Significance of the solar wind

In article <8b42afac.0409160839.1fe45cd5 DeleteThis @posting.google.com>,
kuyper DeleteThis @wizard.net (James Kuyper) wrote:

 > Erik, as far as I can tell, has never said anything that is
 > contradicted by that web site. Would you care to identify the
 > contraction? It points out the usefulness of a protective magnetic
 > field in retaining an atmosphere with a significant water content.
 > Arranging a protective magnetic field for the Ringworld is a trivial
 > engineering detail (compared to the Ringworld itself). So?

I went back over Erik's posts, which I have reproduced below, and he never
once mentions Earth's magnetic field. He keeps saying that Earth has no
rim walls (obvious) and that is the reason that the Ringworld's atmosphere
is stable. His argument is that Earth would have a problem long before the
Ringworld, and that argument completely ignores the contribution of
Earth's magnetic field. That is where the NASA site contradicts Erik as
it states quite clearly how essential the magnetic field is to
maintaining our atmosphere! It totally ruins his arguments.

In article <41268019.996B652F DeleteThis @alcyone.com>, max DeleteThis @alcyone.com (Erik Max
Francis) wrote:

 > Think about it: The dynamics of an air molecule at the exosphere are
 > almost identical on Earth and the Ringworld, the only exceptions being
 > the strength (it's _stronger_ on the Ringworld) and Coriolis forces
 > (which aren't at all relevant here). If you're seriously suggesting
 > that the Ringworld would lose its atmosphere due to exosphere leaking in
 > less than a century, then how come it hasn't happened to the Earth?
 > Simple: Because the analysis is totally wrong. (In fact, by that
 > analysis, the Earth would drain much faster, since it has no retaining
 > rimwall!)

In article <4127C92E.4584B7BE DeleteThis @alcyone.com>, max DeleteThis @alcyone.com (Erik Max
Francis) wrote:

 > How dense are the coronal ejections at Earth orbit? How well do they
 > transfer their heat?
 >
 > The answer is, of course, exactly as well as they transfer their heat to
 > Earth's exosphere. And since Earth has no retaining rimwall, if there
 > were a serious problem with air escaping, the Earth would have a far
 > bigger problem than the Ringworld (lower gravity at exosphere, no 1000
 > mi high rimwall). Since Earth has had a stable atmosphere for longer
 > than a century, your claim cannot be right.

In article <41294F6B.1A968867 DeleteThis @alcyone.com>, max DeleteThis @alcyone.com (Erik Max
Francis) wrote:

 > James Nicoll wrote:
 >
  > > Since Venus manages to somehow cling to its thin wisp of a
  > > 90 bar atmosphere without a magnetosphere to speak of, I expect it
  > > doesn't matter if the RW has an analog, but isn't the RW laced with
  > > superconductors as part of the "anti-meteor" system?
 >
 > Indeed. All the elements he claims are present which would, according
 > to his claim, cause the Ringworld's atmosphere to leak away are present,
 > often to a greater degree, to the Earth's atmosphere. The fact that the
 > Earth still has an atmosphere strongly disproves his claim.

In article <414380F2.580221F4 DeleteThis @alcyone.com>, max DeleteThis @alcyone.com (Erik Max
Francis) wrote:

 > If you've proved that the Ringworld's atmosphere is unstable, then
 > you've proved that the Earth's atmosphere is unstable as well. Since
 > the Earth will not lose its atmosphere in 100 yr (another figure you
 > just totally made up), neither will the Ringworld's -- and the
 > Ringworld's is _more_ stable, since it has rimwalls and Earth does not.
 > How hard is that for you to understand? (Of course, the Earth's
 > atmosphere _isn't_ stable, but it will remain intact for extremely long
 > timescales, much longer than the timescales we've been discussing here.)
 >


Stephen

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 >> Stay informed about: Significance of the solar wind 

