Cold, Laser-Coupled Particle Beams

[matterbeam]

Hi all! This is from: Tough SF: Cold, Laser-Coupled Particle Beams
I hope it can help you build more exciting SciFi worlds.

This is a follow-up to the Particle Beams in Space post.

This time, we look at two concepts that can massively increase the effective range of particle beam: one is being applied every day in modern accelerators, and the other is an outgrowth of a tool used in biophysics.
Everything here is based on science that has been worked upon by physicists and engineers, and will be referenced when possible.

Performance limits

The key characteristics of a particle beam are its divergence, particle energy and average power. Improving these characteristics leads to increases in overall performance. However, we know that there are limits to the performance that is possible.



One limit is the ion source. The emittance of current ion sources are where they are at today due to the need to vaporize the ions into a gas (which imposes a minimum temperature) and the interactions between ions and energetic electrons or strong magnetic fields (which disturbs the ions).


Expanding the beam to convert emittance into low divergence introduces its own errors and disturbances.

Another limit is the neutralization step. Even when an ion beam and an electron beam are exactly matched in velocity and direction, their recombination into an atom releases energy that kicks particles in random directions. The magnitude of the kick cannot be reduced by any means, so there is a minimum divergence in neutral beams.


Optimizing the beam composition to reduce emittance introduces other problems. The elements that vaporize at a low temperature and have a low ionization energy for their weight (like Cesium) are always heavy. For the same energy added to them, they end up travelling much slower than light elements. For example, 250 MeV added to Cesium only pushes it to travel at 0.063 C while hydrogen atoms of the same energy zip past at 0.613 C. This increases the travel time necessary to reach a target, leading to greater beam spread and a lower hit chance.

Finally, there are the accelerator limitations. For a specific emittance, you can reduce divergence linearly by expanding the beam or speeding it up. Beam expansion becomes more and more difficult in terms of magnetic lens field strength requirements as the beam energy and current increases. Speeding up the beam requires quadratic length increases for each small gain in velocity. Attaining the desired level of performance might lead to gargantuan accelerators.

Beating the laser

The limitations of particle beams are particularly relevant when comparing them to lasers. Both are directed energy technologies that try to cross great distances while maintaining a small beam diameter. A fair comparison between the two would use emittance and divergence.


The neutral particle beams that we can produce today are equivalent in emittance to laser beams with wavelengths of about 100 to 200 nanometers. Lasers struggle to produce these wavelengths efficiently and so particle beams should have the upper hand. However, lasers can work around their emittance by using large mirrors. Just like a particle beam expander, laser optics allow for very low divergence even when using longer wavelengths, such as 700 to 800 nanometers.

Cooled diode lasers are achieving efficiencies of over 80% when producing those wavelengths, eliminating that advantage from a particle beam.

In essence, lasers can trade the complex and heavy equipment needed to beat particle beams on an emittance basis, for the simple and lightweight solution that is large mirrors.
Even better, mirrors can relay the beam over great distances with minimal losses, resulting in a Laser Weapon Web.


The cutting edge of existing technology, paired with beam expanding optics and the use of heavy ions, could produce neutral particle beams with a divergence of 1 to 10 nanoradians. Equivalent laser beams of 1 to 10 nanometers can only be produced by an X-ray Free Electron Laser (XFEL). Comparing between advanced particle beams and XFELs is more nuanced.

XFELs use the same accelerator technology to create a high energy stream of electrons. The electrons can be recycled many times and their energy recovered, leading to efficiencies perhaps greater than particle beam accelerators. At the ranges where an advanced particle beam and an XFEL are effective, light lag is significant. Lasers win out here again as they are many times faster than heavy neutral beams.


However, XFELs have their own unique challenges. They need an undulator to convert the energy of their electrons into photons. It can only extract 0.1% of the electron energy with each pass. Recently, we have devised solutions, such as tapered undulators, that extract up to 10% of the electron energy. This is far below the 100% utilization of a particle beam, so while they may have a 10 to 20% advantage in efficiency, they could end up with a 10 to 100 fold penalty to power density. In other words, for the same mass budget, a spaceship is likely to output much less beam power when using an XFEL than when compared to using a particle beam.




