Thought experiment: What would it be like inside a tokamak?
The ITER organization (IO) recently published an article asking, “Have you ever wondered what it’s like inside an operating tokamak?” For speculative answers, the international nuclear fusion project turned to electrical engineer Michael Walsh, the new head of ITER’s Fusion Technology—Instrumentation & Control Division and previous head of ITER’s Diagnostics Division.
“The honest truth is that we cannot know for sure about the inside of a working tokamak,” the article acknowledges, “because of course that could never be experienced firsthand. A burning plasma is no place for humans, or indeed any living thing.”
Sound: That said—if the impossible could happen and a human being were to be inside a working tokamak, that person would not be able to hear sound because of the near-perfect vacuum conditions inside the device. However, IO notes that “If you could hear anything at all in the tokamak, you would probably experience something like the effects of tinnitus—a high-pitched whine, as the burning plasma could sometimes emit a sound wave at around 10 kHz, which is right at the very top end of the human hearing range.”
Light: “Plasma is effectively a very hot gas that emits electromagnetic waves over a very wide spectrum—including but also far beyond what is visible to the human eye,” IO’s article explains. Humans ordinarily can see wavelengths in the range of 380–700 nanometers—what we call visible light. Walsh explains that the shell of the plasma will look reddish; however, the much, much hotter core emits gamma rays, “which can only be ‘seen’ by the diagnostics team using a gamma ray camera,” according to IO.
Electrons inside the tokamak “are traveling at a significant fraction of the speed of light (up to a third), [and] ITER’s diagnosticians need to take into account the relativistic effect when they are measuring particle speeds,” Walsh says. He compares that effect to a much-exaggerated version of the Doppler frequency shift we experience when we hear a police car pass by. First we hear a high pitch as the blaring siren approaches, then we hear a lower pitch as the car and siren speed away.
And so “it makes a huge difference whether the particles are coming towards you or moving away from you,” IO states. Take for instance electrons in the tokamak that have energy levels of around 25 keV. In this case, “there is almost no light behind the electrons . . . almost all light is in the forward direction.” For this reason, ITER’s diagnostics team has to take into account the so-called red shift as they “see” with their instrumentation—the same effect astronomers factor in considering that the universe is expanding and moving away from observers.
Feeling: In terms of what it would feel like inside the tokamak vacuum, a human would not notice much of a perceptible effect compared to normal everyday conditions, according to Walsh. He explains, “So initially at ITER we take out the oxygen, which also removes the impurities, and that brings the pressure down to around 10−6 Pascal—which is less than 100 billion times that of the air pressure we experience in the everyday world. We then put gas back in and that brings the pressure back up to around 100 Pascal. That’s still quite a powerful vacuum, but you wouldn’t actually feel it.” Surprising as it is, Walsh states that although humans certainly notice dramatic increases in pressure, like one would experience deep-sea diving, human bodies simply do not register drops in pressure.
Magnetic field: Some species of life might find being inside ITER extremely disorienting—those with a magnetic “sixth sense,” such as some bacteria, algae, honeybees, birds, and fish. However, Walsh says that the tokamak’s magnetic field would not affect a human much. “Indeed, with only the toroidal field on (no plasma), the center of the ITER chamber would be virtually the same as sitting in a huge MRI scanner,” according to IO, “only of course without air to breathe.”