In article <8b42afac.0409160828.132fd765.DeleteThis@posting.google.com>,
kuyper.DeleteThis@wizard.net (James Kuyper) wrote:

 > steve.DeleteThis@antispam.sforbesa.cix.co.uk (Stephen Forbes) wrote in message
 > news:<memo.20040916001457.8557E.DeleteThis@sforbesa.compulink.co.uk>...
  > > In article <8b42afac.0409142004.16415603.DeleteThis@posting.google.com>,
  > > kuyper.DeleteThis@wizard.net (James Kuyper) wrote:
  > >
   > > > steve.DeleteThis@antispam.sforbesa.cix.co.uk (Stephen Forbes) wrote in message
   > > > news:<memo.20040914211657.19947C.DeleteThis@sforbesa.compulink.co.uk>...
   > > > > In article <8b42afac.0409140657.42e87ca4.DeleteThis@posting.google.com>,
   > > > > kuyper.DeleteThis@wizard.net (James Kuyper) wrote:

snip

 >
  > > ... There are some
  > > obvious problems where the loops touch, where the field is horizontal
  > > not vertical. This problem will remain as long as there is more than
  > > one loop.
 >
 > The loops touch, and the field is horizontal, only in the region
 > between day-streams, where there is little solar wind because it's
 > been blocked by the shadow squares. That was an essential component of
 > my design.

This doesn't make any kind of sense, your day streams will eventually
cover every part of the Ringworld surface in no more than 15 days. There
is no part of the surface which doesn't receive the solar wind on a
regular basis.

 >
   > > > > > Not when the main component of their velocity of the protons is
   > > > > > anti-spinward, and the radius of the spiral is adjusted to be
   > > > > > on the
   > > > > > order of 1 million miles. Then the spiral will simply divert
   > > > > > the flow
   > > > > > either to port or starboard.
   > > > > >
   > > > >
   > > > > What strength of field? This is your baby so its up to you to
   > > > > justify this with numbers and patterns. I can't see it working,
   > > > > please prove me wrong.
   > > >
   > > > That's trivial enough - I assumed you were familiar with the
   > > > formula.
   > > > In the appropriate units, it takes the form B=m*v*c/r*q, where 'm'
   > > > is
   > > > the mass of the charged particle, v is the component of it's
   > > > velocity
   > > > transverse to the the magnetic field, c is the speed of light, r is
   > > > the radius of the spiral, and q is the charge of the particle. I
   > > > don't
   > > > see much point in plugging actual numbers into that equation; we've
   > > > no
  > >
  > > You really should put numbers in and balance it with the current
  > > required to produce that field in your coil.
 >
 > You know of some particular limit on that current? I don't. Without a
 > limit, I don't see why it matters what the current required is.

Even superconductors have their limits, if you put too much current
through them they will lose their superconductivity. I know
superconductivity happens because electrons travel in pairs, if you
increase the current too much those pairs will be knocking into other
pairs and break up their relationship, causing resistance.

 >
   > > > information about the limits on the superconductor being used, and
   > > > therefore no basis for saying that any particular magnetic field
   > > > strength is unattainable. I will point out that the radius of the
   > > > spirals in the Earth's magnetic field is immensely smaller than 1
   > > > million miles, and the required field strength is inversely
   > > > proportional to the spiral radius. As a result, the field required
   > > > to
   > > > keep the Ringworld safe is much weaker than the one needed to keep
   > > > the
   > > > Earth safe.
  > >
  > > Not when your dealing with the Ringworld it isn't. The Earth's main
  > > defence is a field at right angles to the path of the solar wind and
  > > that only needs a relatively weak field. You're trying to produce a
  > > uniform field parallel to the path of the solar wind
 >
 > No, as you yourself have pointed out, the solar wind is coming in with
 > an anti-spinward velocity of 770 mi/sec. Therefore, it's not parallel
 > to the field. If it were parallel, the approach I described wouldn't
 > work.

