AcesHigh wrote:this article claims Wenderlstein 7X was the first in the world ever to produce hydrogen plasma? Other fusion prototypes only produced helium plasma. Is there any veracity to that?
No. That is just a really horrible article. Here is a much better one directly from the source. http://www.ipp.mpg.de/4010154/02_16
W7X is the world's largest stellerator. Today was the first time the system has run hydrogen. Every other major fusion reactor for nearly 100 years now has used hydrogen; there is nothing inherently special or difficult about a hydrogen plasma.
Helium is generally easier to breakdown with microwave heating. This is important on a fresh system which will be full of impurities that interfere with the plasma and degrade performance. Helium is a non-reactive noble gas that does a good job of scrubbing out impurities from the walls while also being easy to pull out of the system later when you no longer want it around. Performance improves with each shot as the system is cleaned. This stage is about testing out all the diagnostics, power, vacuum, cryogenic, and other systems which need to work as a synchronized group for a successful shot.
Starting to use hydrogen is a noteworthy step since it indicates that the initial housekeeping phase is complete and the real science is starting; it makes for a nice milestone and photo-op.