Overview of Experimental and Theoretical Studies of the Periodically Oscillating Plasma Sphere (POPS)
Author: Richard A. Nebel
Submitted: 2005-12-21 11:32:13
Co-authors: J. Park, E. Evstatiev, A. Marocchino, G. Lapenta, L. Chacon
Los Alamos National Laboratory
Los Alamos, New Mexico 87545
Theoretical work1,2 has suggested that a tiny oscillating ion cloud may undergo a self-similar collapse that can result in the periodic and simultaneous attainment of ultra-high densities and temperatures. A remarkable feature of these oscillations is that they stay in local thermodynamic equilibrium (lte) at all times independent of the collisionality of the system (i.e. they are exact solutions of the Vlasov equation for Maxwellian distribution functions).2,3 Theoretical projections1 indicate that such a system may have net fusion gain even for an advanced fuel such as D-D. Reactor schemes have been suggested where a massively modular system consisting of tens of thousands of these spheres can lead to a very high mass power density device (comparable to a LWR).1 Furthermore, the total power produced in these spheres scales inversely with the size so successive generations of experiments get smaller, not larger.2 Thus, we can envision doing breakeven scale experiments on table-top devices which cost ~ $100k-$300k. These systems are a huge paradigm change from magnetic and inertial confinement in both physics and economics.
In recent experimental work on the INS-e device at LANL we have observed the POPS oscillations by resonantly driving the plasma at the POPS frequency.4,5 Furthermore, stable virtual cathodes have been produced on INS-e that are ~ 65% of the applied voltage6 and exceed previous stability predictions7 by about a factor of 4. More recent 1-D spherical kinetic simulations6 have indicated that the angular momentum present in the virtual cathode can provide this stabilization.
Ongoing theoretical work is focused in two areas: multidimensional kinetic simulations of the stability of the virtual cathode and space charge neutralization during the ion collapse phase of the POPS oscillation. POPS simulation results indicate that significant gains in plasma compression can be achieved by properly programming the electron distribution function at the boundary.5 Two dimensional kinetic simulations indicate that the virtual cathode stability to electron-electron two-stream modes is similar to the 1-D result.
INS-e is presently being rebuilt for high voltage pulsed discharges. We are planning to install an electron-beam probe on the machine to measure the POPS compression ratios. This talk will summarize the previous and ongoing work.
1. R. A. Nebel, D. C. Barnes, Fusion Technology 38, 28 (1998).
2. D. C. Barnes, R. A. Nebel, Physics of Plasmas 5, 2498 (1998).
3. R. A. Nebel, J. M. Finn, Physics of Plasmas 7, 839 (2000).
4. J. Park, R. A. Nebel, S. Stange, S. K. Murali, Phys. Rev. Lett. 95, 15003 (2005).
5. J. Park, R. A. Nebel, S. Stange, S. K. Murali, Physics of Plasmas 12, 056315 (2005).
6. R. A. Nebel, S. Stange, J. Park, J. M. Taccetti, S. K. Murali, C. E. Garcia, Physics of
Plasmas 12, 12701 (2005).
7. R. A. Nebel, J. M. Finn, Physics of Plasmas 8, 1505 (2001).
Improvement category: C