Showing posts with label cold fusion. Show all posts
Showing posts with label cold fusion. Show all posts

Friday, July 25, 2008

Bussard Fusion

I have commented on the late Robert Bussard’s efforts to harness fusion energy. This article is an accessible explanation of the technology. As I recently reported the recent effort to replicate aborted earlier work is advancing splendidly and this should result in news.

Their success will put us much closer to a thruster able to lift a large mass by applying and maintaining one G of gross thrust. Although there is obvious enthusiasm for long trips outside the solar system, the real value comes from been able to explore and develop the solar system itself.

Of course having unlimited grid power at a trivial cost is no small bonus also. And it is impossible to overstate the importance of huge amounts of cheap energy. All our difficult processes need huge amounts of energy, usually supplied by very expensive means. To start with, imagine having the energy to disassociate metals in a plasma arc, then blasting them through an electrostatic field to separate them, and then assembling them in a mold to shape a profoundly complex object. All this becomes possible.

Bussard’s work does appear to have a chance and should be watched closely.

Bussard Fusion Systems

I've frequently mentioned a type of electrostatic fusion reactor (and associated rocket systems), designed by Robert Bussard and detailed in the papers listed below. In it the fusion fuel is confined by a spherical voltage potential well of order 100,000 volts. When the fuel reacts, the particles are ejected with energy of order 2 MeV, so escape the potential well of the voltage confinement area. The standard reactor design discused used p+11B (hydrogen and Boron-11) as fuel, since it fuses without releasing any of its energy as radiation or neutrons. All the energy of the reaction is contained in the kinetic energy of released charged particals. If the fusion reaction is surrounded with voltage gradiants or other systems to convert the kinetic energy of high speed charged particals directly to electricity. Virtually all their energy (about 98%) directly to electricity. Making a ridiculously compact and simple electrical generator.

For example: Bussard fusion reactor with a radius of about 2.5-3 meters burning P+11B (hydrogen and Boron-11) produces 4500-8000 megawatts (4.5-8 E9 watts) of electricity and weighs about 14 tons (.00174 kg per KWe (575 KWe/Kg)). That's enough electricity per reactor to power a couple of big cities, and will be the standard power plant of most of our support craft. This isn't nearly enough power for the drive systems of one of the Explorer ships of course, but the system can be scaled up and retain its efficency.

This design is Bussard's variation of the Farnsworth/Hirsch electrostatic confinement fusion technology. Whats important to us is that it makes such a fantasticly small light power plant, that it can be used as part of a high thrust to weight ration propulsion system for space craft and aircraft. Bussard and associates have designed propulsion versions with a specific impulse of between 1500 and 6000 sec. (Best chemical specific impulse is 450.) I'll discus the rocket applications below.

Comparison of Fuel Cycles
As I mentioned above certain fusion fuels release all the energy of their fusion reaction in the kinetic energy of the released particals. The table below lists the various fuels with this charicteristic, and the power they release per kilogram of fuel.

Fuel --> Exhaust
Power / Reaction
Number of Particals
Joule / kg

p + 11B --> 3 4He
8.68 MeV
12
6.926 E13

De + 3He --> 4He + p
18.3 MeV
5
3.505 E14
*





p + 6Li --> 4He + 3He
4.00 MeV
7
5.472 E13
**
3He + 6Li --> 2 4He + p
16. MeV
12
1.277 E14
**
6Li + 6Li --> 3 4He (Combined)
20 MeV
12
1.596 E14
**



3He + 3He --> 4He + 2 p
12.9 MeV
6
2.059 E14
***

* De +3He reactors would have at least some De + De reactions, which produce neutrons. Possibly 2% of the energy will be released this way. This Neutron bombardment could not be directed like the charged particals. So the energy would impact the rear of the ship. Neutron bombardment is a very toxic form of radiation for people and metal, and would cause tremendous heat load on the rear of the ship.

To avoid shielding mass, we could put the reactor behind a shielding wall at the back of the ship, and make the reactor out of open mesh to limit its exposure.

