Creating Stars in the Laboratory

by Paul Gilster on May 25, 2009

The 192 lasers of the National Ignition Facility at Lawrence Livermore National Laboratory in California can focus 500 trillion watts of power onto a pellet of hydrogen fuel the size of a pencil eraser. With full-scale experiments slated to begin soon, we’ll learn much about the feasibility of nuclear fusion on Earth, hoping to extract more energy from the process than goes into making it happen. The forms of hydrogen at play here are deuterium and tritium, which fuse to form helium.

nif_target_capsule

Image: All of the energy of NIF’s 192 beams is directed inside a gold cylinder called a hohlraum, which is about the size of a dime. A tiny capsule inside the hohlraum contains atoms of deuterium (hydrogen with one neutron) and tritium (hydrogen with two neutrons) that fuel the ignition process. Credit: National Ignition Facility.

Inertial confinement fusion using lasers is a different approach than the magnetic confinement method used at the International Thermonuclear Experimental Reactor (ITER), currently being built in Cadarache, France. There, super-heated gas is managed via magnetic fields inside a vessel called a tokamak.

But as multi-track fusion studies continue, it’s interesting to see how the National Ignition Facility will also serve as a laboratory for astronomers hoping to understand the physics of exploding stars. At full power, the NIF lasers will throw a 1.8 megajoule punch at the target. Energies like this, according to a recent BBC story on the NIF, will create temperatures of 100 million degrees and pressures billions of times greater than Earth’s atmospheric pressure, forcing hydrogen nuclei to fuse.

But adjusting the elements in the fuel pellet also sets up experiments that mimic a stellar core. The result is a mini-supernova, says Paul Drake (University of Michigan):

“You choose the material and the structures between them to be relevant to what happens when the star explodes. The laser would strike the centre – the analogue of the core of the star – launching a tremendously strong shock wave that would blow the material apart.”

All this occurs, of course, in billionths of a second, so that the results have to be scaled to the actual astrophysical environment. Nonetheless, ‘supernova’ experiments like these could be productive in helping us understand the stellar explosions that produced the elements so crucial for life. That adds a powerful tool to our arsenal, complementing the observing programs that search for supernovae in distant galaxies.

The BBC also talks to David Stevenson (Caltech) about using the NIF to study the formation of gas giant planets. Because the NIF’s lasers can produce pressures equivalent to billions of times what is found at sea level on Earth, we can study conditions that exist inside such planets, where dramatic changes to chemistry occur. The behavior of hydrogen, helium, carbon and water in such a setting should be fascinating.

We already know that hydrogen can become a metallic fluid at much lower pressures. Ray Jeanloz (UC – Berkeley) paints a graphic picture of such materials in a Jupiter-like setting:

“Hydrocarbons would actually decompose to a mixture of hydrogen and a carbon. The end result being that diamonds would actually be hailing out of the atmosphere. That’s the kind of process you would never have guessed unless you had studied the materials themselves.”

The National Ignition Facility will be the world’s largest and highest-energy laser system, delivering more than sixty times the energy of any previous laser facility. But keep your eye as well on the European High Power Laser Energy Research (HIPER) study, which received a funding boost last October. Construction of HIPER isn’t scheduled to begin for a decade or so, but success at NIF could be followed by a HIPER facility aimed at taking inertial confinement fusion to a truly commercial level.

Kelvin Long May 25, 2009 at 12:41

Achieving sustained fusion burn on earth will be a tremendous achievement for another reason which should be highlighted- application to space propulsion. Although the current fusion technology is massive, there is every possibility that once the physics issues have been ironed out, space probes could be fitted with fusion reactors which work on either the magnetic or inertial confinement principle in future decades. Then there are other facilities like the Sandia Z machine which is also making progress. Fusion pulse was of course, the propulsion drive for historical projects such as Daedalus, Longshot and Vista. Fusion offers massive Isp for both interplanetary and interstellar missions. Big expensive facilities such as NIF, ITER and HiPER will solve the problems and then clever engineers can work out how to do it better, smaller, cheaper and more efficient. The biggest problem is the driver, should it be laser, electron, ion. Daedalus used an electron driver, Vista a laser beam. There are scalability issues. Dyson said ‘Saturn by 1970′ using Orion technology, but how about Alpha Centuri by 2100. Optimistic – perhaps. But let’s watch the results from these facilities with great interest in the next decade. It’s about time as a socity we solved the fusion on earth problem, and got on to applying it to other problems such as leaving the Earth. We cannot stay in this cradle forever as one Russian once said, and with concerns over climate change, all alternative energy sources should be explored with vigour. Fusion is getting that attention. But how about other alternatives – such as zero point energy?

tony May 25, 2009 at 13:21

Hi,
Are you aware of some of the other ways of initiating fusion – such as IEC (Inertial Electrostatic Confinement, aka Polywell, invented by Dr Robert Bussard of Bussard Ramjet fame) and Focus Fusion? In comparison to the NIF and ITER behemoths, these are tiny initiatives, but they are producing terrific results.

