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Fusion Energy 101
Jeff Freidberg PSFC & NSE
January 2012
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Outline
1. What is fusion’s role in energy production
2. How does fusion work?
3. Where is fusion research now?
4. Where might fusion be in the future?
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Consumption of Energy by Sector
Transportation
Electricity
Heating
EIA – DOE 2010 3
Where does fusion fit in?
• Goal of fusion: make electricity
• Lots of it!
• Base load electricity – 24/7
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Electricity Production
Gas 19%
Nuclear 21%
Hydro 6% Other 4%
Coal 49%
EIA – DOE 2010 5
Electricity Production – Other 4%
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Oil 22%
Biomass 25%
Geothermal 9%
Wind 53%
The Big Picture Fusion Pros:
• Huge resources – a renewable • No CO2 emissions • No pollution • Inherently safe • No proliferation issues • Small radiation and waste disposal problems • Small power plant footprint
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The Big Picture Fusion Cons:
• It doesn’t work yet
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How does fusion work? Science
• Nuclear physics • Plasma physics
Engineering • Materials • Magnets • Blanket design • Economics
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Nuclear Physics
Two types of nuclear reactions:
• Fission – split heavy atoms (Uranium)
• Fusion – fuse light atoms (Deuterium)
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The easiest fusion reaction D-T
D + T → He + n + 17.6 MeV
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Fuel Inventory - Coal
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Fuel Inventory - Fusion
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Fuel Supply - Fusion
• Plenty of D from the ocean • No natural T – half life = 12 years • Need to breed T in the reactor
Li-6 + n → He + T + 4.8 MeV • Li-6 is 7% of natural lithium • 1000’s of years of natural lithium
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A Big Problem • Like charges repel
• Huge energies are needed to overcome the repulsive force • This turns the gas into a plasma
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+ +
Definition of a Plasma
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Electrons have enough energy to detach from nucleus Temperature is a measure of energy Energy is measured in electron volts (eV) 1 eV = 11,300 C = 20,400 F Fusion plasma = 15 keV = 17,000,000 C
Properties of a fusion plasma
• We need enough plasma: (air/100,000)
• At a high enough temperature: (air x million)
• Holding its heat for a long enough time:
• For a sustained fusion plasma – Lawson Criterion
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−= 20 310n m
=15T keV
τ = 2 sec
τ > −8 secp atm
Picture of a fusion plasma
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The Dick and Jane Fusion Reactor
• Alphas stay in and heat the plasma
• Alphas (He) stay in and heat the plasma • Plasma cools down by thermal conduction • Balance determines the temperature • Neutrons enter and heat the blanket – makes electricity • Blanket also breeds tritium
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Basic Plasma Physics Questions
• How do we hold a plasma together?
• How do we heat it to 15 keV
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Hold a plasma together – some ideas
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• Put it in a container – dumb idea
• Gravity – not on earth
• Inertial confinement – hurry up
• Magnetic confinement – no hurry
Magnetic confinement
• Cyclotron orbits • Good confinement perpendicular to B • No confinement parallel to B
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Too bad about ends
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A simple solution
• Homer Simpson “Donuts. Is there anything they can’t do?”
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Too simple! • Field is weaker on the outside • Plasma wants to expand • Hole gets bigger • Need to wrap the field lines around the plasma like on a
barber pole • Can do this by passing a current around the plasma • Can do this with corkscrew magnets
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Many attempts at good magnetic field configurations
Belt pinch Reversed field pinch Cusp Screw pinch Elmo bumpy torus Spherical tokamak Field reversed configuration Spheromak Force free pinch Stellarator Heliac Stuffed caulked Cusp High beta stellarator Tandem mirror Levitated dipole Theta pinch Mirror Tokamak Octopole Tormac Perhapsatron Z pinch Plasma focus Z pinch – hard core
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Two have risen to the top – why?
Tokamaks • Best plasma physics performance • But two tough problems remain Stellarators • Performance approaching that of tokamaks • May be able to solve tokamak problems • But other engineering problems arise
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How does a tokamak work?
A tokamak needs three types of magnets
• A toroidal field magnet
• An ohmic transformer
• Poloidal field magnet
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The toroidal field magnet
The ohmic transformer
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⊗
The poloidal field magnet
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⊗
⊗
⊗
⊗
The total magnet system
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Tokamak magnetic field lines
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A real life tokamak-Alcator C-Mod
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Picture of a fusion plasma held together by a magnetic field
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What is good about a tokamak? The B field holds enough plasma together in a stable way for a reactor
Stable Unstable
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What is good about a tokamak?
