Technology.am (Sept. 09, 2009) — Sodium-like tungsten ions (blue) are far smaller than neutral sodium atoms (orange)—the ion’s 11 electrons are pulled in very tightly by the 74 protons in the tungsten nucleus, making their energy jumps far more expensive than in neutral sodium and causing them to emit high-energy ultraviolet wavelengths of light, rather than visible light, as is the case with ordinary sodium.
Just as health-food manufacturers work on developing the best possible sodium substitutes for low-salt diets, physicists at the National Institute of Standards and Technology have acquired new knowledge on a promising sodium alternative of their own.
Sodium-like tungsten ions could pepper — and conveniently monitor — the hot plasma soup inside fusion energy devices, potential sources of abundant, clean power.
Tungsten—having the highest melting point of any metal—will be used in some high-strength structural components in the experimental ITER fusion reactor under construction in France.
When ITER cooks up its hot, dense fusion plasma, it could erode trace amounts of tungsten from its structures and strip away many of its electrons in the process. When 63 of tungsten’s 74 electrons are removed, it becomes chemically analogous to sodium atoms, which have 11 electrons as well.
Ordinary sodium gas radiates bright yellow-orange light, which has proven useful for everything from mundane streetlamps to exotic atom lasers. Sodium radiates approximately 99 percent of its visible light in two shades of orange, which scientists have termed the “D” spectral lines.
Sodium-like tungsten ions emit intense light in analogous “D” spectral lines, but they are at far higher energy levels than sodium, and so are shifted out of the visible spectrum to the extreme ultraviolet.
Measuring the wavelengths and relative intensities of lines in the spectrum of light released by a population of tungsten ions in the plasma can provide information about the fusion plasma conditions, such as its temperature, density and magnetic fields.