Obstacles to ICF (part I: 1-11 of 15)
Posted: 16 July 2012 03:47 AM   [ Ignore ]
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Here are a few obstacles that laser ICF power plants still need to overcome:

(1) Manufacturing the cryogenic fuel capsules requires extremely high-quality surfaces, down to the atomic level. This is prohibitively expensive, especially for a power plant that fires several capsules per second. In addition, current pellet fabrication techniques require that cryogenic temperatures be maintained over a period of several days, to gaurantee uniformity. And, since a power plant would need an inventory of fuel lasting several days, a large stockpile of pellets, composed of extremely rare tritium, must be kept. 
(2) Not only do these BB size targets have to be tracked as they fly through the reactor, but all of the laser beams have to hit them midair from several meters away, a task that for direct-drive ICF requires 50 micron accuracy.
(3) The blast chamber must be evacuated several times per second, between shots, to prevent interference with subsequent laser shots.
(4) The optics (and walls) must be protected or they will vaporize and fail structurally due to the extreme thermal impulse stresses that result from the intense x-ray, 14 MeV neutrons, and 3.5 MeV alphas. The biggest problem for ICF’s final optics is that there is no scheme yet proposed for either Direct Drive or Indirect Drive that has complete credibility. Optics protection is still one of the weak areas for laser driven ICF.
(5) In order to reach the gains necessary for a commercial power plant, self-heating of the fuel by 3.5 MeV alphas is required. Unfortunately, because ICF capsules are small, the alphas escape from the burn zone before depositing their energy. This problem cannot be solved by simply making the capsules bigger, because the blast-chamber constraints would be exceeded by the larger yield.
(6) A major obstacle that ICF capsules encounter is turbulent mixing that can quench the fuel and prevent ignition. Rayleigh-Taylor Instabilities (RTI) arise in situations where low-density fluids push into high-density fluids. ICF capsules are vulnerable to this type of instability twice during their compression, 1st at the start, when low-density, high-pressure plasma pushes the higher-density tamper material inward, and 2nd when the implosion stagnates and high-pressure fuel pushes the higher-density tamper material outward. In 2009, W.J. Nellis of Harvard University wrote a critique of the National Ignition Fusion program. The article was titled “Will NIF work?” It contained the following quotes, “Despite the financial and human resources and time spent on NIF, the key condensed matter and materials physics issues of the fuel capsule remain unsolved and the R-T instability continues to be the limiting feature of NIF performance.” “While both the physics of R-T growth and the equations of state of DT (hydrogen) and shell material must be known, the R-T instability is by far the major issue…” “It is R-T spikes that grow from such R-M instabilities under high accelerations at later times that are the show-stopper of ICF.” “Computational simulations for more than 35 years have provided no insight into eliminating the R-T instability.” If large pellets could be imploded with increased laser energy, then the thickness of the mixed region and loss of the hot-spark region would become less serious, but a method to achieve such an implosion must first be found.
(7) Attaining tritium self-sufficiency might be fusion’s most difficult challenge. There are no practical, external sources of tritium, so fusion plants must breed their own; current inventories are extracted from heavy-water reactors, which produce 1.7 kg/year, and this supply will peak around 2025 at a mere 27 kg, enough to run a 1 GW fusion plant for six months. The main source of tritium is expected to come from breeding by capture of fusion neutrons in lithium contained in a blanket surrounding the fusion core. Because any lost neutrons would result in a tritium-breeding ratio less than 1.0, a neutron multiplier is usually employed with the hope of overcoming the negative effects of having a front wall ahead of the breeding blanket. Ironically, for an unlimited fuel source, fuel supplies (short-term) will determine how quickly fusion plants can be brought online and how effective fusion can be toward addressing our current worldwide energy crisis. Two key parameters, that influence how long it takes to produce enough tritium for a subsequent plant’s start-up are the fractional burn-up rate (low burn-up fractions require extra fuel-cycles, leading to higher retention-times and greater fuel losses through beta decay) and the trapped (inside the blanket) inventory size.
(8) Because laser-compressed ICF capsules obtain temperatures & pressures existing in the cores of stars, they also obtain stellar pressures. Without the weight of an entire star to confine it, ICF plasma disperses rapidly (~0.1 ns) into the vacuum, so that only a small fraction of the fuel gets burnt.
(9) A large portion of the laser energy is wasted, backscatter and bremsstrahlung.
(10) The ICF rocket compression scheme is not very inefficient (5% - 15%); most of the energy is carried away from the target area by high-energy outgoing ablation material. The peak efficiency of an ablation-driven rocket is typically a factor of 4 or more smaller than that of an ideal rocket because the exhaust is continually heated by the incident flux driving the implosion.
(11) High-energy x-ray measurements indicate that up to 50% of the absorbed laser light ends up in hot electrons. The presence of these high-energy electrons, which generally have a temperature of 50-60 keV, make it difficult to achieve the high density compression that is required for a successful burn.

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Posted: 16 July 2012 04:02 AM   [ Ignore ]   [ # 1 ]
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continuing….