** Since p can be reused in the two stage p + 6Li --> 4He + 3He &;3He + 6Li --> 2 4He + p reaction, its mass isn't counted as consumed in the reaction. This two staged reaction effectivly combines into 6Li + 6Li --> 3 4He with 20 MeV of total output.

*** 3He + 3He reactions are difficult to convert into electricity in a Bussard reactor, but can be used as a direct plasma thrust.

Power is given in Million electron volts (MeV). An electron volt is equal to 1.60219 E-19 Joule, and a Joule / sec is equal to a Watt. Mass in this case is the number of Protons and neutrons involved in the reaction. They each weigh about 1.673 E-27 kg. So since p + 11B has 12 P's and N's per 8.68 MeV reaction. (Note I'm ignoring electrons. Life's to short, they're too light).

8.7 MeV
= 8.7 E6 eV per 12 * 1.673 E-27 kg
= 4.324 E32 eV per / kg
= 6.926 E13 watts / kg (1 ev/second = 1.60219 E-19
Joule / sec)
1 j/s = Watt

Since the fusion reactions listed above, release all their energy in the kinetic energy of their exaust particals; the most direct way to power a rocket is to use these particals directly as a fusion rocket exaust stream. This can be done by placing an uncontained fusion reactor (without any electrical power conversion equipment), in the focus of a paraboloidal shell. The shell then reflects the fusion particles to the rear in a narrow beam (20-30 degree width), making a high efficency plasma rocket.

The efficency of such a rocket depends on the exaust velocity of the fuel, and the energy released per pound of fuel. This is decribed in the table below.

QED Direct plasma thrusters

Fuel --> Exhaust
Power / Reaction
(f) Mass conversion fraction
Joules / kg
Exhaust speed m/s
p + 11B --> 3 4He
8.68 MeV
1287
6.926 E13
11,800,000 m/s
p + 6Li --> 4He + 3He
4.00 MeV
1645
5.472 E13

3He + 6Li --> 2 4He + p
16.0 MeV
704
1.277 E14

6Li + 6Li --> 3 4He (Combined)
20.0 MeV
564
1.596 E14
17,800,000 m/s
3He + 3He --> 4He + 2 p
12.9 MeV
437
2.059 E14
20,300,000 M/s
De + 3He --> 4He + p
18.3 MeV
257
3.505 E14
26,500,000 m/s

Note that: watts are Joules per second.

F is the fraction of the fuel mass converted to energy. I.E. An f of 257, means 1/257th of the fuel mass is converted to energy.

For example: the fusion plasma from a P + 11B reaction has an exaust velocity of 11,800,000 meters per second. This translates to a specific impulse of approximately a *million* seconds. I.E. a pound of fuel consumed would provide a million pounds of thrust for a secound. For higher thrust, thou less effecient, rocket. We can use the fusion plasma to heat a working fluid. If you dilute the plasma with 100 times its weight in the following propellents (assuming I figured out the right equations), the direct QED plasma drive generates the following specific impulses:

Fluid

Specific Impulse (Isp) in seconds
H2
Hydrogen
14,000
NH3
Ammonia
3,500
H2O
Water
5,000

For an externally fueled reaction, or for a short range craft, the high thrust to weigh reactions in the mixed plasma table would be desirable. But for the deceleration into the target starsystem using only fuel and reaction mass stored in the ship. Only the high efficency (high specific impulse), low fuel mass, pure fusion plasma reaction would be usable. It is those reactions we will consider in our fuel load calculations below.

The classic rocket equation gives the fuel to ship mass ratio, needed to get a given change in speed, with a fuel that has a given exaust velocity.

dv = Desired change (or delta) in the ships speed.Vexh = Exaust velocity of the materialM = The fuel mass ratio =Exp(dV/Vexh)

The specific impulse of a fuel (The pounds of thrust, a pound of fuel will give, when burned in a second) is determined by dividing the fuels exaust velocity by 9.8 m/s^2.

