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I've been lurking threads on this site for a couple of months and decided that I'd make an account. I've had a few questions, and who better to ask such queries than the SD.net community ?

As the title suggests, I'm sorta confused by the idea that Turbolasers would experience as much recoil as has been said. As has been established, Turbolasers are incredibly powerful. Supposing they fire plasma (according to the canon rather than logic) then how much recoil should they really experience? I'm not asking for any in-depth analysis here unless that's what you're up for. All I don't get is that a huge amount of recoil is expected (enough to push the gun clean through the ship it's mounted on?!), when the plasma bolt need not even be that heavy? Surely it could be a bolt low in mass but high in explosive yield? In the same way that a nuclear warhead could weigh the same as a conventional warhead and yet exert a lot more explosive force?

If however the nature of TL bolts turned out to be nothing but energy then I'd presume that there wouldn't be any recoil? Or am I wrong again? I suppose there could be recoil if it were some sort of beam that used principles which we don't as of yet understand?

I must be missing something I'm sure. If needs be, give me a physics lesson on basic principles that would make sense of this recoil conundrum for me... Sorry if I'm being an idiot by not understanding this, but I just don't ...

Hello fellow lurker.

I seem to remember a diagram of a 'How does it work' of Han Solo's blaster and (Assuming the hand held weapons are similar to the ship mounted ones) then they seem to be a kind of big, glowy particle accelerator/thrower.

There was a cylinder of gas ('Tibbana I think it was called) which was then 'energized' and 'fired' out of the barrel. With a whole range of other Star Wars tech involved in there some where as well.

*Note: Also, Tibbana gas was one of the important things mined on 'Cloud City'. Which, by being an 'independent' state (Until Vader shows up) formed a large part of that place's rather 'shady' economy under Lando's running of the place I seem to recall.

As for recoil and such, I stand aside and await some one with more skills to answer.

Much cheers to you and yours.

The thing to bear in mind about Star Wars is that it is science fiction, with the emphasis on the fiction. The science part is junk.

A laser is essentially a beam of light, which has negligible mass, so it also has negligible recoil. Turbo basically means powerful, so a turbolaser is a powerful laser. (Turbo comes from a Greek word one meaning of which could be turmoil. Wouldn't it be good if they were called turmoil lasers.) But it is still only a laser. According to the figures elsewhere in this site Star Wars turbolasers are not even that powerful. Even today on Earth scientists have developed a petawatt laser for research.

As a weapon a turbolaser would be a joke. This is not to say that light cannot do damage; sunburn proves that it can. But it would do damage through burning. Lasers do not penetrate or explode as depicted on Star Wars. The problem is that a space ship of any reasonable size would be able to absorb an awful lot of energy which could be dissipated throughout the ship by conduction. Also, the easiest defence against a laser would be to make the ship silvered so the laser reflected of it. In one of the Star Trek TNG episodes the Enterprise is attacked by a spaceship that fires lasers at it and Picard and Riker laugh at the idea that lasers could threaten the Enterprise. That would be about right. (However, the real joke is that a maser, which is what phasers were supposed to be, would be equally powerless for the same reason.)

Dass.Kapital has the right answer when he refers to particles. A particle beam would be a much better weapon than a laser because it would have mass and would cause damage by kinetic energy. But these would not explode. They would punch through the target by focussing a lot of kinetic energy on a small area of the target in the same way that a shell does today.

If you wanted a weapon that would explode you would need to fire a missile. Maybe a matter/antimatter bomb, or a straight forward hydrogen bomb would do.

The idea of firing plasma from a hand gun is also nonsense. Plasma is a gas in which the atoms have lost some of their electrons. So basically a plasma weapon that would fire a stream of gas at a target. In space this might have some use, but in an atmosphere you would be better of firing something solid, like a bullet.

Particle beam weapons would have recoil, equal to the kinetic energy they impart, but it is unlikely that this would be a big problem because the recoil of the weapon would be small compared with the mass of the space ship carrying it; rather like guns on fighter plane.

