New Ideas for New Accelerators

One of the largest disadvantages of therapies that require accelerators is the size and cost of the accelerators themselves. These factors limit who can receive care and where. So for medicine and the future of accelerators in general, the community is pushing for smaller and more affordable (but of course, that's the case with all technology isn't it?). At a very intriguing session I got to hear about an approach that a group of scientists at Stanford University and Fluence LLC are developing to make smaller particle accelerators for medical applications.  They are also collaborating with the Stanford medical school and SLAC National Accelerator Laboratory, who are contributing expertise in Monte Carlo simulations for beam transport and dose calculations.

Their technique is called electromagnetic plasma acceleration (not to be confused with other plasma accelerators that use lasers) and it goes something like this: get a neutral gas in-between two electrodes and let it break down into electrons and ions. The currents that flow through the plasma then generate  their own magnetic field (this is a big advantage because no magnets are needed); this exerts a force to the right, and the electrons start to move.

This alone is not a new approach.  But normally the ions upstream form a wall, sort of like a piston, and push the other particles forward.  This works for lower energies, but when one tries to accelerate the piston faster it starts to tilt and downstream gas can blow by it without being accelerated. This is like a piston with a hole in it, which doesn't push anything. So there's a definite limit to how fast you can get those particles to move.

But new research has shown that you can make tweaks to the system and cause the piston wall to disappear. Early work performed on this topic by Dah Yu Cheng in the 1970's already showed that there are two ways to accelerate these particles. One (the piston) moves the particles like an explosion. The other moves them the way a jet engine does, in a more jet or bullet-like shape that is also more efficient. The Stanford team is now trying to understand this second mode of acceleration. While there was previously a limit on how fast you could accelerate the particles until the piston tipped, this limitation does not apply to the second mode.  They've got particles moving at around 100 keV, which is still far short of the 100 MeV's needed for proton accelerators, but that's what the Stanford team is dedicated to reaching. They'll have other challenges as well, including reducing the wide energy distribution that the particle jets tend to have.

Flavio Poehlmann, who delivered the talk in place of professor Mark Cappelli who was unable to attend, said the team expects another ten years of work before they reach their energy goal. They're currently in the process of submitting patents before they publish any papers on the subject.