PPPL
QUIZ: INTRODUCTION TO FUSION ENERGY
The physics and benefits of fusion energy will be reviewed.

(click on a question to show/hide answers)
1. What is fusion?
  • 1.  Fusion is a style of cooking, most popular in westernized Asian restaurants, in which different styles and ingredients are synergistically and holistically combined to create a unique flavor.

    2.  Fusion is a named coined by English electricians to describe what happens when too much current passes through a fuse and it melts (e.g. it “fused on”). This term was later adopted by immigrant American physicists to describe the physical processes occurring in the sub- and super-mesoscopic scale charged atmospheric clouds that produce thunderstorms.

    3.  In physics, fusion means to join two nuclei together to create a larger nuclei. (This releases energy if the initial nuclei are small.)

    4.  Some of the above.

    [#q2]

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      The correct answer is 4
      The dictionary definition of fusion [1] is the act or process of “fusing”, the state of being fused, and to unite or blend into a whole, as if by melting together. The word fusion is used in various contexts, e.g. to describe a style of cooking (or a style of jazz music). In physics, fusion, or more descriptively nuclear fusion, refers to the process of fusing nuclei of light atoms to form nuclei of heavier atoms, and this process releases “binding” energy. The nuclear reactions of most interest [2] for fusion reactors involve D = Deuterium, T = Tritium, He = Helium and Li = Lithium : \begin{eqnarray} D + D & \rightarrow & T \, (1.01MeV) + p \, ( 3.03MeV) \\ D + D & \rightarrow & He^3 \, (0.82MeV) + n \, ( 2.45MeV) \\ D + T & \rightarrow & He^4 \, (3.52MeV) + n \, (14.06MeV) \\ D + He^3 & \rightarrow & He^4 \, (3.67MeV) + p \, (14.67MeV) \\ Li^6 + n & \rightarrow & T \, (1.01MeV) + He^4 + 4.8MeV \\ Li^7 + n & \rightarrow & T \, (1.01MeV) + He^4 + n - 2.5MeV \end{eqnarray} The numbers in parenthesis indicate the amount of energy that is associated with each particle. The energy is created because mass is destroyed (the mass of the particles on the right side of the each of the above reactions is less than the mass of the particles on the left) and this is the energy that can be extracted in a fusion reactor to create energy.
      [1] Dictionary.com
      [2] K. Miyamoto, Plasma Physics for Nuclear Fusion
2. In the famous formula $E = m c^2$, what physical quantities do $E$, $m$ and $c$ represent?
  • 1.  $E = $ ecceleration, $m = $ mass, and $c = $ dimensionless constant. This equation describes the relativistic acceleration of electric charges.

    2.  $E = $ energy, $m = $ meters, and $c = $ the speed of light. This equation describes the energy produced when “length” is compressed.

    3.  $E = $efficiency, $m = $ mass, and $c = $ the speed of light. This equation describes the optimal efficiency of mass to energy conversion.

    4.  $E = $ energy, $m = $ mass, and $c = $ the speed of light. This equation describes the energy produced when mass is destroyed.

    [#q3]

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      The correct answer is 4
      This is Einstein's famous formula! Energy and mass are interchangeable, and the amount of energy, $E$, created when an amount of mass, $m$, is “destroyed” is equal to $E=m c^2$. The speed of light, $c$, is very large, so that even a transfer of small amount of mass can produce a large amount of energy.
      [1] Wikipedia, Mass-Energy Equivalence
3. What is an MeV?
  • 1.  Mega electron volt. It is a unit of energy.

    2.  Micro electron velocity. It is the quantum-mechanical, electronic velocity per unit atom.

    3.  Macro energetic volume. It is the equivalent “volume” of energy in four-dimensional space-time associated with the conversion of a given volume of mass.

    [#q18]

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      The correct answer is 1
      An electronvolt (eV) it is the amount of energy gained, or lost, by an electron moving across an electric potential difference of one volt. $1ev \approx 1.60 \times 10^{−19} J$, where $J$ indicates Joule, which is the “work done” on an object when a force of one newton acts over one metre (i.e., 1 newton metre or N·m). Mega = million, so $1MeV \approx 1.60 \times 10^{−13} J$.
4. What are H = Hydrogen, D = Deuterium and T = Tritium?
  • 1.  These are the first three elements of the generalized periodic table of elements.

    2.  These are all isotopes of Hydrogen.

    3.  These are the reactants (H and D) and products (T) of nuclear chemical reactions.

    4.  Hydrogen is an atom with one proton and one electron. Deuterium is the Norse God with two heads, and Tritium is the Norse God with three!

    [#q24]

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      The correct answer is 2
      Hydrogen, Deuterium and Tritium are isotopes of hydrogen. They have the same number of protons and electrons, namely one, so their electrical and chemical properties are similar. However, they have different numbers of neutrons, with Hydrogen having no neutrons, Deuterium having one and Tritium having two. This means that they have different nuclear properties.
5. If the positively charged ions repel, how can they collide?
  • 1.  Not always do opposites attract; positives and positives accelerate attractively if there are no contravening electrons.

    2.  If the relative velocity is sufficient high, the positively charged ions can come close enough together for the short-range nuclear force to become significant.

    3.  Positively charged ions can only collide if there this a sufficient density of negatively charged electrons, i.e. if the plasma is “quasi-neutral”.

    [#q32]

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      The correct answer is 2
      The electric force (also called the Coulomb force) is a long-range, $1/r$ type force. At large distances positively charged ions repel other positively charged ions, and at short distances the repulsion force becomes arbitrarily large. However, if the ions are moving fast enough (which happens at high temperature), then they may come sufficiently close so that another more powerful force takes effect, namely the short-range nuclear force.