Of course all of this is based on reality physics and it is best not to dwell on it to much when enjoying science fiction.

mutanthamster wrote:A laser is essentially a beam of light, which has negligible mass, so it also has negligible recoil. Turbo basically means powerful, so a turbolaser is a powerful laser. (Turbo comes from a Greek word one meaning of which could be turmoil. Wouldn't it be good if they were called turmoil lasers.) But it is still only a laser. According to the figures elsewhere in this site Star Wars turbolasers are not even that powerful. Even today on Earth scientists have developed a petawatt laser for research.

As a weapon a turbolaser would be a joke. This is not to say that light cannot do damage; sunburn proves that it can. But it would do damage through burning. Lasers do not penetrate or explode as depicted on Star Wars.

Wrong in multiple ways. First, Star Wars turbolasers and for that matter the Death Star superlaser are clearly not real world lasers; they don't act at all like real lasers. They are visible in space, they either travel slowly or have a visible component that does, and the superlaser does that converging-beam thing. Second, lasers are perfectly capable of penetrating objects even in real life; and causing explosions is a straightforward result when lasers or anything else delivers enough energy in a short time. And third, a petawatt laser like we have in the real world works by concentrating a relatively small amount of energy in an incredibly tiny amount of time; they certainly aren't nearly as powerful as even the most conservative estimates of turbolasers.

Also, in theory you could build a laser with recoil, even to the point of using it as an engine, a "photon drive". You'd need a lot of power though. An example from fiction would be Angel's Pencil from Known Space, the "unarmed" ship that destroyed a Kzinti vessel with its drive.

mutanthamster wrote:The problem is that a space ship of any reasonable size would be able to absorb an awful lot of energy which could be dissipated throughout the ship by conduction.

And in the process cooking the crew alive. Not really the best defense. Heat dissipation is a serious problem for spacecraft.

mutanthamster wrote: That would be about right. (However, the real joke is that a maser, which is what phasers were supposed to be, would be equally powerless for the same reason.)

Where in the world did you get the idea that phasers are supposed to be masers? Roddenberry made up the term "phaser" specifically so no one could say "oh, lasers/masers/particle beams can't do that". They have no real world counterpart; that was the idea.

mutanthamster wrote:Dass.Kapital has the right answer when he refers to particles. A particle beam would be a much better weapon than a laser because it would have mass and would cause damage by kinetic energy.

If you can get it to go in a straight line. Charged particles repel each other.

Moved.

Ding ding ding trektard alert.

Lord of the Abyss said it - basing evaluations of turbolaser effectiveness based on the name is bollocks. They clearly aren't lasers. Deal with it.

If you want to argue details of turbolaser effectiveness, base it onwhat we see not some bullshit evaluation of a fucking name.

I'm not going to talk about your assessment of turbolasers, as others have touched upon. Rather, I will focus on what you said of particle beams:

mutanthamster wrote:Dass.Kapital has the right answer when he refers to particles. A particle beam would be a much better weapon than a laser because it would have mass and would cause damage by kinetic energy. But these would not explode. They would punch through the target by focussing a lot of kinetic energy on a small area of the target in the same way that a shell does today.

Particle beams do not act like kinetic impactors at all. From my limited knowledge, I know that they tend to do nasty things such as rapidly heating the target, which I believe may release some radiation, especially if it is metal. Essentially you have the surface of the target being broken up at the molecular and atomic levels in a bunch of mini-explosions. There are others on the forum though that would know more than I, though. Also note that there are two types of particle beams, charged and neutral. They both react differently, and the charged one in particular would be hard to weaponize if it had any appreciable density, at least in space.

Let us take a look at what it takes to get significant levels of recoil out of a laser. A laser's effective mass is related to its internal energy via E=mc^2, since it has no rest mass. What this means is that 1 kg * c^2 = 9e16 J. So let us take a look at 4TJ of energy, roughly that emitted by a one-kiloton nuclear weapon. The momentum of a laser beam is p=E/c, so therefore our 4TJ laser has ~13,000 kg*m/s of momentum. So let us take a look at a railgun which can propel objects at 3 km/s. In order to reach 4TJ of KE with this gun, we would need a projectile of m = 2*4TJ/(3e3 m/s)^2 = ~890 tonnes in mass. The momentum produced by each shot would be 2.6 billion kg*m/s. So we can see that lasers produce tiny, tiny fractions of a percent of the momentum produced by conventional weapons.

