– Released huge amount of energy per energy-mass equivalence
– High energy radioactive elements corresponded to short half lives
– “Induced” radioactivity changed the perceptions of radioactivity
• Discovered by Frédéric and Irène Joliot-Curie
– Made the production of radioactive elements cheaper (less mining)
– Idea of slowing neutrons down contributed to higher success in achieving induced radiation
• Discovered in large part to work done by Enrico Fermi
[1]

• Tests were conducted on much heavier elements
– In 1938, Otto Hahn, Fritz Strassmann, Lise Meitner, and Otto Robert
Frisch conducted experiments bombarding uranium with neutrons, to investigate Fermi's claims
– This resulted in the roughly equal split of the nucleus into two lighter nuclei
• Differed from previous experiments that only involved small mass changes to the nuclei (think α & β decay)
– Potential for immense energy release was immediately recognized
– All occurred immediately prior to WWII
• Focus shifted to creating sustainable chain reactions
– Effective Neutron Multiplication Factor: k
– Energy Generation k = 1
– Weaponization k > 1
• Experimentation and Production continued post-war
• Cold War contributed to exponentially increased weaponization
– Also prompted further exploration into nuclear phenomenon
– Hydrogen Bomb: First large scale man made fusion reaction
• Totally uncontrollable
• Most common type was fission initiated
• Peace time development of nuclear technology has been largely in the realm of energy generation
[1]

• Splitting large nuclei into smaller pieces
• Energy release is very high
• Both parent and daughter nuclei are highly radioactive
– Very long half lives
– Irradiates both reactor components and the water used for cooling and heat transfer
• Extremely dangerous
– Meltdowns
– Environmental Hazards
– Inputs and Outputs can be used to create weapons
• Hard to achieve
– Protons don’t like other protons
– High temps and magnetic fields are a must
• More powerful than fission reactions
– Large nuclei have smaller binding energies than small
• Abundance of inputs
• Only low levels of radioactive wastes
– Mostly just the activated interior panels of the reaction vessel
– Input radioactivity is nonpenetrative

– Deuterium can be extracted from seawater
– Tritium can be made in the fusion reactor with lithium
– Helium-3 can in theory be mined from immense deposits in the lunar surface
– As opposed to fission where uranium is rare and must be mined
– Only small amount of fuel required compared to fission reactors
– Most reactors make less radiation than the natural background
– Risk of accidental release is non-existent since plasma requires incredibly precise control
– No combustion by products
– No weapons grade nuclear by products

– Requires incredibly high temperatures
– Simple classical calculations imply temperatures on the order of
10 11 K
– Taking into account quantum effects decreases this maxima
– Quantum Tunneling would lower threshold temperature to roughly 10 7 K
• QT is best described as the individual nuclei “leaking” through the
Coulomb barrier as opposed to overcoming it
– This means it doesn’t have to technically overcome the energy of the Coulomb force
– Coherent plasma streams are ideal
– In reality plasma flows are incredibly complex requiring equally complex control mechanisms and systems of stabilization
[2]

• Pinch
– Uses plasma’s electrical conductivity
• Induces a magnetic field around plasma
• Force is directed inwards causing plasma to collapse inwards and increase in density
• Chain reaction
– Denser plasma generates denser magnetic fields
– External magnetic fields required to induce the current in the plasma
– Drawbacks:
• Can produce chaotic plasma flow ranging from general instabilities and vortices to reversing the toroidal direction of flow
• Staged Z-Pinch
– Developed to reduced the instabilities that occur in normal pinch type designs
– Injects a linearly stable plasma stream that, upon reaching the critical temperature, loses stability, but keeps the overall plasma flow stable
• Thought to be due to the instabilities being absorbed and dissipated in the stable stream
• These approaches can be thought of as steady state fusion reactions
• Requires long plasma containment time
– Confinement refers to the time τ the energy must be retained so that the fusion power released exceeds the power required to heat the plasma
[3],[14]

• Invented in the 50’s by Soviet Physicists
– Transliteration means:
• Toroidal chamber with magnetic coils
•
Toroidal chamber with axial magnetic fields
• Most common form of magnetic confinement reactor
– Most studied and promising (currently)
• Walls “capture” the heat and pass it to a heat exchanger which produces steam to drive a turbine
• Utilizes two types of magnetic fields
– Toroidal
• Causes plasma to travel around torus
• Created by external magnets
– Poloidal
•
Causes circular plasma rotation in planar cross sections
• Results from toroidal current flowing through plasma and is orthogonal to it
• ITER
– International Thermonuclear Experimental Reactor
– Being built in France
– First tokomak fusion reactor that will become productive
[5],[18]

• Common in plasma physics
• Red arrow poloidal direction (θ)
• Blue arrow toroidal direction (φ)
[12]
[5]