The solar wind is known to redirect magnetic field lines and I see no
reason why it wouldn't do that to the field you are trying to generate. I
cannot see the field lines remaining vertical once the solar wind makes
itself felt just above the atmosphere.

 >
  > > stronger field as you will have to cope with the _inverse cube law_
  > > for a
 >
 > Keep in mind that fields decline according to the standard force laws
 > only for distances that are large compared to the dimensions of the
 > source of the field. The source of this magnetic field is a current
 > loop a million miles wide and millions of miles long; the inverse cube
 > law will be significant only for distances much larger than a million
 > miles.

Actually its an inverse linear relationship in the plane of the Ringworld.
The further away from the loop you go, which is the only source of
magnetism generated, the weaker that magnetism becomes.

To clarify a bit.
A disc magnet will have a uniform field across its surface but that is
because the domains which produce that field are uniformly distributed
across the full diameter. Your superconductor loop is more like a ring
magnet, which is a disc magnet with a large hole drilled through its face
to remove most of the material. A ring magnet does not produce a uniform
field and neither will your loop which is equivalent to one.

 >
   > > > If it seems counter-intuitive that such a tiny field is sufficient,
   > > > keep in mind that the mechanism I describe requires that this very
   > > > weak magnetic field must remain at least moderately uniform over
   > > > millions of miles; the total energy of that volume of magnitic field
   > > > is enormous, despite the fact that the field itself is quite weak.
  > >
  > > It can't remain uniform, apart from the dipole effect the middles of
  > > your loops aren't likely to have a noticable field present. The coils
  > > are so
  > > big that they can be treated at single straight wires and you will be
  > > more accurate that way.
 >
 > Who said anything about coils? I was talking about a single closed
 > loop of current for each day-stream.

What? you don't want to increase the power of your loop simply by laying
more wire?

Stephen

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 >> Stay informed about: Significance of the solar wind 

Stephen Forbes wrote:

 > I went back over Erik's posts, which I have reproduced below, and he
 > never
 > once mentions Earth's magnetic field. He keeps saying that Earth has
 > no
 > rim walls (obvious) and that is the reason that the Ringworld's
 > atmosphere
 > is stable.

So you're admitting that that children's teaching page doesn't
contradict me, then?

 > His argument is that Earth would have a problem long before the
 > Ringworld, and that argument completely ignores the contribution of
 > Earth's magnetic field.

1. That page doesn't say that Venus is losing its atmosphere because of
a lack of a magnetic field. It says it lost the WATER IN ITS ATMOSPHERE
because of a lack of magnetic field.

2. The Ringworld has a superconductor grid and is perfectly capable of
creating a magnetic field around itself similar at least in vague detail
to Earth's. That you refuse to acknowledge this doesn't really change
anything.

3. If you're right, and Ringworld would lose its atmosphere in 100 yr
due to its lack of a magnetic field, why has Venus managed to retain its
atmosphere for billions of years?

--
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 >> Stay informed about: Significance of the solar wind 

steve DeleteThis @antispam.sforbesa.cix.co.uk (Stephen Forbes) wrote in message news:<memo.20040916231157.2877E DeleteThis @sforbesa.compulink.co.uk>...
 > In article <8b42afac.0409160828.132fd765 DeleteThis @posting.google.com>,
 > kuyper DeleteThis @wizard.net (James Kuyper) wrote:
....
   > > > ... There are some
   > > > obvious problems where the loops touch, where the field is horizontal
   > > > not vertical. This problem will remain as long as there is more than
   > > > one loop.
  > >
  > > The loops touch, and the field is horizontal, only in the region
  > > between day-streams, where there is little solar wind because it's
  > > been blocked by the shadow squares. That was an essential component of
  > > my design.
 >
 > This doesn't make any kind of sense, your day streams will eventually
 > cover every part of the Ringworld surface in no more than 15 days. There
 > is no part of the surface which doesn't receive the solar wind on a
 > regular basis.

