Alpha particle physics PDF Print

 

Alpha particle issues present a major problem layer in power producing tokamaks.

 

1.     The alphas require a 10MA plasma current for their classical confinement. This is the first item that obviates the need studying turbulence in small or large tokamaks.  It would be nice not to have turbulence in toy tokamaks but when the tokamaks need to deliver fusion power the soft turbulence will be not significant in promoting needed transport.  

2.     The since their transport is classical (due to their large ballistic orbits) once they are born they do not want to leave. At the moment we do not have tested schemes to facilitate their transport. The hydrogen tokamak proposes to use 300 kV helium beam to see if transport by plasma poloidal rotaion could be used. This would be an "anti H-mode". More powerfull than a particle L-mode.The alpha confinement must not be longer than a few sec. The unburned fule will also be swept out and must be re-inserted.

3.     Since the needed alpha radial current (100-300A) is larger than what is needed to overcome poloidal rotation damping, the resulting (bifurcated)  poloidal rotation will generate turbulence and it will pull the colder plasma ions and alpha particles into the core. This can result in a disruption due reaching the beta limit. Again this problem is totally outside the range of our  experience and even outside of our community conscience (for the most part).

4.     A lesser problem is diverting the alpha flow to active pumping at the boundary. At this time we have not made the relevant computations. However, it is clear that we will also pump out D-T more than alphas ash by a factor of ten. This will require that the fueling be increase 10-20 fold. It is a very scary consequence of ash removal. The Hydrogen demo tokamak can address these issues.