thermonuclear fusion icon image
Created by SURA DADI from Noun Project
Student Guide

Three-legged Challenge for Thermonuclear Fusion

Discovering a crucial criterion to achieve thermonuclear fusion

What are the three crucial variables that determine the success of a thermonuclear fusion reactor? How do we determine these variables by playing a science game with velcros?

  • Brown paper bag (proxy for the volume of a nuclear reactor)
  • Velcro strips. Separate. The “hook” strip will represent deuterium and the “loop” strip will represent tritium. When they stick together it will represent fusion.
  • Scissors (if using large roll of velcro tape)
  • Bulk packing peanuts
  • Pen/pencil and paper
  • Clock or stopwatch (the one on a cell phone works great!)
Intro

We all know that the sun gives us warmth and light, without which life on earth would have been impossible. The sun has been shining for approximately 4.6 billion years. As curious beings, it is natural to wonder about how the sun gets this tremendous amount of energy.

The simple answer is “thermonuclear fusion” and today we shall play a game that will demonstrate what are the three main requirements to achieve fusion. But before that, let us understand what the words “thermonuclear fusion” means.

You probably already know that all the things you see around us (tables, chairs, white boards, water, the air we breathe and even ourselves!) are made up of atoms. They are the smallest indestructible parts of matter with which all other things are built, hence also known as ‘the fundamental building blocks of Nature”. You might also know that there is a very tiny part, called the nucleus, inside all atoms. Now, if the nucleus of one atom merges together with the nucleus of another atom, we call that process “nuclear fusion”. The name simply comes from the fact that one nucleus effectively “fuses'' with another one.

Now, you might also realize that the word “thermo” means “related to temperature”. We all know about “thermometers” (which can measure our body temperature to check if we have fever) and “thermos” bottles (keeps our milk, tea or coffee hot) and “thermals” (clothes that keeps us warm). In the same line of thought, “thermonuclear fusion” refers to nuclear fusion that happens due to “thermal” effects, meaning that the nuclear fusion happens due to very high temperatures. We sometimes simply call this whole process “fusion”. Fusion is the physical process that gives the sun all the energy.

So, what happens inside our sun?

In the sun the nuclei of lighter elements, such as hydrogen [or its heavier forms such as deuterium (D) or tritium (T)] can merge together and produce a nucleus of a heavier element, such as helium (He) and in the process a lot of energy is produced. Similar fusion processes power not only our Sun, but also all the stars that you can see in the night sky.

Why is fusion important to us on earth?

To solve the need for generating almost unlimited amounts of clean energy for future generations, scientists are trying to achieve controlled fusion on earth to replicate the same physics that goes on inside the sun. This can be thought of as “making a sun on earth”. It is one of the biggest challenges facing humankind and is said to be “a holy grail of Physics”. Today we shall use a simple game to demonstrate what are the three main factors that will allow us to achieve controlled fusion on earth.

Objective
  • Students will do experiments

    Students will do experiments with velcros (used as a proxy for a nucleus) to determine the variables that lead to more of them sticking to each other as a model for thermonuclear fusion

  • After reading the introduction, what do you want to know about fusion?

Before the experiment

  • We will imagine that we are the original scientists who were trying to figure out what are the most important factors that will maximize the probability of achieving fusion. To model this phenomena in our game, we will use some regular everyday objects. We will start with velcros that can come together and get stuck (similar to what happens in fusion) to form another bigger object.

  • In this simple model, you can imagine the hooks in the velcro to be deuterium nuclei and the loops to be tritium nuclei. These will represent the smaller, lighter nuclei. After they lock together (“fuses”), the fused bigger object, the stuck velcro, will represent the heavier/bigger helium nucleus.

  • With your group, discuss the following question: What do you think will affect the total number of stuck velcros?

Setting up

  • Get a paper bag and about 30 packing peanuts with velcro

    1. Half of them should be “hooks”
    2. Half of them should be “loops”
During the experiment***
Collecting data
Experiment 1

  • Step 1: Take 10 loops and 10 hooks and put them in the bag

    1. shake the box lightly for 10 seconds.
    2. Open and empty the box and count how many of the hooks and loops are sticking to each other.
    3. Write that number down in the table given below.

    We will name this number N10 (just as an example, if after shaking the box, we find that 7 hooks and loops are stuck/fused together, then in this particular example N10 = 7).

  • Step 2: Take 20 loops and 20 hooks and put them in the bag

    1. shake the box lightly for 10 seconds.
    2. Open and empty the box and count how many of the hooks and loops are sticking to each other.
    3. Write that number down in the table given below. We will name this number N20 (just as an example, if after shaking the box, we find that 13 hooks and loops are stuck/fused together, then in this particular example N20 = 13).

  • Step 3: Take 30 loops and 30 hooks and put them in the bag

    1. shake the box lightly for 10 seconds.
    2. Open and empty the box and count how many of the hooks and loops are sticking to each other.
    3. Write that number down in the table given below. We will name this number N30 (just as an example, if after shaking the box, we find that 20 hooks and loops are stuck/fused together, then in this particular example N30 = 20).