X-rays are very hard to manipulate. There exists no mirror that can reflect them and no lens which can focus them.


An XFEL would have to rely on grazing-incidence optics to aim and focus its beam. Grazing-incidence optics are nestled cones of a dense metal like gold angled at 1 degree or less.

Such an optic would need many, many such cones even at small sizes. As the focal distance increases, the angle of the cones must decrease. A 1 meter diameter optic focused at a spot 10,000km away requires cones of an angle 2.86 *10^-6 degrees. This leads to optics composed of no less than millions of cones, which is incredibly impractical and necessarily heavy. It should also be noted that grazing incidence optics cannot adjust their focal point.



The alternative is a Fresnel Zone plate. It is not as delicate or as intricate as a grazing incidence optic, can adjust its focus and can be a rather lightweight device even when several meters wide. The 'catch' is that it absorbs between 50 and 75% of the laser beam.

The plate also needs to be actively cooled and reduces the efficiency of an XFEL far below that of a particle beam accelerator.
Does this mean particle beams are safe? Not yet!


XFELs might regain the upper hand by using new methods of focusing X-rays.



Bent diffraction crystals can reach high diffraction efficiency, which would make them very good at focusing X-rays. There could be further development of highly efficient Kinoform lenses.


Alternatively, XFELs enjoying improvements in accelerator technology and undulator field strength can produce extremely short wavelengths, lower than 0.0001 nanometers, without requiring structures of several hundreds of meters in length. No focusing optics are needed in this case! Even a millimeter wide opening from an undulator is enough to produce beams of 0.3 nanoradian divergence. This performance is no more than 10x what is achievable today.
We could therefore expect XFELs to end up creating 60 cm spot sizes at million kilometre distances. Their only limitation would be light lag. Can particle beams be competitive with such lasers?

Cold Ions
The most effective way to reduce the divergence of a particle beam down to its neutralization-imposed minimum is to reduce the emittance of the ion source.

The ions released from an ion source usually have a 'temperature' of about 1 eV. We have assumed so far that the particle accelerator uses the ions at this temperature and does not significantly increase or decrease it. This does not have to be the case.

Ions can be cooled after exiting their source and before they are accelerated to higher energies. Beam cooling techniques that can be used here include stochastic, radiative and electron cooling.


Stochastic cooling inside a low-energy ring uses electromagnets to try to correct the path of a beam so that all the particles have a very similar temperature instead of a range of temperatures.



Radiative cooling only works practically with electron beams. It forces the electrons to wiggle to maximize their energy loss through Bremsstrahlung radiation. Energy is then added back to the electrons only in the longitudinal direction, leading to a gradual reduction in transverse temperature.

 

[matterbeam]

Electron cooling involves mixing hot ions with cold electrons (themselves cooled radiatively) to reduce the ion temperature. After mixing, the beam is bent by electromagnets so that the ions and electrons separate into different paths.

All these techniques require multiple passes to be truly effective and therefore work best in a ring-shaped accelerator. Low energy ions produced by an ion source are easily bent into a circle by lightweight magnets. Over the course of several seconds or even minutes, ions are run around and around the the ring and passed multiple times through a cooling section. Eventually, the ion temperature approaches that of the electrons.

Regular electrons will have the temperature of their emitter, 2000 to 3000 K, which corresponds to 0.17 to 0.26 eV. A photocathode emitter, where laser light is used to expel electrons from a surface, can produce electrons as cool as 1.5 meV or 17.4 K. They will be further cooled down to the tens of kelvins.



If such low electron temperatures are accessible, and a ring accelerator can be used to bring ions down to similar temperatures, then there is the possibility of of creating cryogenic ion beams. They would have a near-zero emittance if it were not for electrostatic repulsion and internal collisions between the charged particles.
Cryogenic particle beams are the solution to obtaining divergence no greater than the minimum imposed by neutralization disturbance, and this does not involve any expanding or focusing optics.

There is a secondary advantage to cryogenic particle beams that can allow them to reach divergence even lower than the neutralization minimum.

A bunch of neutral atoms travelling through space in a dense stream is not really different than a quick-moving gas. Cold gases condense.