(12) Most mainline systems (except for liquid-metal-wall ICF reactors, such as HYLIFE) have steel first walls, which are necessary to maintain a good quality vacuum and to endure the intense x-ray and neutron radiation. The first walls of all such reactors will be highly radioactive (2 to 5 billion curies). In addition, these first walls will require replacement every few years because of neutron-induced damage, either from helium embrittlement or from atomic displacements. Because both neutron energy and neutron population are reduced in the steel first walls of these reactors, neutron multipliers (such as lead or beryllium) or isotopic enrichment of Li-6 are usually required to achieve acceptable tritium breeding ratios. The same applies to magnetic fusion reactor chamber walls. For example, the STARFIRE tokamak walls will have a radioactivity of more than 5 billion curies and must be replaced every four or five years. The significance of this should not be ignored, chamber walls exposed to damage rates of 35 dpa/yr (displacements per atom per year) will require replacement every 5-7 years. Assuming that only the inner structural walls need to be replaced at 30% of the original reactor vessel cost, then about 5% of the plants lifetime must be devoted to replacement activities.
(13) ICF laser firing times need to be increased. NIF requires a timeout for cool-down and recovery after each firing. The high precision laser optics that ICF uses must cool for several hours between firings to recover from thermal expansion.
(14) Cooling the laser medium is very inefficient. NIF uses external flash tubes that create significant amounts of non-recoverable low level waste heat which must actively be removed (requiring extra energy) from the gain medium.
(15) The Halite-Centurian tests in Nevada apparently showed the DT targets might require up to 20 MJ to ignite. Current ICF designs produce less than 3 MJ.

I should point out that, none of these 15 are obstacles to Bubble-confined Sonoluminescent-laser Fusion (BSF).

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Posted: 16 July 2012 06:59 AM   [ Ignore ]   [ # 2 ]
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BSFusion - 16 July 2012 04:02 AM

I should point out that, none of these 15 are obstacles to Bubble-confined Sonoluminescent-laser Fusion (BSF).

Good list - I agree these are all major issues for LIFE (Laser Inertial fusion Energy), but you have to remember that this is not the primary role of NIF. 

From the NIF website (https://lasers.llnl.gov/programs/nic/):

NIC’s ICF experiments are designed to advance the National Nuclear Security Administration’s Stockpile Stewardship Program as well as basic high energy density science research in such fields as astrophysics, nuclear physics, radiation transport, materials dynamics and hydrodynamics (see Science at the Extremes). Other experiments will provide scientists with the necessary understanding of the physics underlying the use of ICF for safe, clean energy production (see Inertial Fusion Energy).

Fusion Energy is just under their ‘other experiments’.

Just to pick 2 points from your list (13 & 14) Laser technology has moved on enormously since NIF was designed - for example, new diode pumped lasers are much more efficient, resulting in less heat needed to be dissipated between shots.  They are not quite there yet, but progress is good.

I’m sure someone could come up with an equally long list of points regarding your BSF concept.  Have you submitted any papers to peer reviewed journal that cover it?  I find the paper format easier to scrutinise than a patent application, since journals insist on being suitably succinct.

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Posted: 16 July 2012 07:01 AM   [ Ignore ]   [ # 3 ]
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BSFusion - 16 July 2012 04:02 AM

I should point out that, none of these 15 are obstacles to Bubble-confined Sonoluminescent-laser Fusion (BSF).

(continued from…)
http://focusfusion.org/index.php/forums/viewthread/378/

——————————————————————-

The true obstacles are not even known yet since your approach to Bubble sonofusion has not even be tested in any way yet.  It only exists on paper, and not even a peer-reviewed paper. 
http://home.centurytel.net/bubbles/bubbles.htm
It is very likely that, although your approach is somewhat different, any device based on this would suffer the same problems as conventional bubble sonofusion that Professor Andrea Prosperetti of Johns Hopkins had encountered.

http://www.experiencefestival.com/a/Sonoluminescence_-_Mechanism_of_phenomenon/id/2110704
http://www.me.jhu.edu/MENewsletter2012.pdf
http://pre.aps.org/abstract/PRE/v67/i5/e056310
http://groupsites.ius.edu/physics/~kyle/P310/articles/sonolumin.pdf

Laser ICF projects like NIF have at least achieved fusion on some level… although it is doubtful they will ever get a complete and symmetrical burn of the fuel pellet.  They are, at the very least, way beyond theoretical and hypothetical pondering. 

It is VERY premature to start pointing out dozens of problems with Laser ICF, which as significant scientific credibility, actually achieves consistent results, and may have practical applications for nuclear weapons stewardship… and then try to present your own personal, untested, and highly speculative hypothesis that has more in common with discredited work than with real world research… and claim that it has none of the problems associated with devices that have actually been built, tested, and reviewed.

Sorry if that sounded harsh, but there is a cold reality that every innovator must face.  And that reality is that you must have your own house in order and follow the scientific method, before trying to elevate your own theory above others.

