December 04, 2009

Compact Proton Beam Accelerators and Handheld Fusion Reactors

Previously this site had reported on the DARPA project to create chip scale high energy atomic beams as a path to commercial nuclear fusion.

There is a DARPA budget document with a bit more description that what was previously referenced.

The Chip-Scale High Energy Atomic Beams program will develop chip-scale high-energy atomic beam technology by developing high efficiency radio frequency (RF) accelerators, either linear or circular, that can achieve energies of protons and other ions up to a few mega electron volts (MeV). Chip-scale integration offers precise, micro actuators and high electric field generation at modest power levels that will enable several order of magnitude decreases in the volume needed to accelerate the ions. Furthermore, thermal isolation techniques will enable high efficiency beam to power converters, perhaps making chipscale self-sustained fusion possible.

Program Plans:
FY 2009 Plans:
- Develop 0.5 MeV proton beams and collide onto microscale B-11 target with a fusion Q (energy ratio) > 20, possibly leading to self sustained fusion.
- Develop neutron-less fusion allowing safe deployment for handheld power sources.
- Develop microscale isotope production by proton beam interaction with specific targets.
- Explore purification of isotope systems.
- Develop hand-held pico-second laser systems to introduce wakefield accelerators for x-ray and fusion sources.

UPDATE: Physicist Art Carlson comments:

For those who might not know: Even if you can make a 0.5 MeV ion beam, and even if you can make it with 100% energy efficiency, when it slams into a solid target it will unavoidably lose more energy by heating the electrons in the solid than it will produce by fusion. This is true for D-T and it is 1000 times more true for p-B11.

It seems likely that the higher voltages suggested in Winterberg's fusion proposals (gigavolts) would be needed.

Principles and applications of compact laser–plasma accelerators

There are various laser pumped proton beam systems in the 3 Million EV to the 58 million EV range. Some of the 3 million EV systems are relatively compact.

Testing the first goal:
Develop 0.5 MeV proton beams and collide onto microscale B-11 target with a fusion Q (energy ratio) > 20, possibly leading to self sustained fusion.

Seems to be testable even if making everything chipscale takes longer.

Proton beams

In contrast to electrons, ions are best accelerated by a low-frequency (compared with the electron plasma wave frequency) or even a quasi-static electric field. Indeed, owing to their higher mass, the rapid field oscillations associated with an electron plasma wave average out to zero net acceleration for an ion. In experiments
so far, the mechanisms of ion acceleration can be classified into two categories, on the basis of how the electric charge separation that produces the quasi-static field is generated: ponderomotive or thermal explosion acceleration.

Proton beams produced by rear-surface acceleration show good collimation, increasing at higher proton energy, and very low transverse emittance (below 10-2 mmmrad for protons above 10MeV). Several paths for beam optimization are now being actively pursued. The first is to operate with ultrathin targets, in the sub-100nm range, which requires ultrahigh-contrast laser pulses. Improved acceleration with such targets has been reported recently.

Proton beams with energies up to 58MeV have been measured at the Lawrence Livermore National Laboratory with the now dismantled Nova petawatt laser. With smaller facilities, of the 1 J/30 fs class, distributions extending up to 10MeV have been

The evolution of short-pulse laser technology, a field in rapid progress, will still improve the properties of laser produced particle sources. For example, the development of diode pumped lasers will enable the laser power efficiency to be increased by up to tens of per cent and will also lead to a significant reduction of the size of the laser systems. The rapid evolution of chirped pulse amplification laser technology, coupled to progress in laser–plasma interaction modelling, will soon result in improved performances, lower cost and still wider applicability of these compact particle sources.

The Extreme Light Infrastructure project in Europe and other projects are advancing the technology of lasers and accelerators and are bringing researchers together to look at uses for these new particle and photon beams.

Neely, D. et al. Enhanced proton beams from ultrathin targets driven by high contrast laser pulses.
Appl. Phys. Lett. 89, 021502 (2006).

Antici, P. et al. Energetic protons generated by ultrahigh contrast laser pulses interacting with ultrathin targets. Phys. Plasmas 14, 030701 (2007).

Ceccotti, T. et al. Proton acceleration with high-intensity, ultra-high-contrast laser pulses. Phys. Rev.
Lett. 99, 185002 (2007).

Proton Acceleration with High-Intensity Ultrahigh-Contrast Laser Pulses

We report on simultaneous measurements of backward- and forward-accelerated protons spectra when an ultrahigh intensity ( 5 X 10^18 W=cm2), ultrahigh contrast (>10^10) laser pulse interacts with foils of thickness ranging from 0.08 to 105 micrometers. Under such conditions, free of preplasma originating from ionization of the laser-irradiated surface, we show that the maximum proton energies are proportional to the p component of the laser electric field only and not to the ponderomotive force and that the characteristics of the proton beams originating from both target sides are almost identical. All these points have been corroborated by extensive 1D and 2D particle-in-cell simulations showing a very good agreement with the experimental data.

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