Cold hydrogen atoms condense into H2 droplets. Nitrogen condenses into N2. Cesium atoms condense into solid metal balls. The higher the vaporization temperature (hydrogen boils at 10 K in vacuum, but nitrogen only needs to be cooler than 63 K), the more likely that the particle beam condenses into a stream of higher molar mass entities.

When two atoms join into a molecule, they average their transverse velocities. This effectively reduces the divergence of a particle beam by 42%.

The square root of the mass ratio between the final condensed product and the individual atoms gives the reduction in divergence. This phenomenon was critical to Geoffrey A. Landis's 'Interstellar Flight by Particle Beam' paper, where he suggested that mercury atoms would condense into million-particle droplets.
With ion cooling and condensation, we can obtain the sub-nanoradian particle beams necessary to compete with future XFEL performance.

Going further, we could expect beams of multiple species. Carbon and hydrogen beam are especially interesting. Carbon atoms at 1000 MeV could be released in parallel with hydrogen atoms at 80.3 MeV. Some of the hydrogen condenses into H2 and eventually diverges away, but they only carry a fraction of the energy. Carbon and hydrogen could instead condense into methane. The divergence of the carbon beam would be reduced by a 13.4%, and that of the hydrogen beam by 50%. When the methane molecules strike a target surface, they separate back into carbon and hydrogen. The carbon would stop very quickly and deposit all of its energy near the surface. The hydrogen is much more penetrating and would continue deeper into the material.

A methane beam would deliver both thermal and radiation damage and help defeat protection optimized for one or the other, all while maintaining a divergence much smaller than a pure radiation beam. Even better, the carbon would help 'carry' penetrating hydrogen particles through magnetic fields that would otherwise deflect lightweight hydrogen on its own. Methane is after all just 8% easier to ionize than hydrogen but 16 times harder to deflect.

Laser Coupled Particle Beams
There is another method of reducing emittance which is radically different from those mentioned so far. It is based on optical tweezers that are known for trapping and manipulating tiny particles using laser beams.


The same method can be used to control the motion of particles in a particle beam. It is studied as part of NASA's Innovative Advanced Concepts, promising diffractionless beams across interstellar distances. We will call them 'Laser-Couple Particle Beams' or LCPBs.


Can be applied in the context of distances on the order of 1,000 to 1,000,000 kilometers?

A laser beam can be used to create a column of light pointed at a target. The intensity of the laser varies from the edge to the center of the column in a gaussian profile. To simplify, we can say that the laser at the center of the column is twice as intense as the average intensity.

When a particle beam is inserted into the column and travels parallel to it, it experiences a force pushing its particles towards the center of the column. That is the gradient force.

We are solely interested in particles sitting at the edge of the column, as they determine the divergence. They experience the full pull of the gradient force.

As best that can be determined, the maximal acceleration towards the center of the laser column that a particle experiences is as follows:

• Average Particle Acceleration = (0.5 * AP * IG * DRF)/PM

Average Particle Acceleration is the acceleration of a single atom in m/s^2.
AP is the atomic polarizability.
IG is the intensity gradient of the laser, in W/m^2/m
AAG is the average acceleration factor, drawn from the table below.
PM is the particle mass in kg.

The AAG is the result of the particles experiencing less and less gradient force drawing them towards the center of the laser column as they come closer. It is the result of the intensity gradient falling as they do so. The greater the reduction in divergence we want, the lower the average acceleration the particles experience.


From the table, we can read that if we want to reduce the divergence by a factor 8, the average acceleration the particles experience is 34% of the initial acceleration.
AP values can be found here (CCCBDB list of experimental polarizabilites) in multiples of the radius cubed.
Hydrogen, with a radius of 5.29 * 10^-11 m, would have a polarizability of 0.667 * (2.5 * 10^-11)^3: 1.04*10^-32.

Potassium, with a radius of 2.2*10^-10 m, would have a polarizability of 43 * (2.2*10^-10)^3: 4.58*10^-28.

IG for a gaussian beam is roughly twice the average laser intensity (W/m^2) divided by the laser beam's radius.

Using three worked examples, we can clearly see that LCPBs can have massively extended ranges when compared to either lasers or particle beams alone. We assume that they have received the beam cooling treatment and that their initial divergence is roughly equal to the minimum imposed by neutralization.

