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_LRL Accelerators_




THE 184-INCH SYNCHROCYCLOTRON


LAWRENCE RADIATION LABORATORY

UNIVERSITY OF CALIFORNIA, BERKELEY, CALIFORNIA


Pub. No. 2d

5M
June 1964


[Illustration: Synchrocyclotron Building]




_Contents_


                                                                    Page

THE 184-INCH SYNCHROCYCLOTRON                                          2

PRINCIPLE OF OPERATION OF A CONVENTIONAL CYCLOTRON                     3

THE PRINCIPLE OF PHASE STABILITY                                       6

DESIGN AND CONSTRUCTION OF THE 184-INCH SYNCHROCYCLOTRON               8

  Magnet                                                               8

  Vacuum System                                                        9

  Ion Source                                                          10

  Radiofrequency System                                               10

  Internal Targets and Beam Extractor                                 12

CYCLOTRON EXPERIMENTS                                                 15

  Nuclear Physics                                                     15

  Biophysics                                                          18

  Nuclear Chemistry                                                   19

BIBLIOGRAPHY                                                          20

APPENDIX                                                              21




THE 184-INCH SYNCHROCYCLOTRON


His success with the 60-inch cyclotron in 1939 led Dr. E. O. Lawrence to
propose a much more powerful accelerator, one which could produce new
types of nuclear rearrangements and even create particles. Grants
totaling $1,225,000 permitted work to start on the 184-inch cyclotron in
August 1940.[1] It was designed to accelerate atomic particles to an
energy of 100 million electron volts (Mev), five times that possible
with the 60-inch machine.

[Illustration: Fig. 1. The electromagnet under construction during the
period 1940 to 1942.]

Before the new cyclotron could be finished World War II began.
Construction on the cyclotron was therefore halted. However, because of
interest in separating the isotopes of uranium by the electromagnetic
method, work on the giant magnet continued at an even faster pace. This
magnet would contain 3700 tons of steel in its yoke and pole pieces, and
300 tons of copper in its exciting coils (Fig. 1). By May 1942 the
magnet was completed. During that summer it was used in a pilot plant to
separate the first significant amounts of U^{235} ever obtained. The
184-inch magnet remained in use in a research and development program at
Berkeley until the end of the war, supplying information to Oak Ridge,
Tennessee, where a large separation plant had been erected.

Construction on the rest of the cyclotron was resumed in 1945. By that
time a new principle had been discovered which made it possible to
obtain ion beams of much higher energy than originally hoped for. Yet a
considerably lower accelerating voltage could be used. This important
discovery was made independently by Dr. V. Veksler in Russia and by
Dr. Edwin M. McMillan, present Director of the Lawrence Radiation
Laboratory. Before attempting to discuss this principle, we should first
review the operation of a conventional cyclotron.




PRINCIPLE OF OPERATION OF A CONVENTIONAL CYCLOTRON


[Illustration: Fig. 2. Basic parts of a cyclotron.]

The main parts of a cyclotron are represented in Fig. 2. Charged
particles (ions) are accelerated inside an evacuated tank. This is to
prevent the beam from colliding with air molecules and being scattered.
The vacuum tank is placed between the poles of an electromagnet, whose
field bends the ion beam into a circular orbit.

The operation begins when the ions are introduced into the region
between two accelerating electrodes, or "dees."[2] Because the ions
carry a positive electric charge, they are attracted toward that dee
which is electrically negative at the moment. Were it not for the
magnetic field, the ions would be accelerated in a straight line;
instead they are deflected into a circular path back toward the dee gap.
By the time the ions again reach the dee gap, the sign of the electric
potential on the dees is reversed, so that now the ions are attracted
toward the opposite dee.

As this process of alternating the electric potential is repeated, the
ions gain speed and energy with each revolution. This causes them to
spiral outward. Finally they strike a target inserted into their path or
are extracted from the cyclotron for use as an external beam.

The time required for an ion to complete one loop remains constant as it
spirals outward. This is because its velocity increases sufficiently to
make up for the increased distance it travels during each turn. This
means that the electric potential applied to the dees must alternate at
a constant frequency, called the "resonant frequency."

