WH40K - 1st/2nd edition misc analysis thread (SDN)

[Mr. Oragahn]

Plasma is described as "unstable", and creating a "miniature sun" - which might imply a fusion reaction, but may also just mean a ball of incandescent plasma some diameter (a couple metres is probably a safe conservative estimate - say 2 meters diameter. density of air is about 1.3 kg*m^3 see here
about 5-6 kg of air.

Assuming a temp of around say 2 million degrees Kelvin for plasma, and specific heat see here is around 1 kilojoule per kg*K. So basically aorund 1-2 GJ per kg of matter. so, basically a single/double digit GJ even, more or less.

I think what I dislike most in his calculations are all his assumptions. In this case for instance, why are we supposed to assume the fireball should be two meters in diameter? Why is this a 'safe conservative estimate'?

Based on games mechanics, the area marker is placed where the grenade lands and is 1 1/2" wide.
I don't know how wide this is supposed to be, and, well, scales are not exactly meant to be taken literally. The BFG rulebook clearly states that they take liberties, and in general the figurines for humans don't exactly depict normal looking humans and even weapons (generally way too big to really be good to carry on the battlefield).

And why is this ball supposed to be 2,000,000 degrees K? There’s absolutely no justification given for these assumptions.

That's the "glows like a miniature sun" part. In general, Connor takes any vocabulary that evokes a star that literally. Sometimes, and if we're nice, it may work (but is not necessary and may not fit with the rest of the source it's taken from), but most of the time, as far as I have read, it just doesn't.

I think in this case the problem might stem from the fact that he doesn't understand just what is being described. This 'plasma ball' is nothing exotic or weird. It's the exact same thing we see in nuclear weapons, only smaller in size and yield. In short, it's identical to a nuclear fireball. And it’s not the sphere of plasma that’s the sole thing to be concerned about either - it’s the shockwave that such a thing creates that’s dangerous. Just like in nuclear explosions. And gauging what effects a nuclear fireball would have inside an atmosphere is dirt easy, because it's pretty much identical to what modern explosives do.

If this is a 1-2 GJ grenade, then it will have a similar shockwave as a 1-2 GJ modern explosive.

That and, as I said, the sheer heat that radiates just beyond the range of the ball's radius.

[l33telboi]

Based on games mechanics, the area marker is placed where the grenade lands and is 1 1/2" wide.
I don't know how wide this is supposed to be, and, well, scales are not exactly meant to be taken literally. The BFG rulebook clearly states that they take liberties, and in general the figurines for humans don't exactly depict normal looking humans and even weapons (generally way too big to really be good to carry on the battlefield).

So not only is it based on game mechanics but he's also pegging the effects from the bomb as the diameter of the fireball?

That's the "glows like a miniature sun" part. In general, Connor takes any vocabulary that evokes a star that literally.

So? Our sun has a surface temp of 6,000 K and glows accordingly. Where's the 2,000,000 K figure coming from?

[Mr. Oragahn]

Based on games mechanics, the area marker is placed where the grenade lands and is 1 1/2" wide.
I don't know how wide this is supposed to be, and, well, scales are not exactly meant to be taken literally. The BFG rulebook clearly states that they take liberties, and in general the figurines for humans don't exactly depict normal looking humans and even weapons (generally way too big to really be good to carry on the battlefield).

So not only is it based on game mechanics but he's also pegging the effects from the bomb as the diamater of the fireball?

That's because the area (as area marker, the disc you place on the "board") has undergone a matter/energy transformation and glows like a miniature sun.

It forms a ball of plasma that blocks line of sight and any energy poured into that balls feeds it.

That's the "glows like a miniature sun" part. In general, Connor takes any vocabulary that evokes a star that literally.

So? Our sun has a surface temp of 6,000 K and glows accordingly. Where's the 2,000,000 K figure coming from?

I don't know. He assumes it because it's glowing like a miniature sun.
He thinks of fusion and then voila, two million kelvin.
I didn't use the lower Sol photosphere value because this low temperature corresponds to fusion reactions enabled by considerable masses and gravity, and themselves I think affected by the hotter inner sections (although scientists are still understanding stars in new ways).
Anyway, for a reason or another, that plasma grenade has some ability to maintain a shape, so that's why I likened it to a lightning ball.
6,000 K gives 6 MJ, still using the same volume of air. The lowest luminosity of a star would drop below 3,700 K, so the energy of the grenade would be 3.7 MJ as an absolute low end.

1.5" corresponds to 3.81 cm.
Then comes the problem of figure scale vs ground scale, if you intend to compare a typical guardman figurine to the diameter of the blast marker, which is a sort of modifier for the ground area.
And within the figure scale alone, there's the problem of character height vs. shoulder width.
Nothing in the book indicates that the fireball has to be large enough to swallow an entire man though. Perhaps that line about "any model within the area ... suffers an automatic hit", but then if it meant that the fireball had to be huge to engulf an entire figure to work, then a figure which base would not full cross the marker's edge wouldn't take damage, which is a bit silly.

Still, if you use a 1.5 m diameter, the volume is 1.7671 m³, roughly 2.37 times less than a 2 m wide sphere's one. So basically, even if trying to pull the numbers that low (1.5 m wide sphere, 3,700 K), you'd still get more than 1 MJ.

[Mr. Oragahn]

One more detail about the plasma grenade.

We know it's an exotic device. It manages to retain the "plasma" in a ball shape, while the plasma is naturally bound to expand violently.

I followed Connor's assumption that for a fireball radius x, a sphere of air of that same radius had to be entirely heated up.
But there is nothing that factual. As plasma would expand, its volume would surely increase automatically. We don't know what maintains the fireball as a ball (which may collapse on itself, or more rarely, grow beyond the assumed radius), but the system surely has a limit to how strong it can be. Simply put, it's entirely possible that it only manages to handle the fireball's radius once it has reached a low enough density, so that even if the fireball occupied a volume of 1 cubic meter, nothing tells us for sure that that entire volume had to be heated up. Colder air would, after all, be pushed away by the hot expanding ionized gases.

This clearly reaffirms the upper end nature of the figure.