In the first example, we will calculate the laser parameters needed to reduce the divergence of a 1 meter wide, 100 MeV hydrogen beam from 54 nanoradians to 5.4 nanoradians within a distance of 1,000 km.

Hydrogen at 100 MeV is travelling at 0.428 C or 128,360 km/s, so it crosses a distance of 1,000 km in about 7.79 milliseconds. An initial divergence of 54 nanoradians implies that it spreads at a rate of 6.93 m/s. We therefore need to reduce the transverse velocity from 6.93 m/s to 0.69 m/s within 7.79 milliseconds. That is an acceleration of 801 m/s^2.

We're trying to reduce the divergence by a factor 10, so the average acceleration is 29.3% of the initial acceleration. Conversely, the initial acceleration will have to be 3.41 times greater to achieve the desired average acceleration, about 2732 m/s^2.

We input PA = 2732 m/s^2, AP = 1.04*10^-32 and PM = 1.67*10^-27 kg. From that, we determine that IG = 8.8*10^8 W/m^2/m

Since the beam is 1 meter in diameter, it has a radius of 0.5 meters, so average laser intensity will be 219.4 MW/m^2. This is not unreasonable. The total laser power required is 172.3 MW. It is quite a big penalty to the power requirements of the particle beam.

In the second example, we will calculate the laser parameters needed to reduce the divergence of a 1 meter wide, 300 MeV Xenon beam from 2.5 nanoradians to 0.25 nanoradians within a distance of 1,000 km.

Xenon at 300 MeV is travelling at 0.0697 C or 20,890 km/s, so it crosses a distance of 1,000 km in about 47.87 milliseconds. An initial divergence of 2.5 nanoradians implies that it spreads at a rate of 0.05 m/s. We therefore need to reduce the transverse velocity from 0.05 m/s to 0.005 m/s within 47.87 milliseconds. That is an acceleration of 0.982 m/s^2.

The divergence reduction factor is 10, so the average acceleration is

29.3% of the initial acceleration. We therefore need an initial acceleration of 3.34 m/s^2.

We input PA = 3.34 m/s^2, AP = 5.04*10^-30 and PM = 2.18*10^-25 kg. From that, we determine that IG = 2.89*10^5 W/m^2/m

The average laser intensity will be 72.4 kW/m^2 and total laser power is just 56.7 kW! This is a very minor penalty to a particle beam accelerator with a several megawatt output.

In the final example, let's try for a very narrow beam, using condensation to produce a molecule with very low initial divergence and high polarizability. Lets' also be generous with the particle energy.

Starting with 1000 MeV Cesium (min divergence 0.43 nrad) and 955 MeV Iodine (min divergence 1 nrad), we expect to end up with Cesium Iodide with a polarizability of 1.94*10^-28, based on an average of the two element's Van der Wall's radii figures fromhere. The divergence of the molecule is 0.7 nrad and it will be travelling at 0.126 C or 37,800 km/s.

What laser is needed to reduce the divergence of a 1 millimeter wide, Cesium-Iodine beam from 0.7 nanoradians to 0.035 nanoradians within a distance of 1,000 km?

The 0.126 C beam crosses a distance of 1,000 km in about 26.45 milliseconds. An initial divergence of 0.7 nanoradians implies that it spreads at a rate of 0.021 m/s. We therefore need to reduce the transverse velocity from 0.021 m/s to 0.00108 m/s within 26.45 milliseconds. That is an acceleration of 0.776 m/s^2.

The divergence reduction factor is 20, so the average acceleration is

18% of the initial acceleration. We therefore need an initial acceleration of 4.3 m/s^2.

We input PA = 4.3 m/s^2, AP = 1.94*10^-28 and PM = 4.32*10^-25 kg. From that, we determine that IG = 1.92*10^4 W/m^2/m

The average laser intensity will be 4.78 W/m^2 so total laser power is a rather incredible 0.37 … milliWatts.

