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Laser Fusion

Laser compression & burn of fuel pellets

Shattered wine glass
Twitter resonates with need. Creates an Avalanche of users.
1.Wineglass at high C.
Stacks Image 2576
3 level pump& case
2. Excited energy levels.
Ruby Laser
Maiman at Hughes Research, 1960. Xenon flash pump.
3.The First working Laser
Townes, Basov and Prokhorov: Nobel Prize, 1963
4. Nobel Prizes
Ablation concept
John Emmett & John Nuckolls with Nd-glass amplifier
5.Compression by ablation.
view into chamber
NIF chamber arrives.
6. View into the NIF target chamber.
NIF flashlamps
Neodymium-Yttrium-Aluminium-Garnet glass.
7. Flashlamps & Laser glass.
NOVA beamlines
Cartoon of the NIF facility. Giant laser vs. tiny target.
8. NOVA Laser: Multiple beamlines.
asymmetry problems
Inspecting the target holder. Tiny target drops to chamber centre - laser focus.
9. Targets can splatter, foiling compression.
Rutherford lab
World competition for laser power.
10.RAL UK seeks smaller high power lasers.
Diffraction grating
How to manufacture ultra power pulses.
11.Inspect diffraction grating.
Texas Petawatt laser
VULCAN light factory.
12. PetaWatt Laser, Texas. See VULCAN
hotspot vs compression
Bring a hotspot to ignition and burn the target.
13.Beat the wobbles
LIFE Hybrid reactor.
HIPER Fusion project for the EU.
14. Laser Fusion Reactors
LLNL Dye laser
Free Electron Laser for compact very High power.
15. Dye Lasers for isotope separation.

Laser Fusion requires many extraordinary feats in sculpting light beams to compress and ignite spheres of D-T fusion fuel. The story follows the 30 pictures on the left. The links on the right take you back to the Fusion Primer and into overviews of the technologies. The Laser Fusion Library offers many papers and lectures on all aspects.

1. Resonance
Let us start with some analogies: A thin wine glass may have a natural ring around high C. A strong sustained note at this resonant frequency can build up vibrations to break microscopic flaws and shatter the glass.

Click on this to find a different resonance between a mobile app and a popular messaging need, creating an avalanche of customers. Keep up with Fusion events @EfNFus.

2. Stimulated Emission of Light.

The outer electrons of atoms and molecules can be excited to higher levels by electric currents or by absorbing light at the right frequency. Quantum mechanics sets the precise excitation energy but then allows the energy to be re-emitted, after some decay time, to return to the lowest energy.
Now for the good bit: A photon passing the atom at this resonant energy can cause the prompt emission of its photon. Even better, it is emitted in the same direction and in phase with the passing photon. These two photons can now trigger more emissions and pretty soon you have an avalanche in some direction.
The trick is to excite lots of atoms or molecules in the solid, liquid, gas, or plasma medium and use mirrors to select a preferred direction before triggering the avalanche into a directed beam.
The solution is to find materials with more excited levels above the first. Pump the medium with an intense flash of light to go to an upper level. These rapidly drop to level one so most of the energy is ready to be released in a beam.
Picture 2 illustrates this very well.

3. The Ruby Laser.
The first working laser was built by Maiman at the Hughes Research Labs, California. He was told it would not work - what is new? He used man made ruby doped with Chromium to give a 3 level system. Solids have lots more atoms per cc than liquids or gases, A Xenon flash lamp pumps the rod. The ends of the ruby rod were polished flat and parallel to bounce the resonant photons back and forth many times before escaping as abeam. Maiman's original laser still works today.

4. Nobel Prizes
The theory and many experiments earned Basov, Prokhorov, and Charles Townes a Nobel Prize in 1963. Since then our lives have filled with many types of laser. An average US home has lasers in CD drives, remote controls and light pens. Laser surgery is common for a range of conditions from hair removal to eye surgery.
Almost every Nobel Prize in Chemistry, Physics, and Medicine has lead commonplace applications as another avalanche of inventors make use of the discoveries.
In the case of lasers, the ex-weapons people in Fusion energy research 50 years ago promptly recognised that a door to laser fusion had opened up. The Hydrogen bomb works by compressing a Lithium-Deuterium target with a Uranium explosion. Radiation pressure is a key part of the compression to densities above 1000 times solid density where fusion ignites.
The path was long with much left to invent.

5. Compression by Ablation.

How can one compress a sphere of fuel with light? John Nuckolls at Livermore saw that a laser would heat and evaporate the outer layers, blasting them off the sphere. This ablation of material exerts a backward force on the sphere, compressing it. A surface coating of heavy metal like Gold would create a shock wave to the centre. At the right density a much larger laser pulse can then heat the core to ignition when 100 times as much energy is released by fusion.
Much of the target design could be rapidly evaluated by assuming a perfectly spherical target and laser input so that only the radial compression needed to be computed. This gave a clear set of goals for the laser project.

The classified Livermore Laser programme is entirely funded by the Defense Dept. Academic (NSF) laser programmes have followed the same developments on a different scale. The conceptual breakthrough was widely known. A UK researcher talked at Livermore about his work and was then forbidden to work on it under the US-UK agreements on exchange of nuclear data. And so it goes.