The following table shows the fuel mass ratios nessisary to get a ship fueled with various fuels up to the listed speeds. For example, to accelerate a ship up to 1/4the the speed of light (.25 c or 75,000,000 m/s) a ship fueled with hydrogen and boron-11 (p + 11B) would need to start out with 576 times its own weight in fuel. To get the same ship to half the speed of light, it would need to carry over 300,000 times its weight of fuel! Fuel the same ship with duterium and helium-3 (De + 3He) and you'ld only need 17 and 287 times the ships weight of fuel.

Fuel --> Exhaust
Vexh
75E6m/s( .25c )
100 E6 m/s(1/3rd C)
125 E6m/s(.42c)
150 E6m/s(.5 c)
p + 11B --> 3 4He
11,800,000 m/s
576.0
4,790.0
39,900
332,000
6Li + 6Li --> 3 4He(Combined)
17,800,000 m/s
67.6
275.0
1,120
4,570
3He + 3He --> 4He + 2 p
20,300,000 M/s
42.5
138.0
472
1,620
De + 3He --> 4He + p
26,500,000 m/s
16.9
43.5
112
287

Note: that the fuel ratios listed are only enough to accelerate the ship to, OR decelerate the ship from the listed speed. Carrying enough fuel to do both, would require squaring the ratio. In our case that would mean that the amount of fuel that could get you to 1/2 light speed, would only be enough to get you up to and down from 1/4th of light speed.

One thing the table illistrates clearly is why engineers want high exaust speeds and high energy fuels. Doubling the exaust speed can cut over 70%-80% out of the fuel mass needed to get to a speed. It also, all other things beings equal, allows a small lighter engine system and theirfor ship. This is an especially great advantage when the desired maximum speeds are several times greater than the exaust speeds.

So historically most starship design studies have gravitated toward the higher exaust speed fuels like 3He + 3He or De + 3He. However these fuels have a couple of serious practical problems not normally considered. First Helium-3 (3He) and Deuterium (De) are extremly rare isotopes, virtually unknown on Earth. Starship Design studies that used these fuels, were forced to also assume masive mining operations, scooping the materials out of Jupiters atmosphere. Also these fuels are extreamly light gases.
Unless these gases are kept liquid at cryogenic temperatores in sealed tanks, they will boil away into space. In our case where deceleration fuel will need to be stored for a decade or more, this is highly questionable at best. Also the tanks themselves are very bulky and therefore heavy. A tank could probably not carry much more then 20-30 times its own weight in fuel. Which in our case would require a much bigger heavyer ship, and one that drops its empty tanks along route. This becomes absurdly impractical.

An under considered fuel is Lithium-6 (6Li). As you can see from the table it still has fairly good performance as a fuel. But it also has two very large practical advantages. At room temperature it is a solid structural metal requireing half the volume of Helium-3, and not requireing any tanks or structural supports. It could even be used as part of the engine. Allowing the ship to consume part of its engine structure toward the end of the flight. Its secound advantage is that it is a cheap plentiful material on earth. So we can get access to virtually any amount of it we want, cheaply; and we can carry it in space for years without any tanks or leakage problems. This means we can easily carry far greater amounts of it on the ship. So even though it doesn't seem that efficent on paper. It has critical design advantages for a starship, and is the baseline fuel chosen for our fusion driven starship designs.

QEB Fusion/Electric/Thermal rocket

Fusion/Electric/Thermal-rocket motor configuration.

The QED reactor can be used to produce electricity. That electric power can be efficently converted to heat in a reaction mass such as hydrogen or water. Which makes for a good drive system assumed for secoundary thrusters on the starship, and all the primary rocket thrusters on support ships and shuttles.

Again a Bussard fusion reactor with a radius of about 2.5-3 meters burning P+11B produces 4500-8000 mega watts (4.5-8 E9 watts) of electricity and weighs about 14 tons (.00174 kg per KWe (575 KWe/Kg)).
Bussard and co-authors in his various papers have designed rocket systems using these reactors to heat a reaction mass (usually with relativistic electron beams). Giving a specific impulse of between 1500 and 6000 sec, and thrust to weight ratios of 1.5 - 6. (Best chemical specific impulse is 450.) For example, in the Support_craft web document, I have worked up two classes of support ships using these engines.
These are a high speed aerospace shuttle, and a simpler vacume rocket craft.

