Plasma Guns

[(E)]

Would a pseudo plasma rifle fit the bill better?
Say a railgun type weapon that fires a technobable thermite slug that ignites after it leaves the barrel and has a ceramic shell that causes technobable on impact?

[Anthony]

Originally Posted by Minuteman37

well the weight of the plasma is obviously a limiting factor for small arms what could be done with a WPS of 0.037?

Depends what that weight is made up of. As a microfusion device it would have a detonation energy of up to about 2 kT.

[Rupert]

Originally Posted by (E)

Would a pseudo plasma rifle fit the bill better?
Say a railgun type weapon that fires a technobable thermite slug that ignites after it leaves the barrel and has a ceramic shell that causes technobable on impact?

That's just a railgun with exotic ammunition. That has a different feel to a real plasma gun. Aside from anything else, for many players a 'railgun' implies a choice of ammo types.

[AlexanderHowl]

Hydrogen possesses a thermal capacity of around 14 J per gram per Kelvin, so a 15 gram plasma burst at 10,000 K when it hit would have around 210 kJ worth of energy. That would be sufficient to kill a human being (it would be enough to flash vaporize around 72 grams of water which, when it turns to steam in the human body, would explosively create a hole around 360,000 cubic centimeters in volume). Anything at that level would probably irradiate the attacker with Bremsstrahlung radiation though as the atmosphere and magnetic fields would brake the plasma discharge too rapidly for the safety of anyone (1 J of Bremsstrahlung radiation is the equivalent of around 0.1 rad of radiation exposure at 1m). A modest 30% energy loss to Bremsstrahlung radiation from a 300 kJ plasma bolt (so the final energy hitting the target was 210 kJ) would be the equivalent of 3,000 rads of radiation exposure along the line of attack.

[Anthony]

Originally Posted by AlexanderHowl

Hydrogen possesses a thermal capacity of around 14 J per gram per Kelvin, so a 15 gram plasma burst at 10,000 K when it hit would have around 210 kJ worth of energy.

Well, that specific heat isn't very accurate once temperature exceeds ionization energy, but 15 grams of hydrogen at STP would have a volume of 167L, and at 10,000K (ignoring ionization) that increases to 5,600L. To fit it into a ball with a 2 cm diameter (volume 0.0042L) requires a pressure of 1.3 million atmospheres or 130 GPa.

Originally Posted by AlexanderHowl

Anything at that level would probably irradiate the attacker with Bremsstrahlung radiation

Not from a measly 10,000K plasma, unless the containment device generates radiation.

[Agemegos]

Originally Posted by AlexanderHowl

Hydrogen possesses a thermal capacity of around 14 J per gram per Kelvin

That's molecular hydrogen. A neutral plasma has a higher heat capacity because the electrons offer an extra three degrees of freedom without increasing the mass. Besides that a highly-ionised plasma is opaque and therefore in thermal equilibrium with cloud of entrapped photons, and those can't escape from the magical containment bubble because if they did the plasma would cool rapidly. A fully ionised plasma is going to have a thermal capacity about three times that of an ideal monatomic gas: 37.5 J/mol/K. And since a mole of hydrogen is a gram and the masses of electrons and photons are negligible that's 37.5 J/g/K. I did discuss this above.

so a 15 gram plasma burst at 10,000 K when it hit would have around 210 kJ worth of energy.

That's the thermal energy. The OP envisions not a stream of plasma at ambient pressure but a ball of highly-compressed plasma at millions, billions, or trillions of pascals. (15 grams of hydrogen at 10,000 K and 101.4 kPa would occupy 12.3 cubic metres.) So you can add in the energy release by expansion at ambient temperature: nRT times the natural log of the ratio of the pressures.

A modest 30% energy loss to Bremsstrahlung radiation from a 300 kJ plasma bolt (so the final energy hitting the target was 210 kJ) would be the equivalent of 3,000 rads of radiation exposure along the line of attack.

Plasma bolt? Braking radiation along the line of attack?

The OP envisions plasma contained in magic bubbles that are completely impermeable and delivered ballistically. Not a plasma beam interacting with the air.

[Flyndaran]

"Magical hot air bubble gun" just sounds more like a video game weapon than classic fantasy or science fiction to me.

[AlexanderHowl]

Storing high temperature ionized plasma (and I do not think hydrogen at 10,000+ K is anything but ionized) for prolonged periods would require magic. A slightly more realistic weapon would involve ionizing and accelrating 1 gram of liquid hydrogen (which occupies around 15 cubic centimeters) to 0.01c. Of course, that would be more of a vehicular particle cannon, as it would have an energy of around 4.5 GJ.

[Agemegos]

Originally Posted by AlexanderHowl

Storing high temperature ionized plasma (and I do not think hydrogen at 10,000+ K is anything but ionized) for prolonged periods would require magic.

And we said so upthread. (e.g. post #6). The OP is cool with magitech.

Hydrogen is about 3% ionised at the surface of the Sun (about 6 000 K). I reckon that a gas ought to be 50% ionised at the temperature where the average particle energy is equal to the ionisation energy of the chemical species involved. For hydrogen that is about 12 000 K.

[Flyndaran]

Doesn't that still make the vast majority of damage come from the magically enforced pressures rather than the heat of the plasma itself?
That seems like it would defeat the purpose of the plasma gun concept.