can you fire PPCs in planetary orbit?

[Thunderbolt]

Surely most inhabited worlds possess powerful earth like magnetic fields?

Isn't the cyclotron radius in LEO about 33km?  That would be about 7 AT2 hexes across

https://en.wikipedia.org/wiki/Gyroradius#Relativistic_case

If so, whenever you fired your particle beams in low orbit, they would circle around and possibly get an attack roll on your opposite arc?  ???

[Weirdo]

For sanity's sake, the rules ignore that completely. Fire the PPCs all you want.

[skiltao]

I suspect physics and sanity are in happy agreement in this case.

[Thunderbolt]

I suspect physics and sanity are in happy agreement in this case.

because particle beams are neutralized before discharge?

https://en.wikipedia.org/wiki/Particle-beam_weapon#Beam_generation

[skiltao]

Well, my first question would be, is the Lorentz force strong to halt the particle's forward motion and force it into a perfect circle, or is the particle instead continuing forward in a spiral?

My followup question would be, considering that the Earth's magnetic field is fairly weak, how does the particle's course change as it approaches the relatively stronger magnetic fields emanating from the spaceship (and especially the craft's exhaust)?

[Thunderbolt]

Well, my first question would be, is the Lorentz force strong to halt the particle's forward motion and force it into a perfect circle, or is the particle instead continuing forward in a spiral?

My followup question would be, considering that the Earth's magnetic field is fairly weak, how does the particle's course change as it approaches the relatively stronger magnetic fields emanating from the spaceship (and especially the craft's exhaust)?

cp. http://slideplayer.com/slide/9134557/27/images/18/Radiation+Effects+on+Electronics.jpg

Earth's magnetic field is powerful enough to deflect the solar wind & trap protons & electrons in the inner (exospheric / plasmaspheric, corotating) and outer (magnetospheric, non-corotating) radiation belts

Would a fusion rocket eject electrons along with the He²⁺ ions ??  Otherwise, if the exhaust is not "neutralized", what does the craft do with the ever accumulating electrons ???  Eventually, wouldn't they "help themselves" to the nearest conductor... do ASF & DS spark lightning whenever they come near anything else?

I didn't know, but the "artificial lightning" of PPCs, had they been designed in the 20-21st centuries, would have been "neutralized" to prevent beam dispersion, all charged particles winding up being projected downrange

[cray]

Surely most inhabited worlds possess powerful earth like magnetic fields?

Perhaps the PPCs neutralize their beams like ion thrusters so there's no net charge to be deflected?

[Thunderbolt]

Perhaps the PPCs neutralize their beams like ion thrusters so there's no net charge to be deflected?

lots of advantages all around.  And maybe something to do with the Field Inhibitor safety mechanism ??

[Daryk]

It's all fiction, but probably everything to do with the Field Inhibitor...

[idea weenie]

Surely most inhabited worlds possess powerful earth like magnetic fields?

Isn't the cyclotron radius in LEO about 33km?  That would be about 7 AT2 hexes across

https://en.wikipedia.org/wiki/Gyroradius#Relativistic_case

If so, whenever you fired your particle beams in low orbit, they would circle around and possibly get an attack roll on your opposite arc?  ???

According to the first paragraph in that article, it is used within a constant magnetic field.  Can you guarantee that the magnetic fields in planetary orbit are constant (i.e. no accelerators firing weapons, no fusion reactors putting out exhaust, etc)

Also, what is the trap rate of the planet's magnetic fields?  Is it able to grab all of the particles from a PPC, or will only a few get into the magnetic field, and the rest used to destroy the enemy ship?

To give an idea for the upper limit of trap rate, one of the proposed ideas to reduce the Van Allen radiation belts of Earth is a set of five 100 km long tethers, that are charged.  The charge affects particle path, and would reduce the inner Van Allen Belt to ~1% of its current strength in 2 months.

Assuming that value is optimistic, and it would actually take a year, that means the particles absorbed by Earth's magnetic field could be reduced to 1% their value.  How long has Earth's magnetic field been trapping particles?  Even assuming it has to start over every time the Magnetic Field inverts, that is still over 100,000 year of time trapping particles, and reduced to 1% in about 1 year.

So you might get a few particles returning to sender, but not really noticeable in game.

[The_Caveman]

The confinement beam of the PPC is strong enough to prevent it from dispersing over long distances in a dense atmosphere. IRL particle accelerators (including ion engines and their cousins) have to work in near-vacuum. It wouldn't even notice a magnetic field as weak as a planet's.

Maybe if you were in orbit of a magnetar.

[Thunderbolt]

According to the first paragraph in that article, it is used within a constant magnetic field.  Can you guarantee that the magnetic fields in planetary orbit are constant (i.e. no accelerators firing weapons, no fusion reactors putting out exhaust, etc)

Also, what is the trap rate of the planet's magnetic fields?  Is it able to grab all of the particles from a PPC, or will only a few get into the magnetic field, and the rest used to destroy the enemy ship?

