Question about fusion reactors

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nimbus

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docm":2ehnu6yk said:
Franklin Chang-Diaz has said that VASIMR could be evolved into a fusion drive.
Anyone interested in the compatibility of fusion and VASIMR as an intermediate step to mature fusion propulsion could look at the ARC/QED design described here:
http://www.askmar.com/Fusion_files/From ... 0Moons.pdf
Folcrom":2ehnu6yk said:
Fusion power generators can easily transfer their heat to energy by using a simple liquid lithium blanket.
Unless I'm mistaken, lithium is a bummer for maintenance.
 
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Busterb1959

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Whether a craft be fission or fusion powered, there only has to be one element present, ice. Like the old fashioned steam locomotives, spacecraft can be powered the same way, and since we just found 400 million tons of ice on the moon, why not? It wouldn't take a very large reactor to vaporize water, producing steam, water and electricity. The steam would produce thrust, the water would quench the thirsts of our astronauts, and all of it would provide fuel for the electricity producing fuel cells. I would imagine that our first long journey out into space would only require lots ice and a whole crap-load of food. Does anyone remember the movie "Silent Running"?
 
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richcon

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Fission power's coming to spaceships far sooner than fusion, and for flying around the solar system fission will be pretty useful.

Fission might not have the same sex appeal that fusion has, but it generates a lot of power that can be used for life support, equipment, and thrust (via ion engines). We've been using fission reactors in submarines for a long time now, so spaceships would be the next step.

For now, the only fusion power we're going to be harnessing in space are the solar panels on the ISS. :)
 
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weeasle

Guest
Busterb1959":13d5yt2f said:
Whether a craft be fission or fusion powered, there only has to be one element present, ice. Like the old fashioned steam locomotives, spacecraft can be powered the same way, and since we just found 400 million tons of ice on the moon, why not? It wouldn't take a very large reactor to vaporize water, producing steam, water and electricity. The steam would produce thrust, the water would quench the thirsts of our astronauts, and all of it would provide fuel for the electricity producing fuel cells. I would imagine that our first long journey out into space would only require lots ice and a whole crap-load of food. Does anyone remember the movie "Silent Running"?
Great movie Silent Running- full classic sci-fi - Grade A, B-Grade cheese.

Yes quite logical that water itself makes an excellent radiation shield so it would seem that whatever fusion reactor device was being utilized would have a strong basis on normal H20 possibly augmented with Deuterium somehow involving steam and rankine / Carnot Cycle Turbine/Stirling to pump said water and supply spacecraft drinks, irrigation, etc.etc..

Magnetic fields are wonderful to compress hydrogen gas and theoretically can achieve fusion but would generally require very high energy density EM / Electrical in terms of many many thousands of Terra-watt amps... So essentially there we have (mostly) all the pieces except one: A battery that can store and discharge an extremely large capacitance in a short period of time... The chemistry and physics behind such a high capacitance battery itself could take decades of R&D to achieve...

//End random speculation ramble//
 
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Tritium

Guest
The reaction will be directly converted to electrical energy by ions as they strike an array of cathode collector plates.Ship drive fusion reactors will be modified for use in space so that the electrical output is harnessed directly,and the stream of neutrons will produce tritium,and the excess neutrons will be diverted to a neutron drive propulsion system,which is attached to the fusion reactor. Excess ions could be used for additional drive output.14MeV is more than enough output for the life support systems and power requirements of even a huge ship.There are some theories which suggest that the fusion reactor,once jump started,will produce enough energy to supply it's own demands,plus a generous additional potential . Although we will need to have sufficient stainless steel blanket replacement material aboard to run the reactor for extended tours of duty. :geek:We can get the hydrogen anywhere throughout the known universe=fuel. :shock:
 
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zwheel

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Large, flat PN junction sheets of silicon are placed in orbit around the reactor, usually anchored to a large rock already orbiting the reactor. Sometimes however they are placed in orbit around the rock and on rarer occasions they orbit the reactor directly.
 