The resonant frequency f is given by the relationship

            He
    f = --------- ,                                      (1)
         2[pi]mc

where H, e, [pi], c, and m are constants. H is the strength of the
magnetic field of the cyclotron, e is the electric charge carried by the
ion, [pi] equals 3.14, c is a conversion factor, and m is the mass of
the ion. For example, the resonant frequency for protons accelerated in
a 15,000-gauss magnetic field is 23.7 megacycles (Mc).[3] We call such a
rapidly alternating potential a "radiofrequency voltage" and the
electronic circuit for producing it a "radiofrequency oscillator."

The energy E of an ion emerging from the cyclotron is given by

        H^2 R^2   e^2
    E = -------  ---- ,                                  (2)
           2     mc^2

where H, e, and m are as defined above, and R is the radius at which the
beam is extracted. From this equation we see that for a given type of
ion (where e and m are constant), the energy depends on the diameter and
strength of the magnet, but not directly upon the voltage applied to the
dees.

The number of revolutions that an ion can make in a conventional
cyclotron is limited to about 70 to 100. This is due to a very curious
effect: as an ion is accelerated, its mass increases! [This phenomenon
is explained by Einstein's special theory of relativity (see Fig. 3).]
Referring back to Eq. (1), we see that if the ion mass (m) does not
remain constant, but rather increases, then the resonant frequency (f)
decreases. But since the dee potential continues alternating at a
constant frequency, an ion soon begins to arrive "late" at the dee gap.
By the time it has made about 70 to 100 turns an ion is so badly out of
phase that it is no longer accelerated.

Suppose now that we want to obtain an energy of 10 Mev. Because an ion
can make a maximum of about 100 turns, the accelerating potential would
have to be about 100,000 volts. However, Professor Lawrence hoped to
reach 100 Mev with the new 184-inch cyclotron. This meant that the
accelerating voltage would have to be about 1,000,000 volts. Preventing
such a high voltage from sparking promised to be one of many formidable
engineering problems.

[Illustration: Fig. 3. Graph showing how the mass of an object increases
as its velocity approaches that of light.]

FOOTNOTES:

[1] The grants were as follows: Rockefeller Foundation--$1,150,000; John
and Mary Markle Foundation--$25,000; The Research Corporation--$50,000.
The University of California added a guarantee of $175,000 to bring the
total building fund to $1,400,000.

[2] In the first cyclotrons the electrodes were shaped like the letter
"D."

[3] We have the values H = 15,000 gauss, e = 4.8 × 10^{-10}
electrostatic units, and m = 1.6 × 10^{-24} gram. To find f, we write

        15,000 (4.8) 10^{-10}
    f = ---------------------------------- ,
        2 (3.14)(1.6) 10^{-24} (3) 10^{10}

    f = 23.7 Mc.




THE PRINCIPLE OF PHASE STABILITY


Fortunately, Drs. Veksler and McMillan showed that relatively low dee
voltages can be used to accelerate ions to very high energies. This is
possible if the oscillator frequency is continuously decreased to keep
it in synchronism with the decreasing rotational frequency of the ions.
This would allow an ion to make many revolutions without becoming out of
phase. This principle of phase stability was experimentally verified
with the 37-inch cyclotron before being incorporated into the design of
the 184-inch machine. Because it utilizes this principle, this machine
has usually been referred to as a "synchrocyclotron" or
"frequency-modulated cyclotron." However, it is sometimes called simply
a "cyclotron."

The 184-inch synchrocyclotron was first operated in November 1946. With
a maximum dee voltage of only 20,000 volts, it accelerated deuterons to
190 Mev and alpha particles to 380 Mev.[4] In 1949 it was modified to
permit production of 350-Mev protons also.

