INVENTOR.

METHOD AND APPARATUS FOR THE ACCELERATION OF IONS
Filed Jan. 26 1932 2 Sheets-Sheet . Osci/rr

U Oeflectiuy Field (Volts/Cm) Magnetic FieJd(6ouss)
INVENTOR.

ATTORNEY.
UNITED.STATES PATENT OFFICE
> 94 264
METHOD AND APPARATUS FOR THE
ACCELERATION OF IONS
Ernest O. tatter Berkeley Calif. ass pwr to Research Corporation New York Ni Y„ a awe

aeration of New York cation January 26 1932. Serial No. 689 63 17 Claims. (CL 25I--27)
This invention relates to a method and appa- the production of high speed ions ba successive ratus for the multiple acceleration of ions. The accelerating impulses without necessitating the invention is based primarily upon the cumulative use of an extremely long apparatus such as would action of a succession of accelerating impulses be required by the Wideroe method and to en-
g each requiring only a moderate voltage but even- able the operation to be performed in a compact go
Wally resulting in an ion speed corresponding to or relatively small sized apparatus even for the
a much higher voltage. production of very high speeds with relatively
In order to effect this cumulative action it is light ions.
necessary to cause ions or electrically charged This stated object is attained according to the
10 particles to pass repeatedly through accelerating present invention by causing the ions to travel 66 electric fields in such manner that the motion in curved paths back and forth between a single of the ion or charged particle is in resonance pair of electrodes instead of through a series of or synchronism with oscillations in the electric electrodes in rectilinear arrangement. accelerating field or fields. It has been proposed The movement of the ions or charged particles
16 to produce high speed ions in this manner by in such paths according to the present invention 7o
causing the ions to pass successively in a rec- is effected by the action of a magnetic field by
tillnear path through a plurality of electric fields means of which the moving ions or charged par-
such a method having been disclosed by R. titles are deflected in such manner that their mo-
Wideroe—Archives fur Elektrot. 21 387 (1929). Hon is repeatedly reversed with reference to the
20 The method disclosed by Wideroe is to acceler- electric field between the electrodes and the volt- 76
ate a beam of ions through a series of metal age of such electrodes alternates or oscillates in
tubes arranged in a line and attached alternately synchronism or resonance with the reversal of
to the two ends of the inductance of a high ire- the path of the motion of the particle. The pres-
queney oscillatory circuit. The tubes are made ent invention therefore utilizes the principle of
266 successively longer (proportional to the square resonance of the ions with an oscillating electric 80
roots of integers) so that the time of passage field but overcomes the difficulties inherent in the
through each tube is a constant equal to the use of a long series of tubes by spinning the ions
half period of the oscillating circuit. In this by means of a magnetic field so that the ions move
way it is arranged that during the time of passage successively in opposite directions in an oscillat-
30 of the particle through one of the tubes the elee- ins electric field in curved paths and in reson- 36
tric field between successive tubes undergoes a tee with the oscillations of the field whereby an
half cycle that is a reversal of direction so that extremely large number of accelerating impulses
the particle experiences a force in the same direr- can be produced in a comparatively limited space.
tion each time it passes from one tulle to the next The accompanying drawings illustrate an ap-
35 Thereby an ion arrives at the end of the series paratus suitable for carrying out my invention go of tubes with an energy which is equivalent to the and referring thereto:
sum of the potential drops through which it has Fig. 1 is a diagrammatic elevation and
.•
passed. Fig. 2 is a diagrammatic section of a means
The method developed by Wideroe as above re- for producing electrostatic and magnetic fields
to ferred to has been successfully demonstrated for for effecting the successive repeated accelerations g5 heavy ions for example he succeeded in producing accordingto the present invention; potassium ions having equivalent voltages double Fig. 3 is a side elevation of an apparatus em-the maximum voltage applied to the vacuum tube bodying the invention;
and at the University of California this method Fig. 4 is a vertical section of such apparatus;
45 of rectilinear acceleration has been further de- Fig. 5 is a section on line 5—5 in Fig. 4 said 3W veloped so that ions have been produced having figure also showing diagrammatically the eleeenergies corresponding to 30 times the voltage trical circuits energizing and controlling the apapplied to the tube. This method is conven- paratus;
iently applicable in practice only to fairly heavy Figs. 6 and 7 are graphs illustrating the results
5o ions: for relatively light ions say up to an atomic of the operation of my invention. 105
weight of 25 or 30. the necessary length of the The general principle or mode of operation of
tubes because of the high speeds of the ions the invention will be described with reference to
would be so great as to make it impractical. Figs. 1 and 2 wherein is shown the essential ap-
The main object of the present invention is to paratus for carrying out such mode of operation
65 provide a method and apparatus which will enable said apparatus comprising a pair of electrodes 1 1 g
2
and 2 for establishing the required electric field and magnet means 3 for establishing a magnetic field for reversing the motion of the ions.
