U.S. patent number 3,689,847 [Application Number 05/140,136] was granted by the patent office on 1972-09-05 for oscillator for a cyclotron having two dees.
This patent grant is currently assigned to U.S. Phillips Corporation, New York, NY. Invention is credited to Nico Frederick Verster.
United States Patent |
3,689,847 |
|
September 5, 1972 |
OSCILLATOR FOR A CYCLOTRON HAVING TWO DEES
Abstract
An oscillator for a cyclotron having two accelerating electrodes
which are not connected together. The oscillator comprises two
electron tubes, of which the cathodes are connected together by a
low-loss impedance (capacity or inductance). As a result of this
the oscillator oscillates either with the two accelerating
electrodes in the push-pull mode while excluding the parallel mode,
or in the parallel mode while excluding the push-pull mode.
Inventors: |
Nico Frederick Verster
(Geldrop, NL) |
Assignee: |
U.S. Phillips Corporation, New
York, NY (N/A)
|
Family
ID: |
19810200 |
Appl.
No.: |
05/140,136 |
Filed: |
May 4, 1971 |
Foreign Application Priority Data
|
|
|
|
|
May 29, 1970 [NL] |
|
|
7,007,871 |
|
Current U.S.
Class: |
315/502; 331/56;
331/168; 331/59 |
Current CPC
Class: |
H03B
5/1835 (20130101); H05H 7/02 (20130101) |
Current International
Class: |
H05H
7/02 (20060101); H03B 5/18 (20060101); H05H
7/00 (20060101); H05h 013/00 () |
Field of
Search: |
;328/234
;331/168,56,59 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: John Kominski
Attorney, Agent or Firm: Frank R. Trifari
Claims
1. An oscillator for a cyclotron comprising two accelerating
electrodes, an envelope surrounding the two accelerating
electrodes, two wave tubes each having an inner conductor and an
outer conductor which are shortcircuited at one side, of each of
which on the other side the inner conductor is connected to one of
the accelerating electrodes and the outer conductors of which are
connected to the envelope, two coupling impedances for the two wave
tubes and an electron tube, characterized in that the oscillator
comprises a second electron tube, each electron tube being
connected as an oscillator with a wave tube, an accelerating
electrode and a coupling impedance, a low-loss impedance being
connected between the cathode of the first electron tube and the
cathode of the second electron tube, and being proportioned so that
the oscillator oscillates with the two accelerating electrodes
either in the push-pull mode while excluding the parallel mode
2. As oscillator as claimed in claim 1, characterized in that the
low-loss impedance is capacitive and proportioned so that the
oscillator oscillates with the two accelerating electrodes in the
push-pull mode while excluding the parallel mode.
Description
The invention relates to an oscillator for a cyclotron comprising
two accelerating electrodes, an envelope surrounding the two
accelerating electrodes, two wave tubes each having an inner
conductor and an outer conductor which are shortcircuited at one
side, of each of which on the other side the inner conductor is
connected to one of the accelerating electrodes and the outer
conductors of which are connected to the envelope, two coupling
impedances for the two wave-tubes and an electron tube.
Such an oscillator is known, for example, from the article "The
Design of Cyclotron Oscillators" in "The Review of Scientific
Instruments", vol. 22, nr. Feb. 2, 1951, pp. 84-92.
In a cyclotron having two accelerating electrodes, sometimes termed
Dees, the high-frequency voltages at the Dees must have a phase
difference of 180.degree. relative to each other if atomic
particles in the cyclotron are accelerated by an electric field
between the two Dees mutually. In that case the Dees cannot be
connected together. If atomic particles are accelerated by an
electric field between each of the two Dees and a so-called dummy
Dee present between said two Dees, a phase difference of 0.degree.
is sometimes necessary between the high-frequency voltages at the
dees. It is often desirable not to connect the Dees together,
although it would be possible in this case, so as to enable rapid
commutation to a phase difference of 180.degree..
