the wall is heated to 100 K.
	 The manufacture of porous
walls on the mountin gs are considered.	 Erosion of the
electrodes by slow ions is examined, and the life times of
the ionizers is estimated by means of experimental studies.
The purpose of the electric propulsion system is to brine
about minor corrections in the orbits of Feestationary
satellites;	 the main advantage of this system is that it
weighs less than currently used hydrazine systems.
17.	 Key Words (Selected by Author(%)) 	 1e.	 or.nibut.on Statement
Unclassified-Unlimited
19.	 Security Clossif. (of this repo'll 20,	 Security Closul. (o f this page) 21• No. of Pages 22.	 Pace
Unclassified Unclassified 13
1
4
I
6
MANUFACTURF OF IONIZERS INTF:NDFD FOR FI F CTRIC FROM I SIGN
Andt • c` divert and .Ivan Labbe
Nst tonal Center of Aerospace, Studles Rn,i Research, (V320
Chdtillon, Fraser
I - Introduction
	 /1*
Ma11y appIicaticIs. st:c11 as to It, Communic• nt tens , c1 i rect
television, me• teorologleal surveillance, taking: navigat 1oiInI
bearitirs, etc., require the use of geoststionsry sst ell ites
which are in .I 	 xri po:; t Lion with respe t to the ent• t h, hi s-
turbing ef foot s exerte.i on these sat ell it en tfor ex,Imple, Sol "11.
radInt.1on pressure, lunar att •• ,notion, nni sot ropy it1 the earth's
►ravIty field. et k,	 periodically require t h v npp11enIIon of a
^,r.111 corrective thrust (1-10 mN) sup p llc , .i 1,y kivvices with a
subst snt i al -orvi cc, life (5-7 ye• nrs) .
	 T.r1 co-v. T-ison with the
the hydr.'17ine propulsion systems currently used, the use of
ele: t ri: propulsion for this trsk would permit the t ctnl wt-IFI t
of n smenite wetrhing from tl^0 to 800 kg to bc- increnset mare
111;411 10% [1]. Tho cost of rroduc t loll for the new systerl would
be comparnble to that of the hyc?r t °inr cyst ca m. The principle
of this type of propulsion consists first of all accelerating
`	 henvy ions by means of hi.01-voltace (about 3 kV) electrostatic
opt t cs ntid then in it Second step ndkli nf- to the ! ons , which hnve
then sc• iluired s s peed on the order of FO Rm per secon,t, ttiv
electron:: whi, h were previously vemove.i in order to ree:;t ablish
the electric neutrality of the system.
Among the vsrieus ions ation mothods used to achieve this,
the formation of ceslum ions (an element with -I 	 tenl:-ntion	 1
potential, ',Q eV) in contact with it wnll consisting of a metnl	 ?
with r! high work function snd heated to lr, 00 K has been studied
III
	 g i 1 by CN1,13A nt the request of the CNFS. To obtaln :4 con-
tnct as clone ;ts possible bc, tween the two sut)st nnces • and thus
• Nurt• rrs 'n the mat• c-in ind.i cst e paginnt ton In the foreir•n text .
1
Mty; Ad
an increased coefficient of ionization (greater than 99X), the
cesium vapor is blown in across a porous wall.
II - Required Characteristics and Manufacture of Porous Walls
The choice of the type of porous w111 intended to ionise
the cesium vapor is very restricted since the material has to
combine a hi gh degree of refractoriness and a high wort: function.
In practice, only tungsten sufficiently combines these two
conditions. Moreover, it is riot soluble with cesium. However,
its function as an ionizer imposes on it other necessary and
sometimes contradictory characteristics:
1. Sufficient permeability tc rases or vapors to allow a
suitable flew of cesium with a moderate temperature	 /2
for the vaporizor, which assumes a substantial overall
porosity and a small thickness.
2. Porosity which is homogeneously distributed in t h ey form
of very fine pores ( 1-3 11) so that a minimum of cesium
atoms escapes from the ionizer.
3. Ability to conform a specific radius of curvature in
order to pre-focus the ions.
4. Dimensional and structural stability in a vacuum at
1900 K for thousands of hours.
This last point especially deserves attention because it is
obvious that a high porous, finely-grained material pcssesses
considerable free energy which will tend to decrease as a result
of recrystallization and contraction. A device to block these
unacceptable phenomena must be provided. It tins been shown
earlier at ONFRA that a fire dispersion of thorium oxide in a
nickel powder ensures this blockage provided that the particles
do not exceed 1000 R.
An efficient dispersion process based on tt• e wetting, of
nickel oxalate by A solution of thorium acetylacetonate has been
proposed, Fig. 1, [2].
2
wi	 s
OP
RORODUCIBILM OF THE
C..y • 
Jr	 04
r J1.6
All
r
Fig. 1. Dispers'_on of thorium oxide in a nickel
matrix obtained by the thoriun, acet;ylacetonate process.
Elsewhere, at about the same time, a process for manufacturing
nickel chi-crium porous membranes was developed [3].
It consists of mixing an organic binding agent, which can
be sublimed, with the metallic powder and then making flexible
sheets by calendering.
These sheets can then be cut, dried to eliminate the
binding agent and fritted. The advantages are appreciable.
The porosity which takes the place of the organic binding
agent is very well distributed and, on the whole, it is precisely
determined. The thickness can be reduced to 0.2 mm, and then
after drying the sheets can be shaped by hot stamping, therefore
eliminating any machining and thus any filling of surface pores.
It is the combination of these two techniques which has
permitted the manufacure of these porous tungsten walls required
for ion propulsion experiments [4]. The different steps in the
2
n
3
4.. ..... 
	
