Laser Particle Acceleration: Status and Perspectives for Nuclear Physics

Laser Particle Acceleration: Status and Perspectives for Nuclear Physics (12 pages)

High power short-pulse lasers with peak powers presently reaching Terawatts and even Petawatt levels routinely reach focal intensities of 10^18–10^21 W/cm2. These lasers are able to produce a variety of secondary radiation, from relativistic electrons and multi-MeV/nucleon ions to high energetic X-rays and gamma-rays. In many laboratories world-wide large resources are presently devoted to a rapid development of this novel tool of particle acceleration, targeting nuclear, fundamental and high-field physics studies as well as various applications e.g. in medical technology for diagnostics and tumor therapy. Within the next 5 years a new EU-funded large-scale research infrastructure (ELI: Extreme Light Infrastructure) will be constructed, with one of its four pillars exclusively devoted to nuclear physics based on high intensity lasers (ELI-Nuclear Physics, to be built in Magurele/Bucharest). There the limits of laser intensity will be pushed by three orders of magnitude to yet unprecedented 10^24 W/cm2.

Computational Studies Suggest that Laser Ignition of Aneutronic Fusion is Only Ten Times More Difficult than Deuterium-Tritium Fusion and Not One Hundred Thousand Times Tougher

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A team led by Heinrich Hora at the University of New South Wales in Sydney, Australia has carried out computational studies to demonstrate that new laser technology capable of producing short but high energy pulses could be used to ignite hydrogen/boron-11 fuel using side-on ignition.

The high energy laser pulses can be used to create a plasma block that generates a high density ion beam, which ignites the fuel without it needing to be compressed, explains Hora. Without compression, much lower energy demands than previously thought are needed. 'It was a surprise when we used hydrogen-boron instead of deuterium-tritium. It was not 100 000 times more difficult, it was only ten times,' says Hora.

Fusion reaction   Neutron fraction
DT                   0.80  (80% of the energy is neutrons == radiation)
DD                   0.336
D3 He                0.02
p6Li                 0.05

Journal of Energy and Environmental Science - Fusion energy without radioactivity: laser ignition of solid hydrogen–boron (11) fuel

The full paper is here

The usual laser compression developed for burning deuterium–tritium (DT) fuel cannot be used for H–11B because densities of 100000 times the solid are needed. Instead, the alternative laser fusion scheme of side-on ignition with uncompressed fuel is proposed to enable ignition of the H–11B fuel along with PW laser interactions. This approach employs a recently discovered laser-plasma interaction technique that uses very high contrast ratio laser pulses (i.e. pulses nearly free from pre-pulses). Plasma blocks of modest temperature are generated causing highly directed ion current densities above 10^10 A cm−2. This new ignition process is termed side-on block ignition, and it is described here in some detail.

The NIF laser is expected to produce ignition by delivering pulses of 1.1 MJ on the ICF target over a few nanoseconds. The ignition campaign at NIF is scheduled to achieve ignition in 2010–2011, demonstrating for the first time on Earth a controlled fusion reaction capable of generating more energy than delivered by the input laser pulse. The DT fusion reaction burns (reacts with) isotopes of heavy hydrogen (deuterium, D) with the super-heavy hydrogen isotope (tritium, T), where the laser irradiation compresses the fuel to more than 1000 times the solid density, causing heating to ignition temperatures of several tens of millions of degrees centigrade. Following on this success, LLNL scientists have proposed a prototype power station for 2020, based on use of a very compact, high efficiency, and high repetition rate diode pumped laser which builds on current laser technology. Simultaneous development of a power plant using similar technology is also proposed for use as an actinide burner to resolve the radioactive waste problem from existing light water reactors.

Parallel to these developments, new schemes for ICF power have been proposed based on the new type of laser offering more than PW (petawatt) pulses over picoseconds. The basic scheme is to use a slower pulse laser to initially compress a target to reasonably high density and then use this PW laser to heat (ignite) some volume in the target, which will burn into the rest of the high density fuel. Called fast ignition (FI), this method significantly reduces input power requirements, hence giving higher energy gain operation. If achieved, this approach promises a higher performance power plant than possible with the conventional direct compression and burn of the ICF operation. For one of these FI options, a design by Nuckolls and Wood using electron beam ignition, initial compression to only about 10 times solid state density is needed. The ignition occurs with very intense electron beams (of 5 MeV energy). These PW laser beams interact with the pre-compressed target through highly non-linear effects. This technique arrives at fusion gains of 10000. A pre-compression of the target to about 1000 times solid-state density is required to generate the intense electron beam.