A Dee with its associated wave tube, may be considered as a
parallel circuit having an inductance L and a capacitance C. It is
to be noted that the term wave tube is to be understood to mean
herein a piece of high-frequency conductor of the type which is
sometimes termed coaxial, although this does not imply either an
exact coaxial state or a constant or a circular cross-section. In a
cyclotron having two substantially identical Dees which are not
connected together, the system consisting of the two Dees with
associated wave tubes may be considered as two identical parallel
circuits which are directly connected on one side and are connected
together on the other side with the interconnection of a
capacitance C' which is small relative to the capacitance C. The
capacitance C' is the capacity between the two Dees. In the cited
article it is calculated that such a system which is consequently
has the same equivalent circuit diagram as a band filter, has two
resonant frequencies, namely angular frequencies of the values
(LC).sup.-.sup.1/2 and [L(C + 2C')] .sup.-.sup.1/2. At the
first-mentioned resonant frequency the voltages across the two
circuits are in phase and there is no voltage across C', and at the
last-mentioned resonant frequency, the voltages across the two
circuits are 180.degree. out of phase and there is a voltage across
C'. It is obvious that, because C' is much smaller than C, both
resonant frequencies do not differ much and that for accelerating
particles the system must be compelled to resonate with one of the
two resonant frequencies while excluding the other.
This first way of the resonating is termed parallel mode and the
second way is termed push-pull mode.
In order to compel a system to resonate in the desirable mode, it
is incorporated, in the described known oscillator in which a phase
difference of 180.degree. is necessary, in a circuit in which one
wave tube is coupled to the cathode and the other wave tube is
coupled to the anode of a triode. In a correctly proportioned
circuit the voltages of the cathode and the anode are exactly
180.degree. out of phase. The known oscillator circuit is
furthermore proportioned so that the voltages at the Dees are also
exactly 180.degree. out of phase.
However, the correct proportioning of such a circuit is very
difficult, in particular due to the large dimensions which
cyclotron oscillators have in connection with the required power.
An additional complication is that the cathode side and the anode
side of the circuit must be constructed differently in connection
with the different output impedances which a triode shows at the
cathode and anode, while at the same time the phase shift in both
parts of the circuit must be the same.
It has therefore been found in the known oscillator that
difficulties often occur with respect to the maintenance of the
correct mode of oscillation, in particular if the frequency must be
adjustable over a certain range.
It is the object of the invention to provide an oscillator for a
cyclotron which is compelled, by a special circuit, to oscillate in
a distinct mode and in which the adjustment of the frequency within
a certain range is possible.
According to the invention, an oscillator for a cyclotron
comprising two accelerating electrodes, an envelope surrounding the
two accelerating electrodes, two wave tubes each having an inner
conductor and an outer conductor which are shortcircuited at one
end, of each of which at the other end the inner conductor is
connected to one of the accelerating electrodes, and the outer
conductors of which are connected to the envelope, two coupling
impedances for the two wave tubes and an electron tube, is
constructed so that the oscillator comprises a second electron
tube, each electron tube being connected as an oscillator with a
wave tube, an accelerating electrode and a coupling impedance, a
lowloss impedance being connected between the cathode of the first
electron tube and the cathode of the second electron tube, and
being proportioned so that the oscillator oscillates with the two
accelerating electrodes either in the push-pull mode while
excluding the parallel mode or in the parallel mode while excluding
the push-pull mode.
The invention is based on the recognition of the fact that, if the
circuit with the electron tubes oscillates in the parallel mode,
the impedance connected between the cathodes passes no current and
hence is inactive because in that case there is no voltage
difference between the two cathodes. In the push-pull mode on the
contrary there is a voltage difference between the cathode and
hence the impedance is active. The circuit arrangement is
furthermore proportioned so that either the operation of said
impedance is necessary to satisfy the oscillation condition, or the
inoperation of the impedance is necessary to satisfy the
oscillation condition.