• _	 ^. r*rte
Y !^	 1 ywl
RF.pRODUCIBILXrY OF THP
ORIGNAL PAGE IS POOR
rrr r	 0
A
Fig. 2	 Fig, 3
II	 process are the following: (1) wetting; W0_
,
 with a solution of
thorium acetylacetonate; (2) calcination at 800°C; (3) reduction
in H 2
 at 900°C; (4) mixing the tungsten pcwder with a solution
of methyl polymethacrylate cyclohexanone; (5) caler,dering the
paste to obtain a flexible sheet of suitable thickness (0.6-
1.5 mm); (5) cutting to the desired shape;(7) drying; (8)
(8) smoothing; (9) stamping; (10) elimination of the binding.
agent by gradual heating in H 2 ; (11) fritting in H 2
 at 1550°C.
Fig. 2 shows the surface state of the material obtained. The
number of pores reaches 30 million per s q uare centimeter which
guarantees a good ionization yield. Fig. 3 shows a few types
of porous walls which have been made.
Tre spherical caps are provided to e q uip propulsion systems
called "monobuttons" whose thrust is 0,5 rr.N. The strips are
for propulsion systems called "mono-slits" whose thrust is on
the order of
	 mN. The ring is supposed to be installed on
an annular Pro pulsion s y stem whose thrust mi ght attain 5 mN.
V
REPRODUCIBILITY OF THE
ORIGINAL PAGE' IS POOR
III - Desirn and Fabrication of the Mountings
	
/4
The mountings mmst reliably perform several functions:
(1) hold the p orous wall in place; (2) receive and uniformly
distribute the cesium vapor; (?) transmit to the porous wall
whicn radiates in s p ace the thermal flux necessary to maintain
the temperature enuilibrium around 1500 K. Fig. U shows a section
O ;^
i'
h
CO
^.6
Soudure par bornbordemant e40ronique
Electron bombardment welding
Cs
Monlure Mani!o/d (Mo)
poreu3e . Porou! wall (w)
'111,_ Chvuflayc Healer
W,
- 
SO	
—	 --
72
Fig. 4. Initial emitter mounting.
of a mounting intended for a monoslit propulsion system. The
reason for sloping the partition is to ensure a homogeneous
flux of cesium starting from a single input tube. Heating is
accomplished by coiled tungsten filaments covered with aluminum
oxide inserted into legitudinal cavities.
The required properties of the material to be used are that
it be highly refractory and have a high level of thermal con-
ductivity. The latter condition excludes tantalum. The choice
is limited to molybdenum and tungsten. The first has the
advantage that it can be easily worked either with machines or
5
I..	 M
REPRODUCIBILITY OF THE
ORIGINAL PAGE IS POOR
by electroerosion methods, but its expansion coefficient is
greater than that of tungsten and thus stresses would be expected
to occur between the mounting and the porous wall in the course
of thermal cycles. Tungsten avoids this drawback, but it is
difficult to work even by electroerosion methods. This is why
mountings of this type have been made by pyrolytic decomposition
of tungsten hexofluoride on pieces of copper ultimately elimi-
nated by treating with acid 157.
Fig. 5. Mountinrr s made of
pyrolytic tungsten.
With this technique it is	 /5
even possible to imagine mountings
of molybdenum-tungsten mixtures.
Fig. 5 shows two particular
models for monoslit and annul ar
propulsion systems.
IV - Junction of Porous Walls
on the Mountings
The porous walls, since they
have to remain unfinished at
fritting, cannot meet strict
dimensional tolerances. Therefore
.
	