+ = Plasmas are heated by microwaves or RF waves to fusion reactor temperatures
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Picture of a fusion plasma confined by a magnetic field heated by
microwave power
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What is good about a tokamak? • The cooling down time is long enough to
sustain the plasma in a fusion reactor
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Tokamak Progress
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Two tokamak problems
• The need for steady state
• Avoidance of major disruptions
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• Transformers do not work in steady state • Mechanical and heat cycling bad for structural integrity • Need a way to drive the plasma current indefinitely • This can be accomplished by microwave current drive
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Primary current Plasma current
t t
The need for steady state
Microwave current drive • Launch waves in one direction around the torus • Choose the frequency and wave velocity carefully • Wave scoops up electrons as it travels • Preferential scooping produces a current
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Current drive analogy
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How well does current drive work? • The good news: current drive works
• The bad news: it is not very efficient
• 1 amp requires 10 watts of absorbed power
• 15 MA requires 300 MW of wall power
• Whole reactor produces 1000 MW wall power
• Not economical
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Possible solution • Depend on the good will of the plasma • Naturally occurring transport driven current • Known as the “bootstrap” current • Carefully tailored profiles can produce 75% bootstrap
current • Not easy to tailor the profiles in a reactor • Plasmas are not your friends
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Disruptions • Rapid quenching of the plasma pressure • Rapid quenching of the plasma current • Physical damage to the first wall • Tolerable in existing experiments • Intolerable in a fusion reactor
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The tough little plasma • Start with a little ohmically heated baby plasma
• Feed it some current
• Feed it some particles
• Feed it some energy
• Plasma grows bigger and stronger
• Just a little more to become a grown up “fusion plasma”
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Too much!
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Possible solutions • Build a very sturdy first wall – not really feasible • Avoid disruptions – leads to puny plasma • Disruption “extinguisher” – good to prevent damage
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The bottom line
• Tokamak plasma physics work reasonably well
• Steady state is doable but tough
• Disruption avoidance is doable but tough
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Stellarators may be a better way
• Inherently steady state – no net current flows
in the plasma
• Without net current, stellarators do not
observe major disruptions
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Two big stellarators • LHD in Japan
• W7-X in Germany
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Stellarators have their own problems
• Magnets are very complicated
• Cooling down time is not quite as long as for a
tokamak – at least not yet
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The next big fusion experiment - ITER
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Power out = 500 MW thermal
Pulse length = 500 – 2500 sec
Major radius = 6.2 m
Minor radius = 2.0 m
Plasma current = 15 MA
Toroidal field = 5.3 T
Heating power = 73 MW
Cost = $4B, $10B, $20B
Goals of ITER
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Test most plasma physics, some engineering
Switch from physics to engineering
What are the key fusion engineering problems?
• Materials
• Magnets
• Blankets
• Economics
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The problems are tough but
• We can see a possible solution for magnets
• We can see a possible solution for blankets
• Way too little funding for engineering research
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The first wall materials problem • Survive heat load • Survive neutron load • Maintain good mechanical properties • Maintain good thermal properties • Maintain good electrical properties • No cracking or becoming brittle • Can’t do it right now
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Leading contenders for new materials
• Superbium
• Miraculum
• Unobtainium
• Major research effort needed
• Not well funded
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Economics – a tough problem • Which costs more?
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Which costs more?
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Power Plant Economics
Capital + O&M + Fuel = COE($/kwh)
Compare fission and fusion economics
• Key point: Capital separates into two components
• Nuclear island – basically the “furnace”
• Balance of plant – turbines, buildings, etc.
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Fission vs. Fusion Type Capital + Operating + Fuel = COE Fission (4.2 + 2.8) + 1.3 + 0.7 = 9 c/kwh Fusion (8.4 + 2.8) + 1.3 + 0.7 = 13.2 c/kwh
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But
Fusion has other advantages
• Safety
• Waste disposal
• Proliferation resistance
Will this be enough?
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A long range fission problem • Natural uranium will run out: 50 -100 yrs • What then? • Fission solution: Breeder reactors • Breeder reactors:
• More costly • More delicate to operate safely • Takes 10 – 20 yrs to breed • Entire fleet must be converted to breeders $$$$
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Fusion-Fission Hybrid • Fusion reactor is surrounded by a lithium blanket
• Replace it with a fission blanket
• Fusion neutrons make a lot of fission fuel
• 1 fusion reactor fuels 5 – 8 LWR fission reactors
• High fusion cost leveraged against multiple LWRs
• No need to convert fission fleet
• Plasma physics easier, engineering comparable
• Fission energy for 1000’s of years
• Hybrid – Optimum or Pessimum?
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Hybrid economics Crossover point between hybrids and breeders Break even point where hybrids win
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====
cost of an LWR fission reactor cost of a breeder reactor cost of a hybrid
number of LWRs per hybrid
LWR
BRE
HYB
CCCN
< − ≈
1 2.5HYB BRE
LWR LWR
C CNC C
Summary • Fusion has enormous potential • Problems greater than anticipated • Funding less than anticipated • Hybrids may serve as an intermediate goal • Hybrids may even serve as an end goal • Problems are incredibly interesting
It is worth the effort!!
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