Controlling Beam Length One function of the radio frequency induction gaps is to control the length of the electron
beam.
Due to the physics of a high space-charge beam, there is a tendency for the beam to grow longer. Without a mechanism to control this characteristic of the beam, the
head of the beam would catch up with the tail, creating one continuous ring - an undesirable result.
The induction gaps control the beam by means of electric current, created by running voltage through resistors. Depending on initial conditions, the current will affect the
section of the beam passing through the inductor in one of two ways - it will either slow it down, or speed it up. In this case, as the beam travels around the ring, the
head of the beam is slowed, and the tail is sped up, thus keeping the length of the beam under control.
Beam Acceleration
Eventually the induction gaps will serve a two-fold purpose. Accelerating the electron beam while still controlling beam length.
The process will be similar to that described above. The difference being that an overall accelerating force will be incorporated into the forces applied to the head and
tail of the beam. Each time the beam passes through an induction gap, it will be accelerated slightly as a whole, but a lesser accelerating force will be applied to the head
than to the tail, so that the beam length remains contained.
Dipoles
Dipoles are the beam-steering component of the ring, controlling the beam's position within the ring, and providing the force to continuously bend the beam inwards around the circular ring.
Quadrupoles
Each quadrupole focuses the beam in one direction (along either the x or the y axis), while defocusing it in the other direction. This process is referred to as 'alternating gradient' focusing. Successive quadrupoles alternate the direction of focus. The purpose of focusing the beam is to keep beam particles from spreading out and causing the beam diameter to grow too large for the ring.
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