Physics for fun

Laser generated proton beam or ion beam fast ignition is an idea that I've thought about for some time. Recently, when I discovered a paper in a the December 2006 journal Physics of Plasmas by a Bolivian physicist ( Phys. Plasmas 13, 122704 Fast ignition of a compressed inertial confinement fusion hemispherical capsule by two proton beams by Mauro Temporal ) I was excited to learn what he designed.

His idea is elegant, with the two beams generated by the same cone from targets located at different distances from the point of the same cone, doing two different tasks. One makes the spark, the other does isochoric heating/shock wave generation.

Temporal proposes that a variation on the Japanese cone in capsule method be used, though his variation uses a hemispherical capsule compared with the original Osaka design using a spherical capsule with a cone inserted into the center that channels the beam. ( see for example : M. Tabak et al, Phys Plasmas 1, 1626 (1994) or R.Kodama, T Yamanaka et al, Nature (London) 412,798(2001) :: R. Kodama, T. Yamanaka et al, Nucl.Fusion 44, s276 (2004) and so on.

My idea is to use two colliding beams that meet in the capsule to ignite the burn using conventional laser hohlraum compression, with the proton beams produced by petawatt lasers in the same chain as the compression lasers to ensure correct timing. I suggest that two cones be used, and that the capsule be prolate. Alternately one could employ the colliding beam approach with a Z-pinch for a higher yield.

My idea takes advantage of the fact that colliding beams generate a higher energy though higher energy particles may also escape the assembled system in higher fraction. Using higher Z ions would allow the bragg peak to deposit energy in the right place more precisely though things rapidly get complicated using such schemes.

My two colliding beam design may trigger the burn with a simple geometry and be applicable to z-pinch systems as well. In the Z-pinch system my device design would potentially ignite a larger fraction of the material and use the energy very efficiently.

Anyway, its fun thinking about the dynamics of these tiny energy sources and to explore the concepts even without access to the experimental facilities that would test ideas and expose the many flaws in our designs. As Klaus Berkner (LBL) said " experimentalists keep the theorists from drifting away....". Since I’m not limited by the real known physics, I can dream up science fiction devices that work in my mind but may never work in our world. I can gloss over real issues like RT or M instabilities, or perhaps I can find solutions that work, who knows?


It is wonderful to see Temporal’s original thought process, as most of the thoughts and current developments by the main labs are necessarily obscured from those of us outside the main efforts and seldom see the light of publication in the open journals.

A Bolivian physicist, who knows if his ideas will ever be tested or will work, but the same can be said for my ideas as well. The Andes have produced some great physicists including Peruvian Pier Oddone ( now at Fermi lab I think).

Fun with numbers.

Bruce Bagnoli