Why Deuterium/Anti-deuterium?

Discussion in 'Trek Tech' started by feld, Jan 18, 2012.

  1. feld

    feld Ensign Newbie

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    OK,

    This is really a question for Mr. Rick Sternbach Rick Sternbach Rick Sternbach (which I believe is the approved way to attract his attention - if not please only set phasers on setting 1) but I welcome anyone's ideas. On to the question:

    Why does the TNG era Federation use deuterium/anti-deuterium in it's matter/antimatter reactors?

    The reason I ask is that it would seem simpler to find/make straight hydrogen/anti-hydrogen and the reaction products are cleaner. I know that deuterium is fusion fuel both burning with itself (D-D) or with tritium (D-T) so I understand that carrying some for fusion makes sense. Straight up hydrogen is tougher to fusion burn. D-T's the easiest fusion fuel to burn and D-D's not bad...given Star Trek levels of technology that is...

    I know I'm digging hard at the real science behind the show. If the answer to my question is "because it sounded cool" or "because DAEDALUS used it" then cool. The only reason I ask is because the TNG TechMan and other works indicate that Mr. Sternbach has a better than average grasp of nuclear rocketry and it stuck me as odd.

    v/r
    feld

    PS. oh. and Hi! First post and all that.
     
  2. CuttingEdge100

    CuttingEdge100 Commodore Commodore

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    I don't get it either, especially since hydrogen is easier to find and AFAIK anti-neutrons don't annihilate when brought into contact with regular neutrons.
     
  3. Christopher

    Christopher Writer Admiral

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    Neutrons and antineutrons do annihilate. The neutron as a whole has no charge, but the three quarks making it up do (one has a +2/3 charge and the other two have -1/3 charge each). The antineutron is made up of the respective antiquarks with the opposite charges.
     
  4. feld

    feld Ensign Newbie

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    Concur. They do in fact annihiliate. I've not figured out what they annihiliate down to though and on what timescales. Need to learn more quantum for that. Contrary to much common opinion though, while electrons and positrons react to produce gamma ray photons, hydrogen and anti-hydrogen do produce charged particles from their annihiliation...briefly.

    See article here for more detail.

    I figured that the neutron/anti-neutron annihiliation might make more charged particles for the EPS...but don't have any real science to support that idea.

    Thanks for the responses.

    v/r
    feld
     
  5. Starlock

    Starlock Rear Admiral Rear Admiral

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    I always thought of it as being basic fuel economics in that it takes less energy to condense and store Deuterium.

    And since Deuterium Slush is a probably a bit denser than plain ol' Hydrogen Slush - you could probably squeeze a little extra fuel into the tank.

    Your actual Mileage May Vary. ;)
     
  6. feld

    feld Ensign Newbie

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    Ack. Duh. I never even checked. Shoulda known that. In retrospect, I think it was mentioned in the DAEDALUS papers. That's what I get for thinking nuclear only.
    LH2 density = 67.8 kg·m−3
    LD2 density = 162.4 kg/m3

    good call!

    Do you happen to have a reference for this statement below?

    v/r
    feld
     
    Last edited: Jan 19, 2012
  7. Starlock

    Starlock Rear Admiral Rear Admiral

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    ^Just extrapolating - I've read that Deuterium has a 10 degree higher freezing point than Hydrogen. That would add up in energy savings after a few light years. Sorry if I inferred too much. ;)
     
  8. Ronald Held

    Ronald Held Rear Admiral Rear Admiral

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    Deuterium is easier to use as fuel for the fusion reactors and impulse drive.
     
  9. feld

    feld Ensign Newbie

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    <grin> Certainly no need to apologize to me. I'm always looking for new references (both for RL and ST) :)

    That could certainly be it. Sorry to anyone who saw my previous response to this: I had completely forgotten some numbers and was very confused. I'm better now.

    v/r
    feld
     
    Last edited: Jan 19, 2012
  10. Kaziarl

    Kaziarl Commodore Commodore

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    My personal best guess is deuterium was already a somewhat well known term. Even when talking about hydrogen fuel, I always hear people use the term deuterium instead.

    But as far as any practical reasons why one is better then the other... no clue but it seems others do.
     
  11. Rick Sternbach

    Rick Sternbach Fleet Captain Fleet Captain

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    Yeah, pretty much. :) The folks who helped me understand fusion rockets in the early 1970s (and later) got me on the deuterium/antideuterium kick. I believe one of them was Dr. Steve Howe when he was with LANL; Steve's helped with a lot of nuclear stuff since, including NTR engines for solar system travel. I'm no physicist, so I can't tell you which isotope is going to deliver better performance or be easier to refine and reverse. But for techy bits in an entertainment product, deuterium and its flipped side would seem to work just fine.

    Rick
     
  12. feld

    feld Ensign Newbie

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    Mr. Sternbach,

    Roger all and thanks! That's pretty much what I thought.

    I've been trying to figure out how to build a starship pretty much ever since I saw Mr. Probert's redesign of the big 'E' as an impressionable young person in a movie theater.

    No one had the heart to tell me the thing wasn't real until much later...bastards. Still - been a fun ride ;)

    Incidentally - I think that D/D<bar> is probably a pretty good fuel mix choice. As someone else pointed out: the stuff is much denser than straight hydrogen. Plus, the neutrons/antineutrons should annihiliate and the extra mass doesn't hurt.

