Personal Reflections on Fusion 2

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    Gordon Docherty October 24th

    2014 Page 1

    Personal Reflections on Recent News from the World of Fusion

    (Hot and Cold)

    By Gordon Docherty

    Octoer !"th# !$%"

    Following on from a recent article in the Guardian newspaper:

    Has Lockheed Martin really made a breakthrough on nuclear fusion?

    I put pen!to!paper in response to a re"uest from the article#s author $%arl &athiesen !

    'arl(mathiesen(freelance)guardian(co(u'*+ with the thought that he might be interested in the

    following(

    Hot Fusion

    Firstly+ I often hear it said that fusion re"uires millions of degrees to wor'( ,ctually+ this claim is

    somewhat misleading( It is the e"ui-alent of saying you need burning gasoline in an automobile

    engine( .hile true+ an automobile engine is -ery far from being /ust one big ball of burning petrol(

    Instead+ it is a comple machine+ at the heart of which a small amount of gasoline is mied with air+

    compressed and spar'ed to create a small eplosion ! o-er and o-er again(

    o+ statements such as fusion re"uires millions of degrees to wor' are not really helpful( Instead+

    a statement such as for fusion to occur+ the right conditions need to be in place for elements to

    fuse is of much more use(

    Further+ spontaneous fusion can and does occur in nature( hus+ a theoretical "uantity of deuterium

    gas stored in a perfectly sealed /ar and left on a shelf to be bathed on and off in sunlight for the net

    few million years+ would reasonably be epected to eperience one or two spontaneous reactions !

    "uite by chance(

    o+ the statement for fusion would be better written as for useful le-els of fusion to occur+ the right

    conditions need to be in place for elements to fuse at a rate that would pro-ide an ade"uate amount

    of net+ usable energy ! and this means increasing the probability of fusion e-ents occurring+ that is+

    the probability that two $or more* atoms will approach close enough together under conditions that

    are fa-ourable for the nucleii to combine(

    he important phrase here is right conditions: the right conditions are those that allow each

    atom to o-ercome the repulsi-e barrier present around all atoms $including the atom in "uestion*(

    It is this barrier that stops atoms /ust falling in on one another+ to form massi-e+ unstable super!

    atoms that would brea' apart and reform again and again+ in a continual cycle of fission!fusion!

    fission( 3eedless to say+ life $as we 'now it* would not be possible in such a uni-erse( his barrier+

    'nown as the oulomb barrier+ can be thought of as the edge of the positi-e charge around the

    nucleus+ and it is one of the factors that allows us to eist(

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    Gordon Docherty October 24th

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    For fusion+ howe-er+ this barrier needs to be o-ercome( 5ut+ how can this be done6 .ell+ one way is

    to lea-e it to chance but+ as we ha-e seen+ we would be waiting a -ery long time for e-en a single

    e-ent+ so this is not a practical method+ especially if the end goal is to create a useful energy source(

    ,nother way is to heat things up( In hot fusion+ $heated+ high speed* atoms are collided to

    effecti-ely crash the nucleii together( learly+ for this to happen+ the atomic nucleii ha-e to be on a

    direct collision course( 3ow+ if two+ perfectly aligned guns could be engineered that shot out

    indi-idual atoms directly at each other in perfect alignment and at high speed+ then this would do

    the /ob(

    5y repeatedly firing out atoms in synch to achie-e repeated and perfect collisions+ you would then

    ha-e the basis of a useful energy source ! pro-ided you also had a collector 7 e/ector around the

    crash site to collect the resultant energy and get rid of the fused atom and other material resulting

    from the collision+ ready for the net collision to occur(

    here is only one problem with this approach: we can#t build such a de-ice(

    o+ if we can#t build a nanoscale fusion gun+ what can be built6 .ell+ one way is to lea-e it to chance

    by using a great many atoms+ accelerating them all at once+ and then trying to bring them together

    in a pinch point in the hope that+ out of those billions and billions of atoms+ one or two may fuse

    $remember the /ar in the sunlight ! by accelerating the atoms and pinching them together+ we

    increase the chance of indi-idual atoms colliding together in the now pinching+ confining space*(

