Van de Graaff Generator - hdbk11080098

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DOE-HDBK-1108-97
Student's Guide
These free protons are now introduced into another chamber where again there is an electrical
force on them. This force accelerates the protons, i.e., increases their velocity (speed).
The kinetic energy (the energy of motion) of a particle (at least for velocities much less than the
speed of light) is given by the equation:
KE = ½ mv2
where
KE = the kinetic energy,
m = the mass of the particle, and
v = the velocity of the particle.
The acceleration of the proton by this electrical force also increases the energy of the proton.
The amount of acceleration is determined by the potential difference measured in volts (V) in this
electrical field. One electron volt (eV) is the energy gained by an electron accelerated through an
electric potential of 1 volt. Thus, if a proton is accelerated across a gap by means of a 10,000
volt, or 10 kilovolt (kV), potential difference, it is said to have gained 10,000 electron volts (10
keV) of energy after crossing the gap.
Ten keV was a potential easily achieved, but scientists wanted to accelerate particles to many
times this energy. One way to accomplish this was to apply 10 kV potential to each of many
gaps and have the particle traverse these gaps one after another, gaining 10 keV in energy for
each gap traversed. Alternatively, a voltage many times larger than 10 kV might be applied to a
single gap.
D.
Van de Graaff Generator
One of the first machines to produce laboratory-accelerated particles was the Robert Van de
Graaff an electrostatic accumulator that produces large potential differences
essentially by rubbing. In 1929, Van de Graaff built a pilot machine capable of generating
80,000 volts (80 keV). In 1931, a 1.5 million-volt (MeV) machine was constructed at Princeton
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