Enter the mini TWT, shown here in an example from 元Harris Electron Devices.
But you don't always need that much gain. Most TWTs of the 20th century were designed for extremely high power gain, with amplification ratios of 100,000 or more. The beam is designed to heat the surface of a person's skin, creating a burning sensation but without penetrating into or damaging the tissue below.Īs its name suggests, a traveling-wave tube (TWT) amplifies signals through the interaction between an electric field of a traveling, or propagating, electromagnetic wave in a circuit and a streaming electron beam. This system projects a relatively wide millimeter-wave beam, perhaps a meter and a half in diameter. They have also been explored for nonlethal crowd control, in the U.S. In addition to heating fusion plasmas, gyrotrons are used in material processing and nuclear magnetic resonance spectroscopy. Fusion gyrotrons typically stand around 2 to 2.5 meters tall and weigh around a metric ton, including a 6- or 7-tesla superconducting magnet. The high-frequency waves accelerate the electrons within the plasma, heating the plasma in the process.Ī tube that produces 1 MW of average power is not going to be small. (We tube folks love our -trons and -trodes.) The interaction between the gyrating electrons and the cavity's electromagnetic field generates high-frequency radio waves, which are directed into the plasma. So how does a megawatt-class gyrotron work? The name provides a clue: It uses beams of energetic electrons rotating or gyrating in a strong magnetic field inside a cavity. These experimental reactors can require temperatures of up to 150 million ☌.
Just 37 centimeters long and weighing about 8 kilograms, it's small and light enough to fit the rotating arm of a radiotherapy machine.Ĭonceived in the 1960s in the Soviet Union, the gyrotron is a high-power vacuum device used primarily for heating plasmas in nuclear-fusion experiments, such as ITER, now under construction in southern France. The medical magnetron shown here, manufactured by e2v Technologies (now Teledyne e2v), generates a peak power of 2.6 MW, with an average power of 3 kilowatts and an efficiency of more than 50 percent. High-power magnetrons continue to be developed to meet the demands of radiation oncology. A 2-megawatt magnetron powered the 3-meter-long accelerator. The first clinical accelerator for radiotherapy was installed at London's Hammersmith Hospital in 1952. When electrons in the beam are deflected by the nuclei in a target-consisting of a material having a high atomic number, such as tungsten-copious X-rays are produced, which can then be directed to kill cancer cells in tumors. In a linear accelerator, it creates a high-energy electron beam. It is for this last use that the medical magnetron shines. While the magnetron's use in radar began to wane in the 1970s, the tube found new life in industrial, scientific, and medical applications, which continues today. The magnetron first rose to glory in World War II, to power British radar. When it comes to efficiently generating coherent radio-frequency power in a compact package, you can't beat the magnetron. So here's my take, in no particular order, on some tubes that made a difference. And I've pretty much stuck with radio-frequency tubes, so I'm ignoring the vast panoply of audio-frequency tubes-with one notable exception.īut even within the parameters I've chosen, there are so many amazing devices that it was rather hard to pick just eleven of them. I intentionally left out well-known tubes, such as satellite traveling-wave tubes and microwave-oven magnetrons. Here you'll find no gas-filled glassware like Nixie tubes or thyratrons, no “uber high" pulsed-power microwave devices, no cathode-ray display tubes.
Feel free to add it in the comments section at the end of this article. So, to state the obvious: This is my list of vacuum tubes.
Of course, anytime anyone offers up a list of anything-the comfiest trail-running shoes, the most authentic Italian restaurants in Cleveland, movies that are better than the book they're based on-someone else is bound to weigh in and either object or amplify. To prove it, I've assembled a list of vacuum devices that over the past 60 or 70 years inarguably changed the world.Īnd just for good measure, you'll also find here a few tubes that are too unique, cool, or weird to languish in obscurity. In an age propped up by quintillions of solid-state devices, should you even care about vacuum tubes? You definitely should! For richness, drama, and sheer brilliance, few technological timelines can match the 116-year (and counting) history of the vacuum tube.