Between 1955 and 1957 the synchrocyclotron was rebuilt so that now the
following energies can be obtained:

    Protons  Deuterons  Alpha Particles  Helium-3 nuclei[5]
    -------  ---------  ---------------  ---------------
    730 Mev   460 Mev       910 Mev         1140 Mev

In reaching an energy of 730 Mev a proton, for example, makes 75,000
revolutions in just 6 milliseconds (msec). It travels a distance of 450
miles and attains a velocity of 152,000 miles per second, or 82% of the
speed of light! During this brief journey its mass increases 75%, giving
very convincing evidence for the validity of Einstein's theory. Similar
data for other ions may be found in the appendix.

FOOTNOTES:

[4] A deuteron is the nucleus of an atom of heavy hydrogen and contains
one proton and one neutron; it carries a single positive electric
charge. An alpha particle is the nucleus of a helium atom and is made up
of two protons and two neutrons; it carries two positive charges.

[5] The machine is equipped for helium-3 operation, but to date it has
not been used for that purpose.




DESIGN AND CONSTRUCTION OF THE 184-INCH SYNCHROCYCLOTRON


_Magnet_

During the rebuilding of the cyclotron, the diameter of the magnet pole
pieces was increased from 184 to 188-3/4 inches. Also, the pole gap at
the center was reduced from 21 to 14 inches. These changes increased the
weight of steel in the magnet from 3700 to 4000 tons.

The main exciting coils, which contain 1300 turns of copper-bar
conductor each, were not altered. Two auxiliary coils containing 425
turns each were added. This brought the total weight of copper from 300
to 340 tons. The coils are layer-wound around the pole pieces close to
the pole gap. Other data about the coils are given in the appendix.

The effect of these modifications was to increase the field strength at
the center of the pole gap from 15,000 to 23,400 gauss. This increase
made it possible to obtain the higher-energy ions.

Power is supplied to the coils by two motor generator sets, which
produce the direct current required for a steady magnetic field. The
direct current from the motor generators is regulated so that the
magnetic-field fluctuation is less than one part in 10,000. This is
necessary if one wants an external beam of nearly uniform energy.

In order to prevent the beam from becoming unstable and striking the
dee, the magnetic field must be strongest at the center and decrease
radially (Fig. 4a). With flat pole faces the field does not decrease
uniformly. To give the desired rate of decrease, the pole faces are
shimmed with concentric steel rings of varying thickness, as shown in
Fig. 4b. In a radially decreasing magnetic field, the lines of magnetic
flux bow outward, as represented in Fig. 4b. Ions moving in a magnetic
field are deflected at right angles to these flux lines. Ions above the
midplane of the cyclotron are directed downward; those below the
midplane are directed upward. In this way an ion oscillates about the
midplane and vertical focusing is achieved.

[Illustration: Fig. 4.

(a) Plot of magnetic-field strength vs radius. The field strength
decreases gradually out to a radius of about 83-in., after which it
falls off sharply. This point marks the maximum usable radius for
particle orbits. Further out they are unstable.

(b) Magnetic flux lines are represented as broken arrows, and focusing
forces as solid arrows. An ion above the midplane is directed downward,
while an ion below the midplane is directed upward.]

Radial focusing is accomplished in a somewhat analogous manner. If the
magnetic field decreases with radius, radial restoring forces are
established. An ion at too large a radius is directed inward, and an ion
at too small a radius is directed outward. In this fashion, the ion
oscillates about the synchronous orbit. Thus, radial focusing is
achieved.


_Vacuum System_

The vacuum tank (acceleration chamber) is a steel box 20 × 25 ft and 4 ft
high. It is evacuated to a pressure of 10^{-5} millimeter of mercury
(about one 100-millionth of atmospheric pressure). The pumping equipment
consists of six oil-diffusion pumps and four mechanical vacuum pumps.
The pumping speed of the six 20-in. oil-diffusion pumps is a total of
20,000 liters/sec.


_Ion Source_

The ion source is a simple arc-type. Hydrogen gas is allowed to leak
into the ion-source enclosure near a tungsten filament, which is heated
to incandescence. Electrons emitted by the filament knock off electrons
from hydrogen atoms, leaving free protons. The protons then escape into
the acceleration chamber through a hole in the ion-source housing. Once
inside, the protons are accelerated by the dee potential.

