Welcome to Physics 162
Professor Henry Greenside
1/08/2015
Please mute cellphones, put cellphones and laptops aside.
162 Teaching Assistant:
Kevin Holway
Key Resources
Has everyone found my 162 webpage
www.phy.duke.edu/~hsg/162 and read the syllabus
carefully?
Enrolled in Piazza, visited the Piazza webpage?
Have the Knight book, started reading Chapter 25?
Registered for the MasteringPhysics webpage?
Purchased iclicker2 device?
Bring iclicker2 To All Classes Starting
Friday, January 9
End-of-Class 1-Minute Questionnaire
I will hand these out now, fill them out in last minute of class. I
will then post answers to as many questions as I can within a
few days. Note: your name is optional.
Announcements
First homework assignment posted Wed, due Friday
night, Jan 16.
1)Short MasteringPhysics assignment online before
each Wednesday’s class.
• All future announcements via Piazza.
• Please ask questions first via Piazza.
Any Questions?
Today's Goal: A Non-technical Pep Talk For 162
How to Create a Donut-Shaped Star
And Save the Human Race
Class Discussion:
What is The Energy Crisis, Global Warming?
Pros and Cons of Different Energy Sources?
The Ideal Energy Source
1.
2.
3.
4.
5.
6.
No pollution.
No greenhouse gas emissions.
Accessible to all.
Renewable.
Scalable.
Economic.
Potential Solution: Nuclear Fusion
Energy Source of the Stars
4 protons fuse to one He nucleus
The Sun converts 600 million tons of hydrogen to 596 million tons of He
every second so 4 million tons of matter transformed into energy each second.
Easiest Fusion Reaction On Earth Requires Fusion
of Two H Isotopes: Deuterium and Tritium
+1
+1
0
+2
Hydrogen isotopes best choice since repulsion proportional to
charge and charge is quantized with smallest possible unit of e.
High Energy Neutrons Imply that
D-T Fusion Reactors Can’t Be Small
From movie “Back to the Future” (1985)
How Electricity Is Created From Fusion:
Steam and Faraday's Law of Induction (162!)
A Day in the Life of a Gigawatt Reactor:
Coal Versus D-T Fusion
In:
9,000 tons of coal
Out: Heat
Electricity
30,000 tons of CO2
600 tons of SO2
80 tons of NO2
In:
Out:
~600 coal plants in US
>2000 coal plants in China!
1 lb (.45 kg) deuterium D, 3 lb lithium Li, 1.5 lb tritium T
Heat
Electricity
4 lb helium gas
High-energy neutrons (damages materials)
Some moderately radioactive materials
(short decay times, none useful for nuclear weapons!)
Relative Volume of Fuels for One Year
Where to Get Deuterium? Earth's Oceans!
1 barrel sea water = 42 gallons water = ¾ oz D2O
1 cup seawater ~ 0.24 L seawater ~ 50 gallons oil ~ 190 L oil
Anyone can collect seawater!
Need Lithium To Produce Radioactive Tritium
Brine pools, e.g., Clayton valley, Nevada
Produce Li2CO3
Spodumene crystals LiAlSi2O6
from igneous rock pegmatite
United States has approximately 760,000 tons of lithium. Rest of the
world has about 12 million tons. The leading producers and exporters of
lithium ore materials are Chile and Argentina.
Fusion Looks Great
1.
2.
3.
4.
5.
Non-polluting.
No greenhouse gas emissions.
Fuel accessible to all.
Renewable and scalable.
No meltdowns, no nuclear wastes
that can be used for bombs
6. Economic?
So why not use fusion?
Fusion is hard! 
The Big Question: How Do We Get Repelling
Nuclei Close Enough to Fuse?
F=K
q1q2
d2
q1q2
F=K 2
d
Inverse square law leads to enormous repulsion when
two positively charged tiny particles are about one
proton-diameter apart (d very small)!
Answer: Make Nuclei Very Very Very Hot
How hot is hot?
You are 36o C or about 310 K.
Water boils at 100o C (373 K)
Tungsten melts at 3,700 K
Temperature needed for
D-T fusion on Earth:
150,000,000 K
Surface of Sun is 6,000 K.
Center of Sun is 15,000,000 K
Human race has achieved
600,000,000 K!
Sufficiently Hot Substances Become Plasmas:
Fluids of Electrically Charged Particles.
Most of observable universe is in the plasma state.
Study of plasmas called “plasma physics”.
How to Contain Superhot Plasma?
No material wall will work!
A Clue from Astrophysics:
Use Magnetic Fields To Guide Plasma
Demo: Guiding Charged Particles with
A Magnetic Field
Big Insight: Charged Particles Spiral Along
Magnetic Field Lines Giving Confinement
A Difficulty
Particles in hot plasma are spiraling along
the magnetic field lines at close to the
speed of light.
If the field lines touch a wall, the entire
plasma will rapidly flow into the wall and
be cooled off.
How do we get the field lines to avoid
bumping into any walls?
Answer: arrange---if possible---for the field lines
to close up in circles.
Tokamak
"тороидальная камера в магнитных катушках"
Demo: Why Plasma Confinement is Hard
Why are fusion machines hard to design?
 Moving charges in the plasma create their own
magnetic field.
 The magnetic field from the plasma adds to and
distorts the magnetic field from the external
coils, often causing magnetic field lines to
leaving toroidal region, touch nearby wall.
 Have to change the external fields constantly as
the plasma gets hotter and hotter and denser
and denser, but how? Math + computers +
science + hard thinking + hard engineering!
Princeton Plasma Physics Laboratory
1950’s First-Generation Stellarator
First Try Did Not Look Like Final Try
TFTR: Tokamak Fusion Test Reactor
Interior of TFTR: A Donut Shaped Star!
Generator Rooms: Create 4 MA Initial Current
To Start the Heating to Stellar Temperatures
Death Rays:
100 KeV Large-Current Neutral Beams of D and T
How to Get Fuel Into the Magnetic Bottle?
Hydrogen snowball machine gun
To Understand, Design Fusion Devices:
Lots of Math and Powerful Computers
ITER: International Thermonuclear
Experimental Reactor
Currently being built in Cadarache, France.
Benefit of Solving Fusion:Travel to the Stars
D-T or D-3He reactions
Achieve v ~ 0.2c
Decades to get to nearest stars.
Summary:
Key Physics From Fusion Discussion
1
Charged particles exert forces on each other without
touching each other (long-range force).
2
Motion of charged particles can be deflected by
invisible magnetic field.
3
Motion of charged particles can produce magnetic
field.
4
Many questions: rules about how charges affect each
other, what are electric and magnetic fields, how to
create and manipulate such fields...
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