Focusing 192 lasers on one little target

[n2doc]

David Perlman, Chronicle Science Editor

Friday, January 29, 2010


Scientists at the Lawrence Livermore National Laboratory reported Thursday they have taken a major step toward harnessing the forces that power the sun in an effort to create unlimited energy on Earth.

In experiments at the lab's National Ignition Facility, the scientists successfully fired an array of 192 laser beams at a helium-filled target no larger than a BB shot and instantly heated it to 6 million degrees Fahrenheit. The gas vanished in a tiny explosion.

The scientists said that result marked the most important advance yet in more than 10 years of work at the $3.5 billion facility.



http://www.sfgate.com/cgi-bin/article.cgi?f=/c/a/2010/01/29/MN5K1BOF4V.DTL&tsp=1

[FBaggins]

1. One step closer

Don't know if it's twenty years or fifty... but if something like this becomes a viable energy source... it changes everything.

[FreakinDJ]

2. Dr Mosses says he can have Fusion in 15 yrs

and Safely Dispose of the country's Nuclear Waste at the same time

I'm surprised more people are not advocating for his work to be fully funded

[MicaelS]

3. More information please, sounds interesting

Got a link or links?

[FreakinDJ]

4. links

A nuclear fusion demonstration project could be up and running in 10 to 12 years, they say, bringing fusion energy a step closer toward commercialization.

http://articles.sfgate.com/2009-04-01/news/17192385_1_nuclear-fusion-fusion-energy-national-ignition-facility/2

[TheWraith]

8. The Polywell guys say they can be up and running in 5-7 years.

Just saying.

[eppur_se_muova]

5. Nice article on this as BBC ... Laser fusion test results raise energy hopes

By Jason Palmer
Science and technology reporter, BBC News

***
"For the first time ever in the 50-year journey of laser fusion, these laser-plasma interactions have been shown to be less of a problem than predicted, not more," said Mike Dunne, director of the UK's Central Laser Facility and leader of the European laser fusion effort known as HiPER.

"I can't overstate how dramatic a step that is," he told BBC News. "Many people a year ago were saying the project would be dead by now."

Adding momentum to the ignition quest, Lawrence Livermore National Laboratory announced on Wednesday that, since the Science results were first obtained, the pulse energy record had been smashed again.

They now report an energy of one megajoule on target - 50% higher than the amount reported in Science.

The current calculations show that about 1.2 megajoules of energy will be enough for ignition, and currently Nif can run as high as 1.8 megajoules.
***
more: http://news.bbc.co.uk/2/hi/science/nature/8485669.stm

[leveymg]

6. There's another problem in a laser fusion reactor - harnessing the energy without losses

so there might still be a net gain over the energy expended in triggering the fusion reaction.

The mechanical, heat, and friction losses in a conventional nuclear steam generation plant are pretty substantial, but they are feasible because no external energy source is required to start a fission reaction. The laser fusion prototype requires a huge input of energy to start the reaction.

Plus, with this sort of pulse fusion reactor there's the problem of containment of the explosion as this thing gets scaled up. How do you safely contain a hydrogen bomb, even a small one? How many cycles before the container vessel has to be replaced? What do you do with the radioactive container vessel? Some of the same waste disposal issues as a conventional plant.

We're still a long way from economically feasible commercial applications, and I know what's in the back of everyone's mind - we're still a long way from a pulse fusion reactor for space travel, although it may actually be a better application than electrical generation, as one could theoretically just hang a reactor way, way back behind lots of shielding with a rear-directed outlet (magnetic nozzle), to get a pulse reaction drive. A starship with such a propulsion system have been termed "torchships."


Theoretically, they are capable of sustained 1 g acceleration for many, many years. Long enough to get to a near-light speed velocity with a practical possibility of human flight to nearby star systems. Because time "slows down" according to the relativistic constant the closer one gets to the speed of light, one could travel enormous distances in a perceived period of only a few years, as illustrated by the following equation. 6.58 years (crew perceived time) to get to Vega (27 light years away):

From The Relativistic Rocket in the Usenet Physics FAQ
In the following equations, note that a*T/c = (Ve / c) * ln(R)
Time elapsed (in Terra's frame of reference)

t = (c/a) * Sinh (given acceleration and proper time)

t = (c/a) * Sinh<(Ve / c) * ln(R)> (to expend all propellant, given exhaust velocity and mass ratio)

t = sqrt<(d/c)2 + (2*d/a)> (given acceleration and distance)
Distanced traveled (in Terra's frame of reference)

d = (c2/a) * (Cosh - 1) (given acceleration and proper time)

d = (c2/a) * (Cosh<(Ve / c) * ln(R)> - 1) (when all propellant is expended, given exhaust velocity and mass ratio)

d = (c2/a) (Sqrt<1 + (a*t/c)2> - 1) (given acceleration and Terra time)
Final Velocity (in Terra's frame of reference)

v = c * Tanh (given acceleration and proper time)