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Ajboc

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nimbus":2qtlyovg said:
docm":2qtlyovg said:
Franklin Chang-Diaz has said that VASIMR could be evolved into a fusion drive.
Anyone interested in the compatibility of fusion and VASIMR as an intermediate step to mature fusion propulsion could look at the ARC/QED design described here:
http://www.askmar.com/Fusion_files/From ... 0Moons.pdf
I got to visit the VASIMIR lab as part of a high school program. With NASA's funding such as it is, nice to see it's still making news 9 years later.

I'm not sure if we'll get to the point of cheap fusion power, but as long as new discoveries are being made, it is worth pursuing.
 
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MikeWiggins

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I, too, have been waiting for the announcement of the first working fusion reactor for many decades. And, as many of you have noticed, such a device has yet to make an appearance.

Now I'm not a scientist, but I can put pieces of a puzzle together. We have heard many times of fusion reactors in Princeton and Russia being lit, but we (at least, I) have not heard of anything lasting past the first microsecond "spark". I know enough of the basics of fusion reactor theory to know that the temperature that needs to be achieved is in the order of 30 MILLION degrees (Cent. I believe, but it's a moot point) in order for the reaction to become "self-sustaining".

So with that in mind, it seems logical to believe that the current problem is STILL the old one: containment. How do you build a "bottle" that can contain a 30,000,000 degree plasma, but not lose so much heat that the reaction grinds to a halt within microseconds? Magnetics? Lasers? Anti-matter? Other? How do you transfer the heat? With what medium will the transfer occur with? It seems that many scientists are really going to have to think WAAAYYYY outside of the "box" to analyze the TENS OF THOUSANDS of problems to solve this riddle.

It really does seem like a very tall order. At the rate we are going, we should probably not count on seeing a working fusion reactor in the 20 years we are perpetually being promised. It will probably be more like 20 DECADES!

Just my two cents worth.
 
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billslugg

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MikeWiggins":iwfbtddq said:
.......have not heard of anything lasting past the first microsecond "spark"..........30 MILLION degrees... in order for the reaction to become "self-sustaining"......... How do you build a "bottle" that can contain a 30,000,000 degree plasma, but not lose so much heat that the reaction grinds to a halt within microseconds?
For the Tokamak donut, the magnetic fields could not be made to prevent plasma from squirting out. They never got self sustaining for more than a few seconds.

The laser beam implosion method at NIF skirts many of the problems. It happens in a pencil eraser sized hohlraum inside a giant chamber. The walls are cooled so they don't melt but there is not a lot of heat in the chamber as compared to a Tokamak. The only part of the NIF that gets to 30 million degrees is the pencil eraser sized target. By the time you spread that tiny mass out into the giant chamber, the temperature drops drastically. The energy from the tiny lump of fusing matter will not move by heat transfer but by energetic neutrons. I have read that the chamber would be surrounded by tons of steel containing pipes carrying water for a boiler. The neutrons get moderated by the water and absorbed by the iron.

I suppose you would get deuterium and tritium from the water. The neutrons would join the iron and create any number of stable and unstable isotopes all the way up to Iron 72.
 
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astronomy_fan

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Those are excellent ideas about how to transfer the energy. Now let build the reactor. Well, we now only two decent ways of starting fusion - damn high pressure and damn high temperature. Which way we go first? :)
 
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MikeWiggins

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I am not responding to any one previous post but, rather, an amalgam of them.

As most of you know, we already have spacecraft that use radioactive decay to generate heat and electricity, like the two Voyagers and others. But they do NOT provide thrust. That is because in order to have thrust, an exhaust of some sort must be created. In the case of the Dawn space probe, the Xenon thrusters need electricity provided by the solar panels to create the xenon plasma that gets ejected as thrust.

With trying to use either fission or fusion as a propulsive solution, you have the same problem: installing and running either of the reactors ONLY PROVIDES A SOURCE OF HEAT. In order to make them viable, a PROPELLANT must be provided so that it can become heated in order to become the ejecta that provides the thrust. Heating water is a great idea ..... until you realize how terribly much weight water will add to the total mass of the ship that is headed to deep space. It will cut down on acceleration and increase flight time. So why not use a lighter material? Good question. That DOES mostly solve the weight problem if you use significant amounts of low atomic mass elements such as hydrogen or helium. If you get them cold enough, the storage size might actually be managable. The problem with them is if it is possible to keep 100% of it contained for a 50 year one-way trip to Alpha Centauri without any of it leaking (any chemistry majors, refrigeration, or fueling specialists, feel free to respond).