Captured by an ultra-high-speed camera, a pellet of fuel is injected into a plasma at the ASDEX Upgrade Tokomak in
Garching, Germany. Photo: EFDA.
Plasma image following the injection of a frozen deuterium pellet
[8]
[9] [11]

Spherical Tokomak
[13]

[15]

•
Implosion of micro-capsules of fuel by high power laser beams
– Lasers cause instantaneous sublimation to plasma
– Plasma envelope collapses under the radiative pressure
– Collapse sends a shockwave through the fuel heating it to its critical temperature
•
Final stage the interior fuel reaches 20 times the density of lead and 10 8 K
•
Instead of having to confine the plasma for long periods, IC confines plasma in very short bursts
• Exposed “reactor” core making energy easier to remove from the system
•
No magnetic fields also allows for a wider range of materials for construction
– Carbon Fiber
– More resilient which decreases levels of neutron activation
•
Two types:
– Direct drive – Lasers focused directly on target fuel
• Hard to initiate uniform implosion
•
Suffers turbulence effects similar to magnetic confinement techniques
– Indirect drive – Fuel pellet is placed in a hollow cylindrical cavity (a hohlraum)
•
Lasers strike the metallic surface creating x-rays which are used to heat the pellet
• Causes a much more symmetric implosion
• More stable due to its uniformity
• Still not as efficient as magnetic forms
• Improvements in laser technology and honing the general technique could actually make it more efficient in the long run
– Short plasma confinement times
– Less energy overall to initiate the reaction
[3],[5]

[5],[7]
D-T microballoon fuel pellet

Gold Hohlraum
[10],[16],[17]

[3],[4]

• Easiest and currently the most promising
• Reaction employed with the ITER fusion plant
• Requires breeding of tritium from lithium
– Advanced reactor designs utilize liberated neutrons within the plasma to do this internally
– n + 6 Li → T + 4 He
– n + 7 Li → T + 4 He + n
•
Drawbacks
– Produces lots of high energy neutrons
– Only ≈ 20% energy yield in the form of charged particles
• Rest is lost to neutrons
– Limits direct energy conversion
– Requires handling of the radioisotope tritium
(
τ
1/2
=12.32 yrs) (write down the other facts and note card and bring up)
– Neutron Flux is 100 time higher than current fission reactors
[3], [4]

• More difficult to achieve than D-T
–
Initiation energy is only slightly higher, but confinement times are usually 30 times longer
• Reaction has two branches:
1.
D + D → T (1.01 MeV) + 1 H (3.02 MeV)
2.
D + D → 3 He (0.82 MeV) + n (2.45 MeV)
– Occur with nearly equal probability
– Some D-T fusion will occur but no input tritium is required
–
Neutrons released from (2) will have 5.76 times less kinetic energy than from D-T reactions
• Advantages
– 18% decrease in energy lost to neutrons
–
Lower average neutron flux to internal components
• Decrease material stresses/damage
• Reduces the range of isotopes that may be produced within internal components
– No input lithium or tritium required
• Disadvantages
– Power produced can be as much as 68 times lower than D-T
[3], [4]

• Many potential candidate reactions
– Most can be ruled out due to very high input energies
• Two Main Types:
– D 3
He
– H 11 B
• Fusion power where neutrons are ≤ 1% of the total energy released
• D-T & D-D reactions can release up to 80% of their energy as high velocity neutrons
• Would significantly reduce the damage to reactor wall components
• Decreases the need for measures taken to protect against ionization damage
– Specifically the need for protective shielding and remote handling safety procedures
• Pros:
– Tremendously more efficient
– Dramatic cost reductions (inputs & safety measures)
– Conversion directly to electricity (no steam turbines necessary)
• Cons:
– Incredibly difficult to initiate the reactions
[3], [4]

3
• D + 3 He → p (14.7MeV) + 4 He
(3.7MeV) + 18.4 MeV
• Reaction products comprised mostly of charged particles thus minimal damage to reactor components
• More efficient than Neutronic
Fusion
– Higher Energy Output
• In reality though some D-D reactions occur in the plasma
– Releases neutrons decreasing efficiency and overall energy gain
– Still produces “wear” on internal components
11
• 1 H + + 11 B → 3 4 He + + 8.7 MeV
• More efficient in practice than
D-
3
He
– Side reactions result in ≤0.1% loss in energy through neutron release
– Almost no damage to internal components
• Required temperature is 10 times higher than pure hydrogen fusion (star fusion)
• Confinement time is roughly
500 times that of D-T
[3], [4]

[4]

7

13)
14)
15)
16)
17)
18)
7)
8)
9)
10)
11)
12)
3)
4)
1)
2)
5)
6)
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