Posted tagged ‘fusion’

What I do: Plasma Physics

March 22, 2010

I’ve been meaning for a while to write about what I do. For work, I mean. Usually I am happy blogging only about my hobbies, but I went to a “winter school” in January, a week long workshop in Los Angeles, and I was thinking to myself, “you know, this stuff actually is pretty cool. I should tell people about it.” Additionally, I just fixed the USB ports on my computer, so I can get photos off my camera again. Hurray; an end to my blogging hiatus! So here it goes:

I study plasma physics. Usually if I say this to non-physicists, they ask me, “you mean like in blood?” No, that’s not what I study. This is what I study:

The Aurora Borealis, an example of plasma. photo credit: Nick Russill (link at end of post)

So, what is plasma?

The plasma I study, (which actually is named after the blood stuff), is ionized gas. Let me explain a little about what that means. Think about an ice cube. If you heat up the ice cube, it melts, changing from solid to liquid. If you heat up that liquid water it boils, becoming steam: a gas.

Now as you continue to heat that gas, all those H2O molecules flying around in the steam move faster and faster. These molecules tend to crash into each other as they fly around. Eventually, at a high enough temperature, they crash violently enough that they break apart. They break into ions—charged particles. Even some of the electrons that normally orbit around the atomic nuclei are stripped away. These electrons are then freely flying around in the gas just like the heavier ions; they just weigh a lot less.

Neglecting a few technical details, this gas of charged particles is a plasma. (Those technical details explain why a candle flame or a camp fire is not plasma even though it is an ionized gas).  Because of the little thought journey we just took from ice cube to plasma, people sometimes call plasma “the fourth state of matter” (1: solid, 2: liquid, 3: gas, 4: plasma). In actuality the line between gas and plasma is a little blurrier than that between say solid and liquid or liquid and gas, but that detail is unimportant for the purposes of my blogging. Examples of plasmas you may have seen include: the sun, lightning, neon signs, the aurora, and the pixels in plasma TVs.

One of the remarkable things about plasma is that because the charged particles are roaming around freely, the plasma conducts electricity. Incidentally, this is the same reason that most metals conduct electricity: some of the electrons in a copper wire or an iron slab are freely roaming around, not tied to any particular atomic nucleus.

Why should we care?

Why do we care about this stuff? Well, almost everything we can see in the universe is plasma: stars, most of the space between stars, nebulae, supernovae and their remnants. All these things live out their lives in the plasma state. So from a fundamental point of view, if we wish to understand the universe, then we need to understand plasma.

Plasma glowing inside the Mega Ampere Spherical Tokamak (MAST), an experimental fusion reactor in Culham, Oxfordshire, England. Photo credit: Andrew Back (link at end of post).

More practically, my interest in plasma involves two principal applications. The first is the production of energy by nuclear fusion (above). The second is the prediction and understanding of violent magnetic explosions that occur on the sun (below), and sometimes lead to magnetic storms and auroral activity on earth. I’ll explain each of these in more detail in my next two posts.

x-ray image of solar coronal loops (magnetic field structures on the sun) taken by NASA’s TRACE satellite

photo credits:

aurora image:  Nick Russill

MAST spheromak image: Andrew Back

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