I and I I - ITER Aims and Technical Challenges
Jo Lister
CRPP-EPFL
Centre de Recherches en Physique des Plasmas Ecole Polytechnique Fédérale de Lausanne Switzerland Outline of the first 2 talks
q A previous lecture series was given by Prof. Ambrogio Fasoli q These introduced fusion and ITER but concentrated on the physics q Today and tomorrow we revisit the basic aims and design of ITER, but try to extract the technical challenges, and more importantly, where these challenges come from
Jo Lister, CRPP-EPFL, "ITER Technical Challenges" CERN, May/June 2005 2 Remember why we are doing this ! q Finite oil resource thinking was launched by Hubbert in 1956 when he predicted US oil production would peak around 1970 - no-one listened q It did - he was right - US production was allowed at 100% capacity q Now domestic production is decreasing
q Idem for world oil, idem for gas Provide a long term energy supply
Jo Lister, CRPP-EPFL, "ITER Technical Challenges" CERN, May/June 2005 3 We don’t have a solution for demand exceeding production ! q Swenson’s Law says: “ To avoid deprivation resulting from the exhaustion of non-renewable resources, humanity must employ conservation and renewable resource substitutes sufficient to match depletion.”
q One reason no-one important wants to know is that oil depletion might (?) lead to war, famine, plague…. Match supply and demand
Jo Lister, CRPP-EPFL, "ITER Technical Challenges" CERN, May/June 2005 4 Fusion physics basics - Nuclear ?? q Where does fusion energy come from ? • The nucleus, B/A is the energy “stored” in the nucleus mass Ø So yes, it is nuclear, to a physicist, but to the public …?
fusion fission (statistical)
Create an acceptable energy source - waste, pollution, explosion
Jo Lister, CRPP-EPFL, "ITER Technical Challenges" CERN, May/June 2005 5 The “nuclear” question - Fusion : Fission comparison
• Explosion ? Ø There is no fusion chain reaction Ø There is only enough fuel in the reactor for a minute of energy production Ø The worst case accident requires no population evacuation Ø The waste products do not go into the life-cycle • Proliferation ? Ø There is no risk of increasing the proliferation of atomic weapons, or other weapons of mass destruction • Fuel availability ? Ø There is enough primary fuel in water for over 109 TW-years, no transport/storage problems • Economics ? Ø Studies conclude fusion energy would be competitive at today’s prices • Feasibility ? Ø There is no known physics between now and a successful reactor Create an acceptable and truthful image of fusion
Jo Lister, CRPP-EPFL, "ITER Technical Challenges" CERN, May/June 2005 6 Fusion physics basics - Exothermic fusion reactions
The basic fuel is deuterium, 1/6’500 in water, practically inexhaustible 1011 years D2 + D2 ® He3 (0.8 MeV) + n (2.5 MeV) D2 + D2 ® T 3 (1.0 MeV) + p (3.0 MeV)
D2 + T 3 ® He 4 (3.5 MeV) + n (14.1 MeV)
D2 + He3 ® He 4 (3.7 MeV) + p (14.7 MeV) Tritium is bred in situ from Lithium, equally abundant on earth Li6 + n ® He4 + T + 4.8MeV Li 7 + n ® He4 + T + n' - 2.5MeV The reaction products are : helium, neutrons, protons
Jo Lister, CRPP-EPFL, "ITER Technical Challenges" CERN, May/June 2005 7 Fusion physics basics - Fusion reactivity q When do fusion reactions occur ? 14.1 MeV
3.5 MeV
20 keV is 220’000’000 ºK !! q At these temperatures, all matter is in the plasma state - plasmas are forced on us ! Reach the high temperatures required - OK
Jo Lister, CRPP-EPFL, "ITER Technical Challenges" CERN, May/June 2005 8 Fusion physics basics - Lawson’s criterion q Lawson’s criterion, 1955-57 q based on
2 1/2 • Prad ~ Zeff n T
•
• t = Energy (th) / Power in qnt was only 109 s /cm3 !! q magenta line is the triple product ntT Confine the hot plasma energy for seconds
Jo Lister, CRPP-EPFL, "ITER Technical Challenges" CERN, May/June 2005 9 Approaches to fusion confinement q Inertial confinement (micro-bombs) - military, difficult to do, easy to finance q Cold fusion - DD reactions inside a metal lattice - “far from clear” results q Bubble fusion - DD reactions inside a deuterated liquid when the liquid cavitates with intense acoustic irradiation and neutron seeding of bubbles - the reactivity is never zero, so reactions should occur - no proposal as an energy source q Pyroelectric fusion - High local electric field accelerates nano-amps of deuterons which produce DD reactions, as expected q Straight magnetic fields - energy pours out from the ends q Toroidal magnetic fields lines - mostly the TOKAMAK
Jo Lister, CRPP-EPFL, "ITER Technical Challenges" CERN, May/June 2005 10 Why a tokamak ? q Electrons and ions obey Ø F = m a = q (E + v x B) Ø Confine particles with magnetic fields è magnetic confinement q Of all magnetic confinement devices, the tokamak has been the best Ø Toroidal magnetic field, like a ring Ø Electric current flows along this field inside the plasma Ø The plasma takes up the shape of a car tyre Ø Single particle trajectories are confined
Understand the tokamak - OK
Jo Lister, CRPP-EPFL, "ITER Technical Challenges" CERN, May/June 2005 11 Basics of a tokamak q Create a circular magnetic field - a circular solenoid q Induce a current parallel with this field - a “1-turn secondary” transformer q Create magnetic fields to hold the current in an equilibrium position q Primarily an electromagnetic device
Construct and operate tokamaks - OK
Jo Lister, CRPP-EPFL, "ITER Technical Challenges" CERN, May/June 2005 12 How fast have we progressed ?
