Questions about UT smoke, lasers, and plasma.

[sethbrayman]

Originally Posted by Ulzgoroth

The answer is that the smoke doesn't change anything. To the evacuation laser, all air is opaque whether or not there is smoke in it.

That would be the first option, a laser that can cut through smoke. That means creating a new type of laser, one not in UT. Can I blind people with this laser, kill with it, communicate with it? It raises a lot of questions.

I'm not sure I want to suggest new gear to the GM just yet, but thank you :)

[Ulzgoroth]

Originally Posted by sethbrayman

That would be the first option, a laser that can cut through smoke. That means creating a new type of laser, one not in UT. Can I blind people with this laser, kill with it, communicate with it? It raises a lot of questions.

I'm not sure I want to suggest new gear to the GM just yet, but thank you :)

All lasers can cut through smoke.

This isn't a laser that cuts through smoke better than others, it's a laser that cuts through clear air just as badly as it does smoke.


It may also be implied to be a laser vastly more powerful than is at all sensible, but it's an excuse for a superscience weapon. You're not supposed to look at that bit.

[lwcamp]

Originally Posted by sethbrayman

Under Plasma Guns on UT127 it says "When fired in atmosphere, the plasma bolt will ride a laser beam, which is used to create an evacuated channel, ensuring the plasma does not explode immediately upon contact with air."

1. Does this mean that smoke will stop or cause early detonation of a plasma bolt?
2. If so what laser is it likely using?
3. Does the armor divisor of the plasma weapon count against smoke if the laser portion of the attack is affected?

I am asking this because of UT114 which says "Rain, fog, smoke, snow, and similar weather or atmospheric conditions interfere with all high-energy lasers, adding extra DR to the target equal to the vision penalty (per yard). Thus, if a yard of smoke would be -10 to vision, then each yard gives DR 10; if every 100 yards of haze gives -1 to vision, then 1,000 yards provides DR 10."

The problem here is that the description is, physically, absolute nonsense. You get an explosion from plasma because the plasma has a pressure of several thousand atmospheres - enough to mangle strong solids and drive strong shocks. A measly one atmosphere pressure difference between vacuum and the outside air would make no appreciable difference. The plasma would explode as soon as it left the weapon (or even while inside the weapon), not when it impacted the target.

When you have descriptions based on nonsense, trying to figure out sensible ways for it to work is a futile effort. Really, if you want to use plasma guns, just say they emit glowing bolts that go "pew, pew" and which blow up when they hit something, and have done with it.

Luke

[lwcamp]

Originally Posted by Ulzgoroth

It may well be that the power required for the vacuum-generating laser is actually high enough to be a weapon laser. That would still not be the biggest plausibility problem with plasma guns. They exist because SF writers can't resist using the name, not because they're good science.

More than that - the listed stats assure that it will be a weapon laser. A TL 11 plasma pistol has a maximum range of 1100 yd = 1000 m. Air is about 1000 times less dense than tissue, so to first approximation this laser will drill a hole through 1 m of tissue at close range, or about four people in a row.

Luke

[evileeyore]

Originally Posted by lwcamp

The problem here is that the description is, physically, absolute nonsense. You get an explosion from plasma because the plasma has a pressure of several thousand atmospheres - enough to mangle strong solids and drive strong shocks. A measly one atmosphere pressure difference between vacuum and the outside air would make no appreciable difference. The plasma would explode as soon as it left the weapon (or even while inside the weapon), not when it impacted the target.

When you have descriptions based on nonsense, trying to figure out sensible ways for it to work is a futile effort. Really, if you want to use plasma guns, just say they emit glowing bolts that go "pew, pew" and which blow up when they hit something, and have done with it.

Luke

I always liked "magnetic containment channels' personally.. but that also has an awful lot of handwavian built into it.

