The Physics
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Opus in profectus

Fusion

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Discussion

introduction

The sun has been around for some five billion years and is expected to shine for another five billion years to come.

Size is related to energy. Nuclear energy is to chemical energy as atomic dimensions (10−10 m) are to nuclear dimensions (10−15 m). Nuclear reactions have energies on the order of 100,000 times the energy of chemical reactions.

Paraphrase needed…
F. W. Aston discovered in 1920 the key experimental element in the puzzle. He made precise measurements of the masses of many different atoms, among them hydrogen and helium. Aston found that four hydrogen nuclei were heavier than a helium nucleus. This was not the principal goal of the experiments he performed, which were motivated in large part by looking for isotopes of neon. The importance of Aston's measurements was immediately recognized by Sir Arthur Eddington, the brilliant English astrophysicist. Eddington argued in his 1920 presidential address to the British Association for the Advancement of Science that Aston's measurement of the mass difference between hydrogen and helium meant that the Sun could shine by converting hydrogen atoms to helium. This burning of hydrogen into helium would (according to Einstein's relation between mass and energy) release about 0.7% of the mass equivalent of the energy. In principle, this could allow the Sun to shine for about a 100 billion years. In a frighteningly prescient insight, Eddington went on to remark about the connection between stellar energy generation and the future of humanity:

If, indeed, the subatomic energy in the stars is being freely used to maintain their great furnaces, it seems to bring a little nearer to fulfillment our dream of controlling this latent power for the well-being of the human race — or for its suicide.

Bethe described the results of his calculations in a paper entitled "Energy Production in Stars".

Light nuclei join to form a heavier nucleus. Energy is released in the process. Fusion powers the stars and high yield thermonuclear weapons.

solar fusion

Stars begin as a cloud of mostly hydrogen with about 25% helium and heavier elements in smaller quantities. The sun, 107 K core, hydrogen fuses to form helium through a process known as the proton-proton chain (often shortened to the p-p chain).

stage 1
2(11H + 11H → 21H + 0+1e + 00ν)
 
stage 2
2(11H + 21H → 32He + 00γ)
 
stage 3
1(32He + 32He → 42He + 211H)
 
overall
411H → 42He + 2(0+1e + 00γ + 00ν)

Proton-proton nuclear reactions

More on stellar fusion in another section of this book.

thermonuclear weapons

The first fusion bomb used liquefied deuterium (heavy hydrogen). Current "h-bombs" are dry thermonuclear weapons. The fuel of choice is lithium deuteride (lithium-6 deuteride to be more precise).

lithium 6 half
63Li  +  10n  →  31H  +  42He
 
deuteride half
21H  +  31H  →  42He  +  10n
 
overall
63Li  +  21H  →  42He  +  42He

Lithium-deuterium nuclear reactions

More on fusion bombs in another section of this book.

fusion reactors

magnetic confinement
tokamak — toroidal chamber and magnetic coil

inertial confinement?
laser systems

Approaches to nuclear fusion Source: LLNL
method density (kg/m3) temper­ature (K) confine­ment time
magnetic confine­ment 0.000001 100 million several seconds
inertial confine­ment 1,000,000 100 million 10−11 s
solar core 100,000 16 million as old as the sun
hydrogen bomb ? ? ?
Selected isotopes of the light elements
Z element A mass (u) abundance
−1 [electron] 00 00.000549  
0 [neutron] 01 01.008665  
+1+ [proton] 01 01.007276  
1

 
hydrogen
[deuterium]
[tritium]
01
02
03
01.007825
02.014000
03.016050
099.985
000.015
 
2

 
helium

 
03
04
05
03.016030
04.002600
05.012220

100
 
3



 
lithium



 
05
06
07
08
09
05.012540
06.015121
07.016003
08.022485
09.026789

007.5
092.5

 
4



 
beryllium



 
07
08
09
10
11
07.016928
08.005305
09.012182
10.013534
11.021658


100

 
Z element A mass (u) abundance
5




 
boron




 
08
09
10
11
12
13
08.024605
09.013328
10.012937
11.009305
12.014352
13.017780


019.9
080.1

 
6




 
carbon




 
10
11
12
13
14
15
10.016806
11.011430
12.000000
13.003355
14.003241
15.010599


098.9
001.1

 
7




 
nitrogen




 
12
13
14
15
16
17
12.018613
13.005738
14.003074
15.000108
16.006099
17.008450


099.63
000.37

 
8





 
oxygen





 
14
15
16
17
18
19
20
14.008595
15.003065
15.994915
16.999131
17.999160
19.003577
20.004075


099.76
000.04
000.20