So let us take a look at a Star Destroyer firing one of those one-kiloton lasers. Let us treat it as a pyramid with a height of 1600 m and a rhomboidal base of 700 meters by 180 meters, scaling roughly (very roughly!) from the Mandel blueprints. The area of a rhombus is roughly one-half that of a rectangle with the same dimensions. So we have a pyramid with h 1600 m and b 63,000 m^2. Its volume is thus 1/3 * b * h. So it has a total rough volume, neglecting the bridge tower, of 3.36e7 m^3. Star Destroyers have an unknown metallic composition for the exterior, and are largely open space inside with relatively thin walls between. Let us therefore, for simplicity's sake, use the density of water, 1000 kg/m^3, for a mass of 3.36e10 kg, or 33.6 million tonnes overall. Do not take this as authoritative, this is simply a figure for the sake of argument.

So when it fires a one-kiloton laser, it receives a momentum transfer of 13000 kg*m/s, which causes the Star Destroyer to alter its velocity by 3.9e-7 m/s in the opposite direction from recoil. When it fires a one-kiloton railgun projective, its velocity is altered by 0.077 m/s in the opposite direction from recoil. So what size of laser would we need to shift the Star Destroyer by 1 m/s in velocity?

Let's take a look. We would need 3.36e10 kg*m/s of momentum. Momentum times c gives us the energy of the laser we need. 1e19 J, which is roughly 2.5 gigatons. So what would a 200 GT laser do to this conceptual Star Destroyer? 200 GT = 8e20 J. E= pc gives us 2.67e12 kg*m/s. Dividing that by 3.36e10 kg gives us a delta-v of ~77 m/s. Again, these are using figures solely for the sake of argument- the real mass of a Star Destroyer is probably not quite the same as this.

So one final test. A planet-killing blast of 1e38 J, fired from a Death Star with water-density and 160 km in diameter. The volume of a sphere is 4/3 pi r^3, giving us a total volume of (80,000 m)^3 * pi * 4/3 = 2.1e15 m^3, which is equal to 2.1e18 kg at water density. The momentum of the shot is 1e38/c = 3.3e29 kg*m/s. This gives us a recoil velocity hundreds of times the speed of light. In reality, this would result in significant relativistic mass gain in order to keep us at arbitrarily close to c. So the Death Star, as it was propelled backwards by the shot at arbitrarily close to the speed of light, would in the process gain 1.1e21 kg of mass, significantly outweighing its original mass by a factor of about 500.

In order for the delta-v to be, say 1000 km/s, a tiny fraction of the speed of light but still likely greater than what we see on film, the Death Star would need to mass 3.3e26 kg. This is roughly equal to 50 Earths in mass. Suffice it to say, there is clearly some trickery going on with the Death Star in order to keep it from collapsing into a neutron star (its density is about a hundred times greater than that of a white dwarf star at 1.6e11 kg/m^3) and wiping out all life on planets just by orbiting them. And that renders the question of recoil largely academic- if they can fiddle with the Death Star to achieve this, then they can likely do the same with their other ships.

Quick Edit: Fixing math mistake.

A ton isn't a unit of force! (seriously someone argued that to me on Spacebattles. It can only be a unit of mass. EVER!)

Anyhow, there is that small issue of that self same laser cannon tearing the ship in half with a single shot if it isn't properly braced (which I take to mean it has all that force field tensor stuff activated.) Which creates some interesting limits on the "gigaton" TL shot - for one thing, the bracing (however it is achieved, material, forcefield, a combination, etc.) means that when firing, the turret is more or less immobile. EG a fixed axis mount (limiting its ability to track and fire) or it locks the turret in place. I'm guessing the quote means the former, but the latter could apply to the HTL turrets. This also has some hefty limits for targeting and accuracy (eg probably not going to get very precise firing.) If the stress on the ship frame is significant, there may even have to be a noticable delay between shots to allow the recoil mechanism to cope with the effects of firing.