For example:

Number of D and T nuclei

10

20

30

Fusion Yield (number of stuck velcros)

N10 =

N20 =

N30 =

Now that the experiment is done, let us think about what we can understand from the data:

  1. Question: From the recorded values, do you see any trend?
  2. BONUS FUN: You can even plot the fusion yield on the Y axis and the number on the X axis and see the trend on a graph! Can you pass a straight line through the data points?
Experiment 2

  • Step 1: Take 20 loops and 20 hooks and put them in the bag

    1. Shake the box very lightly for 10 seconds.
    2. Open and empty the box and count how many of the hooks and loops are sticking to each other.
    3. Write that number down in the table given below. We will name this number T1. (just as an example, if after shaking the box lightly for 10 seconds, we find that 11 hooks and loops are stuck together, then in this particular example T1 = 11)

  • Step 2: Take 20 loops and 20 hooks and put them in the bag

    1. Shake the box with medium intensity for 10 seconds.
    2. Open and empty the box and count how many of the hooks and loops are sticking to each other.
    3. Write that number down in the table given below. We will name this number T2. (just as an example, if after shaking the box with medium intensity for 10 seconds, we find that 14 hooks and loops are stuck together, then in this example T2 = 14)
  • Step 3

    Step 3: Take 20 loops and 20 hooks and put them in the bag

    1. Shake the box vigorously for 10 seconds.
    2. Open and empty the box and count how many of the hooks and loops are sticking to each other.

    Write that number down in the table given below. We will name this number T3. (just as an example, if after shaking the box vigorously for 10 seconds, we find that 18 hooks and loops are stuck together, then in this particular example T3 = 18)

For example:

Nature of shaking

Shaking very lightly

Shaking with medium intensity

Shaking vigorously

Fusion Yield (number of stuck velcros)

T1 =

T2 =

T3 =

Now that the experiment is done, let us think about what we can understand from the data:

  1. Question: From the recorded values, do you see any trends?
  2. BONUS FUN: You can even plot the fusion yield on the Y axis and the intensity of shaking as points on the X axis and see the trend on a graph! Can you pass a straight line through the data points?

=> NOTE: In Experiment 2, we kept everything else constant and only changed how vigorously we are shaking the particles inside the box, thus changing their energy due to the motion of the particles of the system (this is also called kinetic energy). “Temperature” of a system is a measure of the kinetic energy of the particles that make up the system. For example, on a hot day the air molecules are moving more vigorously than on a cold day, when the air molecules are moving slower. Thus the nature of shaking the box (lightly, medium or vigorously) represents 3 different temperatures of the Deuterium and Tritium nuclei inside our nuclear reactor.


Experiment 3
  • Step 1

    Step 1: Take 30 loops and 30 hooks and put them in the bag.

    1. Shake the box lightly for 10 seconds.
    2. Open and empty the box and count how many of the hooks and loops are sticking to each other.
    3. Write that number down in the table given below. We will name this number t10. (just as an example, if after 10 seconds of shaking the box, we find that 8 hooks and loops are stuck together, then in this particular example t10 = 8)

  • Step 2: Take 30 loops and 30 hooks and put them in the bag.

    1. Shake the box lightly for 20 seconds.
    2. Open and empty the box and count how many of the hooks and loops are sticking to each other.

    Write that number down in the table given below. We will name this number t20. (just as an example, if after 20 seconds of shaking the box, we find that 17 hooks and loops are stuck together, then in this particular example t20 = 17)

  • Step 3: Take 30 loops and 30 hooks and put them in the bag.

    1. Shake the box lightly for 30 seconds.
    2. Open and empty the box and count how many of the hooks and loops are sticking to each other.
    3. Write that number down in the table given below. We will name this number t30 (just as an example, if after 30 seconds of shaking the box, we find that 25 hooks and loops are stuck together, then in this particular example t30 = 25)

For example:

How long was the experiment ON for?

10 seconds

20 seconds

30 seconds

Fusion Yield (number of stuck velcros)

t10 =

t20 =

t30 =

Now that the experiment is done, let us think about what we can understand from the data:

  1. Question: From the recorded values, do you see any trend?
  2. BONUS FUN: You can even plot the fusion yield on the Y axis and time on the X axis and see the trend on a graph! Can you pass a straight line through the data points?
Conclusion***
  1. Write a claim summarizing your findings from each of the 3 experiments by finishing the following prompt:
    1. Fusion of deuterium and tritium nuclei happens more when…
  2. Based on your claim, draw and label a fusion apparatus that would produce the greatest amount of fusion and therefore the largest amount of energy on a white board for a gallery walk.
  3. Walk around a look at the other apparatuses. As you look at the apparatus of others, think about what you like or would change.

Come back to group to answer these questions

  1. Why do you think fusion energy is so difficult to achieve?
  2. Was your personal essential question answered? If so, what is the answer? If not, what additional information would you need to answer it?

Extension: Review this resource sheet on modern developments in nuclear fusion:

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