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Spheromak: The spheromak is a type of plasma configuration which enables the plasma to contain itself with its own magnetic field, even when external fields aren't present. Plasma's shape with this configuration resembles that of a smoke ring.

So, there is an ongoing plasma rifle design in my head which involves spheromaks of nitrogen plasma flying at speeds of Mach 10 in atmospheric conditions, however, a certain person said, that it's likely that these spheromaks will be eroded by air drag.

I tried to make a few countermeasures, but I'm still unsure if spheromaks would be capable of surviving in an atmosphere until they reach their intended target (an unfortunate terrorist, who stands 90 meters away from me).

The plasma's countermeasures:

  • high degree of ionization in the plasma

Would it be possible for a spheromak to survive in an atmosphere until the end of its "trip"?

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    $\begingroup$ I don't think I'd want to be within 90m of your gun regardless of which direction it's aimed. Plasma is hot. $\endgroup$ – Draco18s Jun 12 '17 at 20:44
  • $\begingroup$ @Draco18s But not too dense. $\endgroup$ – Mephistopheles Jun 12 '17 at 20:50
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All you want to do is kill a terrorist 90 km away? What's wrong with missiles? We know they work. They can be guided or remotely controlled. You can be be very accurate and even know what you hit. Payloads can be of the penetrating type (for hardened targets) or even nukes if you're of the particularly vindictive mindset.

You can't guide a spheromak. It's a line of sight weapon so you have to hope the target conveniently stays put for you. At 90 km, the time of flight at (an insane) Mach 10 is about 32 seconds. Plenty of time for a target to move away from your aim point. This essentially renders the weapon useless for your intended role. In 32 seconds a human at preferred walking speed will travel about 46 m. So you need a weapon with a blast radius of more than 50 m to get a kill. You may as well drop a large dumb bomb to do that.

Spheromak lifetimes are on the order of (at most) 1 ms. That's one thousandth of a second. Even at Mach 10 (really?) you only get 300 cm ranges (say ten feet). You'll never reach your target.

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    $\begingroup$ You're off by 3 orders of magnitude. The question specifies 90 meters not 90 kilometers. $\endgroup$ – sphennings Jun 13 '17 at 0:55
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    $\begingroup$ Even if StephenG is off by 3 orders of magnitude, the answer reasons the OP is also off by at least 2. $\endgroup$ – Rekesoft Jun 13 '17 at 7:44
  • $\begingroup$ @Rekesoft Why am I off by two orders of magnitude? $\endgroup$ – Mephistopheles Jun 13 '17 at 8:31
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    $\begingroup$ I don't know anything about spheromaks. I was pointing only that StephenG's answer says that their lifetime is (at most) 1ms, which means that even at hard to believe speeds they are only going to survive a few centimeters. So, way off the 90m you asked for. I suspect, however, that incresing the speed would actually reduce its lifetime, due to sheer shockwave pressure, so it's a dead end there. $\endgroup$ – Rekesoft Jun 13 '17 at 8:37
  • $\begingroup$ @Rekesoft How would shockwave pressure affect plasma? $\endgroup$ – Mephistopheles Jun 13 '17 at 9:18
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No (given modern technology)

Yes (given scifi technology)

Discussion

GuildsBounty discussed the modern applications and shortfalls here. The short version is that toroidal configurations are presently unstable, only lasting $1 \times 10^{-6} ~\text{s}$ as of the 1990s. You'd need significant improvements in their stability to maintain themselves for a useful amount of time.

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