Electrodes I and 2 are shown as consisting of
b approximately semicylindrical hollow metal plates or members closed at each side and at their peripheral portions but with their diametral portions open and facing one another. The respective electrode members 1 and 2 are connected to
10 means indicated at 4 for maintaining the required alternating or oscillating electric potential difference between said members.
The magnet means 3 may consist of any suit-able magnet having two pole pieces arranged on
15 opposite sides of the members 1 and 2 so as to produce a uniform magnetic field the lines of force of such field extending transversely to the electrodes 1 and 2 and normal to the plane of the electric field between the electrodes.
20 Suitable means are assumed to be provided for supplying ions or electrically charged particles to the space between the electrodes 1 and 2 for ex-ample near the center of the electric field. It will be understood that the effective electric field
25 is substantially confined to the space between the diametral faces of the two electrodes the space within each hollow electrode being of approximately uniform potential and therefore of zero electric field it being further understood how-
30 ever that some electric lines of force may be considered as extending into such hollow spaces within the electrodes to a limited extent as hereinafter explained.
If an Son is present in the diametral region
35 between the two electrodes it will be attracted
to the interior of the electrode having the op-
posite charge. For instance consider a hydro-
gen molecule ion 112+. If electrode 1 is nega-
tively charged the ion will be attracted to it
40 gaining a velocity from the field and passing
into the field free space inside electrode 1. Un-
der the influence of the strong magnetic field
at right angles to its path the ion will travel
in a circular path inside electrode I eventually
45 arriving again in the region between the pair
of electrodes. Now it is evident that if the in-
itial impulse is imparted at time ti and the
particle arrives back between 1 and 2 a time t2
exactly a half cycle later it will find the field
50 between 1 and 2 reversed and will experience an
acceleration toward 2. The time required for
the particle to traverse a semi-circular path in-
side the electrodes is the same for all velocities.
This becomes clear when it is recalled that the
55 radius of a circular path on which a charged
particle travels is proportional to its velocity. If
then the particle arrives from electrode 1 into
the region between 1 and 2 a half cycle later
it will experience a second increment of velocity
60 on passing into electrode 2 where again it will
traverse a semicircular path of larger radius ar-
riving between 2 and 1 again another half
cycle later and again receives another acceler-
ation into electrode 1. Thus for this resonance
65 condition the process continues the particle
gaining velocity with each passage through the
region between the electrodes until it arrives at
a collector placed at the outer edge of the mag-
netic field. The effect of the above-described
c operation is to cause the particle or ion to move
in a curved path in a plurality of revolutions in
an alternating or oscillating electric field within
the space enclosed by the hollow electrodes 1
and 2 in such manner that its path forms an-
_c proximately a spiral of increasing radius the
particle being continually deflected by the action of the magnetic field thereon so as to revolve around the axis or center of the field and the period of half revolution as determined by the strength of the magnetic field coincides or 80 is synchronous with the period of alternation or oscillation of the electric field so that the particle or ion is repeatedly accelerated at successive half revolutions by the action of the electric field. 85
It will be understood that in order for the ion or charged particle to be accelerated in the manner above described it is necessary that the space traversed by the particle shall be sufficiently free
of other particles to prevent any substantial dim- 90 inution in its velocity by reason of collision with such other particles. For this purpose it is necessary that the electrodes between which the electric field is maintained shall be inclosed in a suitable means within which a high degree of 95 evacuation is maintained. It is also necessary to provide suitable means for establishing resonance or synchronism between the alternating electric field and the reversal of motion by the magnetic means. In operating upon light ions 100 the frequency of alternation required is such that it may be conveniently supplied by a high frequency oscillatory circuit.
Figs. 3 to 5 of the drawings illustrate an apparatus which has been successfully used in 105 carrying out the invention and which embodies the principle of operation above described.
