Selector mechanism for mechanical separation and discrimination of high velocity molecular particle

Steinberg, R.

English

NASA Technical Reports Server

NATIONAL AERONAUTICS AND SPACE ADMINISTRATION 
WASHINGTON. D.C. 20546 
REPLY TO 
ATTN OF: GP 
TO: 
FROM: 
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 forwarded 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 Case NO.: X~~-01533 
~ a y l e  Parker 
Enclosure: 
Copy of Patent 
-.I 1; RECEIVED 
- MSA srr Fncrun * 
LL 1 
(THRU) 
- (CODE) 
I f I 
NASA-HQ 
https://ntrs.nasa.gov/search.jsp?R=19710001303 2020-03-17T02:34:44+00:00Z
Nov. 1, 1966 R. STEINBERG 3,282,035 
MOLECULAR BEAM VELOCITY SELECTOR 
Filed Dec. 30, 1963 
FIG. I 
BY 
3,282,035 United States Patent Oace Patented Novm 1966 
It  is still a further objeot of this inventrion to provide an 
3,282,035 improved velocity selector having extremely hlgb resolu- 
MOLECULAR BEAM VELOCITY SELECTOR tion characteristics. Robert Stehberg, Berea, Ohio, assignor to the United A more complete appreciation of &e invention and States of America as represented by the Administra- 
tor of fie N~~~~~~~ Aeronautics Space Adminis- 5 many labtendant a~dvantages thereof will be more readily 
tration appreciated as the same becomes better vnde~rstood by ref- 
Filed Dec. 30,1863, Ser. No. 334,678 erence to the ~ollowing detailed description when consid- 
8 Claims. (Cl. 55-400) ered in wnnection with the accompanying drawing 
wherein: 
The invention describled herein mlay be manufactured 10 FIG. 1 is an elevation view partly in section of the 
and used by or for the Government of the United States molecular beam velocity selecbor with the selector cover 
of America for governmental purposes without the pay- removed. 
ment of any royalties thereon or  therefor. FIG. 2 Cs a curve of maximum velocity of transmitted 
The present invention relates generally to  molecular beam as a function of velocity resolution. 
beam velocity selectors and, more particularly, to a molec- 15 Aocording b the present invention, the foregoing and 
ular beam velocity selector which may be utilized for par- other objects are !obtained by the provisrorz of a novel 
ticles with velocities up to 40,000 meters/second. molecular beam velocity discriminator. The selector 1s 
Research in rarefied gas dynamics using mdecula~r mounted on a ver(tica1 axis and utilizes a tapered disk to 
beam techniques have important applications to space p~ermit extremely high rotational speed and at the same 
technology since such investigations can aid in the de- 20 time to offer an extremely stable configuration. Eongi- 
(termination of the variation of atmospheric conditions tudinal slots #disposed in the disk provide passage for the 
with altitude in the upper seations of the earth's atmos- accelerated particles while disoriminat~ing against tile 
phere. For example, heretofore experimental data on the slower moving particles. The (disk is, advantageorrsly, 
drag coefficients of spheres undsr the low densilty anld high made of aluminum or titanium (depen~ding on required 
velocity conditions corresponding to earth satellite orbits 25 operational speed) to provide a high strength to weight 
was not available anld it  has been necessary ito rely on ratio an'd a stablie base upon which the slots are formed. 
theoretical predictions of spbere dtrag in o~rder to arrive The slots are produced by a n  electnical discharge wa- 
at atmospheric density values from satellilk tracking data. chine so as to insure minimum slot width and close spac- 
It  thus becomes necessary to check the theoretical drag ing for good resolution. The selector disk is rotatably 
coefficient data experimentally in order to place confidence 30 mounted in a lower bearing formed by a pin riding in 
in the density data which has been obtained from several a cup-like depression and is vertically held m this posi- 
satellites curren~lly in orbit. tion by an upper bearing assembly formed by the center- 
Molecular bleam scattering expc~iments provide a pow- ing of a pair of magnets one being fixed to the disk and 
erful method for the investigation of the mechanism the other dampeningly suspended from a fixed suppoi t. 
