I think I should explain the basics in a clearer manner.
The particle accelerator uses an ion source to produce a stream of low energy ions. The ions are transported into the radio frequency cavities to be accelerated to higher energies. No ionization during acceleration. The cross section between the ion's charge and the RF fields is infinite, so it does not play a role here.
After the ions are accelerated, they are neutralized. Cross-section does play a role here. If you are trying to hit the ions with photons from a laser, you will have a hard time because the ions are small - which is why photoneutralization needs a lot of power. When you are neutralizing the ions with a stream of electrons, cross-section has a much smaller role, because the electrons and protons attract each other even across a great distance and some relative velocity. Neutralizing using a foil stripper allows you to ignore cross-sections entirely.
It's been a couple of years since I went to a particle accelerator for a week and did a basic master student special course, so thanks I guess.
Why do we prefer particle beams over bullets? Think of it this way: a typical distance between spaceships in the same orbit is 10s of kilometers. Between spaceships around the same planet, 1000s of kilometers. On the same interplanetary trajectory, 100,000s of kilometers.
Because when I stood at the end of a linear accelerator in the MeV range and saw the burning marks at the probe, I thought "cool, beam weapons like in star trek". But of course quickly I realized that for the potential damage, the cons, starting time, size of the machine, energy requirement, a monkey with a stone could do more damage faster.
A bullet at 500m/s would take 20 seconds to cross the shortest distances and 2.3 days to cross the longest distances. The target has that much time to move out the way or destroy the bullet while in flight. A 1 GeV particle beam would take 38 microseconds and 0.38 seconds respectively. The target cannot escape the beam.
if your argument is, that they are fast, I'll give you that.
Another factor is that the bullet is efficient at delivering its kinetic energy to its target, but it is not mass efficient: you need 8 tons of bullets to deliver 1 GJ of energy to a target. A particle beam would only require 0.03 micrograms as 'ammo' to deal the same damage.
how about a big bullet at 20km/s? Considering we are talking about orbital velocities, this can be achived quite easily.
The range, efficiency and effectiveness of a bullet and a particle beam are incomparable.
yup, one has proven for centuries to work, the other never made it past experimental stage.
There's a vast gulf of ranges between the hundreds of meters where a bullet works, and the million km mark.
yup, there are ranges where you can hit something with luck, and others where you need to win the lottery
It has been done. It is a simple task of resolving the target and pointing the weapon at the center of the image. We have giant telescopes that can track a star millions of light-years away for hours on end despite being buffeted by winds and shaken by earthquakes. The Hubble in the cleaner environment of space achieved 2 milliarcseconds. The Gaia telescope (
Gaia (spacecraft) - Wikipedia) aims for 25 microarc seconds. That's a precision of 12cm at 1 million km away.
So, now to give people some context. Using hubble as an example,
The formula for the angular size of an object is:
%delta = 2 arctan(\frac{d}{2D} )
with
%delta being the angle
d = diameter of the object and
D = the distance to the object
So entering
%delta = 2 milliarcseconds and D = 340000km
we get a resolution of 3 meters. This means we can detect objects within 3 meters at a distance of the moon. Sounds good, doesn't it? Exeeeept that the visual resolution depends on more, for example the camera. Let me qoute the hubble site itself:
HubbleSite - Reference Desk - FAQs
An object on the Moon 4 meters (4.37 yards) across, viewed from HST, would be about 0.002 arcsec in size. The highest resolution instrument currently on HST is the Advanced Camera for Surveys at 0.03 arcsec. So anything we left on the Moon cannot be resolved in any HST image. It would just appear as a dot.
0.03 arcsec translate to roughtly 50 meters. The reason why Hubble couldn't be used to see the moon landing site from the apollo missions? they were too small for Hubble. But that isn't even the main problem. You just said, that we in theory could see distance object. But seeing and aiming aren't the same thing.