In said apparatus two electrodes 6 and 7 are provided electrode 6 being in the shape of a hollow semicylindrical metal plate as above de- 110 scribed and electrode 7 being shown as consisting of metal bars spaced apart a distance equal to the distance between the two side walls of member 6. Both of said electrodes are inclosed within an air tight casing 8 which may be of 115 metal and is mounted in any suitable manner between the pole pieces 9 and 10 of the magnet 11.
The electrode member 6 is insulated from the casing 8 being for example supported by a rod 120 12 connected to the semicylindrical peripheral wall 13 of the member 6 and mounted at its outer end on an insulator 14 which is supported on the casing 8. The casing 8 may be supported on the pole pieces of the magnet or in any 125 other suitable manner.
The electrode means 7 is supported at its ends on the casing 8 and is preferably grounded through said casing.
A connection or conduit 15 leads from the in- 180 terior of casing 8 to a suitable vacuum pump for maintaining the necessary high vacuum within the easing and a connection 16 may be provided for introducing into the easing a regulated amount of a gas such as hydrogen for example. 135
In this form of the invention the high frequency oscillating electrical field is maintained between electrodes 6 and 7 by applying to the insulated electrode 6 a high frequency oscillate
ing potential for example by means of an oscilla- 140 tory electrical circuit such as illustrated in Fig 5 the rounded electrode 7 being connected through the easing to one side of said oscillation circuit.
The oscillation circuit 18 may be of any suitable 145 type comprising an oscillation tube 19 and suit-able capacity and inductance means constituting an oscillator having a definite frequency the input of said oscillator being connected to an griergizing circuit 20 and the output of the mail- 150
1 948 884
later being connected by wires 22 and 23 respec- collector box 51 being provided for receiving the tively to supporting rod 12 for electrode 6 and to ions only when they follow such definite path. electrode 7 through grounded casing B. Insulated collector box 51 is connected to a cur-
The energizing circuit for the oscillator may be rent measuring means 53 shown ac an electrom-
6 of any suitable type comprising for example eter with high resistance shunt and having 80 means including thermionic tubes for rectifying ground connections so as to measure the cur-alternating current and supplied from a service rent draws% from the collector box such cur-line 24 and adapted to apply unidirectional cur- rent being proportional to the number of ions rent to the oscillator for energizing the latter. collected. The electric field strength required
10 The oscillator and energizing circuits shown are for deflecting the ions the required amount in 85
of well known type the connections for energize passing through the channel between electrodes
ing the filaments In the thermionic tubes being 40 and 41 is proportional to the kinetic energy
omitted. due to the speed of the ions and by adjusting
The magnet 11 is preferably an electromagnet the voltage between electrodes 40 and 41 for
16 energized by connections 26 and 27 from a direct maximum current from the collector box it is 90 current circuit said connections including an possible to determine from measurement of such ammeter. 28 and a variable resistance or current voltage the speedof the ions as they leave the controlling means 29 whereby the energization magnetic field.
of the magnet may be variably controlled so as I have also shown at 52 means for controlling
20 to bring the period of reversal of motion of the the magnetic field at a definite. part of the path 95
charged particles into resonance with the free of the ions to assist in withdrawing the ions
quency of the oscillating electrical field. from such field the means 52 consisting of a
Ions may be supplied to the apparatus described channel member of soft iron whose channel 52' by any suitable means. For example as shown in is located in line with the path of the ions issuing
25 the drawings a filament 30 may be mounted with- from the channel between electrodes 40 and 41 100
in the casing 8 adjacent the space between the and serves to reduce the magnetic field intensity
electrodes 6 and 7 said filament being eonnected at such point so that the ions deviate outward-
by conductors 31 and 32 to an energizing circuit ly from the magnetic field by reason of their
including battery 33 adjustable resistance or own momentum. The means 52 may be used
30 current controlling means 34 and ammeter 35. either in conjunction with or instead of the de- 105 The filament circuit as a whole is preferably fleeting electric field means 40 and 41. insulated and maintained at a suitable negative The high speed ions produced by the opera-potential for example by means of a battery 36 tion of the above described apparatus may be of say 200 volts connected between said circuit utilized in any suitable manner for example for
g6 and the grounded connection 37. application to the disintegration or synthesis of 110
Means are provided for withdrawing the ions atoms or for general investigations of atomic from the magnetic field at a definite point in the structure or for therapeutic investigations or circulatory motion thereof. For this purpose applications. For such purposes the high speed I have shown electrode means 40 and 41 defining ions may be delivered from the apparatus for