A favorable embodiment of an oscillator according to the invention
which is to resonate in the push-pull mode is such that the
low-loss impedance is capacitive and proportioned so that the
operation of the oscillator in the parallel mode is excluded.
It is to be noted that from the U.S. Pat. No. 2,701,304 an
oscillator is also known for a cyclotron having two Dees which
comprises two electron tubes (triodes). In this case also a measure
is taken to maintain the correct mode of oscillation. In this
oscillator, however, a wave tube is used having one outer conductor
and two inner conductors which are each connected to a Dee and
coupling loops are used which only comprise magnetic field lines in
the case of the correct mode of oscillation. This construction is
restricted to the coupling by means of loops in the wave tube,
whereas the oscillator according to the invention can also be
constructed with the structurally very simple capacitive
coupling.
In order that the invention may be readily carried into effect, one
embodiment thereof will now be described in greater detail, by way
of example, with reference to the accompanying drawing, the sole
FIGURE of which shows an embodiment of an oscillator according to
the invention with a capacitive coupling. For clarity, the Dees and
the wave tubes are shown slightly diagrammatically. The oscillator
shown as an example is to oscillate in the push-pull mode.
Referring now to the drawing, two Dees (accelerating electrodes)
100 and 200 are arranged in an envelope 2 and have an accelerating
gap 1 between them. The dee 100 is connected to an inner conductor
101 of a wave tube 104. An outer conductor 102 of the wave tube 104
is connected to the envelope 2. A shortcircuit 103 which is
slidable determines the operative length of the wave tube 104. The
dee 200 is connected to a wave tube 204 in quite the same
manner.
High-frequency energy is supplied to the dee 100 via a connection
105 in the wave tube 104 by a part 125 of the oscillator circuit.
High-frequency energy is supplied in the same manner to the dee 200
via a connection 205 in the wave tube 204 by a part 225 of the
oscillator circuit. The parts 125 and 225 of the oscillator circuit
furthermore have a common connection 3 to the envelope 2 which is
connected to earth at 5.
The part 125 of the oscillator circuit is accommodated in a housing
122 which is connected to earth and comprises as an electron tube a
triode 110 having an anode 107, a grid 108 and a cathode 109,
furthermore a coupling capacitor 124, a feedback capacitor 111, a
cathode circuit 126 consisting of a coil 112 and a capacitor 113, a
grid capacitor 118, a grid resistor 119, a choke coil 116 for an
anode supply (not shown) which is connected between 120 and earth,
a capacitor 114 and a connection 123 which is connected to the
housing 122 and is connected to earth with said housing. A filament
supply (not shown) for the cathode 109 is connected between 121 and
earth.
The part 225 is connected in quite the same manner and is provided
with reference numerals which are one hundred larger. The
proportioning is also the same as that of the part 125. The
capacitors 114 and 214 are connected together by means of a
connection 4.
As shown in the drawing, the parts 125 and 225 of the oscillator
circuit are each individually connected as an oscillator. An
impedance between the anode 107 and the cathode 109 is constituted
by the feedback capacitor 111. An impedance between the grid 108
and the cathode 109 is constituted by the cathode circuit 126; in
this connection it is assumed that the grid capacitor 118 forms a
shortcircuit for high-frequency currents. An impedance between the
grid 108 and the anode 107 is constituted by the input impedance,
between the connection 106 and earth, of the wave tube 104
connected in series with the coupling capacitor 124 and a coaxial
transmission line between 105 and 106. It should be noted that the
coil 112 is manufactured from hollow pipe in the interior of which
the connection 115 is provided. In this case the connection 115
with the coil 112 constitutes a coaxial choke coil. If this is not
done, the connection 115 must be constructed as a separate coil to
prevent the cathode 109 from being shortcircuited to earth for
high-frequency currents via the filament supply. In addition it is
to be noted that the grid capacitor 118 and the grid resistor 119
together ensure a negative grid voltage and that the choke coil 116
should be proportioned so that the influence of the same can be
neglected.
