Hi,

yesterday I re-read the part about shielding in the 75 summer study,
especially with an eye towards ionizing particle radiation.

As you probably know, much of this radiation is kept away from us
by the earths magnetic field. (But still we are punctured by
several of these particles per minute.)

The study considered magnetic shielding, concluded it to be too heavy.

It considered electrical shielding, which would mean to create an electric
field of "10 billion volts". This by itself seemed to be enough to
stop thinking about it. But its not obvious to me.

What's the problem of charging some metal-net or metal-sheet up to 10GV?
In vacuum, of course.

Axel Walthelm wrote:
>
> Hi,
>
> yesterday I re-read the part about shielding in the 75 summer study,
> especially with an eye towards ionizing particle radiation.
>
> As you probably know, much of this radiation is kept away from us
> by the earths magnetic field. (But still we are punctured by
> several of these particles per minute.)
>
> The study considered magnetic shielding, concluded it to be too heavy.
>
> It considered electrical shielding, which would mean to create an
> electric
> field of "10 billion volts". This by itself seemed to be enough to
> stop thinking about it. But its not obvious to me.
>
> What's the problem of charging some metal-net or metal-sheet up to 10GV?
> In vacuum, of course.
>

I think it differs if you're talking about potential density, i.e., charge
per square centimeter or something like that. You could charge a large
torus up to ten billion volts and have very little charge per unit area.

They might also have been talking about eV, electron volts, which is a
different measurement, I think.

In a vacuum, wouldn't you would have to keep resupplying the charge? Hard
vacuum offers no resistance to current flow. And if you charged a habitat
to +10GV, where would you put all the electrons you extracted so they
wouldn't bleed back?

Steve

Hi Steve,

chapter 4 page 43 says: "Similarly, electric shielding by a static
charge seems
infeasible since a 10-billion-volt potential would be required
for even moderate shielding."

Assuming American billions (not British billions) that is 10 GV.
On the page before, cut-off energies of 10-15GeV are suggested for
magnetical shields. Assuming a single charge on the particle (e.g. fast
protons)
that would match. Nuclei with many neutrons or which are not completely
ionized would need a bit more.

How to get rid of the charge? Well, if you're in free space, shoot them
away with an energy of 15 GeV per electron.

What I envision is more a way of having a panorama viewing window
protected from particle radiation. So most of the settlement could use
passive shielding. In that case it might be easier to put the excess
electrons
into the part of the settlement which is sufficiently shielded. Right?

Electical resistance of vacuum ... is a somewhat undefined term,
like asking for the temperature of vacuum. Free electrons would be
attracted very much. Hm, beta radiation is electrons, right?
So this might make it a energy-hungry way of shielding.

I'm sure I saw some other publications on the topic of active shielding,
which did seriously consider both electrical and magnetical shielding.
It also involved some effects of strong electric and magnetic fields
on humans...
But I can't remember. Can anyone help?

Steve Long wrote:

Hi Axel,

Just as an aside, in Britian a billion is - to all intents - now
regularly accepted as 1*10^9, following the American practice. The old
British billion (1*10^12 - a US trillion) has ceased to exist in
scientific and popular writings, while the milliard (1*10^9) has gone
the way of the dodo over here.

Andy G

Andrew Goddard wrote:

>Hi Axel,
>
>Just as an aside, in Britian a billion is - to all intents - now
>regularly accepted as 1*10^9, following the American practice. The old
>British billion (1*10^12 - a US trillion) has ceased to exist in
>scientific and popular writings, while the milliard (1*10^9) has gone
>the way of the dodo over here.
>
>Andy G
>
Oh, good to know.
Since when?

(The 75 Summer Study is not exactly new. -- But it sure is American ;*)

Axel Walthelm wrote:
>
> Hi Steve,
>
> Assuming a single charge on the particle (e.g. fast
> protons)
> that would match. Nuclei with many neutrons or which are not completely
> ionized would need a bit more.
>
> How to get rid of the charge? Well, if you're in free space, shoot them
> away with an energy of 15 GeV per electron.
>

I don't think you need to match proton for proton, like an antimissile
missile, in this circumstance. What you want to do is use same-charge
repulsive force to decelerate the charged particles until they pose no
danger to the inhabitants of the space settlement. You need a charged
field whose repulsion is sufficient to slow collision-course 10GeV protons
to a nominal zero during the time they are in the field, and redirect
indirect-path charged particles into tangential tracks, bypassing the settlement.

