h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

A big one.

This Entry is oversimplified and contains some affirmations that could not be stated that way, strictly speaking of course. It's perfectly alright, however, to present things in a less-than-accurate way. But one should keep that in mind. An affirmation like this should IMO appear explicitly in the text of the Entry, especially since this Entry is an Edited one. I have stated that more than once during the PR process, but somehow my objections were ignored.

So, what's wrong with this Entry?

Plasma is presented in the title as being the 'fourth state of matter' (which is alright), then it goes on to explain taht "It is an 'electrically neutral, highly ionized gas composed of ions, electrons, and neutral particles'" That would be equivalent to stating that a liquid is a phase of matter made of ions, solid bodies and gases. That would be a mixture. Plasma per se is not a mixture, if it is to be a phase of matter. Plasma is made of nuclei and electrons, like atoms, with the exception that the electrons and the nuclei are separate.

Fire is not an example of plasma. In some cases a fraction of fire can be present in the form of plasma. In most cases fire is made of hot gas.

Then: As far as we know electrons are not moving 'around' the nucleus.

On Earth plasma is rare. (Fire is not a rare occurence on this planet as I stated in another thread to this entry)

"The Sun itself is a huge plasma due to its incredible heat." Correct, but "It is now widely accepted and understood that the Sun's plasma state is what allows it to generate energy in such a controlled manner, while still providing huge quantities of it." Plasma is the consequence not the cause of the sun's generating energy. The energy the sun generates is due to nuclear fusion, and that one is ignited because of the humongous pressure in the sun's centre.

Then "Mankind is discovering that plasma has many uses." (Fire has been around for quite a while, but hey...) "Plasma-based rocket engine technology is in development." (What is coming out of rocket boosters right now? According to the previous definitions that would already be plasma) "The rockets will be able to run on very simple fuels with a much higher rate of efficiency." (I would love to know how? Fusion? That's blank speculation). "In the more advanced hospitals of the world, it is used to sterilise" (My dentist uses 'fire' to sterilise his dishes - that would be plasma, again... "and cauterise because it is particularly effective at this task." (How? If there's so much energy involved in that, wouldn't a plasma gun cause more harm when applied to a patient? That question should have been adressed...

Sorry, but I had to put that in here, as that all went unheard during PR.

Sincerely,

HELL

If plasma is electrically neutral then how do physicists, for example at CERN, control a plasma flow with magnetic fields?

Although a plasma is electrically neutral overall, as the respective charges of the negative electrons and positive ions cancel out. However, the charged particles that make up the plasma are, like all moving charged particles, affected by magnetic fields.

A charged particle moving in a magnetic field experiences a force perpendicular to both the direction of its movement and to the magnetic field lines. In a uniform mag. field this causes it to move round in a circle. If you have a magnetic field with the right shape then you can trap your particle - a so-called 'magnetic bottle'.

Scientists doing fusion research ( ie at JET in Culham near Abingdon in Oxfordshire, UK. www.jet.efda.org ) exploit this by using magnetic fields to keep the extremely hot plasmas they use away from the walls of the fusion vessel which would otherwise be vapourised.

As far as I know, there isn't any plasma research going on at CERN ( www.cern.ch ). However, the huge particle accelerators - "atom smashers" - there (the latest, the Large Hadron Collider, is currently about to be built) use magnetic fields in the same way, to keep the particles being accelerated inside the accelerator.

Hope this helps!
jfmchivall

It does, thanks.