High Energy Electron Confinement in a Magnetic Cusp Configuration
Jaeyoung Park, Nicholas A. Krall, Paul E. Sieck, Dustin T. Offermann, Michael Skillicorn, Andrew Sanchez, Kevin Davis, Eric Alderson, Giovanni Lapenta
We report experimental results validating the concept that plasma confinement is enhanced in a magnetic cusp configuration when beta (plasma pressure/magnetic field pressure) is order of unity. This enhancement is required for a fusion power reactor based on cusp confinement to be feasible. The magnetic cusp configuration possesses a critical advantage: the plasma is stable to large scale perturbations. However, early work indicated that plasma loss rates in a reactor based on a cusp configuration were too large for net power production. Grad and others theorized that at high beta a sharp boundary would form between the plasma and the magnetic field, leading to substantially smaller loss rates. The current experiment validates this theoretical conjecture for the first time and represents critical progress toward the Polywell fusion concept which combines a high beta cusp configuration with an electrostatic fusion for a compact, economical, power-producing nuclear fusion reactor.
The present experimental result is a major step toward a Polywell fusion reactor in that it validates the conjecture that high energy electron confinement is improved in a high β plasma. However, two additional measurements are needed to estimate the performance of a Polywell fusion reactor. The first is to quantitatively determine the loss rate. The second is to measure the efficiency of ion acceleration by electron beam injection.
In summary, the present experimental results demonstrate for the first time that high β plasma operation can dramatically improve high energy electron confinement in the magnetic cusp system. This result validates the central premise of the Polywell fusion concept which uses high energy beam injected electrons to create an electrostatic potential well for ion acceleration and confinement. The current plan is to extend the present work with increased electron beam power to sustain the high β plasma state and to form an electrostatic well. If the deep potential well can be formed and the scaling of the electron beam confinement is found to be favourable, as conjectured by Grad and others, it may be possible to construct a compact, low cost, high β fusion power reactor based on the Polywell concept.
The URL to the paper is http://arxiv.org/abs/1406.0133.
Together with the paper there are five animations also.
It is very interesting to finally see a paper by EMC2 on their work. It is also interesting to see that the polywell is considered a viable alternative for an reactor, but much work (and funding) is of course needed to go forward with the concept.