[ExI] Physical limits of electromagnetic launchers

[Kelly Anderson]

On Sat, Jun 2, 2012 at 3:11 PM, Anders Sandberg <anders at aleph.se> wrote:
> On 02/06/2012 19:53, Kelly Anderson wrote:
>>
>> If we take a lesson from the particle accelerator folks, can we run them
>> around a big circle speeding them up for a bit before going to the long
>> straight cannon? What point do you have to be at for the sideways G forces
>> to be too much?
>
>
> Particle accelerators use charged particles held in place with a magnetic
> field and accelerated using oscillating electical fields. So the problem
> becomes whether one can charge up the payload enough to make it couple well
> with the field, and how big the accelerator has to be.

Sorry, I wasn't suggesting the same mechanism, merely the same geometry.

> Looking at the formula for the gyroradius of a particle,
> r=gamma*(v/c)*m*c/qB where gamma is the relativistic factor, m the mass, q
> the charge and B the magnetic field one can see that it scales linearly with
> mass. So accelerating a 30 gram mass like the LHC would, would require an
> accelerator ca 1.6e23 times wider. We are talking lightyears here. It can be
> shrunk by increasing the field strength, but probably not many orders of
> magnitude.
>
> We can certainly increase the charge (one electron charge per 30 gram is
> puny). I'm not sure what the limit is: obviously beyond a certain point the
> surface atoms will start sputtering away. Megavolt potentials are however
> entirely doable (especially in vaccum), and assuming ~cm sized spherical
> payloads and using Coulumbs law, I get q=6e12. That would give an
> accelerator just 2.5e10 times bigger than the LHC. Still too big for the
> solar system (about 1600 AU), but maybe if we are lucky there are materials
> that can handle a few order of magnitude more charge.

Regardless of where the breaking point is reached, it seems that
starting with a circle and breaking out to a straight line after a
certain speed is reached seems like a logical way to shorten the
required length of the gun. It's just a question of how much shorter
it would make it, I suppose.

-Kelly