Deuterons or alpha particles are obtained in a similar fashion using
deuterium or helium gas in place of hydrogen.


_Radiofrequency System_

The 184-inch synchrocyclotron has a single dee instead of the double-dee
arrangement described above for illustrative purposes. The accelerating
electric field is developed between the dee and a dummy dee which is
grounded to the vacuum tank. Using a single dee does not change the
principle of operation, yet it offers the advantage of allowing more
space for auxiliary equipment inside the vacuum tank. Also, the
construction is much simpler. The dummy dee is not essential for
operation, but it does improve performance.

[Illustration: Fig. 5. Radiofrequency cycle for accelerating protons.
Sixty-four such cycles are repeated each second.]

Radiofrequency power is supplied to the dee by a vacuum-tube
oscillator. The frequency of oscillation must decrease during the
acceleration cycle, as indicated above. For protons, the frequency at
the start of acceleration is 36 megacycles (Mc). At the end of
acceleration the frequency is only 18 Mc (see Fig. 5). This change in
frequency is achieved by varying the electrical capacitance in the tuned
circuit of the oscillator. (This is what you do when you dial a
different station on a radio.) This tuned circuit, which is called the
cyclotron resonator, is shown in Fig. 6.

[Illustration: Fig. 6. Cyclotron resonator.]

Because the frequency must change over such a wide range (from 36 to 18
Mc), the electrical capacitance must be varied by a factor of 20 to 1.
This is done by a variable capacitor of unique design. It resembles two
giant tuning forks. As the blades of the tuning forks vibrate, the
capacitance is alternately increased and decreased by the required
amount.

These two tuning forks must be kept in step with great precision. This
is to prevent the oscillator from exciting lateral rf resonances. With a
cyclotron of this size, this is a problem. These resonances, if excited,
would cause loss of beam. The method for keeping the blades moving
together is as follows: The blades are made to vibrate at their resonant
frequency, which is approximately 64 cycles per second. One set of
blades operates at its natural frequency as a tuning-fork oscillator.
The second set of blades is driven from an amplified sample of the
signal from the first; its natural period is adjusted automatically to
equal that of the first. The amplitude of each set is regulated to
within 0.003 in.; the phase angle between the blades is regulated to
within 1 deg.

Ions are accelerated only when the radiofrequency is decreasing (Fig. 5).
The remaining portion of the cycle is "dead time." Thus, 64 pulses, each
of about 500 microseconds' duration, are obtained every second. The
average ion current of a pulsed beam is much less than for a continuous
beam, such as that obtained from a conventional cyclotron (see Table I).
This is part of the price paid for higher energies.


_Internal Targets and Beam Extractor_

The simplest target is one placed inside the vacuum tank where the
circulating beam will strike it. The target may be any substance that
the physicist or chemist wants to irradiate. The target material is
attached to a movable probe. If the experimenter wants to use the
full-energy beam, he places the target at the maximum usable radius of
the circulating beam (82 inches). However, if he desires to use ions
having less than the maximum energy, he inserts the target further into
the cyclotron so that it is intercepted sooner.

TABLE I

=============================================================
   Comparison of external-beam energy and current for a
     synchrocyclotron and a conventional cyclotron
-------------------------------------------------------------

                  184-Inch Synchrocyclotron
                  -------------------------

                          Protons  Deuterons  Alpha particles
                          -------  ---------  ---------------
Beam energy --
  maximum (Mev)              730       460           910

Beam intensity --
  peak current ([mu]a)[6]    120       120            40

Beam intensity --
  average current ([mu]a)   0.75      0.75          0.25

                      60-Inch Cyclotron
                      -----------------
Beam energy --
  maximum (Mev)               12        24            48

Beam intensity --
  peak current ([mu]a)       100       150           100

Beam intensity --
  average current ([mu]a)     70        80            60
-------------------------------------------------------------
    [6] [mu]a = microampere
=============================================================

[Illustration: Fig. 7. Plan view of the cyclotron, showing the method
for obtaining an external beam of protons, deuterons, or alpha
particles.]