[lwcamp]

Originally Posted by sethbrayman

Can you explain how a laser wouldn't be stopped by the smoke in this example? I ask because:

• If it doesn't interact with the radiant prism smoke then it does not create a channel, thus the smoke stays and the plasma explodes on contact. For example if it was a gamma laser.
• If it does interact then it can't "push" in the normal sense, it must burn a hole from one side to the other for the bolt to pass though. Since smoke does stop lasers that burn holes through things, then the smoke would stop this type of laser (assuming enough of it).

A gamma ray laser (or x-ray laser, or deep UV laser) would simultaneously heat the air and smoke to an ionized plasma, which would then expand to near vacuum along the beam channel.

When light encounters a material (such as smoke, or air), it can be transmitted, absorbed, or scattered. For visible and near-visible lasers, light is primarily transmitted through air and scattered or absorbed by smoke. When the light is scattered, it is removed from the beam without heating the smoke and surrounding air. When it is absorbed, it is removed from the beam but does heat the particle which in turn will heat the air. Heating the air will cause it to expand, reducing its density. Very hot air will expand enough to be a near vacuum (although it will still be about the same pressure as the surrounding air - just much less dense. The ideal gas law and all, you know).

Luke

[lwcamp]

Originally Posted by Adversary

How about this, as a technobabble solution: the lasers used to make channels for plasma weapons use a frequency of light that is highly efficient at burning through/creating evacuation channels in atmosphere, but highly inefficient for damaging anything solid. In other words, a low-energy laser of this type can create a channel through air, even non-transparent air, but you can't make a super-weapon out of it.

Unfortunately, there is no such frequency. Maybe in the RF range, but you can't get any sort of collimation with RF so that's useless.

Luke

[Ulzgoroth]

Originally Posted by lwcamp

More than that - the listed stats assure that it will be a weapon laser. A TL 11 plasma pistol has a maximum range of 1100 yd = 1000 m. Air is about 1000 times less dense than tissue, so to first approximation this laser will drill a hole through 1 m of tissue at close range, or about four people in a row.

Luke

Which is only about 6d(2), in typical GURPS laser stats.

[lwcamp]

Originally Posted by Fred Brackin

First, the game rules about weapons grade lasers being stopped by smoke are bad science. They have a single hex of smoke that blocks normal vision (-10 penalty) giving DR 10 and basically stopping a 3D laser.

Somebody can come along and work out the equivalency of normal lighting to watts of laser output if they want to bt why don't we stick to comparing lasers to lasers and say that a smoke hex that stops normal vision will also stop a common laser pointer.

Said laser pointer is limited to 5 milli-watts by US law. A modest real world laser such as the US Navy has just deployed will be in the vicinity of 100 kilowatts. Just to put everything in the same units 100 kw is equal to 100,000,000 milli-watts.

From this we can see that the weapon laser is 20,000,000 times as intense as the laser pointer. It would take 20 million times as many smoke particles to absorb the weapons laser. Fairly predictable when Gurps would normally measure the penetration of the weapons laser in millimeters of RHA steel (and get a value of about 3.5mm of RHA).

Smoke that blocked vision would stop a modern laser weapon - but the GURPS model is a bad model for it. Lasers are light, and if the light going through a cloud of smoke is mostly scattered from the beam-path before it gets through (which you can determine by not being able to see through it), then light from a laser would also me mostly scattered away from the beam. Note that DR does not model this well - a smoke cloud that let half the light through would reduce a 2d beam to 1d, a 6d beam to 3d, a 30d beam to 15d, and so on.

Of course, modern laser weapons also don't heat air up much and certainly don't evacuate channels along their beam paths.

Luke

[lwcamp]

Originally Posted by evileeyore

I always liked "magnetic containment channels' personally.. but that also has an awful lot of handwavian built into it.

Yeah - like getting the magnetic source terms to produce a confining channel over a long distance (and if you could, you could also use the source terms - basically electric currents - to blow a hole in the guy you are trying to shoot instead of the plasma).

"Self-contained plasmoids" was always my favorite technobable - now you don't need to worry about containment at all. Just shoot a bolt and it goes on its merry way without mucking around with external guidance. Too bad the virial theorem makes this impossible.

Luke