Summary of results:

Example 1
Particle: 100 MeV Hydrogen
Initial divergence: 54 nrad
Final divergence: 5.4 nrad
Power required: 172.3 MW
Example 2
Particle: 300 MeV Xenon
Initial divergence: 2.5 nrad
Final divergence: 0.25 nrad
Power required: 56.7 kW
Example 3
Particle: 1000 MeV Cesium and 955 MeV Iodine
Initial divergence: 0.7 nrad
Final divergence: 0.035 nrad
Power required: 0.37 mW

These are the theoretical minimum values, assuming maximal optical tweezer gradient force and that 100% of the laser energy goes towards pushing particles together. However, if even a fraction of this performance is attainable (you can always compensate with stronger lasers, rising from milliwatts to watts), then particle beams with a tenth of a nanoradian in divergence are attainable.

In the final example, we find that LCPBs are able to act like 'pencil beams' that barely spread from the moment they exit their millimeter-sized ports to when they produce spot sizes on the order of 3.5 cm at 1 million km.

Fighting with LCPBs

It should be evident by now that if we start off with a beam of low divergence and narrow diameter, we can use very moderate laser power to significantly reduce divergence. LCPB 'pencil beams' would be able to produce small spot sizes at extreme distances. They would dominate the field of directed energy weapons and would be the ideal power transmission tool for interplanetary or interstellar propulsion. A 0.1 nanoradian divergence beam would concentrate its energy within a 0.03 m^2 spot at a million kilometers, or catch a 100 meter wide receiver from a distance of 500 million km. The latter is 33% more than the distance from the Earth to Mars… if they were on opposite sides of the Sun!



LCPBs will dominate only within distances that they can reliably hit a target though. Their main limitation would be their velocity. The beam velocity does not matter when aiming at something that does not move appreciably in the time it takes the beam to reach it, or has a well defined trajectory, like an asteroid or a space station. LCPBs suffer instead when aiming at randomly maneuvering targets. The same random 'jinking' used to avoid lasers at distances where light lag is significant can be used at shorter ranges against the slower particle beams.
Let's take an enemy warship with a hull 10 meters wide. It can accelerate sideways at 1m/s^2.

If the beam travels at 0.07 C, like in the second example, then it will only hit that warship with 100% certainty out to a distance of 66,000 km. Accepting a hit rate of 50% only increases the distance to 77,000 km. It is a great distance, but only a tiny fraction of what the LCPB is capable of.

The enemy warship can reduce these ranges by accelerating harder. At 10m/s^2, the 100% hit distance is 'just' 21,000km. Of course, this consumes ten times more propellant.

A dumb but surefire way to defeat this enemy warship is to keep firing the LCPB until the jinking has consumed of its deltaV and renders it a non-maneuvering target. This might take minutes to days depending on the capabilities of the propulsion technology, and can be greatly extended by moving further away and reducing the acceleration. During this period, the enemy is firing back, a unenviable situation.

Smarter heads would choose to fire along a pattern that touches upon all potential positions the enemy warship can take. This way, a low hit chance can be converted into a low hit rate.

For example, a 0.07 C beam targeting a 10m wide target with 1 m/s^2 of acceleration would only have a hit chance of 1/82 at a distance of 200,000 km.

Instead of shooting spots at a random within the area of probable positions the target can take, the area is divided into sections, with each section given a fraction of the beam's output. This way, instead of doing full damage with a 1.22% chance, we deal 1.22% damage all the time.



A 1000 MW LCPB with a 0.1 nanoradian divergence would have a spot size of 4 cm at 200,000 km. It should be able to burn through 24.6 m/s of graphite or 9.72 m/s of steel against an immobile target. Even after being divided and spread into 82 section to ensure a 100% hit chance, this is enough to maintain an average penetration rate of 30 cm/s against graphite and 11.8 cm/s against steel.
Closing the distance greatly improves these numbers, as the beam becomes more intense and the target can take up less positions, so the beam power doesn't have to be divided as much.