40 an electric field adapted to receive the ions and example by passing through a window 55 of mica 115 to deflect same outwardly from the magnetic or other suitable material in the wall of casing field. Electrode 40 is shown as a metal mem- 8 it being understood that the collector box 51 ber mounted within casing 8 and grounded by may be removed or omitted in that case so that connection to said casing and extending in a curve the ions pass unobstruetedly to the window 55 which is tangent to the curved path of the ions and thence to any suitable means for utilization 120 in the magnetic field but deviates outwardly there- of same. Window 55 or other equivalent means from. Said member 40 is shown as formed with serves as a means for withdrawing and receiving semicircular walls 42 extending therefrom sub- the accelerated ions while permitting the ions to stantially in the planes of the respective side maintain substantially the high speed produced
w0 members of electrodes 6 and 7 so that the ions by the repeated accelerations. 125
may circulate in spiral paths within the space The apparatus shown in Figs. 3 4 and 5 oper-
defined by members 6 7 and 42 such spiral paths ates upon the principle above described in con-
increasing in distance from the center of circula- neetion with Figs. 1 and 2 it being understood
tion until they pass to the outside of the mem- that the electric field in this case is maintained
.h5 ber 40. Electrode 41 is formed as a metal strip between the grounded electrode 7 and the in- 13C
curved in parallelism with electrode 40 and sulated electrode 6 and that the reversal of the
mounted on an insulated post 43. In case posi- oscillatory electric field is effected each time the
tive ions are being operated upon the electrode ions pass through the space between said elec-
41 is maintained at suitable negative potential trodes. It will be understood that instead of
co to draw the ions outwardly from the magnetic the grounded electrode 7 another insulated elec- 135
field. The supporting post 43 for electrode 41 trode opposite electrode 6 and similar in con-
is shown as connected by wire 44 to a potenti- struction thereto may be employed as illustrated
ometer 45 connected to a unidirectional source in Figs. 1 and 2 and in that case the energy of
of suitable voltage for example 1 000 volts an acceleration would be double that which can be
65 electrostatic voltmeter 46 being provided for obtained with a single insulated electrode as 140 measuring the voltage applied between electrode shown in Fig. 5.
41 and the grounded electrode 40. In the operation of the apparatus shown in
The electric field producing means described Figs. 3 to 5 the ions are generated in situ in the may also be used for measuring the speed of the space between the electrodes 6 and 7 by the op-
'C ions as they traverse the channel 47 between eration of electrons emitted from the heated :.#b
electrodes 40 and 41 by measuring the potential filament 30 said filament being preferably main-
difference between electrodes 40 and 41 required tamed at a moderate negative potential say
to deflect the ions in a definite path between in- about 200 volts and being preferably partly in-
let opening 49 and outlet opening 50 of said closed by a housing 57 in electrical connection
75 channel suitable means such as an insulated therewith and open on the side toward the space 150
4
between electrodes 6 and 7 so that electrons are overcomes the effects of stray fields and space ntbject to the action of an electric field tending charge and the like which would tend to cause to force the electrons through the opening into a divergence of a beam of ions spiraling around. the space between electrodes 6 and 7. The space Of course this type of an electric field between
5 within the easing 8 is evacuated to a suitable de- the plates also tends to prevent the spreading of 80 gree for example to a pressure less than 10-' the ion beam in the plane of the plates at right atmosphere and a gas for example hydrogen is angles to the magnetic field as well but this is admitted to said space in regulated manner so not so important because a slight tendency of the as to maintain the desired degree of vacuum and ions to move in a direction which is not exactly
10 at the same time supply a sufficient number of perpendicular to the diametral plane is not quite 85
molecules for production of the ions in the de-so important. This focusing action is a feature
sired amount. The electrons emitted from the of the process which makes it so effective and
filament operate by impact upon such molecules indeed makes it possible in this way to speed up
to produce ions and the results obtained indicate a large proportion of the ions generated in the
16 that both molecular ions and protons are pro- diametral region between the pair of plates. 90
duced. It has also been found that the effect In addition to the focusing by the electric field of the magnetic field is to concentrate the beam as above pointed out there is a focusing action of electrons from the filament into a relatively due to curvature of the magnetic field adjacent limited zone extending from the hottest portion the peripheral portion of such field such curve-
20 of the filament normally to the plane of the ture being shown in Fig. 2 where the magnetic 9$
electric field so that the zone of production of lines of force are indicated by the dash lines m
the ions is rather sharply defined. The ions and resulting in deflection of the circumferential-
produced in this manner are then subjected to ly moving ions so as to impart a radial inward
the multiple acceleration as above described by component of motion as shown by the heavy ar-
25 the successive operation of the electrical field rows the effect of which is to concentrate the 100 thereon the magnetic field serving to maintain paths of the ions toward the medium plane a—a the curved path of the ions necessary for such of the electrode system.
