why are lasers better than neutral particle beams?

kojikun · Post by **kojikun** » 2003-01-20 12:52pm

Always willing to help out. Afterall, I came into this assuming particle beams are shit. :p And now I'm going to build one! Ahh..

ClaysGhost · Post by **ClaysGhost** » 2003-01-20 01:14pm

kojikun wrote: You're forgetting that power and energy are not the same. The petawatt laser may produce billions more watts, but its only putting out 680 joules. The gravitational potential energy of a 80 kilogram person at a heigh of 3 metres is 2,300 joules, if my knowledge about GPE is correct. the petawatt laser would be able to put the person 0.86 metres into the air in a fraction of a second, or boil a few gallons of water instantly, but once those 680 joules are gone, poof, thats it, no more laser.

The 680 joule figure arises because the power levels involved are so high. Lower power levels permit more energy to be tranferred. Note that the power level of this particular laser would have to drop by a factor of 10^9 to equal the LHC's performance, but the total energy transferred only has to rise by a factor of 10^5, four orders of magnitude less. But even if the laser were designed to match this performance, you will still need to keep the beam on the target for over five minutes to transfer all 330MJ! Further, the CPB needs to recharge for minutes before it has accelerated sufficient relativistic particles to make it worth firing again. With the laser, you're not waiting for a bunch of energy-leaking particles to accelerate up to 99.999954% c. You get lightspeed propagation by default.

Fermi Lab plans to mass produce antimatter at a rate of 18e10 antiprotons per hour, topping their previous 12.4e10 per hour best in 2001: http://www.fnal.gov/pub/inquiring/quest ... rprod.html

Although I can't really see the relevance of this, it's again illuminating that they quote "per hour". Research accelerators operate on different timescales to research lasers, and unfortunately to any likely space combat. I think you'd do better to see if there are any concept designs released to the public from the StarWars days, since they would really indicate what a NPB designed for military use would be able to do.

As for radiation, I cant give you a precise link. I was exxagerating ofcourse when it comes to the level of radiation, but let me put it this way: an XRay tube at hospital uses 30KeV to produce its XRays. The Tevatron uses 1,000,000,000 KeV.

An X-ray laser will transfer a lot of energy in the form of X-rays, wouldn't you say?

Melting targets with120GeV during anti-matter production: "The drum is rotated quickly to prevent the beam from hitting the same spot over and over. This prevents the distruction of the target." - http://www.fnal.gov/pub/inquiring/questions/jackie.html

Rotating the target wouldn't save it on a high-energy laser beamline. They want to preserve the target, not obliterate it; the accelerators we're all using as examples are not ideal as illustrating the real capabilities of NPBs. Whilst the situation is similar with research lasers, they are at least investigating material properties under extreme stresses and so the lasers are designed to achieve that.

Arrow Mk84 wrote: Well I think that conclusively smacks down the laser for blasting things apart! Thanks for the info kojikun.

I think that's pretty hasty, and given the examples we've all used here, wrong.

ClaysGhost · Post by **ClaysGhost** » 2003-01-20 01:26pm

Arrow Mk84 wrote:Futhermore, we can already power a particle accelerator. An NPB capable of few gigatons would require more energy than we currently possess, but it is with in the realm of possibility. For the petawatt laser to be a weapon, it needs FAR FAR more energy than 680 joules; hell, to even work as you've advertised it needs more energy than the entire world has ever produced! An I'm willing to bet that our material science can['t?] keep this thing from melting itself. When it comes to destruction, particle beams will simply own lasers.

I'm willing to bet, with rather more confidence than I have in your assessment of optics technology, that the first thing that happens when you try and throw a few gigatonnes of energy into an accelerator is nothing. Design of an accelerator requires that the superconductors are kept away from as much beam flux as possible, or their magnetic fields collapse and you have nothing to bend the beam. Unfortunately, isolating the superconductors will go by percentages, and you'll end up with a system in which most of the energy goes into the superconductors because the accelerator is so big (to minimise the exposure of the superconductors) that the magnetic fields have to be enormously powerful.

Arrow · Post by **Arrow** » 2003-01-20 01:42pm

I have more confidence in our ability to create powerful magnetic fields than I do in our ability to make high temperature optics. We don't need an accelerator that goes up to 99.999whatever%c to be destructive. I believe a 'good enough' linear accelerator with an approprate power source will be a better weapon than an equally powerful laser (note that I mean transfering the same amout of energy in the same amount of time). The materials used in an accelerator, from what I know (which, admittly, may or may not being saying much), will be easier to produce than those in an equally powerful laser and will be placed under less stress. This would make the NPB cheaper.

The big disadvantage of the NPB is its size. The laser will probably always be much smaller.

ClaysGhost · Post by **ClaysGhost** » 2003-01-20 02:02pm

Arrow Mk84 wrote:I have more confidence in our ability to create powerful magnetic fields than I do in our ability to make high temperature optics. We don't need an accelerator that goes up to 99.999whatever%c to be destructive. I believe a 'good enough' linear accelerator with an approprate power source will be a better weapon than an equally powerful laser (note that I mean transfering the same amout of energy in the same amount of time). The materials used in an accelerator, from what I know (which, admittly, may or may not being saying much), will be easier to produce than those in an equally powerful laser and will be placed under less stress. This would make the NPB cheaper.

