A plasma isn’t a solid, a liquid, or a gas. It's a fourth state of matter that exhibits an array of unusual behaviors, which makes it pretty cool in my book. That said, some forms of plasma are hot. Very hot. So hot that no material can contain them. Like other forms of plasma, though, even hot plasmas can be contained by magnetic fields.
Taking advantage of that property, researchers at MIT are attempting to create hydrogen-based plasmas hot enough and dense enough to produce fusion reactions. Their ultimate goal: To create a simple, efficient source of electrical power that doesn’t churn out the radioactive wastes generated by today’s uranium-based fission reactors. Not a bad idea, given the growing demand for electricity worldwide. In China, for example, consumption is growing at more than 4% per year. The overall global rate isn’t far behind, at about 2.4%. Compounded yearly, that’s a lot of juice.
To understand what the MIT researchers are attempting, you have to travel back to the 1980s, when Voyager II detected plasma trapped in Jupiter's magnetosphere. That finding, according to Science Magazine, inspired the physicist Akira Hasegawa to propose a fusion reactor based on a magnetic dipole, which is simplest, most common type of magnetic field in the universe. As the name suggests, a dipole consists simply of a north pole and a south pole.
In a dipole reactor, a magnetically levitated, superconducting torus (picture a big metal donut floating in a vacuum chamber) generates lines of magnetic force similar to those that surround the Earth, Jupiter, and other magnetized planets. The reactor then uses pulses of microwave heating to create plasma discharges, which the magnetic field holds in place.
The MIT researchers call their project, appropriately enough, the Levitated Dipole Experiment (LDX). To levitate the torus, which weighs about 1200 pounds (550 kg), they use a high-temperature superconducting coil, mounted on top of the vacuum chamber. The levitation control system, which uses 8 laser beams to constantly monitor and fine-tune the power of the levitation coil, runs on the QNX Neutrino RTOS.
According to a paper written by members of the research team, QNX Neutrino “ensures that the feedback cycle runs deterministically with high reliability.” To implement the feedback algorithm, the system designers used Opal-RT’s RT-Lab and Mathworks Simulink.
From what I’ve read, the hot, dense fusion reactions inside a dipole-based reactor can produce energetic photons that heat the reactor; this heat can then be used to generate electrical power. The reactions also create charged particles that the reactor will trap in its magnetic fields. The net effect is a theoretically clean, yet efficient method of generating electricity.
Just one thing, though. The MIT researchers warn that levitated dipole reactors aren’t ready for prime time just yet — and probably won’t be for about another 40 years. So turn off that light, will you?
I’ve got two videos to show you. The first one shows the "first flight" of the LDX (times are approximate):
1) A pneumatic launcher raises the torus (donut).
2) The launcher retracts (0:13) downward as the torus begins to levitate.
3) The chamber darkens (0:28) and plasma begins to heat up.
4) The heating stops (0:42) and the plasma begins to dim.
5) The launchers catches the falling torus (1:15).
The second video, filmed by Discovery News, provides a bit more context. If you can, go straight to the -2:35 mark:
Being plasma challenged, I’m the last thing from an expert on the LDX. So I invite you to visit their site — http://alcpc1.psfc.mit.edu/ldx/ — to get the full skinny. (Funny expression, that.)