t 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 x 10^{-10}
electrostatic units, and m = 1.6 x 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 n