Flux tubes are an interesting aspect of astrophysics. Flux or more accurately magnetic flux is the amount of magnetic field line flowing through a given 2D surface. A flux tube is therefore infinitely many circular 2D surfaces stuck together to create a long tube which magnetic field lines are imagined to flow through without ever exiting the sides of the tube. As magnetic field lines near the surface of the tube are always perpendicular to the surface they keep moving through and the total magnetic flux within the tube must stay constant even if the tube bends or grows and shrinks in diameter. Flux tubes and a slightly more advanced example that we’ll get onto in a second are found most prominently in the Sun. When large flux tubes are projecting out of the surface of the Sun then large amounts of magnetic field also flow out at this point, stymieing convection and producing a sunspot.
Despite having been writing these posts for almost two years I cannot remember explicitly mentioning terahertz spectroscopy once. There have been times when I have talked about analysis at the near infrared scale and of course referred to the terahertz frequency range but the exact details of terahertz spectroscopy have not been described in a way I’m satisfied with. Time to remedy that. Terahertz spectroscopy is a spectroscopic technique that uses photons in the area of terahertz (1012 Hz) to interact with the matter being studied.
Nuclear weapon testing has been both a good and a bad thing for the study of radioactive dating. On one hand the nuclear material released into the atmosphere has made it more difficult to accurately determine ages as the released radioactive material alters the naturally present concentrations in the atmosphere. On the other hand it can actually be beneficial in cases such as limnology. If some freshwater is found checking the radioisotopes present will reveal whether it has been recycled during the nuclear age. Another good example is to use the great increase in unnatural radioisotopes produced during a nuclear detonation, caesium-137 for instance, to calibrate other dating techniques. Since we know the exact dates of these explosions we can find the soil layer containing large amounts of caesium and check other dates compare to it.
Stopping power is the ability of a material to slow down charged particles (stopping power is only used for charged particles) passing through it by removing their energy through interactions with the particles in the material. In the early 1930s a physicist named Hans Bethe developed the Bethe formula for calculating the average energy loss over a distance within a material:
where me and e are the mass and charge of an electron; I is the average potential of the electrons in the material and n is their number density; and v and z both refer to the particle being retarded, being velocity and charge respectively (it should also be noted that this is a simplification for a non relativistic particle. Electrons and fast moving particles require corrections to the above formula). Continue reading Calculating Distance Over Which Charged Particles Pause
Nuclear fusion is quite a way off becoming viable although progress is being made with larger and larger fusion reactors being created all the time. So far the largest reactor that is being built at the moment, ITER, will have an exhaust power of about 150 megaWatt. When a proper fusion power plant is created it would have an exhaust power of about 800 megaWatt. A divertor is a component of a fusion reactor which uses a magnetic field to define a plasma boundary. The divertor can be controlled to manage and shape the plasma into a D-shape plasma (a more elongated ovular form). In this state, the heavy ions, which are the main component of the “exhaust” of the fusion, are flung out and separated with greater ease. Unfortunately the current limit of divertors are 10 megaWatt per metre squared and it doesn’t seem this limit is set to increase. Radiative cooling has to be employed in future reactors if they can’t provide the exhaust space for the current divertor ability.
There is condensed matter physics, where particles have to adhere to eachother (hence the word condensed). There’s plasma physics, where electrons have stripped from all the atoms leaving just a gas of ions behind. There is also an intermediate step. This is where the temperature is such that the average kinetic energy of the electrons is about equal to the binding potential energy that holds them to the nuclei. This means it is too cold for condensed matter physics where its a guarantee that the electrons will be liberated, but too hot for condensed matter physics where the electrons are guaranteed to be bound. This is called warm dense matter and is not easily modelled by either branch of physics.
The importance of the Sun in our solar system cannot be overstated. When considered, it is quickly realised that almost all sources of energy on this planet come from the Sun. For solar power it is obvious, but wind power is caused by the temperature gradient the Sun produces and fossil fuels originally started out as plants absorbing energy through photosynthesis. The two main exceptions are tidal power, which is a conversion of the Earth and Moon’s rotational kinetic energy, and geothermal power, which is gained from nuclear decay in the Earth’s core.