Performance table for a 1000 MW 0.1 nanoradian beam vs 10m target:

Base penetration rates

Target Material/Distance: Penetration rate
Graphite / 500,000 km: 0.843 m/s
Graphite / 250,000 km: 3.36 m/s
Graphite / 100,000 km: 20.8 m/s
Steel / 500,000 km: 1.76 m/s
Steel / 250,000 km: 6.46 m/s
Steel / 100,000 km: 32.9 m/s

Beam velocity: 0.01 C

Target acceleration/Distance/Sections: Average penetration rate vs graphite

1m/s^2 / 500,000km / 7,716,050: 0.11 micrometers/s
1m/s^2 / 250,000km / 482,250: 7 micrometers/s
1m/s^2 / 100,000km / 12,345: 1.7 millimeters/s
10m/s^2 / 250,000km / 48,225,300: 0.07 micrometers/s
10m/s^2 / 100,000km / 1,234,570: 16.8 micrometers/s

Beam velocity: 0.1 C

Target acceleration/Distance/Sections: Average penetration rate vs graphite

1m/s^2 / 500,000km / 771: 1.1 mm/s
1m/s^2 / 250,000km / 48: 70 mm/s
1m/s^2 / 100,000km / 1: 20.8 m/s
10m/s^2 / 250,000km / 4,822: 0.7 mm/s
10m/s^2 / 100,000km / 123: 169 mm/s

Beam velocity: 0.5 C

Target acceleration/Distance/Sections: Average penetration rate vs graphite

1m/s^2 / 500,000km / 1: 0.843 m/s
1m/s^2 / 250,000km / 1: 3.36 m/s
1m/s^2 / 100,000km / 1: 20.8 m/s
10m/s^2 / 250,000km / 8: 0.42 m/s
10m/s^2 / 100,000km / 1: 20.8 m/s

Based on these findings, LCPBs for combat would best be designed around produce a beam balanced between having enough speed to catch maneuvering targets and enough weight (molar mass) to maintain a low divergence.

Against large, relatively immobile targets like a space station or an asteroid fort, it is very easy to create very slow and very heavy beams that maintain an extremely low divergence across interplanetary distances.
Space Station.

Such 'anti-fort' beams would have penetration rates that could poke holes through hundreds of meters of rock and steel. The huge mass that serves as a great heatsink and helps ward off smaller warships using weapons of greater power and thus range in a laser vs laser scenario becomes a hindrance in an LCPB vs LCPB scenario.

The asteroid forts could try to retaliate with their own beams, but they will not be able to hurt maneuvering targets (look at how much average penetration drops as the number of sections increases) using LCPBs nor match their range using lasers.

Therefore, we can safely say that any large, mostly immobile structure can be defeated by a maneuvering LCPB-equipped spaceship.

The situation is more nuanced when it is a maneuvering spaceship against a Laser Weapon Web. LCPBs will lose if the LWW is able to bring their 'terminal mirrors' close to the LCPB to match its range faster than the LCPB or a radiation weapon can destroy them. This assumes the battles does not start with the LCPB-equipped spaceship already in range of a Laser Weapon Web, and if the power source of the LWW isn't a planet protected by a thick atmosphere that particle beams cannot get through…

For SF authors and game designers, LCPBs have interesting tactical consequences.

The name of the game is balance.

The low-risk strategy in a one vs one situation is to spread the beam's output and wait for the armor to be whittled away. A high-risk alternative is to drag the beam at random around the target and hope that when the beam does connect, it's full-power penetration rate is enough to cut through the armor layer and get at the vital internal components. With computers and predictive software, a middle ground is likely to be sought instead: the target's motions are predicted to lie along a certain path, and it is better to try to focus on getting a few good hits that get through the armor to start reducing the target's ability to maneuver or fire back.

Minimize cross-section.

Because of these tactics, it is suicidal to have no armor but also pointless to have too much armor. An unarmored craft can be destroyed by a sweep of a low powered beam while even a hundred meter boulder of graphite can be cut through end to end by a good hit from a LCPB.
A balanced strategy with an optimum level of armor would deal damage the quickest and avoid harm the longest. Having massively more powerful beams, thicker armor or faster acceleration will not gain any decisive victory.

That is only passive armor though. We must include the threat from radiation beams and the option of active defenses.

Radiation beams would easily pass through the 'optimal armor' from an LCPB-balanced design. They require powerful magnetic fields to deflect instead. However, the power requirements and weight of equipment to surround a spaceship with a magnetic field sufficient to deflect the beam from an accelerator a fraction of the size and weight quickly becomes untenable. Instead of increasing the field strength to match the bending radius of more and more energetic particles, it is possible instead of physically move a smaller field outwards and into the beam path.