i
.tae
Vader
the groove in the mounting intended to hold a wall must be fitted
-
^ 
it 
j^
 j4W'.{
Fig. G o	 F ig. 6 b
6
a"
R^^^nuc^tt,rr^r or I'xE
UJUGIN'Al' PAGE% IS pUUK
to the wall. Molybdenum, which can be easily machined, does riot
pose any problems. For tungsten mountings, pyrolytic electro-
erosion turns out to be disappointing because of the cracks
which it causes (Fig. 6a). By contrast, machining using ultra- 	
1
sonic techniques has proved its efficiency (Fig. Fb).
As for the ,joint, welding by electron bombardment can 	 /6
reliably be used on small rotating pieces sunh as monobuttons
(Fig. 7)
1	 I
Fig. 7
By contrast, difficulties turn up with rlonoslit propulsion
systems because of the large thermal gradients caused by this
weldinp technique. Substantial wastes have occurred. As fcr
annular propulsion systems, the operation has turned out to
be impossible by performing two bands of welding one after the
other since the second always causes the porous wall to rupture.
This is why recourse was again taken to the pyrolytic deposition
of t-unrsten which, provided that the porous wall is protected
by a copper mask, can insure a tight ,joint with the mounting
under isothermic conditions (FiKs. 8 and 9).
7
W4M=jjj^. V J jrjbM	 Msftw^ , 4
REPRODUCIBILI'T'Y OF T10
ORIGINAL PAGE, IS NY*
r ^ ,
Fig. 8. Section of a monotut- 	 Fig. 9. Annular ionizer
tcn ionizer. 1. molybdenum
base; 2. pyrol,ytic tungsten
mcunting; 3. pyrolytic tungsten
joint.
V - Heating Apparatus
The very rapid increase in the ionization coefficient with
temperature is followed by a thermal threshold called the
"critical temperature T c " beyond which ionization becomes almost
total. So as not to increase the heating power dI ssipat.ed by
radiation the ionizer surface temperature must be kept as uniform
as possible, not exceeding more than 50 0 at any point, i.e.
Ithe critical temperature.
a, ._
/7
.a
Fig. 10. Thermograph of a mono-'
button ionizer (thermal dif-
ference 5 K per zone).
The necessity for heating
the porous wall through the
mounting (by the Joule effect or
by electron bombardment) re-
quires good thermal conduction at
the joint. This conditions has
been verified by means of photo-
graphs taken by a heat-sensitive
infrared camera. The observed
'difference between the center and
I
8
rZ
^	 e
R^^pKt)DU11•s1 ►, IS pooll
^RIGL.A1^ PAGL
the edge does not exceed 30°K for a mean value of 1500 K (Fig. 10)
[6].
VI - Erosion of Electrodes by .S low Ions
A small quanti.y of neutral atoms exists in the beam in spite
of the high ionization coefficient. These atoms, when struck by
rapid-moving incident ions, give rise, by an exchange of charge,
to slow ions which are attracted by the high positive voltage
electrodes of the optical system. Here, in the long run, these
slow ions can cause erosion which is not insignificant. In
order to determine the amount of wear, systematic experiments
have been conducted on various materials and especially on the
refractory metals. Specimens constituting circular targets
measurin g 20 mrr. in diameter and heated to 600 K to facilitate
degassing were subjected to bombardment by cesium ions with an
	 /8
energy ranging between 0.5 and 3 keV.
The electron detachment coefficient (sputtering) expressed
in metallic ions detached per incident cesium ion, was determined
from the change in mass of the specimen after 10 hours of
shooting, the number of cesium ions being calculated by inte-
grating the current running; between the venerator and the
target. The results obtained for molybdenum, tungsten, tantalum
and niobium bombarded at an angle of 90° are shown in Fig. 11.
1
Observation of the surface
scanning electron microscope at
contrary to certain metals such
the appearance of nodules (Fig.
metals exhibits uniform erosion
c, d, e).
state of the targets using a
the end of the test shows that,
as copper whose surface shows
12 a), the surface of refractory
on a microscopic scale (Fig. 12 b,
9
°I Eros
'e
Ll
I,
.^_ —
	 -	
--	 rte•	 -lo!
it
REPRODUCIBILITY OF THE`
ORIGINAL PAGE IS POUR
A. Au
in
	