Some experiments require an external beam of protons, deuterons, or
alpha particles. A beam of this type can be brought out of the machine
by means of a LeCouteur regenerator (Fig. 7). The construction of the
regenerator is very simple. It is made of a number of steel laminations
of various sizes. What the regenerator does is perturb the magnetic
field of the cyclotron at one radial position. Each time the beam passes
through the regenerator it receives a kick. With each kick the beam
builds up its radial amplitude, until finally it enters a magnetic
channel. This channel focuses the beam and steers it outside the main
magnetic field. Once outside, the beam travels through an evacuated
tube, which is integral with the main vacuum tank. By means of a
steering magnet, the beam can be sent into either the physics cave or
the medical cave. (These experimental areas are called "caves" because
they are rooms inside the massive concrete shielding wall.)

Other experiments may require an external beam of mesons.[7] A meson
beam is obtained in the following way (Fig. 8): A movable target such as
a block of carbon is placed inside the cyclotron near the end of the
outward-spiraling proton beam. When the proton beam hits this target, a
shower of mesons is produced. These mesons are bent in various
directions by the main magnetic field. Some of them pass through a thin
metal window in the vacuum-tank wall and are focused by a magnetic lens
into a beam. This meson beam then travels through a hole in the concrete
shielding wall into the meson cave. The maximum intensity of this
extracted meson beam depends on both the charge and energy desired.
Beams of more than 100,000 mesons per second have been obtained through
an aperture 4 × 4 in. in the shielding wall.




CYCLOTRON EXPERIMENTS


_Nuclear Physics_

About 86% of the operating time of the 184-inch synchrocyclotron is
devoted to experiments in nuclear physics. Most of the experiments study
the production and interaction of [pi] mesons. These particles are
considered to be essential factors in the intense but short-range forces
that bind the nucleus together. The three types of [pi] mesons are
designated according to their electric charge as [pi]^+, [pi]^0, and
[pi]^-.[8] These mesons materialize only in high-energy nuclear
collisions.

[Illustration: Fig. 8. Method for obtaining external meson beam.]

Of great importance are those experiments that determine the
probability of producing each of the three types of mesons in a nuclear
collision. This type of experiment is repeated for different beam
energies and target elements. Other experiments measure the energy and
direction of emission of [pi] mesons from a target.

[Illustration: Fig. 9. A typical experiment. Scintillation counters at
A, B, C, D, and E record the passage of charged particles.]

A typical [pi]-meson experiment is represented in Fig. 9. The purpose
of this experiment was to detect the spin directions of protons as they
are knocked out of a liquid hydrogen target by a [pi]-meson beam. (Like
the earth, a proton spins on its axis.) An extracted proton beam from
the cyclotron enters the physics cave from the left, striking a
polyethylene target and producing [pi] mesons. A beam of these mesons is
formed by a series of two bending magnets and three focusing magnets.
This beam passes through a carbon absorber to remove unwanted particles.
The meson beam then strikes the liquid hydrogen target. A few of the
incoming mesons scatter, knocking protons out of the liquid hydrogen.
Scintillation counters at A and B record the passage of a proton, thus
defining its direction. The scattered mesons are counted by a
scintillation counter at C. A few of the protons scatter off the carbon
target and are detected by counters at E and D. From the detection of
such events, the spin directions (polarization) of the recoil protons
can be analyzed. In this way, more is learned about the fundamental
[pi]-proton interaction.

Further studies of the interactions of [pi] mesons are made in the meson
cave. Other experiments performed there are concerned with [mu] mesons.
The [mu] meson (muon) is a particle created in the decay of a [pi] meson
and is the principal constituent of cosmic rays striking the surface of
the earth. The muon is unstable, eventually undergoing a radioactive
decay into an electron. Although the muon does not experience nuclear
forces, it can interact weakly with nuclei. The behavior of the muon is
well understood, but its role as one of the elementary particles is
unknown. That is, if the muon did not exist, what effect would this have
on the structure of matter? The answer to this question, among others,
is being sought by physicists using the 184-inch cyclotron.