More details on IEC and Focus Fusion at http://omyomyom.com/2009/05/many-roads-lead-to-fusion-power/ and (the mother lode for IEC) http://iecfusiontech.blogspot.com/2009/01/easy-low-cost-no-radiation-fusion.html

Cheers,
Tone

tony May 25, 2009 at 13:38

Regarding using fusion for space travel, that was one of the overriding wishes of Dr Bussard, and he came up with some incredible figures. For example, (this is from The Worlds Simplest Fusion Reactor,

Low Earth Orbit (LEO) to Mars: 33 days, more or less, for high performance
designs, or 6 weeks for economical freight-hauling variations. The craft are
single-stage, with a 15-20% payload fraction.

LEO to Saturn’s Moons: as low as two months, with a short coasting period.
Again, the craft is single-stage, and has a 14% payload fraction.

Cost to LEO: $27/kg (a price that compares favorably to the cost of riding the
Concorde across the Atlantic).

4000 people on Earth’s moon, each person with 25 metric tonnes of equipment, and each person receiving an annual visit back to Earth: $12 billion over 10
years.

1200 people on Mars, each with 50 tonnes of equipment, and an annual visit
back to Earth: $16 billion over 10 years.

400 people on Titan, each with 60 tonnes of equipment, and an annual visit back to Earth. $16 billion over 10 years.

This is using a fusion reactor with a 10 GW capacity, that is around 5 metres in diameter.

Interesting times ahead!

Administrator May 25, 2009 at 14:38

tony writes:

Are you aware of some of the other ways of initiating fusion – such as IEC (Inertial Electrostatic Confinement, aka Polywell, invented by Dr Robert Bussard of Bussard Ramjet fame) and Focus Fusion? In comparison to the NIF and ITER behemoths, these are tiny initiatives, but they are producing terrific results.

Yes, we continue to track these here with interest, in hopes that fusion may one day prove to be as practical as many think it can be. But what a long road it’s been… I like the spirit behind the smaller ventures which, as is only natural, also have their share of skeptics. So we wait for results.

Kelvin Long May 25, 2009 at 16:23

Tony,
Thanks for these excellent tips. I will look at these links. I too am keen on fusion for space propulsion. My only regret is I never got to meet Bussard who seems like a remarkable man. Anyone else know of other credible ideas for achieving fusion please let me know. Regards Paul’s comment on fusion being a long road – indeed it has. Hopefully the current generation will end that road and see it to fruition.

JD May 25, 2009 at 16:39

I once read that the fusion rocket might become possible far earlier than an actual power-producing reactor, since in order to exploit fusion propulsion (directly), you only need a Q slightly above 1 (maybe 5), whereas actual reactors would need much higher energy gain factors.

Is that true?

Kelvin Long May 25, 2009 at 19:08

JD, I would say that credible fusion propulsion systems need >>1. Vista for example specified a requirement of Q=1000-1500. I would argue that a propulsion system needs to have a higher Q (i.e. more efficient) because you can’t just replace the components such as the optics in the laser where you could in a ground reactor and you want to get more ‘bang for your buck’. Also, I guess the more Q you get per pulse, the less fuel you need to carry overall which is good from a mass fraction point of view. Current fusion schemes such as the HiPER proposal discuss a Q=100 which is reasonably high gain, but I think a lot more is required. These are just random thoughts.

djlactin May 26, 2009 at 0:15

500 trillion Watts in what amount of time?

tony May 26, 2009 at 1:52

Admin, Kelvin,
My interest in fusion was re-ignited (groan) when I saw the video of Dr Bussards’ Google techtalk “Should Google go nuclear?”. It’s fast paced, and sometimes quite hard to follow, but he knew time was running out and wanted to start things up. Since then, I’ve found out that other ‘small’ initiatives are taking place, such as Focus Fusion and the Tri-Alpha company, at least partly funded by Paul Allen.