roan	 1+00
	 Joao	 J»oo
	
^.
77t.
'1,
. _
Fir. 12 a. surface of copper after
after bombardment by ions with
an energy of 1500 eV.
Mr
	
Fig. 11. Compared variation
in erosion rates.
VII - Conclusion
	
/9
Estimation of the surface life of ionizers produced in this
way has given rise to a series of tests undertaken si,rultaneously
by CNS and 011EFA in which several ionizers have been subjected
either to periods of operation in a vacuum at 1450 Y. without
cesium for several thousand hours, or to series of several
dozen successive bombardments, with cesium, each for a period of
P hours, without any change in the metallurgic properties being
found. The cyclic tests were Fenerally interrupted as a result
of defects in the electric insulation.
The methods employed have led to the development of ionizers /10
10
•Rvi'llonUCIBII.ITY OF THE
I^I^II^i^AI. 1^,1^^1, T^ 1'^11^ft
• \	 ^J	 N ♦ 	
1
^	 al
'	 r	 ♦ 
`iJ	 \
,.	 I	 -.r
.	 r	 ^
1•
C
Tamale	 ^^_	 ^^1^,	 ^,	 Tunystlne	 I
Fig. 12. Microscopic examination of specimens after
bombardment by ions with an energy of 3000 V.
Key: c - molybdenum; d- tantalum; e - tungsten
havinF either a larp-e em.ttinF surface suitable for increasing
the level of thrust of ion propulsion systems, or complex
geometric shares determined by calculation and which can
scarc-- y be ebtained by classical machininF methods.
Beyond the realm of ion propulsion, all of these techniques
11
i
1
J
can be considered as suitable for the fabricatinn of ion emitters
designed for certain fundamental studies (e.g. standard ion
zources, porous emitters for field effect ionization, etc).
:I
J
12
1 `-
REFERENCES
1. Pearson, J.J., "Resu'.k:s of the definition studies for the
application of electrical propulsion systems to the
station-keeping of ruropeaii communication satellites,"
Conference on Prop ulsion of Space Vehicles, 10-12 April
1973 - IEE Conference publication no. 100.
?. Marty, M., A. Walder and A. Iiivert, "Making of a dispersed
phase alloy from orrranometallic cempo- ids," 7th Plansee
Seminar, Peutte, 1971, High Temperatures, Hiph Pressures,
Vol. 3, 1971, pp . 677-685.
3. Hivert, A. and P. Galmiche, "Fabrication of porous metallic
membranes," La Fecherche Aeronautique, 1, 56 (1971).
4. Hivert, A., "Metallurgy of thoriated tungsten powders and
the making of ionizers," Acta Electronica 17/ L , 415-420
(1974).
5. Shroc , A., A. Hivert and J. Labbe, "A new technique for
making cesium ion emitters for electrostatic propulsion
systems," La Recherche Aerospatiale, 3, 149-155 (May-Junes
19I
6. Benois t., R., J. Labbe and E. Le Grives, "Metro;ogy of
cesium ion propulsion systems," Acta Electronica, 17/4,
435-443 (1974).
13


Manufacture of ionizers intended for electric propulsion

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server