Just my two cents worth.
 
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nimbus

Guest
I had a nice concise reply but the forum ate it.
You have a couple of assumptions wrong. Thermal confinement isn't the only scheme. There are many different approaches, and I've listed a couple of them further upthread and linked to a couple of pertinent papers (e.g. one where you will see that at least one kind of fusion reactor does provide thrust). I am linking to a few resources that I estimate are accessible enough to you.

Bussard's talk at Google on his decades long Navy embargo while researching "Polywell", and the then (2007) latest state of things.
A blog that does a fairly good job of compiling info on Polywell developments. Incl some chronicling of the author's own progress on understanding the polywell fusion scheme, which went fairly well considering that the head of Polywell research (Dr Nebel) has himself recognized the author's contributions. The documentation is on a few separate pages, starting with "Polywell As I Currently Understand It - Basics I, with the rest in that same part of the right sidebar titled "Polywell Primer".
A page with a very comprehensive index of polywell applications, including space propulsion designs that include some you're interested in. Scroll down to "fusion propulsion".
 
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bdewoody

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aaron38":1mno7t4h said:
It's likely that the first true fusion power reactor will be an MHD power take-off on a ship's drive. The MHD efficiency won't be high, so it'll need a high flow rate. That's the thrust propelling the ship. It'll be a D-He3 reactor, which will probably have it's first application on a ship. The technology roadmap will be from ship propulsion to terrestrial power.
What kind of ship? My post was about using fusion to generate cheap electricity globaly so we can quit burning oil and coal, not about space ships.
 
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bdewoody

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richcon":3lfvhdxh said:
Fission power's coming to spaceships far sooner than fusion, and for flying around the solar system fission will be pretty useful.

Fission might not have the same sex appeal that fusion has, but it generates a lot of power that can be used for life support, equipment, and thrust (via ion engines). We've been using fission reactors in submarines for a long time now, so spaceships would be the next step.

For now, the only fusion power we're going to be harnessing in space are the solar panels on the ISS. :)
This thread is about power generation on earth not in space. Can't you people read?
 
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armorsmith

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An interesting subject in it's own right, but if it's about power generation on Earth, why are you posting on a space site?
 
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bdewoody

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Because this is the physics forum. The same reason there are aviation, and forces of nature forums. All things related to science are discussed here and I think I made it pretty clear from the start that this thread was about generating electricity on earth and not about powering space ships.

If I had wanted it to be about that I would have posted on the space science and engineering forum
 
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Tritium

Guest
bdewoody":2v2cgspn said:
Because this is the physics forum. The same reason there are aviation, and forces of nature forums. All things related to science are discussed here and I think I made it pretty clear from the start that this thread was about generating electricity on earth and not about powering space ships.

If I had wanted it to be about that I would have posted on the space science and engineering forum
OK,simple heat transfer by water turned to high pressure steam in pipes wrapped around the fusion chamber which produces temperatures way above the point needed to produce simple steam.The steam goes to steam turbines which turn generators,which produce electricity.That is how it will be done on Earth.
In space it will be a different device altogether,with the primary focus being propulsion,and the secondary use being a breeder for more tritium,and a direct electrical power take -off grid to provide life support and ship power requirements.
 
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js117

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bdewoody":cs8n65m2 said:
OK, I know how a fission reactor transmits it's energy to electricity, the rods sit in a water bath which heats up and transfers this heat to a non radioactive water loop which then becomes steam to drive turbines which generate the electrical current.

How will a fusion reactor transfer it's energy to become electricity? It seems you can't run water thru the fusion chamber so I'm a little fuzzy on how the energy transfer takes place.