It is known from elementary oscillator theory that a circuit having
a triode -- if between anode and cathode a capacitive impedance is
present which is the case here in connection with the feedback
capacitor 111-(211)-- can oscillate only if between the cathode and
grid a capacitive impedance is also present and between the grid
and the anode an inductive impedance is present.
The parts 125 and 225 of the oscillator circuit shown are
proportioned in accordance with the invention so that the cathode
circuits 126 and 226 each have a resonant frequency which lies
slightly above a frequency at which the overall oscillator circuit
is to oscillate. In addition the proportioning is so that circuits
which are constituted by the circuits 126 and 226 with capacitors
114 and 214, respectively, connected parallel thereto, (so if the
connection 4 would be connected to earth) each have a resonant
frequency which lies slightly below the frequency at which the
total oscillator circuit is to oscillate.
Both resonant frequencies of the system of the dees 100 and 200 in
the envelope 2 and the wave tubes 104 and 204, namely in the
push-pull mode and in the parallel mode, lie very close together
and are adjusted by means of the slidable shortcircuits 103 and
203, such that the resonant frequency of the push-pull mode lies
slightly above the frequency at which the total oscillator circuit
is to oscillate. Actually, the impedance between the anode and the
grid (earth) must be inductive. Furthermore, said two resonant
frequencies lie between the two resonant frequencies mentioned in
the preceding paragraph.
With this proportioning the total oscillator circuit can oscillate
only in the push-pull mode. In that case, actually, the connection
4 has earth potential, the capacitor 114 is parallel to the
capacitor 113, and a capacitive impedance is present between the
cathode and the grid of the triodes 110 and 210, which is necessary
for oscillation. In the parallel mode, the cathodes 109 and 209
have the same voltage and the capacitors 114 and 214 are
inoperative, as a result of which an inductive impedance is present
between the cathode and the grid of the triodes 110 and 210 and no
oscillation is possible.
It is to be noted that the capacitors 114 and 214 could be combined
to form one capacitor. From a point of view of manufacture and
equal construction of the housings 122 and 222, however, it is
convenient to use two capacitors. It is to be noted in addition
that in the circuit described the triodes 110 and 210 operate with
a grid which is earthed for high-frequency currents so that no
neutrodynisation is necessary. Of course, the invention is not
restricted to this type of circuit.
All kinds of variations of the circuit are possible, for example,
by using inductive impedances instead of the feedback capacitors
111 and 211, or by using inductive coupling with coupling loops in
the wave tubes 104 and 204.
Inductive coupling also makes it possible to cause the dees 100 and
200 to resonate in push-pull, while the triodes 110 and 210 operate
in the parallel mode. Instead of the capacitors 114 and 214 an
inductive impedance would have to be used in this case. All these
variations fall within the characterizing feature of the invention
that the cathodes 109 and 209 are connected by an impedance which
is not operative in the parallel mode (of the electron tubes) but
is operative in the push-pull mode.
In the circuit chosen as an example, two transmitter tubes
(triodes) are used which have an amplification factor of
approximately 30. The circuit arrangement oscillates at a frequency
of approximately 16 MHz. The values of the most important
components are as follows: feedback capacitor 111 (211):
approximately 100 pF. coil 112 (212): approximately 70 nH.
Capacitor 113 (213): approximately 900 pF. Coupling capacitor 124
(224): approximately 200 pF. Capacitor 114 (214): approximately
1000 pF.
the transmitter tubes convey an anode voltage (relative to the grid
earthed for high-frequency currents) with an effective value of
approximately 7 kV and an anode current with an effective value of
approximately 10 A.
The voltage between the connection 4 and earth can be used as a
signalling and, possibly, safety of the correct mode of
oscillation. This voltage is zero in the push-pull mode of the
triode and equal to the cathode voltage in the parallel mode.
* * * * *