The big disadvantage of the NPB is its size. The laser will probably always be much smaller.

PBs require the use of large superconducting magnets. They aren't exactly easy to produce, nor particularly resilient, nor small, and especially not cheap! How many replacements can you afford to carry for monster magnets? Fewer replacements than you could carry optical components. As for "I believe ...", I have no real comeback to that. I just state that I believe the opposite, and until someone comes up with a decent design study on both solutions in space I don't think the discussion can progres. I have not yet seen an example from the NPB side of a device that would be effective; as I've pointed out, these research devices are designed to discharge over long periods. The low power ratings of existing NPBs worry me far more than the low energy transferred by the Vulcan upgrade (plenty of lasers exist that transfer far more energy, and you've probably all seen the picture of an ICBM stage shattering under a mid-IR laser strike). 330MJ is only of use if you can apply it to the target. If it takes you five minutes to transfer such energies, forget it. I could point to, for example, THEL, and say that this indicates the military place more faith in laser development and performance than in NPBs, but the fact is that NPBs are not very effective in air and their size mitigates against them, both factors that would be significantly reduced or eliminated in space combat (although the size thing, as you note, will probably never go away). I will state that the laser will always have a speed advantage and probably a recharge time advantage as well. Quicker to charge a capacitor than get a bunch of particles in step and running round a ring at significant fractions of c.

kojikun · Post by **kojikun** » 2003-01-20 02:57pm

Only Tevatron-energy SYNCHROTRONS require superconductors. Linear accelerators do not require magnets that powerful because the beam isnt constantly trying to exert force on the walls in the same way that synchros do.

Your silly petawatt laser still only delivers 680 joules of energy. No matter how quickly it does that, the end result will never include an increase of more then 680 joules. Like I said, I person can jump and produce more energy then your petawatt laser.

No matter what your arguement, Ckays, your laser is still woefully too weak.

Graeme Dice · Post by **Graeme Dice** » 2003-01-20 04:10pm

ClaysGhost wrote:Unfortunately, isolating the superconductors will go by percentages, and you'll end up with a system in which most of the energy goes into the superconductors because the accelerator is so big (to minimise the exposure of the superconductors) that the magnetic fields have to be enormously powerful.

Saying that "most of the energy goes into the superconductors" is meaningless. Superconducting magnets require no energy input to maintain their magnetic field, except when energy is removed by some external action. In this case, that would be the acceleration of the particles.

Arrow · Post by **Arrow** » 2003-01-20 04:46pm

Just for my clairification, the damage done by a laser is dependant about the frequency (energy), number of photons striking the target at any given time (intensity?), the target area and the laser's time on target?

kojikun · Post by **kojikun** » 2003-01-20 05:15pm

Just for my clairification, the damage done by a laser is dependant about the frequency (energy), number of photons striking the target at any given time (intensity?), the target area and the laser's time on target?

<Trebek>
I'm sorry, this isnt jeopardy. Please reword that so it is not in the form of a question.
</Trebek>

Arrow · Post by **Arrow** » 2003-01-20 05:29pm

Alright, I wanted to know if the damage done by a laser depends on the combination of its frequency, intensity (number of photons striking at any target), the tightness of its focus and is duration.

kojikun · Post by **kojikun** » 2003-01-20 05:36pm

yes, ofcourse it does, but the maximum damage it can do is depended wholly and entirely on energy. 680 joules aint jack shit no matter what frequency or intensity you have it at. A 100 watt light bulb kicks out 100 joules per second. By the time I finish writing this my room will have been bombarded with over 6,000 joules (60 seconds). Condense that down to a nanosecond (giving you 6,000 x 1,000,000,000 nanoseconds = 6TeraWatts) and you might get some damage, mostly from rapid heating, but you aint getting an explosion

kojikun · Post by **kojikun** » 2003-01-20 05:40pm

let me put it another way, Arrow, 680 joules is approximately 162 calories. it takes 1 calorie to rase 1 gram of water by 1 degree celsius (at 1 atmosphere of pressure). Your petawatt laser couldnt even make 1 kilogram of water a whole degree warmer, let alone flash boil it.

Arrow · Post by **Arrow** » 2003-01-20 05:49pm

Ok, thanks. Just making sure I was correctly understanding how a laser weapon would work. I'm still voting for the NPB.

aerius · Post by **aerius** » 2003-01-20 07:11pm

kojikun wrote:Only Tevatron-energy SYNCHROTRONS require superconductors. Linear accelerators do not require magnets that powerful because the beam isnt constantly trying to exert force on the walls in the same way that synchros do.

True, but linear accelerators of any significant power such as SLAC are well over a mile long, and you can't shrink them down without seriously degrading their power.

Your silly petawatt laser still only delivers 680 joules of energy. No matter how quickly it does that, the end result will never include an increase of more then 680 joules. Like I said, I person can jump and produce more energy then your petawatt laser.

