- 2851 - FUSION - how does it work in the stars? - The fusion in the core of stars can be analyzed as simple hydrogen nuclei, which are protons, fusing together to create heavier elements. Each fusion process up to the element Iron releases some amount of energy. Knowing how much energy our Sun puts out we can estimate the lifetime of our star, how long it will take to “burn up” all of this proton fuel.
--------------------------- 2851 - FUSION - how does it work in the stars?
-
- This is how fusion work in the stars? See Review 2638 to learn how fusion works on the planet Earth. If we can get Earth’s nuclear fusion reactors working above a breakeven point they could supply all the electrical energy needs of the planet with no pollution.
-
- You look into the night sky and every shining star is a fusion reactor. It is so common, it can’t be that complicated. Well we have been seriously trying for 60 years and the breakeven point is still another many more years away, maybe 50 to 100 years away. Fusion is “simple“, it is just not “easy“. This review will focus on how the stars do it. 2638 Review is how engineers on the planet are doing it.
-
- Our Sun is a star that is a big ball of hydrogen. It originally collects as a ball of gas out of a cloud of hydrogen gas. Gravity constantly pulls matter into the densest center of gravity. Eventually it all condenses into a sphere of gas.
-
- As the mass and gravity of the sphere grows the center of the sphere gets hotter and denser until the hydrogen gas ionizes into a “plasma“. Essentially this plasma is the nucleus of the hydrogen atoms separated from the negatively charged electrons.
-
- The electrons become free electrons and the nuclei remaining are positively charged protons. The protons are heavier and get pulled into the center of gravity with immense density and temperature.
-
- Protons are like positive charges that repeal each other with the electromagnetic force. When the mass reaches 10% of the mass of our Sun the force of gravity can begin to overcome this electromagnetic force separating the protons. Nuclear fusion can begin.
-
- The Sun is fusing these protons into Helium nuclei with its core temperature at 15,000,000 Centigrade. (The surface temperature of the Sun is 6,000 Centigrade). This same process occurs in all the stars.
-
- However, if the mass of the stars is larger then fusion can continue beyond 2 Hydrogen , H-1, nuclei fusing into Helium nuclei,(He-2). When 3 protons fuse together they form Lithium, (Li-3). When 4 protons fuse together they form Beryllium, 5 - forms Boron, 6 - Carbon, 7 - Nitrogen, and this continues right up each of the heavier elements in the Periodic Table to 28 protons fuse to form Iron, Fe-28).
-
- At the element Fe- 28 - Iron the fusion process does not release excess energy. Up until iron each element is slightly lighter than the sum of its parts( i.e.: protons). The excess mass is converted to energy according to E = mc^2. Elements heavier than Iron require the addition of energy in order to fuse together rather the having an excess of energy.
-
- When the core of the star becomes Iron no more excess energy is produced. The star collapses and rebounds into a massive explosion called a supernova. It is in this explosion that higher energies are reached and elements heavier than iron are produced.
-
- The natural elements all the way up to 92 protons fusing to form Uranium, (U-92). But, supernovae are another Review. This review will cover the first step in the fusion process and the one we are trying to replicate here on the planet Earth.
-
- 2 protons fuse into Helium, or, said in another way, 2 Hydrogen nuclei fuse into one Helium-2 nucleus. Or, to be more accurate to where we are heading, 4 protons fuse into a heavy isotope of Helium-4 which contains 2 protons and 2 neutrons with energy left over for 26.8 electron volts of sun power heading toward the surface of the Sun.
-
- This “sun power:” eventually leaves the surface with a total output power of 3.9 *10^26 watts. 8 minutes later it reaches the surface of Earth providing 1,300 watts of sun power on every square meter area, about yhe size of a solar panel on the roof of many houses.
-
- Let’s go back to the core of the Sun and see step by step how this fusion actually happens:
-
- (1) One proton fuses with a proton electron pair which is a neutron forming a Hydrogen isotope nucleus, called Deuterium. The Deuterium nucleus is one proton and one neutron. In addition to the H-2 Deuterium nucleus an anti-electron, an electron- neutrino, and 0.4 million electron volts of energy are produced. The anti-electron is also called a positron. The energy produced is abbreviated 0.4 MeV, million electron-volts.
-
- (2) This process is repeated with 2 other protons. The total reaction now contains: 2 H2. Deuterium nuclei + 2 anti electrons + 2 neutrinos and a total of 0.8 MeV.