That would in turn suggest high powered weapon shots are designed for fixed or relatively immobile targets (Battle stations, planets, or starships either crippled by ion cannon or hampered by tractor beams. Which would explain part of that weapons mix alongisde turbolasers, I imagine.)

Ironically, the Venator TL turrets were also noted to have poor accuracy (in the NEGV&V IIRC) and being designed mostly for planetary bombardment. At the same time the fixed axis superguns on the Trade Federation frigates/destroyers also had some pretty significant limits on them do to the recoil and forces involved with firing (exactly what those problems were, aside from potentially propelling the target back at thousands of km/s if it were a massless beam and having a handful of shots that required close to half an hour to charge up, I don't recall.)

Also I'm pretty sure that some sources have depicted turbolasers as using turbines as part of the weapon (to convert the reactor output into usable energy, stored in capacitors to fire the gun, or something.)

Ding ding ding trektard alert

Is that between a yellow alert and a red alert?

mutanthamster wrote:

Ding ding ding trektard alert

Is that between a yellow alert and a red alert?

It's waaaaaay more serious than a red alert.

Destructionator XIII wrote:That wouldn't work too well because a mirror doesn't reflect all the light.

Some of it gets absorbed (I think about 5% for a silver mirror), which leads to the mirror being damaged by the heat... which makes it less reflective, which means it absorbs more, and the cycle continues until it's destroyed.

The result is just about any laser powerful or focused enough to do damage in the first place will probably eat through a mirror very quickly (as in a fraction of a second) too.

I don't mean to derail the thread, but I was thinking of something like this and I figured I'd ask the question here instead of starting a whole thread just to get a short answer in like one post with little discussion value (also, this is basically the exact thing I was thinking about anyway).

What if someone had a kind of armor designed to degrade over time against lasers, like layers and layers of relatively thin material that, when exposed to an extreme heat source (like a laser or re-entry) breaks up into a kind of fine dust or cloud of soot. Then it, at least theoretically, disrupts and distorts the laser, like how an atmosphere breaks down a laser somewhat only stronger, so that the layer under that can then resist the beam or it breaks down and the layer after that will, and so on. Sooo it'd be a kind of combination of reactive armor on a tank and the mirror armor mentioned above, or that's hwo I'd describe it.

Would that work? I mean could you make some kind of, I don't even know what to call that exactly but I called it "laser-reactive armor" in the story I wrote. Would that work at all? I mean against a laser beam of roughly several terawatts.

It depends on the wavelength of the laser and the composition of the armor. It would reduce intensity to an extent, but the exact amount depends on a couple factors. One issue is that the boiled armor will diffuse quickly. It might be better to build "bubble-armor" with transparent vapor-filled scattering sections over thicker heavy armor to diffuse lasers. This would make it more vulnerable to projectile weapons and to massive particle beams that can't pass through the transparent sections, but trade-offs are pretty good for creating drama.

Well, the composition of the armor is "hard-cast decasteel", sooo...yeah it's bullshit. It's basically made of "whatever it would need to be to do this"-ium alloy. :v

In the story they're a kind of free-electron laser rigged up to fire x-ray lasers, if that makes sense. I'm going to admit, I ripped the idea off wholesale from Atomic Rockets, fucked the idea horribly and then sold the sextape to TMZ, but basically it's a shitass huge laser about a mile long the whole ship is built around. Think, like, those ion cannon frigates from Homeworld only it's laser cannon frigate.

What you're basically asking about is ablative armour. It can work, but as Bakustra says it has its trade-offs. But that can work for drama, and in a hardish setting you don't want to rely on just one defensive system. Ideally every weapon system has it's own counter.

Imperial528 wrote:Particle beams do not act like kinetic impactors at all. From my limited knowledge, I know that they tend to do nasty things such as rapidly heating the target, which I believe may release some radiation, especially if it is metal. Essentially you have the surface of the target being broken up at the molecular and atomic levels in a bunch of mini-explosions. There are others on the forum though that would know more than I, though. Also note that there are two types of particle beams, charged and neutral. They both react differently, and the charged one in particular would be hard to weaponize if it had any appreciable density, at least in space.