To give an idea for the upper limit of trap rate, one of the proposed ideas to reduce the Van Allen radiation belts of Earth is a set of five 100 km long tethers, that are charged.  The charge affects particle path, and would reduce the inner Van Allen Belt to ~1% of its current strength in 2 months.

Assuming that value is optimistic, and it would actually take a year, that means the particles absorbed by Earth's magnetic field could be reduced to 1% their value.  How long has Earth's magnetic field been trapping particles?  Even assuming it has to start over every time the Magnetic Field inverts, that is still over 100,000 year of time trapping particles, and reduced to 1% in about 1 year.

So you might get a few particles returning to sender, but not really noticeable in game.

well, IDK what fraction of a non-neutralized PPC bolt's ions would get trapped in the planetary magnetic field, and start spiraling magnetic pole to magnetic pole around and along the field lines, joining the planet's radiation belts... vs. what fraction would escape outwards or move inwards and generate mini-aurorae

but EM, like Gravity, is a fundamental natural interaction which "never forgets", always acting, every charged particle moving through a B field automatically experiences a Lorentz force F_B = q v x B = m a

So all positive ions would spiral one way, and all negative ions & electrons would spiral oppositely

If ASF & DS exhaust plumes are not perfectly re-neutralized, they'd generate twin tails vaguely like the gas vs. dust tails of comets, pointing (increasingly) in different directions

electrons, being 2000x lighter, would experience 2000x greater acceleration for the same conditions... the gyroradius would reduce 2000x from 30-50km to 15-25m... electron exhaust could definitely spiral right around into the ASF's own cockpit!  Obviously only if you triggered your thrusters perpendicularly to the field lines, otherwise they would spiral around the line safely away from you

but re-neutralized plasma, from thrusters as well as PPCs, would have many advantages

[skiltao]

Earth's magnetic field is powerful enough to deflect the solar wind & trap protons & electrons in the inner (exospheric / plasmaspheric, corotating) and outer (magnetospheric, non-corotating) radiation belts

Over a span of seconds or minutes and a distance several or many times the width of Earth. What you're asking for has to happen much, much faster.

[Thunderbolt]

Over a span of seconds or minutes and a distance several or many times the width of Earth. What you're asking for has to happen much, much faster.

well, I think the formula for cyclotron gyroradius works for particle velocities all the way up to lightspeed

F = q v x B

more speed, more force, more acceleration, more curvature, more quickly

FYI, earth's magnetic field as as powerful as a that of a solid magnetized iron sphere-magnet the size of earth's solid inner core, about as big as Pluto

And any space ops around Jovian gas giants would experience significantly more magnetic field FX

Neutralization of plasma for PPCs and fusion drives would solve everything, what actually gets projected is a stream of neutral particles ("mini atomic scale GR rounds")

Actually, what would happen to highly magnetic GR rounds whizzing through a magnetic field ???

[The_Caveman]

Magnetic field strength falls off with the cube of distance. Earth's magnetic field at the surface isn't that strong. A typical refrigerator magnet is 80 times stronger. The coils in a PPC that keep the beam aligned would be at least thousands of Gauss, probably a few orders of magnitude higher since a PPC beam can travel a couple hundred km in space and still hit things. Millions or billions of times more powerful than the planetary field. By the time the particles were far enough from the muzzle for the planetary magnetic field to be dominant, they would have long since dispersed and wouldn't resemble anything we'd call a beam.

[Thunderbolt]

Magnetic field strength falls off with the cube of distance. Earth's magnetic field at the surface isn't that strong. A typical refrigerator magnet is 80 times stronger. The coils in a PPC that keep the beam aligned would be at least thousands of Gauss, probably a few orders of magnitude higher since a PPC beam can travel a couple hundred km in space and still hit things. Millions or billions of times more powerful than the planetary field. By the time the particles were far enough from the muzzle for the planetary magnetic field to be dominant, they would have long since dispersed and wouldn't resemble anything we'd call a beam.

