Fermi National Laboratory


Accelerator Update

About the Fermilab Accelerators

Most proton synchrotrons (circular accelerators) built before Fermilab's Main Ring used a linear accelerator to inject protons directly into the synchrotron. But that scheme of injection wouldn't work with the Main Ring. A linear accelerator capable of accelerating protons to the 8 GeV injection energy would have had to be four miles long.

The History and Design of the Booster Accelerator

Rather than have a four-mile LINAC, designers decided that a "booster accelerator" would give an intermediate boost to the beam energy between the LINAC and the Main Ring. As with all things, a main factor affecting the injection energy was the cost of the LINAC energy versus the cost of the Booster RF. (RF stands for Radio Frequency, which is the electromagnetic energy used to accelerate particles.) As LINAC energy increased, the Booster RF requirements were reduced. The 200 MeV energy selected for LINAC extraction was a modest cost increase but considered worth the better beam quality. In a further cost give and take, the extraction energy of the Booster was reduced from 10 to 8 GeV.

With the injection energy decided upon, the proposed Booster designs differed only in radius and the cycling time. The idea of a large radius Booster was abandoned due to the high cost of construction and possible beam resonance problems. The final design resulted in a circumference 13.25 times smaller than the Main Ring.

In 1999, the new Main Injector replaced the Main Ring. The Booster is 1/7 the size of the Main Injector. To fill the Main Injector with beam, the Booster must go through repeated acceleration cycles, transferring each cycle's worth of beam. Each of the extracted beam pulses is referred to as a "batch."

The Booster delivered 12 of 13 possible batches to the Main Ring. A gap had to be preserved in the beam to allow time for kickers to rise to their proper voltage. (A kicker is a very fast magnet usually used to divert beam from one machine to another.)

The design of the Main Injector allows six Booster batches, but only holds five due to those same kicker rise time limitations.

When the Main Ring was built back in 1972, it had the highest final energy (200 GeV) of any other accelerator. In 1983 the Main Ring became, in effect, a second booster, injecting 150 GeV beam into the Tevatron. In 1998 the Main Injector took over Main Ring responsibilities, providing 150 GeV beams for the Tevatron.

last modified 10/26/2001   email Fermilab

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