# Bunched electrons: How many and how fast?

Gold Member
I am wondering how many electrons have been successfully bunched and how fast they have been accelerated to in a particle accelerator. Is there an upper limit on how many electrons can be bunched? Does the possible acceleration level of that bunch depend on the number of electrons in that bunch?

Thanks,

Jake

ZapperZ
Staff Emeritus
The facility that I work at holds the "world's record" (meaning, it isn't in the Guinness Books, but we haven't found anyone beating it in the literature) for the largest amount of charge per bunch, which is 110 nC. These were accelerated at 18 MeV, which is low, and which is why we're constructing a new one.

To put this into perspective, for most electron accelerator facilities, 1nC is large. For us, we sneeze and we get 1 nC.

Zz.

Gold Member
Thank you. I have a couple questions. What is "nC"? I used Wikipedia and my best guess is Nanocoulomb. So, how many electrons does it take to get 110 nC? From Wikipedia, the charge of an electron is about −1.6x10^−19 C and 1 nC is 1x10^-9 C. Are my calculations correct that about 7x10^11 electrons were used? But MeV is a relativistic speed, right (I can't find an eV to speed converter. Do you know of one? I can't get the energy amplification using Einstein's equations without the speed)? Also, what counts as "relativistic speed" (what's the cutoff range of speeds or speed?)? So, my calculations must be wrong because the 110 nC must have been amplified to that level from a smaller nC due to the relativistic energy amplification. Can you tell me how many electrons are in the bunch at 18 MeV and 110 nC?

Thanks,

Jake

Gold Member
Also, is the energy of the bunch as a whole measured when bunched electrons are run through an energy resolving chamber in a particle accelerator?

Check out my blog, or the thread "perfect symmetry"
jal

Gold Member
ZapperZ?

ZapperZ
Staff Emeritus
Thank you. I have a couple questions. What is "nC"? I used Wikipedia and my best guess is Nanocoulomb. So, how many electrons does it take to get 110 nC? From Wikipedia, the charge of an electron is about −1.6x10^−19 C and 1 nC is 1x10^-9 C. Are my calculations correct that about 7x10^11 electrons were used? But MeV is a relativistic speed, right (I can't find an eV to speed converter. Do you know of one? I can't get the energy amplification using Einstein's equations without the speed)? Also, what counts as "relativistic speed" (what's the cutoff range of speeds or speed?)? So, my calculations must be wrong because the 110 nC must have been amplified to that level from a smaller nC due to the relativistic energy amplification. Can you tell me how many electrons are in the bunch at 18 MeV and 110 nC?

Thanks,

Jake

nC = nanocoulomb. It is the amount of charge. To get the number of electrons, you simply divide this by the charge of an electron.

For an electron, anything above 1 MeV is considered as relativistic. A a general rule of thumb, if the KE is larger than the rest energy, then you should consider it relativistic. At more than 1 MeV, most calculation of electron dynamics can be solved with a good degree of accuracy by assuming that the electron speed is c.

You can't find how many electrons with the energy value. You need the charge value.

Zz.

Gold Member
Thanks!