_Biophysics_

Experiments in biophysics are conducted in the medical cave. In these
the interest lies not in nuclear interactions but in the effect of
ionizing radiation on living tissue. High-energy beams of particles can
be used for selective destruction of specific areas of the brain. This
permits physiological mapping of the functions of the brain in
experimental animals. It further offers a therapeutic approach to the
treatment of brain tumors. One of the important investigational programs
is concerned with the relationship of the pituitary gland to the growth
rate of certain cancers and to some endocrine disorders.


_Nuclear Chemistry_

For techniques of radiochemistry to be employed successfully, high
interaction rates (and therefore high beam intensities) are needed. For
this reason, chemistry targets are usually inserted right into the
cyclotron so that they can be bombarded directly by the circulating
beam. After the bombardment is completed the target is removed from the
cyclotron. It is then taken to a chemistry laboratory and subjected to
detailed chemical procedures. Individual elements are removed, and the
radioactive isotopes of each element are identified by quantitative
counting techniques. In some cases a mass spectrometer is used to
analyze the products. Many deductions about the nature of the breakup of
the target nucleus can be drawn from the pattern of the observed
radioactive products. Sometimes the nucleus splits almost in half. This
is called fission. More frequently smaller parts of the nucleus are
split off. Two general types of reactions, known as spallation and
fragmentation, are distinguished. One of the goals of this research is
to learn more about the constitution of the nucleus and of the forces
which bind the particles in the interior of the nucleus.

FOOTNOTES:

[7] Mesons are elementary particles intermediate in mass between the
electron and proton.

[8] It may be interesting to note that the [pi]^0 meson was discovered
with this cyclotron in 1950. This was the first particle to be
discovered with an accelerator. All particles that had been previously
discovered were observed first in cosmic rays or some other form of
natural radiation.




BIBLIOGRAPHY


1. Gerald A. Behman, Particle Accelerators: I. Bibliography, II. List
   of Accelerator Installations, UCRL-8050, January 1, 1958.

2. Samuel Glasstone, The Acceleration of Charged Particles, in
   _Sourcebook on Atomic Energy_, Second Edition (Van Nostrand,
   Princeton, 1958), Ch. IX.

3. M. S. Livingston, _High-Energy Accelerators_ (Interscience
   Publishers, New York, 1954).

4. M. Stanley Livingston and Edwin M. McMillan, History of the
   Cyclotron, Physics Today _12_, 18-34 (October 1959).

5. E. M. McMillan, Particle Accelerators, in _Experimental Nuclear
   Physics_, Emilio Segrè, Editor, Vol. III (Wiley, New York, 1959),
   Part XIII.

6. Bob H. Smith _et al._, The Electrical Aspects of the UCRL 740-Mev
   Synchrocyclotron, UCRL-3779 Rev., October 2, 1957.

7. Robert L. Thornton, Frequency-Modulation and Radiofrequency System
   for the Modified Berkeley Cyclotron, UCRL-3362, April 3, 1956.

8. Robert R. Wilson, Particle Accelerators, Scientific American _198_,
   64-76 (March 1958).




APPENDIX


SUMMARY OF SPECIFICATIONS

  Present fields of research    % of time
  --------------------------    ---------
    Nuclear physics                 86
    Nuclear chemistry                2
    Biophysics                      12

  _Scheduled operation_         156 hours/week


_Performance_

_Internal Beams_

                                                      Alpha     Helium-3
                                Protons  Deuterons  particles     ions
                                -------  ---------  ---------   --------
  Maximum energy (Mev)             730       460        910        1140
  Energy spread (Mev)               55
  Beam intensity
    Average current ([mu]a)       0.75      0.75       0.25
    Peak current ([mu]a)           120       120         40
  Beam radius, maximum (in.)        82        82         82          82
  Time required for
    acceleration (msec)              6       4.5        4.5
  Number of revolutions
    during acceleration         75,000    60,000     60,000
  Distance traveled during
    acceleration (miles)           450       360        360
  Velocity at maximum energy
    (% of speed of light)           82        60         60          69
  Mass increase at maximum
    energy (% of rest mass)         75        25         25          40
  Range of full-energy
    particles (in. of aluminum)     37        12          7

