Questions tagged [fusion]

The fusion tag is used for questions about nuclear fusion, both the basic process at a physical level and it's use as a potential energy source.

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What mass fraction of a main sequence star produces energy?

Only some fraction of the total mass of a main sequence star produces energy in the star's centre through the pp-chains, or in heavy stars, the CNO-cycle. My question is about the mass fraction where ...
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Muon-catalyzed fusion: muon number

I recently read a paper "Meson-catalyzed fusion in ultradense plasmas" (it is behind a paywall: only subscribers to Physical Reviews E can read it) that claims that muon-catalyzed fusion in ...
S.T. Zweig's user avatar
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Efficient way to convert hydrogen atoms to neutrons?

Can a hydrogen atom be converted to a neutron with a sufficiently high energy photon? Or perhaps via a pair of photons having total energy of about 800 keV? One photon would have an energy of say ...
Mike J's user avatar
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High-energy neutron multiplier

Are there any materials that can function as efficient high-energy neutron multipliers? I have read about the utilization of Beryllium and Lead as neutron multipliers, but they seem to only be ...
S.T. Zweig's user avatar
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Green's function for a Hirsch-Farnsworth fusor

I'm writing a proposal for building a Hirsch-Farnsworth fusor at my university using a vacuum chamber, deuterium, and high voltage power. A loop of wire inside the chamber is set at a negative voltage ...
Tyler Mark's user avatar
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Ideal ignition temperature for a D-T plasma fusion reaction

I've been trying to calculate the ideal ignition temperature for a 50-50% Deuterium-Tritium (D-T) reaction. In the literature this value is $4.4$keV and I'm getting $5.2$keV. Here's how I'm carrying ...
kid_a's user avatar
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Are there spectra that "prove" that measured energy excesses came purely from deuterium-tritium fusion reactions at the NIF during ignition events?

More energy was produced than was supplied by ultraviolet (UV) lasers (creating x-rays in the gold chamber wall to compress the spherical hollow capsule creating a dense, high-temperature, high-...
Alden Park's user avatar
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HB11 fusion Engine

Looking for a way to achieve torch ship performance (https://www.projectrho.com/public_html/rocket/torchships.php#torchdrive) Without strapping my reactor/engine to the outside of my ship. The main ...
Michael Ferrell's user avatar
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During fusion, how does mass turn into energy?

This is my (flawed) understanding of how fusion basically works: Let's assume that a fusion reaction has a net gain in energy. First, there is an input amount of kinetic energy to get the two light ...
Edward Chen's user avatar
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Power from CNO Cycle Fusion

There are all sorts of projects trying to get power from fusion reactions. The best known and funded are the Tokamaks, big expensive crush Deuterium and Tritium (He3 sometimes) plasmas and spew ...
MongoTheGeek's user avatar
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How is volume defined and measured in nuclear physics, in particular regarding the Sun’s core? [closed]

The Sun’s core is, from the micro/quantum perspective (from what I've read) the constantly moving phenomena of nuclear fusion (as the Earth is mostly the constantly moving phenomena of stable atoms ...
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In a tokamak, is there a density-dependent limit on plasma current?

In a tokamak, the kink limit places an upper bound on the magnitude of the plasma current. For example, Parisi and Ball (2019) write this limit as (p. 246) $$I\lesssim\frac{1}{q}\frac{2\pi}{\mu_0}\...
SapereAude's user avatar
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Could lithium deuteride sustain a "cold" chain reaction?

When Lithium 6 absorbs a neutron (thermal or not) it reacts forming an alpha particle and a tritium. The formed tritium has an average kinetic energy of 2.5 MeV. That kinetic energy is way higher than ...
Peter S.'s user avatar
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Why lasers are used in inertial nuclear fusion?

Why in inertial fusion are used laser rays but not, for example, merely focused light? Is there a problem with precision of focusing or power density?
Nonexistent user's user avatar
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Confusion about energy conservation for fusion and fission (binding energy and $Q$-value)

In a nuclear reaction, a system consisting of a nucleus or nuclei lose mass, and this mass gets turned into energy, which is quantified by $E=mc^{2}$. But I'm conceptually confused. According to ...
beancurdedward's user avatar
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Improved estimate of density of free neutrons in solar core

In an answer to this question: Free neutrons in the sun's core? I made a very rough attempt to estimate the density of free neutrons in the solar core. There is some non-zero rate for production ...
Andrew Steane's user avatar
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Why does the Nuclear fusion rate decrease with temperature after a point?

