# The Naked Scientists Forum

### Author Topic: Force on LHC to keep particles travelling in circular motion?  (Read 2974 times)

#### m44ttg

• First timers
• Posts: 1
##### Force on LHC to keep particles travelling in circular motion?
« on: 10/09/2008 11:30:14 »
Hi,
Just a random question really....

What is the total force the LHC magnets are exerting on the particles to keep them in a circular motion as they travel around the tunnel when the the experiment is going at full tilt? (assuming the LHC is perfectly circular... which i don't think it is.)

I guess this force is called the centripetal force?

Thanks!
Matt

#### rich42

• Jr. Member
• Posts: 20
##### Force on LHC to keep particles travelling in circular motion?
« Reply #1 on: 10/09/2008 12:39:21 »
It's not quite the same as the centripetal force as the protons have their direction changed by a series of 2000 very large magnets. As the particle travels through one of these magnetic fields, its direction is changed by about 0.2 degrees, a very slight deflection but enough to keep it travelling round the ring. Energy will be lost from the beam of protons as they are deflected by synchrotron radiation at a power of 6.1kW.

Edit: The force on each proton as a result of this magnetic field will be F=m(v^2)/r with v~c, m=mass of proton, r = 4.2km:
F = 2.6 x 10^(-10) N on each proton.
This doesn't seem like much but it is just on one proton. For two beams of ~2800 bunches of protons, each containing 10^11 protons (when the collider is operating at full power), that makes a total force on the protons (and hence a reaction force on the detector) of 17 tons, quite a lot when you're dealing with particles with summed rest masses of a billionth of a gram!

Richard
« Last Edit: 10/09/2008 12:46:30 by rich42 »

#### The Naked Scientists Forum

##### Force on LHC to keep particles travelling in circular motion?
« Reply #1 on: 10/09/2008 12:39:21 »