I know you hate the comparison, but it is still a fair comparison… The scientific method is designed to weed out unsubstantiated claims.  And bubble sonoluminescence has already one (once credible) scientist fail at the proper method for research and thus, his work was discredited. 
http://articles.latimes.com/2008/jul/19/science/sci-misconduct19
So any sonoluminescence fusion concept, even if the approach is significantly different, must provide extraordinary evidence to be taken seriously.

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Posted: 16 July 2012 03:39 PM   [ Ignore ]   [ # 4 ]
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Please try to stay on topic of ICF.
Certainly criticism is needed on every approach, but there is no need to use red herrings as a means to end a discussion or prove your point.
Instead please focus on dealing with the criticism so that it can produce valuable points of interest for the future.

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Posted: 17 July 2012 04:51 AM   [ Ignore ]   [ # 5 ]
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@BSFusion, To me you are coming across as trolling to promote you’re own concept.

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Posted: 21 July 2012 06:18 AM   [ Ignore ]   [ # 6 ]
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annodomini2 - 17 July 2012 04:51 AM

@BSFusion, To me you are coming across as trolling to promote you’re own concept.

In Internet slang, a troll is someone who posts inflammatory, extraneous, or off-topic messages in an online community, such as an online discussion forum, chat room, or blog, with the primary intent of provoking readers into an emotional response or of otherwise disrupting normal on-topic discussion.

Contrary to your implications, my post titled “obstacles to ICF” was dead-on the forum topic “NIF et al.” But yes, I was hoping to get some feedback on BSF, which, you should know, is a hybrid of, and superior to, orthodox ICF ... errr ... in my opinion. wink

 

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Posted: 21 July 2012 06:28 AM   [ Ignore ]   [ # 7 ]
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@Jamesr,

Just to pick 2 points from your list (13 & 14) Laser technology has moved on enormously since NIF was designed - for example, new diode pumped lasers are much more efficient, resulting in less heat needed to be dissipated between shots. They are not quite there yet, but progress is good.

Yes, diode pumped lasers are more efficient than those pumped by flashlamps, I agree. The reason for this is that diodes have a narrow optical bandwidth that allows them to pump directly to certain transitions of laser-active ions without losing power in other spectral regions. In addition, there has also been progress made toward raising the electrical-to-optical efficiency, which is now greater than 80%, and lowering the cost per Watt (see chart below). But, there is another inefficiency, unrelated to the pump frequency mismatch mentioned above, that produces a significant amount of waste heat.

The term quantum defect refers to the fact that the input energy of a pump photon is generally higher than that of the output laser photon. The energy difference goes into heating the laser medium. The quantum defect of a laser can be defined as the part of the energy of the pumping photon which is lost (not turned into photons at the lasing wavelength) in the gain medium upon lasing. At given pump frequency vpump and given lasing frequency vlaser, the quantum defect equals h*vpump - h*vlaser, where h is Planck’s constant and v stands for frequency. For example, if an 808 nm pump is used to produce 1060 nm laser output, then [1-(vlaser/vpump)] = 23.7% of the energy goes into waste heat.

Unfortunately, the quantum defect in ICF turns into low-level waste heat, which costs additional energy to remove, because it has to be actively removed in order to prevent damage to the solid-state gain medium. BSF was designed to avoid this handicap; BSF pumps directly into the hot, circulating, liquid coolant, so the quantum defect can be recovered in subsequent heat cycles. And, because BSF uses a reflective spherical mirror, instead of using transparent lens for its laser optics, there is no danger of optics damage (warping, melting, or fracturing).

I’m sure someone could come up with an equally long list of points regarding your BSF concept. Have you submitted any papers to peer reviewed journal
that cover it? I find the paper format easier to scrutinise than a patent application, since journals insist on being suitably succinct.

Perhaps a list of obstacles facing BSF could be started, but, so far, no potential objections have even been raised. wink A peer-reviewed paper might be a good idea too, but what journal would publish it, and who would write it? Not me, I have neither the time nor the skill to undertake a major writing project. So, unless someone wants to volunteer, that idea is DOA.

 

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Posted: 22 July 2012 05:51 PM   [ Ignore ]   [ # 8 ]
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BSFusion - 21 July 2012 06:28 AM

Perhaps a list of obstacles facing BSF could be started, but, so far, no potential objections have even been raised. wink A peer-reviewed paper might be a good idea too, but what journal would publish it, and who would write it? Not me, I have neither the time nor the skill to undertake a major writing project. So, unless someone wants to volunteer, that idea is DOA.

No real objections CAN be made until a concise set of claims are made in some sort of a scientific paper.  Plenty of objections over the last decade have been raised over other approaches to bubble sono fusion.  But since yours claims to be very different, the scientific community would need to review those differences.

“So, unless someone wants to volunteer, that idea is DOA.”

Unless someone does the actual work… the WHOLE IDEA of BSF is DOA!

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Posted: 22 July 2012 11:14 PM   [ Ignore ]   [ # 9 ]
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ICF as an energy source seems almost as far away as Tokamak power generation. Both beg off the issue by claiming their real focus is plasma science and/or military applications.  That leaves the field of generating electricity wide-open and unoccupied.  Polywell, General Fusion, Focus Fusion, etc., at least are trying to be useful and usable!

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