Δv = c * Tanh<(Ve / c) * ln(R)> (given exhaust velocity and mass ratio)

v = (a*t) / Sqrt<1 + (a*t/c)2> (given acceleration and Terra time)
Time elapsed (in starship's frame of reference, "Proper time")

T = (c/a) * ArcSinh (given acceleration and Terra time)

T = (c/a) * ArcCosh (given acceleration and distance)
Gamma factor

γ = Cosh (given acceleration and proper time)

γ = Cosh<(Ve / c) * ln(R)> (given exhaust velocity and mass ratio)

γ = Sqrt<1 + (a*t/c)2> (given acceleration and Terra time)

γ = a*d/(c2) + 1 (given acceleration and distance)
where
a = acceleration (m/s2) remember that 1 g = 9.81 m/s2
T = Proper Time, the slowed down time experienced by the crew of the rocket (s)
t = time experienced non-accelerating frame of reference in which they started (e.g., Terra) (s)
d = distance covered as measured in Terra's frame of reference (m)
v = final speed as measured in Terra's frame of reference (m/s)
c = speed of light in a vacuum = 3e8 m/s
Δv = rocket's total deltaV (m/s)
Ve = propulsion system's exhaust velocity (m/s)
R = rocket's mass ratio (dimensionless number)
γ = gamma, the time dilation factor (dimensionless number)
Sqrt = square root of x
ln = natural logarithm of x
Sinh = hyperbolic Sine of x
Cosh = hyperbolic Cosine of x
Tanh = hyperbolic Tangent of x
The hyperbolic trigonometric functions should be present on a scientific calculator and available as functions in a spreadsheet.

In many cases it will be more convenient to have T and t in years, distance in light-years, c = 1 lyr/yr, and 1 g = 1.03 lyr/yr2.

Here are some typical results with a starship accelerating at one gravity.
T Proper time elapsed t Terra time elapsed d Distance v Final velocity γ Gamma
1 year 1.19 years 0.56 lyrs 0.77c 1.58
2 3.75 2.90 0.97 3.99
5 83.7 82.7 0.99993 86.2
8 1,840 1,839 0.9999998 1,895
12 113,243 113,242 0.99999999996 116,641

Of course, as a general rule starships want to slow down and stop at their destinations, not zip past them at 0.9999 of the speed of light. You need a standard torchship brachistochrone flight plan: accelerate to halfway, skew flip, then decelerate to the destination (which makes sense, since such starships will have to be torchships). To use the above equations, instead of using the full distance for d, divide the distance in half and use that instead. Run that through the equations, then take the resulting T or t and double it.

Example: The good scout starship Peek-A-Boo is doing a 1 g brachistochrone for Vega, which is 27 light-years away. Half of that is 13.5 light-years. How long will the journey be from the crew's standpoint (the proper time) ?
T = (c/a) * ArcCosh
T = (1/1.03) * ArcCosh<1.03 * 13.5 / (12) + 1>
T = 0.971 * ArcCosh<13.9 / 1 + 1>
T = 0.971 * ArcCosh<13.9 + 1>
T = 0.971 * ArcCosh<14.9>
T = 0.971 * 3.39
T = 3.29 years
That's the crew time to the skew flip. The total time is twice this
T = 3.29 * 2
T = 6.58 years

[Ter]

7. No way in hell the Earth lasts another 200 years or so

Guaranteed some mad scientist blows it up. It's inevitable that at the very least, mankind will destroy itself.

[TheWraith]

9. Ah, yet another "SCIENCE BAD!" troll. Joy. nt

[Ter]

10. Think before you post

Science is amazing and I support as much funding as possible. We're still gonna destroy ourselves by 200 years though. We will NEVER get to Star Wars level technology. Sad but true.

[gtar100]

11. The oil industry folks will get right on it.

Sure they can play around with these things, but if they get anywhere near to something workable, there is an army of maggots feeding on oil ready to smother it.

Sorry...30 years of hearing about promising technologies and we're still driving cars getting 20-30 mpg. I'm not skeptical, just disillusioned by human greed and short-term thinking. These inventors and scientists need to not only come up with ideas that work but also find a way avoid getting their research smothered by those who would lose big if energy became cheap, plentiful and clean. It's a nasty world in which there are a lot of investors who are no better than Gollum.