-
- (3) Both of these processes fuse with other neutrons creating a Hydrogen-3 isotope with one proton and 2 neutrons, plus Gamma Rays, and plus energy of 5.5MeV. For a total of 6.3 MeV, for the first fusion and 6.3 MeV again for the second fusion.
-
- Now the grand total of particles and energy in the fusion reaction is 2 protons and 4 neutrons in the 2 H-3 nuclei, 2 Gamma Rays and 11.8 MeV.
-
- (4) When the above two processes fuse together the grand total of particles and energy released becomes 2 protons and 2 neutrons fuse to form Helium-4 and the 2 free neutrons decay to form 2 protons, and + 7 Gamma Rays, and + 2 neutrinos, and + releasing an additional 13.0 MeV of energy.
-
- This brings the total energy released to 24.8 MeV.
-
- (5) The last step involves the 2 anti electrons that were produced which collide with 2 free electrons and annihilate each other into 4 Gamma Rays and 2.0 MeV of energy.
The total energy released from this 5 step process becomes 26.8 MeV.
-
- Note that 4 protons were consumed for 26.8 / 4, or 6.7 MeV per proton. And, 2 protons were left over to repeat the process starting with step (1) again. This is referred to as a “chain reaction” that will continue over and over again until all the protons are consumed.
-
- There are other fusion processes occurring in the dynamic plasma at the core of the Sun, but this is one of the fundamental fusion processes going on. If we used purely this process and assumed the Sun was a giant ball of protons how long would it shine before it ran out of protons to fuse?
-
-------------------- The total mass of the Sun is 2.0 * 10^30 kilograms.
-
-------------------- The mass of a single proton is 1.67 *10^-27 kilograms.
-
- Their simple division tells us that there are 1.2*10^57 protons in the Sun. Of course, only the protons at the core of the Sun are at the pressures and temperatures necessary to cause a nuclear fusion reaction. Approximately 10% of the Sun’s mass can be considered the core. So, the core would contain 1.2 * 10^56 protons.
-
- We know that the total energy output the these core protons are producing is 3.9 * 10^26 Watts. A Watt is a Joule of energy per second. There are 1.6022*10^19 electron-volts in one Joule of Energy. Therefore the Sun’s total output power in electron-volts per second is:
-
---------------- 3.9 * 10^26 / 1. 6022 *10^-19 = 2.434*10^45 eV / second
-
---------------- Sun’s energy = 2.434 * 10^39 MeV / second
-
- We have calculated the energy contribution per proton to be 6.7 MeV. Again simple division tells us how many protons are being consumed each second in the core of the Sun.
-
-------------- 2.434 * 10^39 MeV / second / 6.7 MeV = 3.6 * 10^38 protons / second
-
- The Sun’s core has 1.2 * 10^56 protons and it is burning 3.6 * 10^38 protons each second, how many seconds can this last?
-
--------------- 1.2 * 10^56 protons / 3.6 * 10^38 protons/ second = 3.3 * 10^17 seconds. There are 31,560,000 seconds in a year.
-
- So, that means that the Sun’s core can burn protons for about 10 billion years. This has been going on for about 5 billion years so the Sun has burned through about half of its supply of protons. We have another 5 billion years to go.
-
- More massive stars than our Sun actually have shorter lives because they burn hotter and faster and go through their supply of protons with a shorter lifetime.
-
------ 25 Solar Mass Star --------- 80,000 Luminosity of Sun ----- 3 million years
-
------ 3 Solar Mass Star --------------- 60 Luminosity of Sun ----- 500 million years
-
------ 1 Solar Mass Star ---------------- 1 Luminosity of Sun ----- 10,000 million years
-
------ 1/2 Solar Mass Star ----------- 3 % Luminosity of Sun ----- 200,000 million years
-
October 3, 2020 1249 2851
----------------------------------------------------------------------------------------
----- Comments appreciated and Pass it on to whomever is interested. ----
--- Some reviews are at: -------------- http://jdetrick.blogspot.com -----
-- email feedback, corrections, request for copies or Index of all reviews
--- to: ------ jamesdetrick@comcast.net ------ “Jim Detrick” -----------
--------------------- --- Saturday, October 3, 2020 ---------------------------
No comments:
Post a Comment