Of course. That's why the configuration of the magnetic field needs to
change with time. If you pay close attention to my specification,
you'll see that the location of the current loop is determined by the
location where the day-streams impact the Ringworld. As the
day-streams move, so must the the current loops. They don't move
physically, of course; the current simply gets re-routed.

   > > >
   > > > You really should put numbers in and balance it with the current
   > > > required to produce that field in your coil.
  > >
  > > You know of some particular limit on that current? I don't. Without a
  > > limit, I don't see why it matters what the current required is.
 >
 > Even superconductors have their limits, if you put too much current

"Even" superconductors? Our real world superconductors are rather
finicky about magnetic fields. They don't allow magnetic fields to
penetrate them. However, a sufficiently strong magetic field will make
their superconductivity break down. I think that we have to assume
that the Ringworld's Engineers took that into consideration.

 > through them they will lose their superconductivity. I know
 > superconductivity happens because electrons travel in pairs, if you
 > increase the current too much those pairs will be knocking into other
 > pairs and break up their relationship, causing resistance.

OK. So what is current density limit on Ringworld superconductors? How
big are they in cross-section? I don't believe that Niven has ever
answered either of those questions. I think that we are therefore
entitle to assume that the cross-sections and current density limits
were known to the Ringworld Engineers, and were therefore adequate to
the task.

....
 > Actually its an inverse linear relationship in the plane of the Ringworld.
 > The further away from the loop you go, which is the only source of
 > magnetism generated, the weaker that magnetism becomes.

Yes, but only for distance much larger than the size of the current
loop. In the immediate vicinity of the loop, the magnetic field
follows the same force law as an infinitely long current.

The switchover to the force law for a small isolated dipole doesn't
apply until the distance is comparable to the size of the current
loop.

....
 > to remove most of the material. A ring magnet does not produce a uniform
 > field and neither will your loop which is equivalent to one.

I never said that it produced a highly uniform field, only that it
would be sufficiently close to uniform.

....
  > > Who said anything about coils? I was talking about a single closed
  > > loop of current for each day-stream.
 >
 > What? you don't want to increase the power of your loop simply by laying
 > more wire?

For my purpses, all that matters is the total current flowing in one
direction. It doesn't matter whether it's all traveling in a single
superconducting wire, or is spread out over many parallel strands of
superconductor, However, there's no advantage to be found from
coiling up the superconductor. That would just tend to produce strong
magnetic fields inside the coil, which would not extend for any
significant distance from the coil, and would therefore be uses for
such purposes as the Meteor defense. Also, that magnetic field would
make it harder for a conventional superconductor to remain
superconducting. Of course, the Ringworld's supercondouctors don't
have to be conventional.<!-- ~MESSAGE_AFTER~ -->
 >> Stay informed about: Significance of the solar wind 

James Kuyper wrote:

 > OK. So what is current density limit on Ringworld superconductors? How
 > big are they in cross-section? I don't believe that Niven has ever
 > answered either of those questions. I think that we are therefore
 > entitle to assume that the cross-sections and current density limits
 > were known to the Ringworld Engineers, and were therefore adequate to
 > the task.

We know they're strong enough to direct and lase material from the
Ringworld's _sun_ in order to fire at incoming threats, so any talk
about the Ringworld's magnetic field being insufficient for this or that
is pretty patently ridiculous.

--
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 >> Stay informed about: Significance of the solar wind 

On 9/16/2004 3:35 PM Paul Vader cranked up the brainbox and said:

 > Dark2112.DeleteThis@FakeEmail.com writes:
  > > Some of you say that Ringworld's atmosphere is unstable, and needs
 > At this point, I think it's down to Steven. I got what I asked for weeks
 > ago - smart people telling me where my thinking was flawed. They even
 > taught me how to fish, and running their math verifies they're right.