q Progress has been very rapid q 6 orders of magnitude from the first tokamak q A power plant is within sight
... but ....
q Why have we progressed ? Ø Tokamaks have become bigger Ø Tokamaks have become more expensive Ø Tokamaks have bigger currents in the plasma
q Extrapolation is still empirical
Jo Lister, CRPP-EPFL, "ITER Technical Challenges" CERN, May/June 2005 13 Where have we got to - JET q World’s largest fusion device q EU multi-national collaboration q First operated in 1983
q Energy confinement > 1 sec q Temperatures > 40 keV (400M°C) q Densities > 1020 m-3
Jo Lister, CRPP-EPFL, "ITER Technical Challenges" CERN, May/June 2005 14 How do we extrapolate to ITER ?
q An empirical scaling law appears to hold over 2.5 orders of magnitude in confinement time
q Can we go one more step
q Density of points ~ price….
Develop enough empirical knowledge to extrapolate - OK
Ask whether the extrapolation is correct = ITER
Jo Lister, CRPP-EPFL, "ITER Technical Challenges" CERN, May/June 2005 15 What does the extrapolation lead to ?
Large plasma current 15MA (7 on JET) - OK
Large device (diameter 28m) - OK Large magnetic field 6T (9T on C-MOD) - OK Large equilibrium currents ~ plasma current - OK
q But currents flow in the fields produced by the other currents - F = IÙB
Huge static forces (MA * T ~m ) ~ 106 N/m - these are design drivers
Jo Lister, CRPP-EPFL, "ITER Technical Challenges" CERN, May/June 2005 16 What do we find ?
q Large currents to create the high fields
q Electrical power consumption if we fill the whole device with copper to make just the toroidal field
Ø >>100MW(e) for 500MW(th) !!!!
Large currents must be in super-conducting coils - see later
Like the forces, the super-conducting currents are in crossed magnetic fields - see later q Tore Supra has super-conducting coils. q Korea, China and India are building fully super-conducting tokamaks
Jo Lister, CRPP-EPFL, "ITER Technical Challenges" CERN, May/June 2005 17 It gets a bit more difficult q The tokamak is a pulsed device (even if the pulse lasts up to 6,000 seconds) q All the equilibrium fields are time-varying, so the mechanical forces are time- varying q The fields across the super-conductors are time-varying
The super-conducting coils will have to survive in the environment of an operating tokamak
Jo Lister, CRPP-EPFL, "ITER Technical Challenges" CERN, May/June 2005 18 What about the plasma itself ? q Assume we have a hot plasma, heated by 73 MW q The alpha-power is 500MW * (3.5MeV/17.6MeV) q How does this power get out ? • Core radiation, but this cools the centre • Edge radiation, not so bad • Conducted and leaves as kinetic energy q We make a magnetic divertor configuration q But this creates a large local power flux q The power flux has transient peaks too
Jo Lister, CRPP-EPFL, "ITER Technical Challenges" CERN, May/June 2005 19 The power at the solid surface causes erosion q What material should we use for the first wall? q Carbon/Be Ø Popular now Ø Ionises and radiates little in the core Ø Large concentrations in the core Ø Causes serious fuel dilution Ø C creates tar deposits in present devices v C + H --> CxHy Ø C will trap tritium by co-deposition in ITER v C + T/D --> CxTy v This could quickly reach the licensing limit !! Ø Not neutron resistant q Tungsten Ø No experience of a full tungsten machine - but coming Ø Radiates strongly in core, but weak concentrations Ø No co-deposition, no chemical erosion Will have to handle large power fluxes (10-20 MW/m2) - learning curve
Jo Lister, CRPP-EPFL, "ITER Technical Challenges" CERN, May/June 2005 20