Carrie
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Hi Carrie,
We both calculate and measure the speed. First of all, we keep track of how much energy we have given the particles. Then, using a relationship derived by Einstein, you can calculate their speed:
Here, c = speed of light, E = total energy a particle has, and mc^2 = the rest energy
of the particle = its mass times the speed of light squared. You can see that as E gets larger and larger, v gets closer and closer to c (but never quite reaches it).
[p.s. -- let me know if my notation isn't understandable. It's hard to embed equations in the written text, at least for me...]
As for actually measuring the speed, we can time the particle beam as it goes around our accelerators. For instance, the time it takes -- at the speed of light -- to go around the Tevatron is 0.000021 seconds (21 microseconds). That seems pretty small, but we have oscilloscopes and other equipment that can measure this time extremely accurately (like to +/- picoseconds or better). Of course, to get a good measurement of the speed this way, we need to know the distance traveled. The circumference of the Tevatron is actually 6283.19 meters (two pi kilometers!), accurate to a fraction of a centimeter. As the particle beam wanders around, we can steer it with small electromagnets to make sure it is centered within the pipe that it travels in. We can move it around by small fractions of a millimeter to make sure it is on the right orbit everywhere.
-Mike Syphers
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It sounds like you really enjoy to travel and see the United States. That is something that I would really like to get the chance to do one day. Have you ever traveled out of the country for your job?
I do understand how you calculate and measure the speed of the accelerators. I do have another question though. How often does the speed increase getting closer to the speed of light?
-Carrie
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Hi Carrie,
"Have you ever traveled out of the country for your job?"
Yes, I have. Over the past 20 years, I've traveled on business several times each to France, Switzerland, Italy, and Germany, and once each to Austria, The Netherlands, and Russia. I've had a couple of opportunities to go to Asia (India, China, and Japan) during that time, too, but I couldn't make those trips for various reasons; maybe some day...
"How often does the speed increase getting closer to the speed of light?"
We have a series of accelerators that give the particles energy. It's like the gears in a bicycle, say, where each stage or accelerator is better suited for its particular energy range. So, at Fermilab for example, the accelerators go something like this:
Proton at rest: energy = 938 MeV (= mc^2 of the proton)
Then, Kinetic Energy is provided by...
Straight accelerators:
Preacc: provides 0.75 MeV; total energy = 938.75 MeV
speed goes from 0 --> 4% the speed of light, c
Linac: provides 399.25 MeV; total energy = 1338 MeV
speed goes from 4 --> 71% c (takes a few microseconds)
Circular accelerators:
Booster: provides 7600 MeV; total energy = 8938 MeV = 8.938 GeV
speed goes from 71 --> 99.45% c (this takes 0.33 sec)
Main Injector: provides 142,000 MeV; total energy = 150.938 GeV = 0.151 TeV
speed goes from 99.45 --> 99.998% c (this takes about 1 sec)
Tevatron: provides 830,000 MeV; total energy = 981 GeV = 0.981 TeV
speed goes from 99.998 --> 99.99995% c (this takes about 20 sec)
Once particles in the Tevatron are at that final energy, we keep them at this energy/speed while they collide head-on with particles moving in the other direction around the circle.
Below is a plot of the speed (fraction of the speed of light) versus the kinetic energy we've given each of the protons. You can see how quickly the speed starts to approach the speed of light. By the time a proton goes through a billion volts (1 GeV), it's almost at 90% c. We can keep giving it energy (and that energy is real, and can do real work), but its speed doesn't change much after a few billion electron volts.
-Mike Syphers
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Hi Dr. Syphers,
The places you have visited sound very interesting, and a lot of the same ones that I would enjoy seeing. Since you have been so many places, are you able to speak any other languages? If so, how many and what ones.
Finding the speed of an accelerator seems very long and complicated. How long has it taken you to fully understand everything that goes into them?
Thanks
Carrie
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Hi Carrie,
a) I studied French in school, and one semester of Russian, for good measure. But, I only speak a little (tiny bit) of French these days. Most of the large physics labs that I visit and the conferences I go to tend to speak English, so that's been nice (for me). I always feel a bit odd, though, when the people from these other countries know English, but I don't know their native language. It's too bad for Americans that we don't have as many opportunities to need to learn other languages; it's not enough to just study them in High School.
b) To really understand the speed of the particles in these accelerators, one needs to have a good grasp of Einstein's special theory of relativity. While I learned a little about it in my senior year in high school (2nd year physics class), I studied it in much more detail in a course my sophomore year in college. To be very comfortable with it, however, probably took a few more years and more experience using it in problem solving.
Cheers,
-Mike Syphers
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Hi Dr. Syphers,
a) That is really cool. Is is hard to learn Russian? I do agree that it is a bit odd that we do not get the chance to learn other languages unlike other countries that learn English at a young age.
b) This sounds very interesting. I have enjoyed my physics class so far and I cannot wait to learn so much more in the rest of the year!
Thank you,
Carrie
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Hi Carrie,
a) Yes. It was hard for me, at least. It was learning a whole different alphabet, and we had to learn how to write all over again. (We actually started out with the large, lined paper that you use in 1st grade to learn how to print and write in Russian!) But, it was cool to learn about the language, even if I didn't go very far with it.
b) Thanks for your insightful questions and participation. I hope you enjoy the rest of your experience studying and thinking about physics!
-Mike Syphers
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Hi!
Thank you very much for taking time out of your day for the past three weeks to talk to me. I enjoyed learning about your job, and your travels.
I wish you the best!
Carrie
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