whereby the neutral molecules of ia rarefied gas exchange 35 Rotation is imparted to the particle selector by a cir~ular  
momentum and energy during collision with a solid plate fixed to the tapered disk imd magnetically coupled 
source. However, conventional molecular beam sources to the windings of an electric mo.tor. 
do not provide the larger n~olecular energies correspond- Referring now to FIG. 1, there is shown the novel molec- 
ing to satellite velocities. Consequently, it is required that lar particle discriminator which forms the instant in- 
beams be produced by the electrostatic acceleration of 40 vention. The discriminator is indicated, generally, by the 
ions. Unfortunately, space charge difficulties limit the numeral 10 and includes a velocity selector subassembly 
attainable beam intensity at low energy. Newrrheless, 12 amounted for rotation in a vertical plane by upper 
the neutralized ion molecula~ bleam source appears to  bz and lower bearing subassemblies 141 and 16, respectively 
an attracttive method of evaluating experimentally the A tdtamping mechanism 18 is disposed above the upper 
laerodynamic drag on a solid surface subjected to the en- 45 bearing assembly and is provided to prevent vibration at 
vironment corresponding to a satellite orbit. resonance, while a drive system 2@ rotatabl~~ drives the 
Neutralization of the ion beam by charge exchange in discrimina~bor disk assembly. 
the parent gas can be acwmplished either by passing the The selector subassembly 12 mrnp~ises a disk 22 hdv- 
beam through a differentially pumped gas cell or by cross- ing tapped upper and lower faces 24, 26 to insure dimen- 
ing the ion beam with la jet of the parent gas. The use 50 sional stability at the extremely high speeds at  whrch the 
of the gas jet methiod 'of beam neutralization while main- disk rotates (up to 125,000.r.p.m.). Either @Iuminum or 
taining a low pressure in the vicinity of the test sudace titanium may be utilized in forming this disk, both being 
requires large pumping speeds relative to the gas cell satisfactory materials for this purpose smce they exhibit 
method. As a consequence, this method is less attractive a high strength to weight ratio and are stable and thus 
than the gas cell method, however, the gas cell method 55 cap~able of having closely space sllots formed themin. In- 
presents la problem as a result of the gas emerging from tegral with the upper dace of the ldis'k, an upper stub 28 
the exit aperture along with the neutralized beam. The is provided for connection of the upper bearing assenlbly 
force on the (test surface ,due to these slow mfoving gas Similarly, a lower stub 30 is provided in the bottom face 
molecules can easily be larger than the force due the 6o of the disk for attachment of the lower bearing assembly 
molecular beam itself. One method of greatly reducing Helical slots 32, formed in the rim or periphe~y 34 
this background force is the use of a mechanical chopper of the disk 22 provide passage for the higher velocity 
$to discriminate lagainst the slow gas molecules from the molecular particles while a t  the same time preventing 
gas cell relative to the faster beam molecules. passage of b w  velocity molecules. These slots ale de- 
Accordingly, it  is an objewt of this invention to provide 65 fined by land portions 36 and depressed, groove portions 
a mechanical separation and discrimination apparatus for 38 situated around the rim 34 of the disk. Although 
molecul~ar particles. these slots may be formed by carefully controlled sawing 
It is an additional object of this invention to provide by, for example, a circular saw, the slots formed by this 
a molecu,iar beam velocity selector capable of selecting method must have rather large separations or land por- 
particles of very high velocities. 70 tions between them, thereby reducing selector transmis- 
3,282,035 
3 4 
sion. A inrich piefelred method of slot formation is Ziavels the length L of the slot 32. It should l?c obviouc 
accomplished by the use of ,;:I electric discharge ma- that high rotat~onal speed is required for the extended 
chine. The slots formed by this nlelhod are on the range particles unless resoit is had to selectors of extreme 
order of 8 . 8 9 ~  10-3 cm. wide, with the space between and cumbersome length. 
slots being on the same order since the electrode which 5 The instant invention is capable of a peripheral velocity 
form5 the slot ilever conies iii contact will; ;he slot wa!! ~f 800 m./sec. (100,900 1.p.m ) when nr? aluminum se- 
and therefore does not prestress the disk material. Be- lector disk is utilized and 1,000 m./sec. (125,000 r.p.m.) 
