Transcript Nuclear Fusion Basics

Nuclear Fusion Basics
The only fusion reactions thus far produced
by humans to achieve ignition are those
which have been created in hydrogen
bombs.
Sources:
EFDA-JET
Wikimedia
핵융합연구센터
Mohamed Abdou
The Biggest Challenge
Energy
10
For 10 People
• At MINIMUM we need 10 Terawatts (150 M BOE/day)
from some new clean energy source by 2050
• It’s got to be cheap.
• But, not with current technology.
Remaining Oil Resources
8 ZJ/0.18 ZJ/yr = 44 yr
19 ZJ/0.2 ZJ/yr = 95 yr
35 ZJ/0.2 ZJ/yr =175 yr
2005 Oil consumption was
0.18 ZJ/yr = 44 yr
What is Fusion?
Nuclear Fusion is the
process powering the Sun
and stars.
In the core of the Sun, at
temperatures of 10-15 M K,
Hydrogen is converted to
Helium by fusion providing enough energy
to keep the Sun burning and to sustain life on Earth.
Plasmas occur at very high temperatures - the
electrons are stripped from the atomic nuclei.
(Image courtesy CEA, France)
Energy Released by Nuclear
Fusion and Fission
• Fusion reactions release much higher
energies than Fission reactions
Candidates for terrestrial reactions
(1) D+T→ 4He(3.5 MeV)+ n(14.1 MeV)
(2i) D+D→ T(1.01 MeV)+ p(3.02 MeV)
50%
(2ii) → 3He(0.82 MeV)+ n(2.45 MeV)
50%
(3) D+3He→ 4He(3.6 MeV)+ p(14.7 MeV)
(4) T+T→ 4He +2 n+ 11.3 MeV
(5) 3He+3He→ 4He +2 p+ 12.9 MeV
(6i) 3He+T→ 4He + p +n+ 12.1 MeV 51%
(6ii) → 4He(4.8 MeV)+ D(9.5 MeV)
43%
(6iii) → 4He(0.5 MeV)+ n(1.9 MeV)+p(11.9 MeV) 6%
(7) D+6Li→2 4He+ 22.4 MeV
(8) p+6Li→ 4He(1.7 MeV)+ 3He(2.3 MeV)
Nuclear Fusion in the Sun
(9) 3He+6Li→2 4He + p+ 16.9 MeV
(10) p+11B→3 4He+ 8.7 MeV
D-T Fusion
• To harness fusion on Earth, different, more
efficient fusion reactions than those at work in the
Sun are chosen: Deuterium (D) and Tritium (T).
• D and T nuclei fuse and then break apart to form a
He nucleus and an uncharged neutron.
D-T Fusion
Deuterium (D) → D+ 13.6 eV
Tritium (T) → T+ 13.6 eV
5He 2+
0.01 MeV
D+ + T+
17.6 MeV
4He 2+
+n
Lawson Criterion for D-T
The product -(density, and confinement time) neTτE
For the D-T reaction,
The minimum of the product occurs near T = 25 keV(300MK).
Triple product-(density, temperature, and confinement time) neTτE
For the D-T reaction,
Fusion Triple Product
Plasma Confinement
Gravitational Confinement Magnetic Confinement
Inertial Confinement
Some other confinement principles:
muon-catalyzed fusion, the FarnsworthHirsch fusor (inertial electrostatic
confinement), and bubble fusion.
Gravitational confinement
One force capable of confining
the fuel well enough to satisfy
the Lawson criterion is gravity.
The mass needed, however, is
so great that gravitational
confinement is only found in
stars.
Inertial Confinement
• Laser implosion of small (3mm diameter) solid deuterium–tritium
pellets produces fusion conditions
• Pressure generation
• Compression
Fuel is compressed by rocket-like blow off
200,000 million atmospheres in core
• Ignition and burn
– Peak compression fuel reaches 1000-10000 times liquid density for
extremely short time (10–11 seconds)
– Core is heated and ‘spark ignition’ occurs
Inertial Confinement
Magnetic plasma confinement
Magnetic fields cause
charged particles to spiral
around field lines. Plasma
particles are lost to the
vessel walls only by
relatively slow diffusion
across the field lines
Magnetic Confinement
• Toroidal (ring shaped) system avoids plasma
hitting the end of the container
• The most successful Magnetic Confinement
device is the TOKAMAK (Russian for ‘Toroidal
Magnetic Chamber’)
The Tokamak:
A Transformer Device
Cutaway diagram of JET's tokamak
Simplified cutaway diagram of
JET's tokamak
ITER
• ITER is an international collaboration with seven partners (EU, Japan,
USA, South Korea, Russia, China and India) - and is a more advanced,
larger version of JET. It will be capable of producing 500MW of fusion
power (ten times that needed to heat the plasma). In comparison, JET can
only produce fusion power that is ~70% of the power needed to heat the
plasma.