I quote your original post:
We can work out that a 10 meter long accelerator built using modern technology, using a Microwave Ion Source to produce extract single-charge Cesium ions with 0.0018 mm-mrad emittance, expanding the beam from 1 mm radius to 0.05 meter radius (LR = 0.05), causing 10% emittance growth (EG = 1.1) and using electron beam neutralization (IE 3.89, M 133, BV 18,900,000), could be expected to produce 250 MeV particles with a divergence of just 40.5 nanoradians
I admit, that is way more precise than I thought. However, that also means the aiming has to be in this region of precision, or you miss your traget or hit it at random places. 40.5 nanoradians should be
0.8 microarcseconds, a precision even our planned best space telescope cannot achive. Also remember again, seeing and aiming is not the same. ups, got some zeros wrong, 8 milliarcseconds, still small.
We regularly hit mirrors about a meter wide on the Moon with lasers, 384000km away, and we are able to target interplanetary probes with radio dishes at Jupiter or Saturn, hundreds of millions to billions of kilometers away
Let me quote
Lunar Laser Ranging experiment - Wikipedia
At the Moon's surface, the beam is about
6.5 kilometers (4.0 mi) wide
[11] and scientists liken the task of aiming the beam to using a rifle to hit a moving
dime 3 kilometers (1.9 mi) away. The reflected light is too weak to see with the human eye. Out of
1017 photons aimed at the reflector,
only one is received back on Earth every few seconds, even under good conditions. They can be identified as originating from the laser because the laser is highly
monochromatic. This is one of the most precise distance measurements ever made, and is equivalent in accuracy to determining the distance between Los Angeles and New York to 0.25 mm (0.01 in).
[8][12] As of 2002, work is progressing on increasing the accuracy of the Earth–Moon measurements to near millimeter accuracy, though the performance of the reflectors continues to degrade with age.
[8] The upcoming
MoonLIGHT reflector, that will be landed in 2019, is designed to increase measurement accuracy 100 times over existing systems.
[2][13]
You do not aim for the mirror, you aim for an area with a width of 6.5 kilometers. Still very challenging, but obviously doable. Btw, if you wonder why it isn't so important, that you exactly hit the mirror, or radio antena of distant satellites, the purpose it the transmission of information. So even if you lose most of your intensity and thus energy, the important part is, that you are able of detecting something. For a weapon this isn't workable.
The reason why Nasa has problems with laser based communication is exactly the extreme high precision you need, which cannot be done mechanically so they have to use
Piezoelectricity - Wikipedia methodes. No easy task.
Btw, from you web site:
Advanced Accelerator
Output: 1000 MW
Divergence: 3.9 nanoradians
Beam velocity: 48,270 km/s
Total mass: 131.2 tons
You want to aim a 131 ton satellite with 1GW output within a precison of from
microradians up to
3.9 nanoradians for distant targets, good luck, you will need it.
2nd btw, from cern, the biggest accelerator at the momment:
https://indico.cern.ch/event/321880...Talk_Accelerator_Energy_Efficiency_141126.pdf
slide 10 : 4% efficiency
slide 19: 6% efficiency
So not the most efficient weapons platt form. A lot of heat which is a problem in space.
But Dr. rer. nat. Gilga, when the target is close ( up to 100000 km) they should be super awesome!
good question my fried, but now it should be mentioned, that a particle accelerator needs a activation time. It has been some time for me, but I remember even simple linear accelerators needs hours to get ready. Why? you have to heat/ready your ion source, have to calibrate all the magnetic and electric fields in the machine, and so on. So unless you want to have your weapon on constant ready to shoot modus, which consumes power and depletes the ion source, it will take hourse to get ready to fire.
A time in which a space ship just can shoot a space missle, say 0.1c travel velocity, and destroy your beam satillite.
Also in general, beams lose their energy density quadratically with the distance they travel D^2. So in general beams are actually short distance weapons, if they would work.
Also again, I would argue that beam weapons are one of the most commen weapon types in SciFi, so what is the point of this thread?
