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starship-design: Fusion

Hello Isaac,

This is the rest of the previously "abandoned" letter about a pellet track.

>>>2. You don't have to bend over backwards trying to ignite fusion (since
>>>   you're using the pellet's kinetic energy).  It's actually _easier_
>>>   to implement a fusion ramjet than it is to implement a onboard
>>>   fusion drive.
>>Why is it easier?
>Because in order to initiate fusion, you need high temperature and
>pressure.  In a traditional pulsed fusion rocket design, this is
>achieved with either very powerful lasers and/or a fission reaction.

OK, actually I ment to ask why is it easier than continous MCF fusion.
But you already answered that:

>In a traditional continuous fusion rocket design, you need magnetic
>confinement, but you can't use superconductors because the field
>strengths needed are too high.  Thus, the confinement will be
>leaky--but this is sort of okay because you'll use the leaks for
>the thrust.  However, those leaks mean a drain on the energy in
>the system, and if it's too leaky then you don't have the energy
>to sustain fusion.  So far we haven't solved that problem but
>let's suppose we have.  That _still_ leaves the problem of the
>big heavy non superconducting magnetic coils needed to confine
>the fusion reaction.

But what about these 1 second sustained fusion reports we've heard about?
Did they fail because they are too leaky?

>The ramjet design is essentially a pulsed fusion rocket design.
>The big difference is that it uses the kinetic energy of the
>incoming pellets to provide the energy to initiate fusion.
>Conveniently enough, this power is directly "generated" within
>the pellet itself, so no equipment at all is needed to get the
>energy where it's needed!  The ship still needs powerful magnetic
>coils to provide confinement, but these only need to be powerful
>enough to handle pulsed fusion (like the laser confinement pulsed
>scheme), and don't need the strength to sustain the pressure
>and concentration needed for sustained fusion.

But if a super conducting magnet is strong enough for pulsed fusion, why
isn't it strong enough for sustained fusion?