_External Beams_

                                  Physics cave             Meson cave
                            -----------------------  -------------------
                            Protons Neutrons [pi]^+   [pi]^+    [pi]^-
                            ------- -------- ------  --------  ---------
  Energy (Mev)               730              310     100|250   100| 300
  Energy spread (Mev)         14                       10| 20    10|  30
  Beam area (cm^2)            25               40     100|100   100| 100
  Flux (particles/cm^2-sec) 2×10^10  5×10^5  5×10^4  1000|100  1500|1000


_Acceleration chamber (vacuum tank)_

  Size
    length (ft)                                              25
    width (ft)                                               20
    height (ft)                                               4

  Material: mild steel

  Operating pressure (mm Hg)                                 10^-5

  Vacuum pumps: six 20-in. oil-diffusion pumps with 8-in. boosters:
                one Beach-Russ 750-cfm; one Kinney 300-cfm; two
                Kinney 105-cfm.

  Pumping speed of oil-diffusion pumps (liters/sec)      20,000


_Magnet_

  Core diameter (in.)                            184
  Pole-tip diameter (in.)                     188.75
  Pole gap at center (in.)                        14
  Magnetic field strength (gauss)
    at center                                 23,400
    at radius of 82.2 in., where n = 0.2      22,275
  Weight of steel (tons)                       4,000
  Magnet coils              Main coils    Auxiliary coils
                            ----------    ---------------
  material                 solid copper    hollow copper
                          (1/4 × 4 in.)  (1-3/16 × 1-1/16 in.)
  weight of copper (tons)         300             40
  number of turns (total)       2,600            425
  ampere turns             1.9 × 10^6     1.1 × 10^6
  current (amp)                  1600           2800
  voltage (v)                     550            560
  power (kw)                      900           1600
  coolant                    oil            water


_Radiofrequency system_

  Dee system
    number of dees                                         1
    size
      length (in.)                                     126
      width (in.)                                      180
      height (in.)                                      48
    material: 1/64-in.-thick copper, stretched over a stainless
              steel frame
    dee aperture (in.)                                4-3/16

  Oscillator
    type: self-excited grounded-grid                      10
    tube: one Machlett ML5681
    dc input, operating condition (kw)                    10
    dee bias, maximum dc (v)                            2000

                             Protons  Deuterons  Alpha particles
                             -------  ---------  ---------------
    rf duty cycle (%)          38        28            28
    dee-to-ground voltage,
    peak (kv)                   9         6             6

  Frequency-modulation system
    type: vibrating-reed (tuning-fork) capacitor
    number of units: two (two blades each)
    blades
      size
        width (in.)                                       45
        length (in.)                                      32
        thickness: tapered from 1.4 to 0.06 in.
        weight (lb)                                      500
    vibrational frequency (cps)                           64
    electrical capacitance ([mu][mu]f)          300 to 6,500
    peak-to-peak excursion (in.)                           1
    minimum separation of blade and stator (mils)         50

                            Protons   Deuterons   Alpha particles
                            -------   ---------   ---------------
    frequency sweep (Mc)     36-18    18-13.5        18-13.5

  Ion source: conventional open-arc type


_Beam extractor_

  LeCouteur-type regenerator combined with magnetic channel


_Building and facilities_

  Room dimensions
    diameter (ft)          160
    height (ft)             90

  Crane
    type: radial
    capacity (tons)         30
    overhead span (ft)      77

  Concrete shielding: 15 ft thick on sides, 4 ft on top


_History_

  Design started: January 1940.
  Construction started: August 1940.
  First operation
    for deuterons and alpha particles: November 1946.
    for protons: December 1948.
  Rebuilt: 1955-1957.

[Illustration: Synchrocyclotron Building]


[Transcriber's Note:
  The following changes have been made to the printed text:
    Page 15, added closing quote (are called "caves" because)
    Page 19, "iostopes" corrected to "isotopes" ]





End of Project Gutenberg's LRL Accelerators, by Lawrence Radiation Laboratory