Pages

May 18, 2011

FP Generation fusion project was funded and built prototypes

Schematic of MIX-8 device using Octahedral Electromagnet

FP Generation was first formed in 2005 by two Columbia graduate students in the department of Applied Physics. In April of 2009, FPG raised $3 million in series A financing from two leading cleantech venture funds to demonstrate the viability of the MIX concept for net fusion power generation. After some initial theoretical, computational and design work, and a meeting of the technical advisory board in September 2009, FPG hired a team of physicists, engineers and technicians, and built a lab in Woburn, MA, 10 miles north of Boston.

As of April, 2011, FPGeneration is running out of funds to carry on the research. After two years of operations, our VCs have decided the technology is looking more like an extended research project than what they had signed up for initially. Unfortunately, in the absence of additional investment, this technology will be mothballed.

The MIX machine construction was completed by May 2010, but by the fall of that year it became clear that there were fundamental problems with the approach. In November, the team invented the MARBLE concept; this new device seems to solve the problems inherent in the MIX design. FPG built a prototype, which has been running since March 2011.



Alex Klein

Alex is founder and chief scientist at FPG. In 1999 he invented the MIX concept, which formed the basis for the experiments at FPG. For several years he was experimental physicist at EMC2, where he worked with R.W. Bussard and N. Krall on Polywell IEC fusion experiments. Just prior to FPG, he was employed by MIT to work at the largest fusion experiment in the world, the JET tokamak in the UK.

Technology

Linear Electrostatic Ion Traps - Just as photons can be trapped in an optical cavity by bouncing light waves between reflecting curved mirrors, charged particles, subject to electromagnetic forces and the laws of charged particle optics, can also be confined indefinitely using electrostatic reflectors. This principle, pioneered at the Weizmann Institute in Israel a decade ago, forms the basis for a radically new means to trap energetic ions in a table-top device. Ion beam storage otherwise had generally involved, cumbersome, and expensive magnetic storage rings. FPGeneration is taking linear electrostatic ion traps to the next level, with the innovative addition of magnetic fields and electrons.

Inertial electrostatic confinement (often abbreviated as IEC) is a concept for retaining a plasma using an electrostatic field. The field accelerates charged particles (either ions or electrons) radially inward, usually in a spherical but sometimes in a cylindrical geometry. Ions can be confined with IEC in order to achieve controlled nuclear fusion.

First Steps: Multi-pole Ion beam Experiment (MIX)

The magnetic field produced by the MIX magnet is known as a multi-pole field, effectively an alternating arrangement of north and south poles arranged about each other to produce a field null in the center. This type of field produces a plasma confinement topology that is stable to magneto-hydrodynamic (MHD) perturbations, and is an effective means to trap not only electrons, but also a cold plasma. This core-trapped plasma can reach fairly high densities and may serve as a target for fusion collisions with the recirculating ion beams.

MARBLE: Multiple Ambipolar Recirculating Beam Line Experiment

One of the main problems with beam-based fusion efforts is the existence/requirement of unneutralized space charge. Child-Langmuir limitations for charged particle beams are simply such that unimpressive currents, and thus unimpressive densities, will always prohibit useful fusion power densities for any reasonable device size. Unneutralized space charge forms the basis of the limitations of a number of technologies, not only IEC fusion generators, but wherever intense charged particle beams are required.

The MARBLE achieves a large source region by combining multiple ion beams which lie on a common axis, with each beam at a unique energy which differs from the others. The underlying idea is that charged particle electrostatic mirrors consist of equipotential surfaces, and not material surfaces as is the case with photon reflectors. Particles with total energies equal to a particular potential surface are reflected by that surface, but particles with substantially higher energies can pass through unimpeded. An electrode geometry can easily be found where ions and even electrons (hence ambipolar) of several different energies are contained in a linear electrostatic trap. Regions which act as mirrors for one group of particles serve the dual function of acting as a lens for the other groups of particles.

In addition, it turns out that it is possible to electrostatically confine not only multiple beams which share the same focusing electrodes, but also to confine both positive and negative charges together and at the same time.They key is to provide accel-deccel focusing to create a stable optical cavity for several types of particles. The idea can be extended to larger and larger energies, using alternating voltages with increasing magnitude on the electrodes.

The addition of an axial magnetic field produces an extraordinary effect: electrons are constrained to travel axially, regardless of their energy. Using a single external electron source, virtual cathodes are easily established along a MARBLE device, located near the "valleys" of the free space vacuum potential.The peaks of that potential are transformed into classical Penning traps, where any cold electrons are extremely well confined and may be used to ionize a rarefied population of neutrals.

Of course, multiple MARBLEs may be still be arranged about a common core, provided the axial magnetic field is due to two opposing solenoids (cusped geometry). The final result: a dense and very energetic collection of ions, whos lifetime is limited only by Coulomb scattering and fusion collision rates.

In early 2011, FPGeneration designed and constructed a MARBLE prototype designed to trap five distinct recirculating beams. The system was assembled using only simple conically shaped electrodes, inexpensive parts, and went from design to pump-down in only six weeks.



Initial results look promising. Penning discharges form spontaneously even at very low pressures, and by adjusting the magnetic field strength we are able to dial in electron densities (given by the Brillouin limit). For this device, a mere 200 Gauss appears to be optimal. We've also run hundreds of hours of LSP PIC code simulations, which confirm that five separate ion beams should form and be trapped in the device. Beam dump Faraday cup diagnostics produce signals consistent with our expectations, though this is subject to further testing and refinement of the measurment techniques.


If you liked this article, please give it a quick review on ycombinator or StumbleUpon. Thanks
blog comments powered by Disqus