
Scientists Develop Plasma Thruster That Could One Day Power Planes - everybodyknows
https://www.bloomberg.com/news/articles/2020-05-08/emission-free-flying-a-step-closer-with-chinese-plasma-thruster
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ortusdux
Previous discussion:
[https://news.ycombinator.com/item?id=23095701](https://news.ycombinator.com/item?id=23095701)

Publication:
[https://doi.org/10.1063/5.0005814](https://doi.org/10.1063/5.0005814)

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NGC404
Can someone maybe with lab experience in propulsion or comparable knowledge
confirm that their method to measure the thrust of the plasmathruster is in
any way comparable to proper thrustmeasurement / produces forcevalues
correlatable to those measured with an unobstructed outlet and proper
equipment?

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qchris
Measuring low-force, high-temp flows like can be pretty difficult, especially
in academic labs where researchers are typically pretty limited in terms of
instrumentation. I don't have 1-to-1 experience in this field but have briefly
worked in plasma physics and ion thruster propulsion.

Doing a quick scan of the group's AIP paper, I'm generally okay with the
methodology and the results they've drawn from it. It seems like their results
are mostly establishing a rough thrust value with a force ceiling on each
measurement, not a high-precision continuous dataset. Assuming the quartz tube
and sphere don't seriously deviate from one another, the equations and
physical assumptions they're using check out fine. It's not something you'd
want to doing a full characterization on a flight model or anything, but for
lab-scale experiment, I think it works.

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mannykannot
One question I have is this: would the point at which the hollow ball rattles
possibly be dependent on the Reynolds number, which in turn is dependent on
the temperature? And if so, would that not have to be compensated for when
comparing plasma-on and -off measurements?

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qchris
I don't think so--it doesn't look like the rattling of the sphere is caused by
flow around the sphere itself, but rather by the rate of the
displacement/return to equilibrium of the sphere over the opening of the
quartz tube. I'm assuming (and I could be wrong) that the vibration patterns
between plasma-on/off varies pretty significantly, so that rattling, as
opposed to occasionally shifts only happens when the plasma flow is actually
happening and that the force is significant enough to be consistently
displacing the sphere rather than the long-period pressure cycling you'd
otherwise see. I don't think that turbulence in the classical sense would play
much into it.

Not sure if this is helpful, but based on the video I'd guess that rattling
only occurs in the plasma regime (as opposed to the normal, standard temp
airflow), at which point I'm don't think the physical basis of the Reynold's
number holds. Plasmas, especially under an external magnetic field, are only
quasi-stable and so their bulk behaviours don't necessarily track with those
of classical fluids.

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yeetman21
Can we stop posting reddit tier click bait articles about "REVOLUTIONARY THING
WILL CHANGE EVERYTHING" based off one tiny study or speculation?