It's weaponizable if you can get the beam velocity up high enough relative to the number of charged particles involved. There's multiple ways to explain that, but it all boils down to special relativity- how you do a Lorentz transform on the electric fields between the particles in the beam, or how much time elapses in an outside frame of reference during one nanosecond in the beam's frame of reference, blah blah blah... short form, if you can get up to ridiculously close to light speed (which is probably the easiest way to turn particle beams into megaton-per-second or higher directed energy weapons), then the dispersion of a charged particle beam actually becomes less of a problem than it would be otherwise. Especially at relatively short combat ranges (such as the visual-range combat that figures so prominently in Star Wars).

...

Bakustra wrote:Let us take a look at what it takes to get significant levels of recoil out of a laser. A laser's effective mass is related to its internal energy via E=mc^2, since it has no rest mass. What this means is that 1 kg * c^2 = 9e16 J. So let us take a look at 4TJ of energy, roughly that emitted by a one-kiloton nuclear weapon. The momentum of a laser beam is p=E/c, so therefore our 4TJ laser has ~13,000 kg*m/s of momentum. So let us take a look at a railgun which can propel objects at 3 km/s. In order to reach 4TJ of KE with this gun, we would need a projectile of m = 2*4TJ/(3e3 m/s)^2 = ~890 tonnes in mass. The momentum produced by each shot would be 2.6 billion kg*m/s. So we can see that lasers produce tiny, tiny fractions of a percent of the momentum produced by conventional weapons.

So let us take a look at a Star Destroyer firing one of those one-kiloton lasers. Let us treat it as a pyramid with a height of 1600 m and a rhomboidal base of 700 meters by 180 meters, scaling roughly (very roughly!) from the Mandel blueprints. The area of a rhombus is roughly one-half that of a rectangle with the same dimensions. So we have a pyramid with h 1600 m and b 63,000 m^2. Its volume is thus 1/3 * b * h. So it has a total rough volume, neglecting the bridge tower, of 3.36e7 m^3. Star Destroyers have an unknown metallic composition for the exterior, and are largely open space inside with relatively thin walls between. Let us therefore, for simplicity's sake, use the density of water, 1000 kg/m^3, for a mass of 3.36e10 kg, or 33.6 million tonnes overall. Do not take this as authoritative, this is simply a figure for the sake of argument.

So when it fires a one-kiloton laser, it receives a momentum transfer of 13000 kg*m/s, which causes the Star Destroyer to alter its velocity by 3.9e-7 m/s in the opposite direction from recoil. When it fires a one-kiloton railgun projective, its velocity is altered by 0.077 m/s in the opposite direction from recoil. So what size of laser would we need to shift the Star Destroyer by 1 m/s in velocity?

Let's take a look. We would need 3.36e10 kg*m/s of momentum. Momentum times c gives us the energy of the laser we need. 1e19 J, which is roughly 2.5 gigatons. So what would a 200 GT laser do to this conceptual Star Destroyer? 200 GT = 8e20 J. E= pc gives us 2.67e12 kg*m/s. Dividing that by 3.36e10 kg gives us a delta-v of ~77 m/s. Again, these are using figures solely for the sake of argument- the real mass of a Star Destroyer is probably not quite the same as this.

So one final test. A planet-killing blast of 1e38 J, fired from a Death Star with water-density and 160 km in diameter. The volume of a sphere is 4/3 pi r^3, giving us a total volume of (80,000 m)^3 * pi * 4/3 = 2.1e15 m^3, which is equal to 2.1e18 kg at water density. The momentum of the shot is 1e38/c = 3.3e29 kg*m/s. This gives us a recoil velocity hundreds of times the speed of light. In reality, this would result in significant relativistic mass gain in order to keep us at arbitrarily close to c. So the Death Star, as it was propelled backwards by the shot at arbitrarily close to the speed of light, would in the process gain 1.1e21 kg of mass, significantly outweighing its original mass by a factor of about 500.