cause of the narrow slot width, high resolution is obtained when a titanium disk is utilized. Turning to FIG. 2, it 
and, additionally, the rougher slot formed by an electric can be seen that extremely good velocity resolution is 
discharge machine advantageously also provides a 10 obtained with either disk material, the numerals 72, 74 
ro~~gher  slot swface which reduces wall scattering prob- indicating the characteristics of aluminum and titanium 
lems. material disks, respectively. The percent velocity reso- 
Fixedly attached to the upper stub 28 is a permanent lution (abscissa) extends from about 1-10% (dependent 
magnet 40 which forms a part of the upper bearing on beam velocity) and indicates the relative measure of 
assembly. This portion of the bearing assembly centers 15 non-uniform velocity particles passing through the se- 
on an upper magnet 42 suspended thereabove to provide, lector in relation to  the number of uniform velocity 
as the disk rotates, a non-engaging mating surface there- particles. 
between allowing magnet 40 and the attached tapered While a preferred embodiment of the invention has 
disk to Aoatably rotate at the upper bearing with only been disclosed and described, it will be appreciated that 
the magnetic force between the two magnets attracting, 20 various modifications may be made to the disclosed 
centering, and partially suspending the tapered disk. structure without departing from the spirit of the inven- 
Mounting the upper magnet 42 is a circular disk 44, tion or the scope of the subjoined claims. For example, 
this disk forming a portion of the upper bearing assem- the helical slots 22 may be replaced by straight slots 
bly and also providing an attachment area for the beaded where a very small helical angle is reqt~ired for resolution 
chains 46, 46, 46, disposed at 120" angular spacing 25 and then the molecular beam source inclined at this 
around the disk. The upper ends of these chains are angle relative to the rotational axis of the discriminator. 
attached to the cover 48 of the selector (shown only What is claimed is: 
fragmentarily) to  again insure free centering of the 1. A molecular beam velocity selector comprising: 
magnets 40, 42 and also to provide a slight damping a vertically supported disk having tapered upper and 
force for the upper bearing assembly 14. The cover, 30 lower faces and an outer rim composed of longitudinally 
of course, provides a vacuum tight shell and a shrapnel extending land and groove portions whereby said disk 
retainer in the event of disk failure. has optimum dimensional stability at high rotational 
The damping mechanism 18 is also attached to the speeds; a first permanent magnet attached to the upper 
disk 44 and consists of three right-angled arms 50, which face of said disk; a second permanent magnet dampingly 
are arranged in depending relation therefrom to extend 36 suspended above said first permanent magnet; a needle- 
into oil filled perforated portions 52 of a damping plate like pin bearing extending outwardly from the lower 
54. The damping plate 54 is fixed to and supported face of said disk; a cup-like bearing surface disposed be- 
from the cover 48 in any convenient manner such as by neath said pin bearing; and driving means attached to 
studs 58, and is provided with a bore 56 which, as can said disk for driving the same at extremely high rota- 
be easily seen in FIG. 1, prevents interference with the 40 tional speeds. 
upper bearing assembly 14. 2. Apparatus for selecting particles of predetermined 
Beneath the tapered disk the lower bearing assembly high velocities up to 40,000 meters per second emanat- 
16 is disposed, it includes needle carrying bushing 60 ing from a source while discriminating against particles 
attached to the lower stub 30 by threads or the like, a having other velocities comprising: 
needle bearing 62 and cup-like bearing race 64 disposed 45 a discriminator of a rigid material comprising a disk 
on lower bearing member 65. The needle bearing 62 having tapered upper and lower faces t o  insure di- 
is fixedly attached to the bushing 60 to depend into and mensional stability at high rotational speeds be- 
contact the bearing race 64 to provide a bearing having tween 100,000 r.p.m. and 125,000 r.p.m., said disk 
very low friction losses. The lower bearing member 65 having a plurality of longitudinally extending slots 
is supported by any convenient connection (not shown) 50 spaced about the periphery thereof to provide pas- 
attached to or integral with the cover. sages for accelerated particles from the source, 
Tapered disk 22 is capable of being driven at very drive means for rotating said discriminator so that 
high rotational speeds by a hardened steel, drive plate particles having a predetermined velocity pass 
66 which is held rigid with the tapered and slotted disk through said slots while particles having other veloci- 
22 by shoulder 68 on bushing 60. Magnetically cou- 55 ties impinge on the sides of said slots, and 
pled to this plate is the drive coil '70 which is the field means for mounting said discriminator for rotation 
coil of a three-phase motor (not shown), the drive coil about a vertical axis thereby enabling said drive 
inducing eddy currents in the d ~ i v e  plate to cause the means to  rotate said discriminator at extremely high 
velocity selector to rotate at high speed. rotational speeds with a minimum of vibration near 
In operation, the upper and lower bearing assemblies 60 the yield point of said rigid material. 