successive operation of the electrical field. The production of the ions required for the
When one considers the spiraling of the ions above described operation may be effected in any
30 back and forth from one hollow electrode to an- suitable manner and in the form of the apparatus 105
other on ever widening paths and estimates the above described this has been effected by main-
distance the ions travel in their course it may ap- taming the electrodes in an atmosphere of the
pear at first sight that only an exceedingly small gas at such a pressure that the ions are able to
fraction of the ions starting will arrive at the traverse the course of their spiral paths without
35 periphery of the apparatus. A superficial view of too great scattering and to cause a beam of elec- 110
the matter would suggest that the electric field teens to pass down between the pairs of plates
between the pairs of plates and the magnetic ionizing the gas and thereby forming the ions
field would have to be very precisely perpendicu- in situ. In the laboratory at the University of
lar to each other and that the interior of the California using this method approximately its
40 plates would have to be field free to a high order of one micro-ampere of protons were caused to 115
of magnitude so that the ions would experience spiral around approximately 50 times gaining
forces only tending to keep them in a plane in an energy corresponding to % of a million volts
the interior of the plates. In fact consideration in this way. That is to say z'a a micro-ampere
of this matter might lead one to believe that it of protons were produced having energies 200
45 is a requirement that is practically impossible to times that corresponding to the maximum voltage 120 achieve. It is therefore to be emphasized par- applied across the electrodes.
ticularly that this requirement has been so ob- Another method of producing ions would be viated that in the experimental tests of this of course the well known discharge tube method method it was found that a very satisfactory wherein a hot cathode discharge would be main-
50 portion of the ions starting the spiral paths reach tamed in the gas at fairly high pressure and the 125
their ultimate goal. ions let out into the region between the pairs of
Consideration of Fig. 2 shows the important plates through a suitable canal; and with a suit-feature of the experimental arrangement which able pumping arrangement pressure difference gives a focusing action of the ions keeping them between the discharge tube and the region of the
55 approximately in a plane central and parallel to pair of plates could be made as great as desired. 130
the plates. In this figure dotted lines e show A third method for the producing of protons
qualitatively the way the lines of force of the and H molecule ions is that of Dempster who has
electric field extend between the electrodes in found that protons are emitted when lithium
the part of the field under consideration other metal is bombarded by electrons. In this in-
00 lines of force being omitted the shape and posi- stance the lithium could be placed in the region 135 tion of the electrodes being such that the lines between the plates and suitably bombarded with of electric force converge from within each elec- electrons. There is also available the method of trode toward the central part of the other elee- gunman for the production of alkali ions. trode. A dot and dash line p shows in a quali- By means of apparatus constructed and oper-
95 tative manner also the effect of the electric field ated as above described it has been possible to ob- 140
on an ion traveling in a plane which is near the taro high speed ions of a voltage of 1 million. The
side walls of the electrodes that is away from following mathematical analysis is given as ex-
the central plane a—a. As the ion approaches plaining the fact that the frequency of reversal
electrode 1 it not only experiences an acceleration by operation of the magnetic field is constant '?3 towards 1 but an acceleration at right angles to-
wards the center plane. An electric field of this throughout the circulation of the ion in said 145 form thus produces a focusing action which keeps field and therefore can be maintained in resothe ions traveling approximately in the central nance with a definite frequency of oscillation of part of the region of the interior of the plates. the accelerating electric field. It may be stated This focusing action is a very strong one and that the results of actual operation of the appa- 150
        5
ratus agree with the estimated velocities derived from this analysts.
The two forces acting to keep the ion in equilibrium while traversing this path are the centrifu-
I gal force due to its circular motion and the force due to the magnetic field. A charged particle moving with a velocity v in a magnetic field H experiences a force at right angles to the direction of its motion and to the magnetic field given
10 by the relation
nev F= c
where c is the velocity of light and e the charge of the particle. The centrifugal force due to the
15 motion of a particle of mass in in a circle of radius r Is
(1)
f0 Equating we obt
rase* F=-