According to here the Fusion rate for D-T peaks at a little under 1E9 Kelvin and decreases afterwards. Why is this? Why does the rate stop increasing?
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How do protons fuse in the sun?

I know that Nucelar fusion in the sun requires quantum tunneling to occur, as otherwise the Sun's core wouldn't be hot enough to overcome the Fusion barrier. However while the 2nd and further stage of ...
blademan9999's user avatar
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What’s the lightest you could make a "star" if you made it out of different materials?

What’s the lightest you could make a "star" if you made it out of different materials? How large would the "star" be? For example according to here https://astronomy.stackexchange....
blademan9999's user avatar
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Randomly think about how the world will end because I have homework to do. Please help me think this through [closed]

First off, I just want to say that i do not hold any degree of any kind, except a forklift certification but I do love space and I think about it to the point where I believe. As I am sitting in front ...
ME with no middle name.'s user avatar
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Determing for particle density of many particle species in plasma

For quasi-neutrality plasma of many species, the relation of electron density and ion density said that \begin{equation} n_{\text{e}} = \sum_{s}Z_{\text{i},s}n_{\text{i},s}, \end{equation} where $n_{\...
nirama_xox's user avatar
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What’s the minimum mass required for a star to burn helium?

What’s the minimum mass required for a star to burn helium? I’ve liked online but I’ve gotten inconsistent answers.
blademan9999's user avatar
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What are some practical problems with static electrical confinement of plasma?

Plasma and fusion physics experts, help me with this one: Suppose we have a D-T plasma with net positive electrical charge inside a positively charged metal sphere. As the containment sphere's net ...
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How Should the True Energy Gain of the NIF's "Scientific Breakeven" Fusion Experiment be Calculated?

According to this article "LLNL’s experiment surpassed the fusion threshold by delivering 2.05 megajoules (MJ) of energy to the target, resulting in 3.15 MJ of fusion energy output." It isn'...
phil1008's user avatar
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Theoretical calculation for deuterium tritium fusion

How would a deuterium-tritium fusion feynmann diagram look like in terms of QHD (i.e meson exchange like eta,pi,sigma,omega,...)? I couldn't find anything online whilst this would be quite an ...
nemo's user avatar
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Why it is not possible to reach the sun if we are able to create plasma? [closed]

if we are able to create plasma in isolated environment possessing temperature much more than temperature of sun then why are we not able to create something that can go to the sun?
Mohammad Sameer's user avatar
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How does an electron absorb the energy released during inelastic collision between a neutron and the nucleus of a hydrogen atom?

In atomic collisions,does the neutron fuse with the proton of hydrogen and release a photon which is absorbed by the electron which then gets excited to higher energy state? Or do the neutron and ...
Timmy's user avatar
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Is there an intuitive picture for quasi-isodynamic versus quasi-axisymmetric versus quasi-helically symmetric flow in stellarators?

I recently read a paper in which Alan Boozer says, The W7-X stellarator was made quasi-isodynamic rather than quasi-symmetric in order to minimize the parallel currents as well as the ripple-trapped ...
SapereAude's user avatar
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Are there any research mentioning the principle of tornados or maelstroms in plasma physics related to fusion?

There are many different ideas and concepts related to design of fusion reactors and handling plasma confinement, but what about designing one around the principles of a maelstrom or a tornado? Is ...
Andreas Zita's user avatar
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Nuclear fusion by Z-pinch without Marx generator?

The Marx generator was invented by Erwin Marx in 1924 (1). This electric generator is an assembly of capacitors and spark-gaps. The capacitors charged in parallel and are discharged in serie. This ...
Daumic's user avatar
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How does the second stage of a fusion bomb create and maintain the needed pressure?

My understanding of the second stage of a thermonuclear bomb is as follows: X-rays from the first stage compress the "tamper", thereby igniting the fission sparkplug, and that the resulting ...
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Why do most MRI machines and fusion reactors use helium-cooled superconducting magnets instead of cheaper, higher-temperature nitrogen-cooled ones?

I am always hearing about the high (and increasing) costs of helium, as well as the difficulty of handling it.... Are there no high(ish) temperature superconductors that can create a strong enough ...
Kurt Hikes's user avatar
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Why are nuclear fusion reactors difficult?

The first fission bomb was created in 1944, and the first fission reactor in 1951 (and actually productive one in 1954). This delay seems possible to explain by there being a larger amount of initial ...
user56834's user avatar
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What "changes" in the quantum state of bound nucleons that cause that system to have mass defect?

