# Fermilab

## Inquiring Minds

High Frequency Beams

Hi, I'm a physics student and I love the work you are doing at Fermilab. I've been watching closely your progress and I believe some of the best mind are working there. My question is about high frequency beams. I'd like to know what are the highest frequencies (in Hz) you have been using at Fermilab and in what kind of research. What is the theoretical limit for frequencies and how far are we from it?

Best regards,
Pedro Bonatto de Castro

Hi Pedro,

I sent your question,to an expert on beams here at Fermilab. Here is his reply:

You pose an interesting question and one that is fairly complicated to answer. We use radio-frequency waves to accelerate the beam. We use frequencies of 200 MHz (200,000,000 Hz) and 800 MHz to accelerate the beam in the Fermilab linear accelerator. In the circular accelerators, we use a frequency of about 53 MHz. The frequency has to match the particle revolution frequency, so the frequency is increased as the particle velocity is increased. Since the particle velocity cannot exceed the speed of light and is already close to the speed of light at the end of the linac, the frequency change during the entire accelerator cycle is fairly small. From one point of view, these frequencies are the highest beam frequencies we generate.

You probably are aware that electromagnetic radiation comes in many forms and has many different names such as radio waves, microwaves, radiant heat, light, xrays, and gamma-rays. The existence of so many names for the same phenomena underscores the wide range of forms electromagnetic radiation can take. The fundamental difference in electromagnetic radiation is the difference in frequency.

High energy particles generate electromagnetic radiation when they are subjected to acceleration. This radiation occurs throughout the electromagnetic spectrum. One of the most interesting forms of radiation is the highest energy gamma-ray radiation that emerges from our high-energy proton-antiproton collisions. Theoretically, the gamma-ray radiation energy could be as high as the beam energy, namely 980 GeV. In practice, the gamma-ray radiation never reaches this value, but energies of 10 to 20 GeV are fairly common.

The energy of electromagnetic radiation is related to its frequency by Einstein's other famous equation: Energy = h x frequency, where h is a number known as "Planck's constant." The numerical value of Planck's constant is 6.582x10^-25 GeV/Hz. The frequency of a 10 GeV gamma-ray is therefore 1.519x10^25 Hz, which can be written out as 15,190,000,000,000,000,000,000,000 Hz. And that's a pretty high frequency.

John Marriner

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