No matter what your arguement, Ckays, your laser is still woefully too weak.

Quite fixating on the 680 joule figure, you're acting as if it somehow makes lasers impotent. I put the link to the Petawatt laser so you can see the effects that a high power laser will have if we get around to building one that can fire longer pulses or operate in continuous beam mode. The point being a laser will act a lot like a particle beam at PW range power levels. Let's put it this way, a mere 10W laser can burn holes through 1/8" ceramics in under 10 seconds and metal in even less time, and we already have 20kW continuous beam cutting & welding lasers being used in industry. References provided here. By the way, a 20kW laser is about the size of a car, I could put one in a small rental truck and drive around blowing up cars by burning through them to their gas tanks.

Effects of 10 watt laser see middle of page.
20kW industrial laser

kojikun · Post by **kojikun** » 2003-01-20 07:33pm

True, but linear accelerators of any significant power such as SLAC are well over a mile long, and you can't shrink them down without seriously degrading their power.

quite correct. But small Synchrotrons could do similar things and not need to be as long. The Tev is a mere 4 miles around. It's smaller accelerators are quite powerful however. I'm looking around for energy levels right now :p

Quite fixating on the 680 joule figure, you're acting as if it somehow makes lasers impotent.

It does if thats all the laser puts out.

[/quote]
I put the link to the Petawatt laser so you can see the effects that a high power laser will have if we get around to building one that can fire longer pulses or operate in continuous beam mode. The point being a laser will act a lot like a particle beam at PW range power levels. Let's put it this way, a mere 10W laser can burn holes through 1/8" ceramics in under 10 seconds and metal in even less time, and we already have 20kW continuous beam cutting & welding lasers being used in industry. References provided here. By the way, a 20kW laser is about the size of a car, I could put one in a small rental truck and drive around blowing up cars by burning through them to their gas tanks.
[/quote]

We're not talking about continuous beams, we're talking about a 680 joule petawatt laser. No shit constant power lasers can burn through things. And if it does burn through ceramic with only 10 watts of power, I want to buy one immediately

kojikun · Post by **kojikun** » 2003-01-20 07:34pm

uh.. bad quoting.

kojikun · Post by **kojikun** » 2003-01-20 07:37pm

thats a really interesting concept Aerius. the FEL I mean. theyre using a LINAC to power it. I wonder .. ::gets evil ideas:: >D

Arrow · Post by **Arrow** » 2003-01-20 07:59pm

Take a look at this thread (specifically page 2):http://bbs.stardestroyer.net/viewtopic. ... t=railguns

Lasers can convert only 10 to 30% of their input energy into output energy. Ouch.

kojikun · Post by **kojikun** » 2003-01-20 08:14pm

If thats true (no sources were cited) then 20KW lasers require 200KW power to drive them O_O;

Arrow · Post by **Arrow** » 2003-01-20 08:24pm

Given that bit of information, I can see lasers being used as light to medium weapons, but the particle cannons will take the high end.

Arrow · Post by **Arrow** » 2003-01-20 08:28pm

BTW, just what would be the affect of dumping a couple gigatons of energy (regardless of how you did it) on particular spot? Take the insane leader that got vaped in an earlier post for the example.

kojikun · Post by **kojikun** » 2003-01-20 08:42pm

One word:

BOOM

Arrow · Post by **Arrow** » 2003-01-20 08:51pm

Well duh! But how big a BOOM??? Nuke size "level a city" boom or everything within several hundred feet is thoroughly fucked boom.

aerius · Post by **aerius** » 2003-01-20 10:04pm

By the way, I decided to work out how much energy a linear accelerator uses and the energy of the final beam. Using the SLAC (Stanford Linear Accelerator & Collider) which can be referenced on the web, it uses about 30-40MW of power. This is used to accelerate bunches of about 10^10 electrons to near light speed, and only a few bunches can be accelerated at a time. Let's be generous and assume a bunch is accelerated to 99.99999% of lightspeed. That gives a relativistic energy of just over 100J. From the info I've found so far, they can accelerate about 120 bunches/second, giving a final energy of 12kJ/s, or 12kW for the particle beam. Efficiency = input power/output power, giving an efficiency for SLAC of 0.04% at best. Compare that to an industrial 20kW CO2 laser that has about a 25-30% efficiency.

So that's see here, a 12kW laser will use 48kW at worst, compared to 30MW at best for a particle beam. For an equivalent output power the particle beam will need 625 times the input power of a laser. So much for your high powered particle beam fantasies. Still think you'll be using particle beams for your big main weapons?

kojikun · Post by **kojikun** » 2003-01-20 10:51pm

Arrow, you said a gigaton of energy. Hiroshima was in the kiloton range. Youd probably knock out a small state with a gigaton explosion.

>> aerius

::holds up a mirror and blinds aerius:: You forget that industrial lasers need to be directed and to do this they use mirrors. Chrome coat your ship and your 12kW laser is useless.

actually kind of makes you wonder why the STARWARS laser program will work, since chrome coating a missile would be simple.