In order for the delta-v to be, say 1000 km/s, a tiny fraction of the speed of light but still likely greater than what we see on film, the Death Star would need to mass 3.3e26 kg. This is roughly equal to 50 Earths in mass. Suffice it to say, there is clearly some trickery going on with the Death Star in order to keep it from collapsing into a neutron star (its density is about a hundred times greater than that of a white dwarf star at 1.6e11 kg/m^3) and wiping out all life on planets just by orbiting them. And that renders the question of recoil largely academic- if they can fiddle with the Death Star to achieve this, then they can likely do the same with their other ships.

Quick Edit: Fixing math mistake.

Destructionator XIII wrote:I'm in a rush but pondering something now:

~13,000 kg*m/s of momentum imparted over the time the laser is firing, which looks to be idk, a frame or two? Let's call it a tenth of a second.

3e4 kg*m/s / 0.1 s = 3e5 kg*m/s^2 = 3e5 N.

Then if we consider the size of these things, we can get a pressure and a torque... my gut is telling me the bracing is going to be pretty insane...

Yes and yes, to both of you. The bracing is insane, the recoil is equally insane, even for a laser.

An ultra-relativistic particle beam (say, one traveling at 0.9999c)*, the recoil calculation is effectively the same. As a first order approximation, you can use the same E=pc relationship you'd use for massless photons (or a beam of other massless particles). It's not perfectly true the way it is for a massless particle, but it's close enough to save you a boatload of time.

*Which is not nearly as impractical as it sounds. They already do it in real particle accelerators, just with very low-mass beams. For instance, the LHC beams running at full power have a combined kinetic energy of around 300-400 MJ (I last did the math on this a few years ago). That's the kinetic energy of a freight train... but they have the momentum of a charging gerbil, because the beam is moving at a speed best measured as "c minus a few meters per second."

18-Till-I-Die wrote:In the story they're a kind of free-electron laser rigged up to fire x-ray lasers, if that makes sense.

Makes perfect sense to me. X-ray FELs are quite real; you're envisioning something like the Linac Coherent Light Source built along the keel of your ship. And with the power cranked up, because the LCLS isn't that good a weapon.

Armoring against an X-ray laser is going to revolve around picking materials that won't create problems with secondary radiation and scattering against X-rays. This is a very different problem from picking materials that will reflect, absorb, or vaporize into puffy ablative clouds, when hit with a laser in the visual spectrum.

If we want to go full hard sci-fi on this, we can look at Bragg's law of diffraction, which tells us that diffraction patterns through a lattice-structured material are dependent on the separation between the lattice planes, the wavelength of the diffracted ray, and the angle between the incident ray and the planes. So with nanotech and microscale manufacturing, we could build layers of delicate crystal structures so that the second layer diffuses the peaks from the first, and so on until the rays are highly diffused. Then we could add some shielding beneath and a layer of "artificial muscle" to shift the armor for best defense. Undoubtedly expensive and not a perfect shield, but possibly worth it for shielding delicate structures that can't be exposed to X rays. Or you could build even more complex structures to redirect the X rays away from whatever you're protecting, until momentum and energy transfer degrade the structures. This would also work with visible-light lasers, but there it's just the same as ablative armor for greater expense.

EDIT: Visible light would require larger crystal structures (e.g. colloidal crystals) to achieve the same effect, of course.

Bragg-style diffraction isn't all that helpful against an X-ray beam powerful enough to cause significant surface damage to targets. The kind of X-ray laser that makes things go "bang" when you shoot them has to be countered with ablative material; the only question is how much ablates in the process of absorbing a given amount of X-ray flux. And, possibly, whether it has a minimum damage threshold that makes it effectively immune to long-range sporadic fire sprayed in its general direction.

That last is a desirable feature for space combat armor- even if it can't protect you from something like a nuclear warhead or a head-on strike from a kinetic impactor going at 100 km/s, it can still protect you from lesser effects. The laser that would kill quickly at 10000 km now only kills quickly at 1000 km, and the impactor won't break up your ship unless it hits directly; it can't just use a fragmentation charge to burst into a 100 m wide of shrapnel fragments any one of which could punch deep into your hull.