It staggers me that these smaller, quicker initiatives are operating on peanuts, when the ITER-type operations work at the international level with all the squabbles over siting that you’d expect from government ‘prestige’ projects, with their ‘only another 40 years to go’ mantra.

Meanwhile, there’s reason to believe that the IEC (Bussard) fusion guys will know whether their approach will lead to commercial energy in a time scale of 18-24 months.

Interesting times ahead!

Administrator May 26, 2009 at 8:21

djlactin, the 500 trillion watts covers 20 billionths of a second, according to the BBC.

Bob Steinke May 26, 2009 at 12:23

JD and Kelvin,

Fusion rockets could be useful with a very small Q. You just have to consider what the mission is and what the propulsion alternatives are. Electric propulsion systems like ion thrusters and VASIMIR are basically equivalent to a fusion drive with a Q of zero. So for any mission where you are planning to use VASIMIR, changing to a fusion reactor with a Q of 0.5 would be an improvement.

This wouldn’t work for interstellar, but it would work for any mission that can use present day electric thrusters.

James M. Essig May 27, 2009 at 0:57

Mankind stands ready to soon harness nuclear fusion on a wide scale, a cosmic energy source of potentially unlimited scope.

Not to drift too far off subject here, but imagine a fusion trail of fusion fuel pellets laid out in the form of a wick that had a linear mass density of one metric ton per kilometer wherein a manned interstellar space craft would be launched and powered by the fusion wick as it raced along the wick as the wick was ignited or made to burn at an ever faster rate to match the velocity of the space craft. Assume the craft would be able to extract and convert 50 % or more of the fusion energy into space craft kinetic energy through an unspecified fusion energy collection mechanism which provides the power to operate an ion, electron, photon, or neutrino or even a tachyon rocket propulsion system, an electrodynamic-hydrodynamic-plasma drive system, a magnetic field effect propulsion system and/or the like electrical propulsion system.

If the wick was constructed to be 200,000 thousand light years long, then the terminal kinetic energy of the craft would be > (1/2)(2 x 10 EXP 5)(10 EXP 13)(10 EXP 3)[C EXP 2] Joules which is the equivalent of 10 EXP 18 metric tons of mass converted into energy. For a space craft with a rest mass of 10 EXP 15 metric tons, the terminal gamma factor would be 1,000; a space craft with a rest mass of 10 EXP 12 metric tons, a terminal gamma factor of 1 million, a space craft with a rest mass of 10 EXP 9 metric tons, a terminal gamma factor of 1 billion; a rest mass of 10 EXP 6 metric tons, a gamma factor of 1 trillion, and so on.

I can imagine examples of this technology that are ever more so extreme that such would sound absurd to post in this scientific forum.

Adam May 27, 2009 at 6:50

We only know one way to produce fusion reliably at present and it produces a pretty damned good Q. Of course pure fusion pulse-units in an “Orion” would perform better, but it’s doable technology – if we pitched the world’s economy into the task.

Anyone for city-sized “Orion” starships?

James M. Essig May 27, 2009 at 8:59

Hi Folks;

It seems to me that building larger starships would enable to complexity required to capture and recycle waste heat and electromagnetic emmissions from fusion power generation systems. The recaptured energy, along with the primary energy source could power laser beams directed virtually exactly antiparallel to the ships velocity vector. This way, we would have the advantage of a light speed highly directed exhaust stream.

Adam;

I like the idea of ciity sized Orion starships. We could power such star ships with nuclear devices in the 100 kiloton to 500 kiloton range typical of contemporary nuclear warheads. I cannot think of a better use for such devices. However, due to the mass factor such as the chemical explosive, and structural housing of today thermonuclear warheads, the mass specific yield is considerably lower than that of pure fusion bombs. But heck, there in nothing to say that we could not build hundreds of millions or more of these warheads inorder to have a high fueled wieght to dry weight vehicle ratio.

If we can crack the human longevity problem within the next 20 years so that I can live another 80 years or more, I would love to be a crew member on such a vessel. I think once we augment human life expectany by 50 to 100 years, Orion style vehicles, powered by todays warhead designs could look might good for precursor missions to our stellar nieghboors.

ljk June 19, 2009 at 7:45

ITER fusion experiment faces three-year delay

New construction timetable puts back first deuterium-tritium plasma to 2026:

http://physicsworld.com/cws/article/news/39530

Comments on this entry are closed.