14, 16 in conjunction with the damping mechanism 18 3. Apparatus as claimed in claim 2 wherein the dis- 
permits extremely high selector rotational speeds without criminator comprises a lightweight metal disk providing 
excess vibration. Because of this vibrationless motion a high strength to weight ratio and a stable base for the 
the tapered disk 22 may be operated near the yield point slots. 
of the material from which it is formed to permit dis- 65 4. Apparatus as claimed in clairn 3 wherein the dis- 
ciirnination of molecules of the higher velocities. criminator comprises an alum~nnm d~sk,  and 
To select molecr~les of a partrcirlar velocity, rhe n-toiec- the drive means includes a rnagnct~c coupling for 
ular beam source 1s d~rected at the bottom face of the rotating said aluminum disk at about 100,000 levo- 
tapered d~sk.  The velocity of the moiecules success- luiions per minute wi~eieby the peripheral velocity 
fully traversing the slots 32 is given by the expression 70 of the discriminator at the slots is about 800 meters 
tu L per second. IT,,,= -- + 5. Apparatng as claimed in claim 3 wherein the dis- criminator comprises a titanium disk, and 
where iv is the angular velocity of the rotor and g, is the drive means includes a magnetic coupling for ro- 
the angle through which the rotor turns while a particle "6 tating said titanium disk at about 125,000 revolu- 
3,282,835 
5 6 
tions per minute whereby the periplleraf velocity of References Cited by the Exan~f~zer 
the discriminator at the slots is abo-i~i 1006 meters UNITED S U T E S  PATENTS per second. 
6. Apparatus as claimed in claim 2 wherein the diive 1~700~928 2'1929 Fawkes ------------ 55-17 * 
means comprises, 3,097,167 7/1963 Beyerle ------------- 233-23 
an electric ii~otoi haying a fieid coil, 3,216,655 11/1965 Wind et a1 ---------- 233-27 
a drive plate rigidlv secured to the discriminator and 3,219,265 11/1965 LOS et al. ------------ 233-27 
magn~tically coupled to said field coil whereby eddy FOREIGN PATENTS 
currents induced by said field coil in said drive plate 1,293,g38 4/1962 France, 
rotates said discriminator at high speeds. 
7. Apparatus as claimed in claim 2 wherein each of 10 985,668 3/1965 Great Britain. 
the longitudinally extending slots about the periphery of OTHER REFERENCES 
the discriminator have a helical configuration formed by Hostettler, H. U., et al.: "Improved Slotted Disk Type 
an electrical discharge machine thereby insuring mini- Velocity Selector for Molecular Beams." The Review 
mum slot width and close spacing for good resolution and 15 of Scientific Instruments, vol. 31, number 8, pp. 872-877, 
a relatively rough surface to reduce wall scattering. August 1960. 
8. Apparatus as claimed in claim 7 wherein each of Miller, R. C., et al.: "Velocity Distributions in Potas- 
the helical slots have a width of about 8.89X centi- sium and Thallium Atomic Beams." Physical Review, 
meters and the spacing between said slots is substantially vol. 99, number 4, pp. 1314-1321, August 15, 1955. 
'he same as the width of said slots for high resolution. 20 
ROBERT F. BURNETT, Primary Examiner. 


Molecular beam velocity selector Patent

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