The electric field in an excited hydrogen atom is non-zero over a bigger volume than the electric field in a ground-state hydrogen atom. The energy associated with this extra electric field must be ...
TheJeran's user avatar
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Derivation of pressure balance equation for a toroidal geometry [closed]

Derivation of pressure balance equation in toroidal geometry $$ \boxed{ \frac{\mathrm{d}p}{\mathrm{d}r} + \frac{\mathrm{d}}{\mathrm{d}r} \left( \frac{B_{\phi}^2}{2\mu_0} \right) + \frac{B_{\theta}}{\...
147875's user avatar
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1 answer
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Exchange interaction and nuclear fusion

Most texts about nuclear fusion say that the reason it is so hard to get protons to fuse is the strong Coulombic repulsion between them. However, it seems to me that at close distances, protons should ...
slithy_tove's user avatar
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148 views

Why does deuterium fusing with a proton produce a gamma ray?

For the pp chain, the second process is listed as the d(p,γ) 3He reaction: D + p --> 3He + gamma ray. I cannot find an explanation why a gamma ray is created in this process. Can anyone explain why ...
Justin Pelzer's user avatar
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Would an intersecting plasma in a fusion reactor increase yield due to the collision of particles in the plasma?

It seems to me that having a plasma “stream” in a tokamak that intersected itself would increase the number of collisions happening between particles. Is this feasible or is it negligible in the face ...
CuriousHoneyBadger's user avatar
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1 answer
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How is the branching ratio defined for nuclear reactions?

The Wikipedia page for candidate nuclear reactions for terrestrial fusion power notes that the D + D and He-3 + T reactions can proceed through either of two alternative routes; for example: (2i) D ...
mitte's user avatar
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1 answer
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Is the universe getting hotter? Brighter?

Due to their fusion processes every star is radiating massive amounts of photons and (to a lesser extent) neutrinos. Are all of these getting absorbed in matter over time, warming it, or is the total ...
WaveInPlace's user avatar
1 vote
1 answer
68 views

What would the nucleus of a water planet be like?

If we have a planet made out of water, would it be all solid? What about the nucleus? Would it depend on the size of the planet?
Pablo's user avatar
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3 answers
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Is the energy of matter (via $E=mc^2$) actually available to do work?

If energy is functionally defined as the capacity to do work, then in what sense does mass offer a lot of energy (via $E=mc^2$). Most people responses I've seen to similar questions state “there’s a ...
Sam Dull's user avatar
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It is possible to combine two heavy elements into one?

Is it possible to combine say two uranium atoms into very heavy new element? Periodic table ends around 115 today, but can it go forever technically?
Lukasz Skowron's user avatar
1 vote
1 answer
135 views

How can the binding energy per nucleon graph be useful if you can't compare "all" products with "all" reactants?

How can the binding energy per nucleon (BEN) graph be useful if one can't compare "all" products with "all" reactants? Take the fission process of Uranium to Thorium: $${}^{238}U \...
Authentic Melody's user avatar
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1 answer
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What does thermal (non-)equilbirum mean in the context of a fusion reactor (such as the Helion reactor)?

A while ago, there was a question here asking about the impact of Todd Rider's thesis about various fundamental limitations to fusion reactor efficiecy. That question was mainly concerned with why ...
tobalt's user avatar
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Mass per nucleon graph

I am a high school student and am struggling with understanding the significance of the mass per nucleon graph. What does this graph show with regard to nuclear reactions? (y-axis: M/A, x-axis:A) I ...
Authentic Melody's user avatar
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1 answer
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How do the atoms and electrons move around space when the solar core presses them into a dense plasma? [closed]

It takes a lot of intelligence to compute the center of the sun. As far as I imagine, it's compressed by the hand of gravity and high energy fusion radiation wants to escape one way or the other. ...
bandybabboon's user avatar
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Are there any calculations that "backup" magnetized inertial fusion by steam pistons?

Piston driven MTF can generate fusion. General Fusion has released data on the plasma confinement that they do in their machines, so there is no doubt to the feasibility of the approach. Nonetheless, ...
Evamentality's user avatar
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Neutronization process

How can I find the neutronization density for cold hydrogen plasma? Does it happen within the fusion process of protons and electrons which yields neutrons and neutrino?
TTT's user avatar
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NIF Ignition Achievement

Although the National Ignition Facility achieving positive energy output is hailed as an achievement in fusion energy, I am curious whether their configuration could ever be adapted to produce ...
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