6. The scale of the NIF facility
This is illustrated by the size of the target chamber.

7. Flash lamps & Nd Laser Glass
The NIF uses 192 beam lines, combined into 48 injection ports for pellet compression and ignition. The slightest flaw in any glass module could absorb incident laser light and shatter the glass.

8. NOVA Laser & NIF Cutaway
The NIF predecessor, NOVA, developed the laser construction technologies. Visitors were required to wear three layers of goggles to protect them against any stray laser beams.

9. Possible Compression Problems.
Nature is not one dimensional so perfectly spherical compression is not possible even with 48 beams into the target chamber. Surface roughness , imperfections in the tiny targets, and simple fluid motion instabilities reduce the total compression. The NIF has not quite achieved its goal of fusion break-even by 2013.

It is now facing a 10% layoff for LLNL.

This decline of support began when management of the Lab was privatised by transfer from the University of California to Bechtel Corporation. Running major science projects on a business basis with short term financial goals and corporate management salaries rarely works.

10. Smaller Lasers at higher power.
The methods for timing and shaping laser pulses for NOVA, NIF and other large lasers of the same generation opened up new variations. On a much smaller budget, the UK Rutherford Appleton Lab (RAL) designed much higher power lasers (VULCAN) but with much shorter pulses. At a peta-watt, 10^15 watts/sec., or the total world electricity output, but for only a femtosecond , or 10^-15 secs., delivers a puny 1 watt-second of energy. Properly focussed this can deliver a large amount of heat to a tiny spot. (Comparing a watt of energy with the power of the world electricity supply is a bit daft and misleading.)
The chart on display shows how such lasers compare with much bigger ones.

11. Sculpting High power spiked pulses.
We must now explain how a spark works: A student house in Berkeley insisted on playing loud music late every night, despite city ordinances against it. A distressed scientist neighbour brought home a spark generator from her lab and plugged it in at 10.00pm every week night. The students heard the crack of this spark on every TV, radio, headset, and cd player on every channel. The spark radiated on every RF frequency. This is the difference between a cracking sound and a single note.
The different frequencies in a short light pulse can be split up and recombined by diffraction through a pair of prisms, as described so clearly by Isaac Newton. A well cut crystal on your windowsill can scatter rainbows around your room.

Stay with tour! The ending will be good.

A short petawatt pulse in a laser amplifier could melt the glass, but now we know how to beat that problem: Start with a very short pulse, split the different frequencies with a diffraction grating and make them travel different distances before recombining them into a long pulse. Amplify the long pulse and reverse the diffraction steps to compress it aback to a very short pulse.

This is the story in the diagram behind the diffraction grating.

Had the lady in Berkeley used the same processes to amplify her spark to a 10kW jolt she might have actually burned out the students' equipment - domestic EM Pulse weapon. As it was they all took their equipment to be checked out before admitting defeat.

12. Petawatt Lasers
Many Petawatt lasers have now been built. The big picture shows the layout of the Vulcan light factory for femtosecond pulses.

13. The Spark for Ignition.
Controlling a laser pulse down to one thousandth of a trillionth of a second is daring stuff. This spike of energy could spark fusion in a well compressed but imperfect target.
NIF may have missed its primary goal so far, but it developed startling technologies. It is now using Petawatt laser pulses to photograph pellet implosions - the fastest shutter speed ever! These revealed the differences between computer simulations and real behaviour. Knowing what is wrong as a step to getting it right.
NIF is capable of exploring the internal physics of supernovae or even neutron stars. Perhaps with a Plutonium outer shell it could add fission energy to the fusion for hybrid pellets and still be a power source.

14. Hybrid Fusion-Fission

The future can be explored with supercomputers. A sub-breakeven laser fusion plant may still serve as a fusion core to a liquid fuelled Fission reactor blanket around the chamber. These studies are fascinating in their details.
The UK RAL HIPER project with a Petwatt spark laser is a creative concept to be explored.

15. Other Energy Uses for Lasers.
Lasers have proved to be a hugely flexible toolkit. Lasers using organic molecules as the gain medium can be tuned very finely to distinguish between isotopes of an element.
The Australian SILEX process allows for separation of U-25 from U-238. A SILEX enrichment plant is to be built by GE at Paducah, Kentucky.
A SILEX process may be devised to separate Lithium isotopes to make Tritium manufacture easier.

The Page Background
The one use that seems most unlikely is the Star wars application to blow up missiles at a 100-1000 mile range in space.The background to this page is of a Star Wars laser shooting an aircraft. The only thing Reagan's Star Wars project destroyed was the Livermore Magnetic Fusion programme in order to redirect money and scientists into the weapons research. The Russians knew it would not work but Gorbachev & Reagan used it as a crutch to engage in strategic talks anyway. Being right is not sufficient reason to listen to a scientist.

DT Fusion reaction
How D-T Fusion works
Fusion Overviews
pellet ablation
Laser ablation compression
Laser Fusion Overviews
Laser Fusion Library
Natnl Ignition Facility
Target Chamber
Laser Fusion Library
Vulcan Diffraction grating
Laser Fusion Reports
Townes inventor
Laser Fusion Lectures