    5y 'eeping the atoms spinning around a loop+ and repeatedly feeding this stream of particles

    through one or more pinch points+ we hope to increase the number of collisions ! and hence energy

    released ! until we get more energy out than we put in to accelerating the atoms and 'eeping them

    together through the use of pinch!points(

    5y speeding the atoms up+ we also ma'e them hot+ so stripping the electrons from the nucleii+

    ma'ing it e-en easier to bring the nucleii into close proimity(

    3ow+ I hope from the description gi-en+ it is clear why early fusion reactor designers loo'ed at

    building race trac's around which accelerating atoms could be raced and pinched( 3ow+ these race

    trac's were doughnut shaped+ leading to the name to'ama'+ as in to'ama' reactors: to'ama' is

    /ust another name for doughnut!shaped( his is the type of reactor used by I89+ which is

    attempting to do essentially what was /ust described(

    3ow+ creating a to'ama' reactor is not "uite as easy is building a doughnut!shaped race trac' and

    blowing a load of atoms around it with a big fan( For one thing+ blowing atoms around would mean

    that they were mo-ing /ust too slowly to e-er o-ercome their natural repulsion of each other( For

    another+ they would still be wearing their electrical shells+ ma'ing repulsion e-en more li'ely(

    o+ instead+ the atoms are accelerated to near light speed and super!heated( his is where the claim

    millions of degrees needed comes from+ as it is en-isaged that the stream of particles are now li'e

    those in the un( he problem is+ if you fire a super!heated stream of particles into a doughnut!

    shaped ring+ the particles /ust crash straight into the side of the ring and+ eactly li'e a welding flame

    hitting metal+ the beam would super!heat the ring and "uic'ly burn a hole through it(

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    o+ something has to be done to stop this+ and this is where powerful magnets come in to

    magnetically hold and guide the hot+ high speed atoms round the ring( Fortunately and

    unfortunately+ these atoms do tra-el around in perfectly aligned orbits so that they don#t bump into

    each other( Fortunately+ because if this were the case+ there would ne-er be any fusion e-ents(

    nfortunately+ the nucleii are continually running toward one another+ li'e stoc'!cars on a race trac'

    ! with drun' dri-ers at the wheel(

    his causes atoms to -eer and swer-e and try to eit the loop( .e therefore need to create pinch

    points to hold the magnetic maelstrom together and increase the chance of collision( .e also need

    collectors 7 etractors to capture the energy and fused nucleii as they fly away from the trac' ! such

    collision products are /ust too energetic and7or electromagnetically neutral to be held in the ring(

    3ow+ as collisions can happen anywhere around the ring$though mostly at or near the pinch points*+

    the collectors 7 etractors are pro-ided as a full!wrap blan'et around the whole of the ring( he

    pinch points+ on the other hand+ are pro-ided as uniformly spaced discrete collars around the ring(

    .ith such a design+ then+ it would seem that all is now ready to start fusing(

    .e still ha-e one more problem+ howe-er( he beam inside the ring is continually in flu+ so -ery

    cle-er software has to be written for the system of pinch rings to continually bring the beam bac'

    under control+ with+ as it happens+ a D!cross section pro-ing useful to maintain the stability of the

    beam(

    .ith much refinement of the software+ and a sufficiently large ring+ it is hoped that this nai-e

    approach to fusion will e-entually deli-er energy for any longer period of time( his is what is being

    done at I89( 8-en there+ though+ the engineering is a long way from producing a full!functioning+

    continuously running commercial reactor(

    .hat I ha-e /ust described+ howe-er+ is only one+ rather primiti-e way of getting nucleii to bump

    together( ,nother way is to accelerate far smaller numbers of atoms in to a ball+ using the instability

    energy created when the atoms come in close proimity to focus the reaction $shrin' the ball* still

    further(

    his approach is 'nown as inertial confinement: instead of using a ring $as a race trac'*+ the atoms

    are now pac'ed into a small sphere+ a sphere that is sub/ect to intense heat and pressure and forced

    to collapse in on itself( o+ now we ha-e high!energy atoms imploding to a single point( he result is

    a high rate of fusion e-ents ! for the small sphere+ that is( he collapsing sphere shines li'e the un

    for a split!second+ and then is gone(

    his slightly less primiti-e approach was the one adopted by the 3uclear Ignition Facility $3iF* in the

    + which used -ery high power lasers to sub/ect a tiny glass bead containing atoms to intense heat

    and pressure in order to create a high!rate of fusion e-ents: by sending all the atoms toward a

    central point+ many more atoms hit atoms coming