• ITER being built at Cadarache in France, plan to operate from 2018.
• The so-called fast track to commercial fusion power is a strategy designed
to ensure that a demonstration fusion power station puts electricity into the
grid in 30 years time. During the operation of ITER, a parallel materials
testing programme will be undertaken - developing and assessing the
materials needed for a powerplant. The experience from both these
facilities will enable the first demonstration powerplant to be operational in
~ 30 years.
Heating the plasma
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Ohmic Heating and Current Drive
Currents up to 5 million amperes (5MA) are induced in the JET plasma - typically via the transformer or solenoid.
As well as providing a natural pinching of the plasma column away from the walls, the current inherently heats the
plasma. A few MW of heating power is provided in this way .
Neutral Beam Heating
Beams of high energy, neutral deuterium or tritium atoms are injected into the plasma, transferring their energy to
the plasma via collisions with the plasma ions. The neutral beams are produced in two distinct phases. Firstly, a
beam of energetic ions is produced by applying an accelerating voltage of up to 140,000 Volts. However, a beam
of charged ions will not be able to penetrate the confining magnetic field in the tokamak. Thus, the second stage
ensures the accelerated beams are neutralised before injection into the plasma. In JET, up to 21MW of additional
power is available from the NBI heating systems.
Radio-Frequency Heating
As the plasma ions and electrons are confined to rotating around the magnetic field lines in the tokamak,
electromagnetic waves of a frequency matched to the ions or electrons are able to resonate - or damp its wave
power into the plasma particles. As energy is transferred to the plasma at the precise location where the radio
waves resonate with the ion/electron rotation, such wave heating schemes have the advantage of being localised
at a particular location in the plasma.
In JET, eight antennae in the vacuum vessel propagate waves in the frequency range of 25-55 MHz into the core
of the plasma. These waves are tuned to resonate with particular ions in the plasma - thus heating them up. This
method can inject up to 20MW of heating power.
Waves can also be used to drive current in the plasma - by providing a "push" to electrons travelling in one
particular direction. In JET, 10 MW of these so-called Lower Hybrid microwaves (at 3.7GHz) accelerate the
plasma electrons to generate a plasma current of up to 3MA.
Self Heating of Plasma
The Helium ions (or so-called alpha-particles) produced when Deuterium and Tritium fuse remain within the
plasma's magnetic trap for a time - before they are pumped away through the divertor. The neutrons (being neutral)
escape the magnetic field and their capture in a future fusion powerplant will be the source of fusion power to
produce electricity.
The fusion energy contained within the Helium ions heats the D and T fuel ions (by collisions) to keep the fusion
reaction going. When this self heating mechanism is sufficient to maintain the required plasma temperature for
fusion, the reaction becomes self-sustaining. This condition is referred to as Ignition.
Resources
Fission (PWR)
Fusion structure
Coal
Tritium in fusion
Advantages of Fusion-Abundant fuels
• Deuterium is abundant as it can be extracted from all forms of
water. If all the world's electricity were to be provided by fusion
power stations, present deuterium supplies from water would last
for millions of years.
• Tritium does not occur naturally and will be bred from Lithium
within the machine. Therefore, once the reaction is established,
even though it occurs between Deuterium and Tritium, the external
fuels required are Deuterium and Lithium.
• Lithium is plentiful in the earth's crust. If all the world's electricity
were to be provided by fusion, known Lithium reserves would last
for at least one thousand years.
• The energy gained from a fusion reaction is enormous. To illustrate,
10 g of Deuterium (which can be extracted from 500 L of water)
and 15g of Tritium (produced from 30g of Lithium) reacting in a
fusion power plant would produce enough energy for the lifetime
electricity needs of an average person in an industrialized country.
Advantages of Fusion-Inherent safety
The fusion process in a future power station will be
inherently safe.
The amount of Deuterium and Tritium in the plasma
at any one time is very small (just a few g)
The conditions required for fusion to occur (e.g.
plasma temperature and confinement) are difficult
to attain, any deviation away from these
conditions will result in a rapid cooling of the
plasma and its termination.
There are no circumstances in which the plasma
fusion reaction can 'run away' or proceed into an
uncontrollable or critical condition.
Advantages of Fusion-Environmental
advantages
• no 'greenhouse' gases.
• The fusion power plant structure will become
radioactive - by the action of the energetic fusion
neutrons on material surfaces. However, this
activation decays rapidly and the time span before
it can be re-used and handled can be minimized
(to around 50 years) by careful selection of lowactivation materials.
• In addition, unlike fission, there is no radioactive
'waste' product from the fusion reaction itself. The
fusion byproduct is Helium - an inert and
harmless gas.
Available renewable energy
15/86000= 0.017%
2008 Total World Energy Consumption
474 EJ(1018 J = 0.5 ZJ)/yr
= 133 Petawatt•hr(132.8×1015 Wh)/yr
=~15 TW