Accelerator Details: Linac RF power sources

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Accelerator Details:
RF Power Sources for the Linac

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RF Power Amplifiers - The Triode

The Triode is in itself is a miniature electron accelerator. The filament boils electrons off the cathode. The electrons are accelerated by the DC power supply to the anode. The voltage on the grid controls how many electrons make it to the anode. The number of electrons flowing into the anode determines the current into the
load.

The triode can be thought of as a voltage controlled current source.

Triodes work well at low frequencies and are used in the first (old) part of the Linac
and operate at a frequency of 201.25 MHz.

RF Power Amplifiers - The Klystron

The Klystron is in itself is a miniature electron accelerator. The filament boils electrons of the cathode. The electrons are accelerated by the DC power supply to the anode. The velocity (or energy) of the electrons is modulated by the input RF. The electrons drift to the anode. Because of the velocity modulation, some electrons are slowed down, some are speeded up.

If the output cavity is placed at the right place, the electrons will bunch up at the output cavity which will excite a high intensity RF field in the output cavity.

Klystrons need a minimum of 2 cavities but can have more for larger gain.

A klystron’s size is determined by the size of the bunching cavities.

The size of these cavities are inversely proportional to the frequency.

Klystrons are used at high frequencies and is used in the second (new) part of the Linac at 805 MHz.

Questions? Contact Ernie Malamud. rev. August 18, 2000

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