Smaller magnetic field generators can be fitted on drones and placed a kilometer or so away from the main spaceship. The 'mag-shield' drones only need to be strong enough to cause the incoming radiation to bend by an angle sufficient to miss the main spaceship.

For example, protecting a 10 meter wide spaceship using a mag-shield drone 1000 meters in front of it only requires that incoming beams be deflected by 0.29 degrees! This naturally allows for very small and weak fields to be used.

The downside to mag-shield drones is that they only work against beams coming from a small number of directions. An unexpected attack would be devastating. It wouldn't have to be very powerful or intense to severely harm a living crew or sensitive electrons, as was demonstrated in the previous Particle Beam post. In fact, it could be the ideal weapon for deployment by cryogenic stealth craft, as they are the ones which could sneak into flanking attack vector and the low power requirements of a radiation weapon allows its waste heat to be entirely absorbed by the on-board cryogenic heatsink for minutes or even hours at a time.
A second line of defense in the form of quick response mag-shield drones, that shoot out into the direction of an unexpected radiation beam, could be the difference between 0.1 seconds of sickening radiation and death.

What is the relationship between mag-shield drones and LCPBs?

The same concept can be used at even greater distances. The magnetic field will not be powerful enough to promptly ionize heavy particle beams approaching far below the speed of light, but it can work use its field to hold in a bubble of plasma. LCPB particles traversing a plasma can be quickly ionized, allowing them to be affected in turn by the magnetic field.


The further away the mag-shield drones are from the main ship, the weaker and lighter they can be, but also protect it from fewer directions.

Counter-beaming is another option. A LCPB's arrival will be announced by a guide laser to give several seconds of warning at longer ranges. The targeted ship could aim down the beam path with its own laser. This 'counter-LCPB' beam would have an intensity profile opposite to that of a gaussian beam: weak in the center and intense at the edges. It would use the same Laser Coupling technique to push particles out of the center of the beam and therefore increase divergence.
C-LCPBs will have a tough time as they have a narrow window of opportunity to get themselves aligned as well as possible with the incoming LCPB. They can never be perfectly parallel with the incoming beam, so they are less efficient. Worse, their need for large lenses makes them hard to protect when they become targets themselves.

From a visual perspective, battles involving LCPBs are more interesting than laser-dominated combat.

The neutralization step emits a small bit of light at the beginning of the particle beam's journey. Its guide laser will leave a dim trail of scattered photons from where it interacts with the particle beam. A brighter flash will occur where an ionizing laser meets an incoming LCPB, with the most spectacular sight being the interaction with a plasma bubble. C-LPBs have to make up for their reduced efficiency by using more power. This power ends up scattered as photons anyone can see.

This was prepared with the gracious help of GerritB, Kerr and Imallett.

 

[We Just Write]

I do find it fairly humorous that a gun of this type could look an awful lot like the death rays of 50's schlock sci-fi. You've got a long barrel sticking out of the turret for the particle accelerator, with a parabolic focusing element for the laser somewhere along its length. Maybe not the strictly speaking best design, but still rather amusing for a brief chuckle.

It should also be noted that like all direct-fire weapons, these beams will be limited by aiming wobble, which probably puts an effective cap on their range.

 

[matterbeam]

I do find it fairly humorous that a gun of this type could look an awful lot like the death rays of 50's schlock sci-fi. You've got a long barrel sticking out of the turret for the particle accelerator, with a parabolic focusing element for the laser somewhere along its length. Maybe not the strictly speaking best design, but still rather amusing for a brief chuckle.

It should also be noted that like all direct-fire weapons, these beams will be limited by aiming wobble, which probably puts an effective cap on their range.

Click to shrink...

You're right!
Something like this:

 

[We Just Write]

Of course, using particle beams in atmosphere (outside of a tank) is a bad idea for reasons of radiation backscatter, but the general point still stands. I wonder what those sci-fi screenwriters would think if told that there was actually a rather viable deep space weapons system that looked like that.