I heard that the LHC smashes two protons together to research the universe.

But how does it create the protons for collision? If we strip off the electrons won't there be neutrons along with protons?

A "Duoplasmatron source" is used by the LHC, it ionises atoms into negative or positive ions but how is the proton separated from that?

  • $\begingroup$ With an electric field. The electrons are not tightly bound to the proton, so it's not a big deal. The story is different for lead atoms, though, where some of the 82 electrons are tightly bound to the lead nucleus. $\endgroup$
    – pfnuesel
    Commented Mar 22, 2016 at 18:03

2 Answers 2


See this article on the LHC proton source.

Hydrogen gas is ionised using a strong electric field, and the resulting protons are accelerated and focused then injected into a linear accelerator.

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    $\begingroup$ Won't there be neutrons along with protons? $\endgroup$
    – nihaljp
    Commented Dec 28, 2015 at 11:02
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    $\begingroup$ Then they will take protium isotope atoms of hydrogen which has no neutrons. $\endgroup$
    – N.S.JOHN
    Commented Dec 28, 2015 at 11:58
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    $\begingroup$ The number of deuterium atoms is natural hydrogen gass is very small compared to those with just a proton. The small number of deuterons that do result from the ionization are easily seperated from the protons via the magnetic acceleration mechanisms since they have the same charge but twice the mass. $\endgroup$ Commented Dec 28, 2015 at 14:48
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    $\begingroup$ Google gets you lots of info quickly. Duoplasmatrons are pretty standard ion sources, using an electron emitter and magnetic fields to ionize and contain the plasma, allowing for high ionized fractions and thus good beam currents. $\endgroup$
    – Jon Custer
    Commented Dec 28, 2015 at 16:38
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    $\begingroup$ Any traces of deuterium which were included in the proton beam would be ejected from the beam at the bending magnets; the protium and deuterium would have charge-to-mass ratio different by a factor of two. $\endgroup$
    – rob
    Commented Dec 29, 2015 at 17:52

From the horse's mouth:

The proton source is a simple bottle of hydrogen gas. An electric field is used to strip hydrogen atoms of their electrons to yield protons. Linac 2, the first accelerator in the chain, accelerates the protons to the energy of 50 MeV. The beam is then injected into the Proton Synchrotron Booster (PSB), which accelerates the protons to 1.4 GeV, followed by the Proton Synchrotron (PS), which pushes the beam to 25 GeV. Protons are then sent to the Super Proton Synchrotron (SPS) where they are accelerated to 450 GeV.

The protons are finally transferred to the two beam pipes of the LHC. The beam in one pipe circulates clockwise while the beam in the other pipe circulates anticlockwise. It takes 4 minutes and 20 seconds to fill each LHC ring, and 20 minutes for the protons to reach their maximum energy of 4 TeV. Beams circulate for many hours inside the LHC beam pipes under normal operating conditions. The two beams are brought into collision inside four detectors – ALICE, ATLAS, CMS and LHCb – where the total energy at the collision point is equal to 8 TeV.


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