Nuclear Fusion Basics

Sources:EFDA-JET

Wikimedia핵융합연구센터

Mohamed Abdou

The only fusion reactions thus far produced by humans to achieve ignition are those which have been created in hydrogen bombs.

EnergyFor 1010 People

The Biggest Challenge

• 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.

35 ZJ/0.2 ZJ/yr =175 yr

19 ZJ/0.2 ZJ/yr = 95 yr

8 ZJ/0.18 ZJ/yr = 44 yr

2005 Oil consumption was 0.18 ZJ/yr = 44 yr

Remaining Oil Resources

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 NuclearFusion 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)

(9) 3He+6Li→2 4He + p+ 16.9 MeV

(10) p+11B→3 4He+ 8.7 MeV

Nuclear Fusion in the Sun

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 eVTritium (T) → T+ 13.6 eV

D+ + T+

5He 2+

4He 2+ + n

17.6 MeV

0.01 MeV

Lawson Criterion for D-T

Triple product-(density, temperature, and confinement time) neTτE

For the D-T reaction,

The product -(density, and confinement time) neTτE

For the D-T reaction,

The minimum of the product occurs near T = 25 keV(300MK).

Fusion Triple Product

Plasma Confinement

Some other confinement principles:

muon-catalyzed fusion, the Farnsworth-Hirsch fusor (inertial electrostatic confinement), and bubble fusion.

Gravitational Confinement

Inertial Confinement

Magnetic Confinement

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.

• Laser implosion of small (3mm diameter) solid deuterium–tritium pellets produces fusion conditions

• Pressure generation

• CompressionFuel is compressed by rocket-like blow off200,000 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

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

• 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’)

Magnetic Confinement

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• 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 low-activation 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.

15/86000= 0.017%

2008 Total World Energy Consumption474 EJ(1018 J = 0.5 ZJ)/yr= 133 Petawatt•hr(132.8×1015 Wh)/yr=~15 TW

Available renewable energy