    Now to find my quantum textbook and figure out what the reaction products would be... I'm working on what my wife has dubbed the "Grand Unification Theory of Treknology" and, if I'm right, there's some useful Real-Science(tm.) that can rationalize quite a bit of Federation starship engineering.

    v/r
    feld

    p.s. I think Dr. Howe wrote one of the first papers on laser induced fusion microexplosions for rocketry which got me started on this kick in college. Cool!
     
  13. Rick Sternbach

    Rick Sternbach Fleet Captain Fleet Captain

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    I think it was Steve who told me that a straight 1:1 "intermix" ratio would produce mostly gamma rays, which is why we started with 25:1 M:A. Makes a nice hot plasma, and then we adjust it closer to 1:1 to get higher warp values, but never actually go with equal amounts. Works for me. It's a lot more fleshed out than what was devised for TOS, but bless 'em, they did try back in '67.

    Rick
     
  14. Christopher

    Christopher Writer Admiral

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    Though it contradicts what they said in TNG: "Coming of Age," which was that 1:1 is the only intermix ratio. Which always sounded a little hinky to me anyway.
     
  15. feld

    feld Ensign Newbie

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    With respect, I don't think it ... quite...contradicts that episode. That is, if the screen play is correct.

    The question is:

    Mordock's line is somewhat troublesome ... but there's a relatively convenient retcon...since the question specified warp 8 and the TM says that the intermix ratio plateaus at 1:1 at warp 8.

    Incidentally, while I applaud the realization that having some mundane matter around to form the warp plasma is a good thing, 1:1 would appear to work just fine for proton/antiproton (p/ap) reactor. We know what the reaction products from a p/ap reaction are ... and they're not just gamma rays...or, at least, not immediately just gamma rays. The reaction products are largely charged pions which can be ducted electromagnetically. This is why there is persistent interest in p/ap rocketry. None other than Dr. Forward shows a figure on page 3 of the linked pdf showing the process (again for a p/ap). The first reaction products produced are neutral and +/- charged pions. Each of these reaction products decays further. The neutral pions decay into really nasty they-go-through-schools type gamma rays. The charged pions travel roughly 21 meters before they decay into more “stable” neutrinos and charged-muons. The muons then travel for a further 1.85 km before decay.

    Hence each stage has some charged particles that can be "ducted" electromagnetically and I'd wager that much of the rest of the history of M/ARA development involved trying to capture the rest of the energy to increase efficiency to the highest possible levels.

    Anyway, this all touches on the reason I asked the original "why deuterium" question and also why I'm going to go confirm what the reaction products of a D/aD reaction are. Because p/ap seems to work just fine...so it got me wondering if the Federation always used D/aD or switched to it at some point latter in its history.

    Hmmm...hey...are there any references to deuterium tankage on early Federation starships (aka refit Enterprise in TMP or TWOK) or do they start with the A and Excelsior from TUC? The Enterprise Flight Manual (written by Mr. Sternbach?) for Phase 2 and console footage show are unclear on the actual fuel in use.

    v/r
    feld
     
  16. Christopher

    Christopher Writer Admiral

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    eNotes says it's 2 gamma-ray photons at c. 1.8 GeV each, or pions that then decay into gamma rays in the 100 MeV range (although I'd guess there would be neutrinos produced there as well?).


    As far as I can recall, the first mention of deuterium was in TNG's behind-the-scenes materials (TUC was produced later, of course).

    And the Enterprise Flight Manual was mainly the work of Lee Cole, I believe, though Rick did contribute to it.
     
  17. feld

    feld Ensign Newbie

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    Apologies on the Flight Manual...that's what I get for going by my memory for credits.

    Yes...thank you much. :)

    Sadly, I've got that piece already and a little more here.

    What I'm going to have to figure out is:
    1. the probabilities of each branch
    2. the delay time for decay of the pion branch
    3. also need to know if the bound state changes the reactions any.

    This data is out there in nuclear reaction tables...I'm just so rusty that I don't recall where to go to find what I need. I knew I should've taken more quantum...

    v/r
    feld
     
  18. Ronald Held

    Ronald Held Rear Admiral Rear Admiral

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    doesn't dilithum take all of the final decay products and channel them into the warp plasma?
     
  19. feld

    feld Ensign Newbie

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    I don't think they ever *say* that anywhere and I'm uncomfortable with saying that dilithium produces warp plasma from the final decay products for several reasons.
    1. The first stage reaction products from the one reaction that I know about (proton/antiproton) don't decay for at least 21 meters (in vacuum). The second stage products are stable for 1.85 km (again, in vacuum). I am uncomfortable with giving our characters the ability to "hold" the reaction products in a crystal less than a meter in length because it seems to beggar lots of continuity killing "if they can do that why didn't they just X in episode Y" unintended technical consquences. Sure, the technological level described even in the TNG:TM already lead to many of these sorts of questions...but I'd rather my retcons didn't make more of them.

    2. Many of the final decay products of the p/ap reaction are either massless or chargeless or both. Ick. Hard to control. Hard to get power out of. Keep them out of my reactor engineering please. Seems better to make warp plasma out of the earlier stage products which are charged and have mass.

    v/r
    feld
     
  20. Jimmy_C

    Jimmy_C Fleet Captain Fleet Captain

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    The distance pions, muons, etc can travel before decaying depends on their speed too. If you don't accelerate them quickly, they don't travel far. If you accelerate them to relativistic speeds, they can travel very far. Your numbers (at least for pions) are for relativistic speeds.