This paper now reports on another method8 that uses PW–ps laser pulses without high pre-compression of the target. It uses side-on ignition of the target at normal solid state or slightly increased density. The technique follows mechanisms which were actually observed in 1972. However, according to these early results, it appeared impossible to use this in a practical system.

The use of nonlinear force driven plasma blocks with the ultra-high current densities using a PW–ps laser-plasma interaction permits a come-back of the side-on ignition of uncompressed DT.

Side-on ignition for fusion using plasma blocks driven by nonlinear forces laser interactions is based on preventing self-focusing of the laser beam as previously described. This requires strong suppression of laser pre-pulses, i.e. a contrast ratio higher than 10^8, for times dozens of ps before arrival of the main pulse. The resulting plasma blocks have high momentum and are directed back towards the incoming laser beam. Momentum conservation causes an imploding block of plasma towards the inner portion of the target fuel. This implosion produces an inward moving thermonuclear reaction shock front as elaborated in the work by Chu. If the laser is obliquely hitting the plane target, the direction of the nonlinear force accelerated blocks is mainly perpendicular to the target surface, with minor deviations due to collision absorption, anticipating the later derived TNSA (target normal sheet acceleration) by Wilks from his discovered particle-in-cell computations

A much more detailed analysis is needed but at least the basic characteristics for side-on ignition are clearly visible. Most significant are the very surprising results that uncompressed H–11B can be ignited. This fusion energy generation with laser pulses in the range of few dozens of PW power and ps duration can achieve H–11B power production. The remarkable fuel avoids neutron generation, results in negligible radioactivity, and allows direct energy conversion, which in turn reduces heat pollution. Such a power plant is ideal for stationary electrical generation in a power station or for space propulsion. Modest pre-compression by chemical driving or with high density cluster methods55 could improve performance even further especially for p–11B. The X-ray radiation produced in the reaction chamber is 200 keV which can be screened off and does not lead to nuclear reactions in the power stations. This provides an exciting vision of a very attractive sustainable future power plant for worldwide use. Its achievement will depend on continued advances in laser optics, target physics and power conversion technology. However, the studies reported here show that such a system is rather close at hand—something not realized before, since p-11B ignition had always been viewed as virtually impossible

The advent of ultra-high power lasers allows laser power levels that are about 1000 times the power of all the power stations in the USA. This opens the way to new approaches for inertial confinement fusions (ICF) that in turn can drastically reduce the laser input energy needed to achieve practical ICF power. The specific approach discussed here involves inducing a fusion burn wave by laser-driven impact of a relatively large block of plasma on the outside of a solid density fusion target. This new method is specifically selected to enable the extremely attractive, but demanding, neutron-free proton–B-11 fusion that potentially can lead to the long sought goal of an ultra clean fusion power plant.

Conventionally, the fusion process occurs with deuterium and tritium as fuel. The fuel is spherically compressed - meaning compression occurs from all directions - with laser irradiation to 1000 times its solid state density. This ignites the fuel, producing helium atoms, energy and neutrons which cause radiation. Fusion is also possible with hydrogen and boron-11, and this could produce cleaner energy as it does not release neutrons, explains Hora.

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Petawatt lasers now and Exawatt and Zettawatt Lasers on the Way

The Texas Petawatt laser was completed March 31, 2008, allowing an immediate demonstration of its 1.1 petawatt power by producing, 200 J, 167 fs pulses.