You should have stated this was for earth only not space!


bdewoody wrote:
Because this is the physics forum. The same reason there are aviation, and forces of nature forums. All things related to science are discussed here and I think I made it pretty clear from the start that this thread was about generating electricity on earth and not about powering space ships.

If I had wanted it to be about that I would have posted on the space science and engineering forum


There are planty of space related subjects in the Physics such as:

space propulsion
Question about Delta-V
heat and faster than light travel
 
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MeteorWayne

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He didn't have to. This is the Physics forum, to discuss Physics of all kinds. There is a Space Business and Technolgy forum to discuss propulsion ideas for spacecraft.
 
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bdewoody

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Tritium":n371fuhi said:
bdewoody":n371fuhi said:
Because this is the physics forum. The same reason there are aviation, and forces of nature forums. All things related to science are discussed here and I think I made it pretty clear from the start that this thread was about generating electricity on earth and not about powering space ships.

If I had wanted it to be about that I would have posted on the space science and engineering forum
OK,simple heat transfer by water turned to high pressure steam in pipes wrapped around the fusion chamber which produces temperatures way above the point needed to produce simple steam.The steam goes to steam turbines which turn generators,which produce electricity.That is how it will be done on Earth.
In space it will be a different device altogether,with the primary focus being propulsion,and the secondary use being a breeder for more tritium,and a direct electrical power take -off grid to provide life support and ship power requirements.
If it were this simple we would already have fusion reactors all over the planet generating mega-watts of electricity. My whole point is that it has turned out not to be so simple, hence the 35 years and counting wait for a successful fusion power plant.
 
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Tritium

Guest
bdewoody":38uyqgbi said:
Tritium":38uyqgbi said:
bdewoody":38uyqgbi said:
Because this is the physics forum. The same reason there are aviation, and forces of nature forums. All things related to science are discussed here and I think I made it pretty clear from the start that this thread was about generating electricity on earth and not about powering space ships.

If I had wanted it to be about that I would have posted on the space science and engineering forum
OK,simple heat transfer by water turned to high pressure steam in pipes wrapped around the fusion chamber which produces temperatures way above the point needed to produce simple steam.The steam goes to steam turbines which turn generators,which produce electricity.That is how it will be done on Earth.
In space it will be a different device altogether,with the primary focus being propulsion,and the secondary use being a breeder for more tritium,and a direct electrical power take -off grid to provide life support and ship power requirements.
If it were this simple we would already have fusion reactors all over the planet generating mega-watts of electricity. My whole point is that it has turned out not to be so simple, hence the 35 years and counting wait for a successful fusion power plant.
I said the heat transfer around the fusion chamber would be "simple".I am aware of how highly complex a fusion reactor is,and by no means intended to say it was a simple process.I also earlier described direct electrical conversion in a fusion reactor designed for power needs of an electric plasma drive propulsion system aboard a spacecraft,which also was cause for some corrective comments.I am new to this "forum" thing and am trying to participate in thoughtful,scientific discussions which I find very interesting.The problem seems to be that the energy required to achieve the fusion and contain the plasma is greater than the energy output because of the short duration of the plasma flow within the chamber.I believe the solution is very close,and that once the reactor can achieve a steady,stable reaction,that a system of pipes around the fusion chamber could easily turn water to steam to turn steam turbine generators for enormous amounts of electrical output. :D
 
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EarthlingX

Guest
Here is a video of a fusion powered spacecraft concept, i think related :
[youtube]http://www.youtube.com/watch?v=oqHFowOge_M[/youtube]

I think i saw somewhere fusion reactors in development, looking just like that. Not so sci-fi anymore.
 
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Tritium

Guest
A fusion reactor will be a great source of energy,period.
It will be used on land,undersea,and in space.
The question perhaps should be-what the hell do we have to do to get this dang thing to work? :roll:
 
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bdewoody

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Tritium":1m7ribh0 said:
A fusion reactor will be a great source of energy,period.
It will be used on land,undersea,and in space.
The question perhaps should be-what the hell do we have to do to get this dang thing to work? :roll:
It's beginning to look like to me that some sort of fundamental breakthrough still needs to be made, as much of what has already been done seems to have lead to dead ends.
 
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