Thanks for the information, you guys. I literally have no idea what half of it means but I'm prepared to parse through it with wikipedia open in another tab to try and figure it out, and I'm sure it just means I was right all along so I can shove it down my friend's throat for saying it sounds imposisble.

But seriously though, assistance is much appreciated.


Sidenote: I was also thinking of, like, these space muskets called "Slammers" (mile long one-shot space artillery) that use a series of timed nuclear explosions to fling a big hunk of metal out of the barrel at hellish speed. I figured it'd be like an Orion ship in that the explosions propell the "bullet" forward using a pusher plate, but due to it being contained it'd get more propulsive force and the "bullet" would be going some sickeningly high speed by the time it leaves the barrel. Not a practical antiship weapon singly perhaps, but I thought if used in huge numbers, like large trains of them pulled by ships, maybe they could be effective due to volley fire. Or against planets as siege weapons. Though obviously they're one-shot, throw-away weapons that destroy themselves as they fire, but seeing as it's just a metal tube, a hunk of tungsten and some nukes I'd imagine they're not expensive for a spacefaring society to build.

Would that even work?

Elements heavier than iron actually can be rare for a space society- they're just not all that common in the Earth's crust, mostly, with a few exceptions.

That said, I don't really think this is practical. The 'barrel' of the weapon will be very heavy, and I doubt it will achieve much that a bunch of missiles couldn't accomplish. Over a practical barrel length, you won't be able to line up multiple nukes, either; the blast effects from the first one will wreck the second one before the 'bullet' passes it.

Nuclear explosions in space don't produce all that much gas pressure, only the vapourised mass of the bomb; there's nothing much to contain, and friction losses to the barrel are going to be disastrously higher- the gun tube idea's counterproductive, as far as I can tell. Anything that heavy isn't going to be inexpensive, either; even if there's minimal financial cost, there's the operational cost of having to lug the bastard thing around.

As an aside, nuclear bombs in themselves are surprisingly cheap; it's the surrounding "furniture" where it starts to mount up. The command and control systems to make sure they go boom exactly where and when a properly authorised person tells them to and nowhere else, and the delivery systems to get them there, made up something like 87% of the cost of the total program, for the Americans at least.

Back to the OP, ish- and think superscience for a moment. Can we invent a plausible-for-Star-Wars explanation of how to control that kind of recoil?
Which shouldn't be a surprise, incidentally, we're basically talking about chucking the energy of thousands of tons of matter converted to light out of the barrel of even a standard HTL.
Two things that comes instantly to mind are the fabled neutronium, and inertia control. Containing/maintaining it would be challenging, but seeing as how it's a superdense fluid, the idea of a neutronium shock absorber seems to make first order sense.
Practical? Compared to reality, no, but as it is more or less canon that neutronium is involved in the construction of warship hulls somehow, then using it as shock mountings for the big guns and buffers round the joining ends of major structural members seems the most reasonable way to square canon and practicality.
(Now all I need to do is rough out a Physics-for-Poets level design for a containment chamber that keeps the stuff in one blobby piece and at the same time passes on enough of the pressure to the blob instead of the containment vessel to actually be useful. Damn.)

The other idea, inertia control, may be a bit wilder but let's follow it and see where it goes.
Using a definition simple enough for me to understand, and assuming that you can separate gravitic and inertial mass, then it seems the ideal recoil and general acceleration compensator;
with massively reduced resistance to motion, the crew do not go squishily to their deaths against the sternward bulkhead of any ship that fires up it's main engines- with massively increased resistance to motion, the Death Star does not become it's own pinball after firing a blast from the main gun.
If it momentarily, for the duration of the beam, possesses an inertial mass that counterbalances the acceleration of the gun- it obviously has the generated power for it, and there's a lot of space on the cross section labelled 'computer core' that could be put to better use- that's a basic solution.
Less basic is the problem of stopping the fun ball of doom being squashed like a melon between two piledrivers; further thought may be required on that.

Is there any evidence, apart from the above, of this technology actually being used in universe- any supporting evidence? Any sign of what else it should be able to do?