See:

H. D. Froning, Jr. and R. W. Bussard, "Fusion-Electric Propulsion for Hypersonic Flight," AIAA paper 93-261.

R. W. Bussard and L. W. Jameson, "The QED Engine Spectrum: Fusion-Electric Propulsion for Air-Breathing to Interstellar Flight," AIAA paper 93-2006.

R. W. Bussard and L. W. Jameson, "Some Physics considerations of Magnetic Inertial-Electrostatic Confinement: A New Concept for Spherical Converging-Flow Fusion," Fusion Technology vol 19 (March 1991).
\
R. W. Bussard and L. W. Jameson, "Design Considerations for Clean QED Fusion Propulsion Systems," prepared for the Eleventh Symposium on Space Nuclear Power and Propulsion, Albuquerque, 9-13 Jan 94.

R. W. Bussard , "The QED Engine System: Direct Electric Fusion-Powered Systems for Aerospace Flight Propulsion" by Robert W. Bussard, EMC2-1190-03, available from Energy/Matter Conversion Corp., 9100 A. Center Street, Manassas, VA 22110.

(This is an introduction to the application of Bussard's version of the Farnsworth/Hirsch electrostatic confinement fusion technology to propulsion. Which gives specific impulses of between 1500 and 5000 secounds. Farnsworth/Hirsch demonstrated a 10**10 neutron flux with their device back in 1969 but it was dropped when panic ensued over the surprising stability of the Soviet Tokamak. Hirsch, responsible for the panic, has recently recanted and is back working on QED. -- Jim Bowery)

Friday, June 20, 2008

Brussard Fusion Energy Advancing

This post by Alan Boyle on the recent progress made on the pioneering work commenced by the late Robert Brussard is heartening.

I have always suspected that solutions to the fusion riddle would take the form of complex geometries with simple convergence points. Unfortunately the only useful mathematical modeling tool available is intuition, and Robert had it more than most.

I expect that my own work on higher ordered cyclic functions and their derivative Pythagoreans will go a long way toward formalizing the geometry and giving grad students a headache.

The cold fusion model could only work if the curvature geometry about densely bound atoms permitted appropriate geodesics that allowed for the possibility of a fusion interaction. That it may have shown up empirically is nice. Designing something that actually works will not be done empirically unless we are simply lucky.

Everyone forgets that the tokomak gained favor for exactly one reason. Natural symmetry permitted a high level of modeling to be conducted before the advent of real computer power.

Today we actually have the computer power to tentatively model complex geometries and using higher ordered cyclic functions it become possible to achieve convergence on exact solutions. This type of work is possible only recently.

Right now they have a machine working smoothly and the prognosis for scaling looks excellent. The proponents could not ask for better news to give the funders. The next stage should also go ahead, and if the funders are out of their depth, replacements are very findable.

It also sounds like a ten fold scaling will make or break this model. If it works, it would also be the industrial prototype. It would be lovely to wake up one day knowing that a fusion power plant coming to your town shortly will supply your electric car for a small charge.

Fusion quest goes forward

Posted: Thursday, June 12, 2008 7:05 PM by Alan Boyle

Emc2 Fusion's Richard Nebel can't say yet whether his team's garage-shop plasma experiment will lead to cheap, abundant fusion power. But he can say that after months of tweaking, the WB-7 device "runs like a top" - and he's hoping to get definitive answers about a technology that has tantalized grass-roots fusion fans for years.

With $1.8 million in backing from the U.S. Navy, Nebel and a handful of other researchers have been following up on studies conducted by the late physicist Robert Bussard before his death last October - studies that Bussard said promised a breakthrough in fusion energy.