The protons in earth's inner radiation belt have energies up to 100s-1000s MeV, i.e. some are relativistic and traveling at transluminal speeds

doubt a PPC can project some kind of Tokamak like containment field 100s of km downrange ?

we don't notice earth's B field on the surface, because the gyroradius is 30-50km...

actually, just carried out the calculation... if you fired a charged, non-neutralized PPC bolt, across Earth's B field lines (i.e. generally in an E-W direction) from a firing height of 6m (+1 level), the bolt would arc downward and impact the ground about 600m down-range

the short 18hex PPC ranges are actually bang on for (shooting across, perpendicular to) terrestrial-strength planetary B fields  :o

the EM interaction force is so much inherently stronger than gravity it is hard to actually have a "weak" EM field, a planetary field is quite powerful in the cosmic scheme of things, and if you tried to fire an un-neutralized charged PPC bolt E-W over the surface of the earth, you'd witness w/ your own eyes how strong our planetary field is -- even a high-energy bolt wouldn't get farther than 600m downrange (from a +6m elevation +1 level firing position)

of course, if you fired parallel to the field lines, N-S, you'd get much more of a straight LOS trajectory

[The_Caveman]

The protons in earth's inner radiation belt have energies up to 100s-1000s MeV, i.e. some are relativistic and traveling at transluminal speeds

doubt a PPC can project some kind of Tokamak like containment field 100s of km downrange ?

The radiation belt particles are also an extremely low density gas. 20k particles per cm³ is typical. A PPC bolt would have a density probably in the same order of magnitude as air. The behavior of individual protons is substantially different from the behavior of a packet of dense gas.

It's not about the energy of the individual particles, it's about the density of the beam. The particles in the beam are going to follow a probabilistic distribution that will get fuzzier and fuzzier as distance from the muzzle increases. To keep most of the beam confined to a narrow cylinder over long distances so it can do meaningful damage, you're going to need a very strong field. Tokamak-level field strength at the muzzle is probably about right. Even with that, some of the particles are going to escape the beam and go on their merry ways.

Furthermore, an unconfined PPC beam would dissipate just a few cm from the muzzle if fired in an atmosphere due to particle interactions with the air. Instead of a beam you'd get a brightly glowing cloud. Even a neutral beam would have its electrons sheared off by particle collisions so without a confinement field you would have less a weapon and more a very expensive bug zapper. Compensating for the curvature of the magnetic field would be an afterthought.

But in any case, you've fallen victim to one of the classic blunders. The most famous is "Never get involved in a land war in Asia." But only slightly less well known is: never try to apply real science to BattleTech. The rules are going to rudely ignore your equations and the fiction will at best negate them with absolute balderdash.

[Thunderbolt]

The radiation belt particles are also an extremely low density gas. 20k particles per cm³ is typical. A PPC bolt would have a density probably in the same order of magnitude as air. The behavior of individual protons is substantially different from the behavior of a packet of dense gas.

It's not about the energy of the individual particles, it's about the density of the beam. The particles in the beam are going to follow a probabilistic distribution that will get fuzzier and fuzzier as distance from the muzzle increases. To keep most of the beam confined to a narrow cylinder over long distances so it can do meaningful damage, you're going to need a very strong field. Tokamak-level field strength at the muzzle is probably about right. Even with that, some of the particles are going to escape the beam and go on their merry ways.

Furthermore, an unconfined PPC beam would dissipate just a few cm from the muzzle if fired in an atmosphere due to particle interactions with the air. Instead of a beam you'd get a brightly glowing cloud. Even a neutral beam would have its electrons sheared off by particle collisions so without a confinement field you would have less a weapon and more a very expensive bug zapper. Compensating for the curvature of the magnetic field would be an afterthought.

But in any case, you've fallen victim to one of the classic blunders. The most famous is "Never get involved in a land war in Asia." But only slightly less well known is: never try to apply real science to BattleTech. The rules are going to rudely ignore your equations and the fiction will at best negate them with absolute balderdash.

I think BT usually gets a bad wrap undeservedly  :)

Neutral particles have immense penetrating power, it takes a column density of around 3000 kg/m² to stop a neutron (~1m of concrete):



Air's density is only ~1 kg/m³, so you'd need a column 3km long to accumulate the same column density = interaction cross-section

Neutrons from Chernobyl penetrated miles into the sky, irradiating all the doomed helicopter cleanup crews

Similarly, particle beams must be neutralized to have any useful range whatsoever at all:

There are two basic components of note, here: ion (particle) accelerators and neutralizing gas chambers. Our ammo atoms need to have an electric charge so we can ramp them up to the near-light speeds they must achieve in order to be in any way harmful – they are just atoms, after all. Charged particles, or ions, are easy to accelerate...but if we take those ions and simply shoot them out they will repel one another and the beam will spread horribly. If we want particle beams to be useful over range we need a neutralizing chamber that lets us maintain a focused beam of neutral particles that are quite happy to be packed into a small space together.

