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Re: starship-design: Blackhole, Railgun and superconductor

Timothy van der Linden wrote:

>>Particularly pertinent to this discussion is research into hydrogen
>>pellet accelerators for magnetic fusion reactor fueling, since these
>>same pellets would be ideal for the fusion ramjet I'm proposing.
>>Muzzle velocities of over 3km/s have been demonstrated, but I
>>suggest thinking in terms of only 1km/s or so because the fuel packets
>>will ideally have a lightweight railgun with a limited power supply
>>(on board fission and/or collection panels for ship based beamed

>Like Kelly mentioned, these velocities of 0.00001c are not near to what we
>like. Especially not near to the velocities we need for the deceleration track.
>I'm afraid that you/we need to work hard on the pellet beaming part.

I already mentionned in another reply what the deal with the muzzle
velocities was.

Anyway, the thing which makes current fusion pellet research applicable
is that it precisely addresses the problem of accelerating a frozen
hydrogen pellet with a puff of hot plasma in a railgun.  That's the
sort of thing which on the face of it sounds dubious.

>>Anyway, the sort of pulsed fusion I'm proposing is similar to
>>magnetic target fusion, which requires starting densities of
>>10^18 nuclei per cm^3.  The specifics of the plasmatizing of
>>the pellet would determine what mass of pellet is needed.
>>I'm not familiar enough with the factors involved to make a
>>good assessment of that part.

>Knowing that our engine will be several magnitudes larger than any magnetic
>fusion proposal you've heard of; Can you estimate what the change in
>magnetic fieldstrength would need to be?

I don't know.  I'm sure a plasma physicist would be able to pull
off a BOE calculation in minutes, but I don't know what the most
important factors would be.

>>>>>A more practical question: How are the superconducting magnets kept from
>>>>>blowing up? The charged particles that fly trough the magnets will create a
>>>>>magnetic flux. Normally as long as the particle flies trough without
>>>>>velocity gain, the superconducting magnets will have the same current before
>>>>>and after the particle flew trough. But in the ramjet design the particles
>>>>>will exit faster than they arrived and thus will leave a non-zero flux.
>>>>>I do know little about how superconductors are given a current and a
>>>>>magnetic field, so the above question is more likely a result of not knowing
>>>>>then of doubting the design.

>>>>The superconductors resist any change in the magnetic field, which
>>>>is one of the ways they are so different from normal conductors.

>>>If I understand correctly, the way that they resist that change in magnetic
>>>field is by changing the current inside the superconductor.
>>>In the situation explained above, the current would rise more and more until
>>>the current would become too high and break down the special properties of
>>>the superconductor.

>>Yes, but since the magnetic field they are resisting is only momentary,
>>so is the opposing electric current.  It doesn't build up.

>Momentarily? Having a pulsed engine doesn't change things. Instead of
>increasing constantly, the current in the superconductor will increase with
>If it has nothing to do with a pulsed engine, then you have to explain to me
>why it is momentarily.

It is momentary because the magnetic field generated by any bit of
plasma goes away once that plasma goes away.  It doesn't have
anything to do with it being pulsed or not.
    _____     Isaac Kuo kuo@bit.csc.lsu.edu http://www.csc.lsu.edu/~kuo
/___________\ "Mari-san...  Yokatta...
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