The US National Ignition Facility is to start firing in 2010

Zettawatt-Exawatt Lasers and Their Applications in Ultrastrong-Field Physics

From 1992-2001, however, we have seen a surge in our ability to produce high intensities, five to six orders of magnitude higher than was possible before. At these intensities, particles, electrons and protons acquire kinetic energy in the mega-electron-volt range through interaction with intense laser fields. This opens a new age for the laser, the age of nonlinear relativistic optics coupling even with nuclear physics. We suggest a path to reach an extremely high-intensity level 10^26−28 W/cm2 in the coming decade, much beyond the current and near future intensity regime 10^23 W/cm2, taking advantage of the megajoule laser facilities. Such a laser at extreme high intensity could accelerate particles to frontiers of high energy, tera-electronvolt and peta-electron-volt, and would become a tool of fundamental physics encompassing particle physics, gravitational physics, nonlinear field theory,
ultrahigh-pressure physics, astrophysics, and cosmology.

A zettawatt system could be built using Yb:glass, with the advantages of being
relatively compact due to the high Fsat of this material and being diode pumpable, much development work needs to be accomplished to reach this intensity level with this material. The proposed systems described below have been stimulated by the construction , both in France and in the U.S, of lasers delivering a few megajoules of energy as well as the availability of large telescope technology (10m diameter) and deformable mirrors

An exawatt system on the other hand,which would produce 10 kJ in 10 fs, i.e., 10^25 W/cm2, could be readily constructed. Only one percent or 30 kJ of the NIF/LMJ energy would be necessary. The beam size will be of the order of one meter in diameter. The amplifying method will be composed of a matrix of 25 Ti:sapphire 20×20 cm2 crystals and two gratings of meter-size.

A tutorial on the Technology and Economics of laser Inertial Fusion by Per Peterson

How IFE works








Europe has extreme light project to plan and build an exawatt laser

Europe also the Hiper project to develop laser fusion.

HiPER proposes to build a demonstrator diode-pump system producing 10 kJ at 1 Hz or 1 kJ at 10 Hz depending on a design choice yet to be made. The best high-repetition lasers currently operating are much smaller; MERCURY at Livermore is about 70 J, HALNA in Japan at ~20 J, and LUCIA in France at ~100 J. HiPER's demonstrator would thus be between 10 and 1000 times as powerful as any of these. HiPER construction is to begin in 2011 or 2012.

Construction of the HiPER facility is envisaged to start mid-decade, with operation in the early 2020s.

Military defense may get a step up on offense

There are two developing technologies.

The millimeter radiation system for Active denial. The pain beam. It works out to 500+ meters. They are talking deployment in 2010. They are already in various field trials.

I wrote about theHPM (High Power Microwave) pulses--powerful enough to destroy enemy electronics--can be produced without the need for explosives or huge electrical generators. They are talking systems in the terawatt range to fry navy ships and 100 gigawatts to take out cruise missiles.

They could also make better sensor system on a fighter-size aircraft that could generate enough power, with a 1-ft. resolution, to see stealthy objects at 100 miles.

If Russia and China and other military powers can see through US stealth then a big US advantage will go away.

The next link talks about petawatt power, blowing apart protein molecules in a coluomb explosion.

So some observations and questions:
1. If the active denial system power was boosted. by say US, Russia and China (or any other major country) then it would easily be a longer range death to the unshielded beam. This would be a hinderance and would bog down attacking forces. If military personal in planes, on the ground have to be constantly shielded they will be slower. Can planes fly with the necessary shielding? Can high power versions of the active denial systems get enough range.

2. Combining the anti-electronics and anti-personal beams from large shielded ground installations combined with stealth defeating sensors would shift the balance of power significantly back towards defense. It is easier to make heavy beam shielding than it is to make it mobile for flight or vehicles.
I believe Russia and China are about as advanced as the US in terms of microwaves and millimeter wave technology. The Russians in the cold war were ahead in the high powered version.
I think the Chinese ability to hit the GPS satellites, possibly soon be able to see through stealth and these new beam technologies would mean that the aspects of recent significant US domination would be taken away. Fights against Russia and China would now be even more less likely to happen because they would be even longer slower slogs in the initial phases.

Human directed fighters and unmanned UAVS would both be vulnerable to one of the two beams How much can the effective range of the beams be increased ?

3. What happens in the molecular nanotechnology (MNT) world ? If you make bigger and more efficient beam projection arrays.
Could the right frequencies be manipulated to spot any MNT built UAVs. Could the MNT UAVs get hardened against the radiations?
Could the beams be used to detect and slow any MNT UAV attack to protect nuclear or some other deterrence. How would the nuclear electronics get protected to get payload to target?