The neutralizing chamber is by far the simpler of the two pieces, and could be miniaturized quite nicely. However, the accelerator currently can’t — at least, not if we hope to ramp our hydrogen ions up to drone-killing levels of energy. Accelerators can be linear or circular, but the circular kind will almost certainly be the future, since they can give us a path-length for acceleration that increases by as many trips around the loop as we’re willing to take.

https://www.extremetech.com/extreme/153585-a-deeper-look-into-lasers-particle-beams-and-the-future-of-war/2

BT has no issues whatsoever if all of its particle beams & fusion plumes are neutralized (which all hard scientific evidence suggests would always have been the case)

A PPC is not a "proton cannon" but an "atom cannon / thrower / hurler / slinger"

[Thunderbolt]

Some PPCs may actually be "electrolaser" weapons:

https://en.wikipedia.org/wiki/Electrolaser

[skiltao]

well, I think the formula for cyclotron gyroradius works for particle velocities all the way up to lightspeed

F = q v x B

more speed, more force, more acceleration, more curvature, more quickly

From the link in your OP, a particle takes the same amount of time to complete a gyrocircumference no matter what its initial velocity is.

[Thunderbolt]

From the link in your OP, a particle takes the same amount of time to complete a gyrocircumference no matter what its initial velocity is.

yes, requiring greater acceleration, quicker change of velocity vector

[skiltao]

Okay, I follow that, but neither you nor the wikipedia page actually establish that the gyration completely and perfectly subsumes that component of the particle's velocity, and doing the proof myself requires more effort than I care to invest. ;)

What you and others have said about confinement and neutralization seems to be necessary and sufficient, in any case.

[Thunderbolt]

Okay, I follow that, but neither you nor the wikipedia page actually establish that the gyration completely and perfectly subsumes that component of the particle's velocity, and doing the proof myself requires more effort than I care to invest. ;)

What you and others have said about confinement and neutralization seems to be necessary and sufficient, in any case.

well, any accelerating charge emits (synchrotron, Larmor) radiation, transferring energy away from the charged particle... Think that is where some of your radiation belt RF comes from?

And yes I think confinement and neutralization close the case  :)

[pheonixstorm]

So I skipped most of the technobabble and came up with something.

BT is a product of the 80s
SDI "Star Wars" is a product of the 80s which included a particle beam weapon.

And so I give you an article from the 80 about said weapon.

https://www.latimes.com/archives/la-xpm-1989-07-18-mn-4091-story.html

[Thunderbolt]

So I skipped most of the technobabble and came up with something.

BT is a product of the 80s
SDI "Star Wars" is a product of the 80s which included a particle beam weapon.

And so I give you an article from the 80 about said weapon.

https://www.latimes.com/archives/la-xpm-1989-07-18-mn-4091-story.html

thanks for the article

"Within experimental error then the hydrogen atom has been shown to have a magnetic moment equal to one Bohr magneton"
https://phys.cst.temple.edu/~napolj/PHYS4702/PhippsTaylor.pdf

The magnetic dipoles of the electron and proton are parallel (their mechanical spins being as opposite as their charges), but the proton magnetic moment is minuscule compared to the electron's, so the total atomic magnetic moment is just a smidgeon more than the electron moment

http://physicsinsights.org/force_on_dipole_1.html

The atomic magnetic moments would plausibly quickly align with the ambient field lines, but a gradient in field strength -- increasing towards the planet -- would still induce a force on the neutral beam atoms of

F = m dB_z/dr = ma

 a~1e-7 m/s² (with Wolfram alpha)

Your beams would pull planetward ever so slightly but the acceleration induced would be 50 million times smaller than anything which would matter in the game

Might not work over a magnetar, but otherwise neutral beams again appear to resolve this question favorably, neutralized beams and exhaust plumes would not be significantly affected by even strong planetary magnetic fields

[Daryk]

Thanks for doing the math!  :thumbsup:

[Thunderbolt]

Thanks for doing the math!  :thumbsup:

well the approximate formulae are quite simple, I'm pretty sure I set everything up right for that powerful calculating app  :)

The real issue in space combat, in rotating orbital reference frames representing say the space around some space station, is Coriolis effect on ballistic weapons

In LEO, every 15 hexes of weapon range (= weapon muzzle velocity) generates 1 thrust point perpendicular to the original LOS

at 150km range and up, when your rounds are traveling across the board for most of the turn, everything would veer off track quite far to one side

If you had spare thrust and a radar, probably feasible to adjust your course enough for the ballistic trajectories to not intersect yours

[Weirdo]

The rules probably ignore that stuff because if they didn't, the game developers would have gone the unfun kind of mad ages ago.

Remember, Battletech and its offshoots are not simulations, they're games. There's a big difference between the two.

[Thunderbolt]

The rules probably ignore that stuff because if they didn't, the game developers would have gone the unfun kind of mad ages ago.

Remember, Battletech and its offshoots are not simulations, they're games. There's a big difference between the two.

optional advanced rules, so seasoned players have room to grow?

[Weirdo]

I'd say what you're suggesting is a few levels beyond optional advanced.

Also, please remember that all fan rules or discussion thereof belongs in Fan Rules.