> Electical resistance of vacuum ... is a somewhat undefined term,
> like asking for the temperature of vacuum. Free electrons would be
> attracted very much. Hm, beta radiation is electrons, right?
> So this might make it a energy-hungry way of shielding.
>

A vacuum has both poor thermal conductivity and poor dielectric capability,
which is why Thermos bottles and vacuum tubes and neon lights work. I
believe that if you set a Van De Graff generator in a vacuum-filled room,
it would not work because the charge you can build up on the globes at
atmospheric pressure would just dissipate in the vacuum. You would have an
electron breeze flowing from points of negative potential to their opposites.

> I'm sure I saw some other publications on the topic of active shielding,
> which did seriously consider both electrical and magnetical shielding.
> It also involved some effects of strong electric and magnetic fields
> on humans...
>

As The Dane said, stroking a balloon with a piece of felt, "Aye, there's
the rub!" I think static charges stay on the outside of curved surfaces,
but I don't know whether any of the field could be felt inside. It's
probably not conducive to good health to live 24/7 with your hair sticking
straight out. :-)

Steve

Steve Long wrote:

>Axel Walthelm wrote:
>
>>Hi Steve,
>>
>> Assuming a single charge on the particle (e.g. fast
>>protons)
>>that would match. Nuclei with many neutrons or which are not completely
>>ionized would need a bit more.
>>
>>How to get rid of the charge? Well, if you're in free space, shoot them
>>away with an energy of 15 GeV per electron.
>>
>>
>>
>
>I don't think you need to match proton for proton, like an antimissile
>missile, in this circumstance.
>
Of course not.
The energy is so they escape the electrical potential field to infinity
(galactic space) and
won't come back immediately to neutralize the overall charge of the
vessel or station.

>What you want to do is use same-charge
>repulsive force to decelerate the charged particles until they pose no
>danger to the inhabitants of the space settlement. You need a charged
>field whose repulsion is sufficient to slow collision-course 10GeV protons
>to a nominal zero during the time they are in the field, and redirect
>indirect-path charged particles into tangential tracks, bypassing the settlement.
>

Exactly.

And why should this be difficult? What's the problem with that?
==========================================
>>Electical resistance of vacuum ... is a somewhat undefined term,
>>like asking for the temperature of vacuum. Free electrons would be
>>attracted very much. Hm, beta radiation is electrons, right?
>>So this might make it a energy-hungry way of shielding.
>>
>>
>>
>
>A vacuum has both poor thermal conductivity and poor dielectric capability,
>which is why Thermos bottles and vacuum tubes and neon lights work. I
>believe that if you set a Van De Graff generator in a vacuum-filled room,
>it would not work because the charge you can build up on the globes at
>atmospheric pressure would just dissipate in the vacuum. You would have an
>electron breeze flowing from points of negative potential to their opposites.
>
Well, as soon as an electric charge is free to move in space (we still
call this space vacuum, even though
it's no longer empty now with the charge in it) this charge will move
according to the electrical field.

But as long as the electrical charge is confined in a metal, which might
be covered by some isolation
to hinder escape of charges (electrons or ions) further, no electricity
can flow.

[So for your experiment the question would be at what electrical
potential electrons start to
leave the globe in relevant quantities (thermal electrons are a
stochastic thing).]

>
>>I'm sure I saw some other publications on the topic of active shielding,
>>which did seriously consider both electrical and magnetical shielding.
>>It also involved some effects of strong electric and magnetic fields
>>on humans...
>>
>>
>>
>
>As The Dane said, stroking a balloon with a piece of felt, "Aye, there's
>the rub!" I think static charges stay on the outside of curved surfaces,
>
If they are conductors, yes.

>but I don't know whether any of the field could be felt inside. It's
>
Inside a globe they cancel out. But with other geometries it's much more
difficult.

>probably not conducive to good health to live 24/7 with your hair sticking
>straight out. :-)
>
Yes, could get annoying after a while.
Maybe we also need some shielding from the electrical field. Faraday
cage etc., easy, right?