Nebel, who is on leave from Los Alamos National Laboratory, picked up Bussard's mantle at Emc2 Fusion Development Corp. in Santa Fe, N.M., and is trying to duplicate the results that were reported from the last machine Bussard built. The WB-6 device supposedly worked by setting up a high-voltage electrical field that was configured in just the right way to get ions slamming into each other, creating a fusion-fueled plasma.

Unfortunately, WB-6 was destroyed during one of its last scheduled test runs in 2005, and Bussard was never able to build another device. Fortunately, Nebel's five-person team has succeeded in building a new, improved device on a shoestring budget.

"We're kind of a combination of high tech and Home Depot, because a lot of this stuff we make ourselves," Nebel told me today. "We're operating out of a glorified garage, but it's appropriate for what we're doing."

The Emc2 team has been ramping up its tests over the past few months, with the aim of using WB-7 to verify Bussard's WB-6 results. Today, Nebel said he's confident that the answers will be forthcoming, one way or the other.

"We're fully operational and we're getting data," Nebel said. "The machine runs like a top. You can just sit there and take data all afternoon."

So was Bussard correct? Will it be worth putting hundreds of millions of dollars into a larger-scale demonstration project, to show that Bussard's Polywell concept could be a viable route to fusion power?

No answers just yet


Nebel said it's way too early to talk about the answers to those questions. For one thing, it's up to the project's funders to assess the data. Toward that end, an independent panel of experts will be coming to Santa Fe this summer to review the WB-7 experiment, Nebel said.

"We're going to show them the whole thing, warts and all," he said.

Because of the complexity, it will take some interpretation to determine exactly how the experiment is turning out. "The answers are going to be kind of nuanced," Nebel said.

The experts' assessment will feed into the decision on whether to move forward with larger-scale tests. Nebel said he won't discuss the data publicly until his funders have made that decision.

For now, Nebel doesn't want to make a big deal out of what he and his colleagues are finding. He still remembers the controversy and the embarrassments that were generated by cold-fusion claims in 1989.

"All of us went through the cold-fusion experiences, and before we say too much about this, we want to have it peer-reviewed," he said.

At the same time, he can't resist talking about how well WB-7 is operating. "I've been very pleased, frankly, with the sorts of things we've been getting out of it," Nebel said.

High hopes for low-cost fusion


Nebel may be low-key about the experiment, but he has high hopes for Bussard's Polywell fusion concept. If it works the way Nebel hopes, the system could open the way for larger-scale, commercially viable fusion reactors and even new types of space propulsion systems.

"We're looking at power generation with this machine," Nebel said. "This machine is so inexpensive going into the 100-megawatt range that there's no compelling reason for not just doing it. We're trying to take bigger steps than you would with a conventional fusion machine."

Over the next decade, billions of dollars are due to be spent on the most conventional approach to nuclear fusion, which is based on a magnetic confinement device known as a tokamak. The $13 billion ITER experimental plasma project is just starting to take shape in France, and there's already talk that bigger budgets and longer timetables will be required.

If the Polywell system's worth is proven, that could provide a cheaper, faster route to the same goal - and that's why there's a groundswell of grass-roots interest in Nebel's progress. What's more, a large-scale Polywell device could use cleaner fusion fuels - for example, lunar helium-3, or hydrogen and boron ions. Nebel eventually hopes to make use of the hydrogen-boron combination, known as pB11 fusion.

"The reason that advanced fuels are so hard for conventional fusion machines is that you have to go to high temperatures," Nebel explained. "High temperatures are difficult on a conventional fusion machine. ... If you look at electrostatics, high temperatures aren't hard. High temperatures are high voltage."

Most researchers would see conventional tokamak machines as the safer route to commercial fusion power. There's a chance that Bussard's Polywell dream will prove illusory, due to scientific or engineering bugaboos yet to be revealed. But even though Nebel can't yet talk about the data, he's proud that he and his colleagues at Emc2 have gotten so far so quickly.

"By God, we built a laboratory and an experiment in nine months," he said, "and we're getting data out of it."