In which I post about a TL9 solar system

[AlexanderHowl]

I do not know if that would work. The rings would have to exist outside of the spacecraft, as you would need 10 km wide superconducting rings to create the proper deflection, so the exhaust comes out within the field (unless you have an absurdly long spacecraft).

[Anthony]

Originally Posted by AlexanderHowl

I do not know if that would work. The rings would have to exist outside of the spacecraft, as you would need 10 km wide superconducting rings to create the proper deflection, so the exhaust comes out within the field (unless you have an absurdly long spacecraft).

I'm unclear what problem you even think needs solving. The exhaust is a plasma with no net charge, being primarily aimed along the axis of a large but only modestly intense dipole field; it's simply not going to have a super strong interaction with the magnetic field in the first place because its net charge isn't that high and its direction of motion is parallel to the field lines.

[AlexanderHowl]

Why would it have no net charge? You have to use magnetic or electrostatic nozzles to direct the exhaust as the plasma produced by the fusion engine would vaporize any material nozzle, so it has to be charged or else it will burn through the engine and vaporize the spacecraft.

[Anthony]

Originally Posted by AlexanderHowl

Why would it have no net charge? You have to use magnetic or electrostatic nozzles to direct the exhaust as the plasma produced by the fusion engine would vaporize any material nozzle, so it has to be charged or else it will burn through the engine and vaporize the spacecraft.

It has to be conductive, not charged, and in any case, the shielding is just a larger version of the nozzle -- in both cases, exhaust can escape because its traveling along the axis of a magnetic field.

[Say, it isn't that bad!]

Originally Posted by Anthony

It has to be conductive, not charged, and in any case, the shielding is just a larger version of the nozzle -- in both cases, exhaust can escape because its traveling along the axis of a magnetic field.

I think what AlexanderHowl is saying is that, with the rings being somewhat far outside of the ship, they'd then collect said hot exhaust, which would cause problems when it the rings.

I guess my edit from a couple hours ago got missed: "Edit: Alternately, it may need a gap at the back so the drive plume can get through, which would mean it doesn't protect the rear hull." ;)

I don't know enough about magnetism to know for sure if that is the case, but it sounds plausible.

[Anthony]

Originally Posted by Say, it isn't that bad!

I think what AlexanderHowl is saying is that, with the rings being somewhat far outside of the ship, they'd then collect said hot exhaust, which would cause problems when it the rings.

There's some proper shaping required, but the distance really doesn't matter; there are actually configurations specifically designed to capture exhaust that are also relevant as shielding, such as mag-orion and magsails.

Originally Posted by Say, it isn't that bad!

I guess my edit from a couple hours ago got missed: "Edit: Alternately, it may need a gap at the back so the drive plume can get through, which would mean it doesn't protect the rear hull." ;)

I don't know enough about magnetism to know for sure if that is the case, but it sounds plausible.

The standard configuration for a dipole field will not protect the center of the ship (in fact, it will amplify radiation there), it protects a habitat ring at a distance from the core. The situation is different for electrostatic shielding (which I suspect you'd have to just turn off while using the drive).

[AlexanderHowl]

The problem with the dipolar electromagnetic design is that an electromagnet strong enough to deflect the relativistic iron nuclei would literally pull apart the spacecraft. Magnetic fields follow the inverse square rule and, in order to deflect the 100 GeV GCR at sufficient distance to protect the inhabitants of the spacecraft, would require a magnetic field around 500 million Tesla in intensity. A neutron star runs at around 100 million Tesla.

[Say, it isn't that bad!]

So I'm not sure who's right in this debate, but for now I'm putting the entire "electromagnetic and electrostatic shields" post as super-science TL9, because at least that idea isn't right.

[Anthony]

Originally Posted by AlexanderHowl

The problem with the dipolar electromagnetic design is that an electromagnet strong enough to deflect the relativistic iron nuclei would literally pull apart the spacecraft. Magnetic fields follow the inverse square rule and, in order to deflect the 100 GeV GCR at sufficient distance to protect the inhabitants of the spacecraft, would require a magnetic field around 500 million Tesla in intensity.

You're off by a whole bunch of orders of magnitude. The radius of curvature of a charged particle in a magnetic field is mv/qB; the stuff you really have to care about is typically a couple GeV per unit charge (the 100 GeV particles exist but are rare enough to just ignore; also, they like have a charge of more than 1). Since m = e/c^2, an object at 5 GeV/electron charge has a mass of 5e9J/C or 5.5e-8kg/C, and has V on the order of 2.7e+8m/s; thus, r = 5.5e-8 * 2.7e8 / B or 15m/b, so to achieve a 100 meter radius of curvature you need a field strength of 0.15 Tesla. Which is certainly a significant field, but hardly impossible to manage.

Also, magnetic fields don't follow the inverse square law. They aren't even in all directions, are complex at short ranges, and approximate inverse cube at long ranges.

[Anaraxes]

Originally Posted by Say, it isn't that bad!

Ultimately, though, Apple changing from x86 to Arm may be an indication that they are attempting to get around the soft wall of transistor size as much as practical.

Two reasons, really:
(1) Making their own processor so they make more money on the hardware. ARM's long been in the business of providing processor cores to people doing their own ASICs. They don't sell a lot of standalone processors.
(2) Power efficiency. Intel's made a lot of improvements in that metric, but x86 has always been more about flagship processing power. ARM, on the other hand, has a customer base of people doing embedded devices, as well as mobile ones. To that market, power efficiency and low cost generally matters more than top-end performance. Apple laptops need to save power more than they need maximum MIPS, as do iPhones.

ARM doesn't make transistors any smaller than anyone else. In fact, transistor size comes from the chosen process; ARM's stuff is one level higher up.