And this is the basis for one of humanities enduring legacies. Not building
physical things, but building knowledge that can be self-reinforcing and
self-teaching. not just facts in a book, but how to get those facts yourself.
Fantastic stuff.

 > I started this mess because I had some wacky ideas about the atmosphere not
 > becoming coupled to the ringworld's spin, mostly because I wasn't taking
 > the angular momentum of the atmosphere into account. Another flaw in my
 > thinking, which I corrected myself later, was over-estimating the altitude
 > of breathable pressure, thinking incorrectly that it wouldn't look like
 > Earth's.

I'm not sure I would even say it was flaws in your thinking, as much as it's
just that the Ringworld is huge on a scale that we have nothing to compare it
to, but just small enough that we can actually figure out a lot of things about
it, like how various parts should work.

--
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 >> Stay informed about: Significance of the solar wind 

On 9/16/2004 6:11 PM Stephen Forbes cranked up the brainbox and said:
 > This doesn't make any kind of sense, your day streams will eventually
 > cover every part of the Ringworld surface in no more than 15 days. There
 > is no part of the surface which doesn't receive the solar wind on a
 > regular basis.

You only need to protect the parts that are receiving it at any given moment.
Anything shielded by the shadow squares at any given moment are already
protected. So, you set up the field in the superconductor grid, and move it as
the shadow squares move.

  > > You know of some particular limit on that current? I don't. Without a
  > > limit, I don't see why it matters what the current required is.
 > Even superconductors have their limits, if you put too much current
 > through them they will lose their superconductivity.

But the limit is dependent upon the properties of the conducting material. We do
not know the material of the superconductor grids, nor their intrinsic limits.

 > The solar wind is known to redirect magnetic field lines and I see no
 > reason why it wouldn't do that to the field you are trying to generate. I
 > cannot see the field lines remaining vertical once the solar wind makes
 > itself felt just above the atmosphere.

The point of the field would be to push the solar wind away from the top of the
atmosphere. Sure it will be deflected just as Earth's is, but that deflection
has a limit, it doesn't continue to deform the field to infinity, it only
deforms it to a specific point, as which the forces at that limit are equal.
Earth's magnetic field would extend further towards the sun and closer to the
Earth were there no solar wind, but the solar wind doesn't push the field right
down to the surface.

 > Actually its an inverse linear relationship in the plane of the Ringworld.
 > The further away from the loop you go, which is the only source of
 > magnetism generated, the weaker that magnetism becomes.

That's basic physics. And completely irrelevant. We're only looking to keep the
solar wind from hitting the Ringworld, so we only need to deflect it half a
million miles from the center.

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 >> Stay informed about: Significance of the solar wind 

JRS: In article <memo.20040916231157.2877E.TakeThisOut@sforbesa.compulink.co.uk>,
dated Thu, 16 Sep 2004 23:11:00, seen in news:alt.books.larry-niven,
Stephen Forbes <steve.TakeThisOut@antispam.sforbesa.cix.co.uk> posted :
 >
 >Even superconductors have their limits, if you put too much current
 >through them they will lose their superconductivity. I know
 >superconductivity happens because electrons travel in pairs, if you
 >increase the current too much those pairs will be knocking into other
 >pairs and break up their relationship, causing resistance.

Your understanding of Cooper pairing is inadequate; indeed, it is
approximately negligible. It is not, however, untypical.

--
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 >> Stay informed about: Significance of the solar wind 

JRS: In article <8b42afac.0409162023.7fc62a07.RemoveThis@posting.google.com>,
dated Thu, 16 Sep 2004 21:23:28, seen in news:alt.books.larry-niven,
James Kuyper <kuyper.RemoveThis@wizard.net> posted :

 > Our real world superconductors are rather
 >finicky about magnetic fields. They don't allow magnetic fields to
 >penetrate them.

How about Type II superconductors, then? It is those which are of
greatest technological use.

Of course, the Ring-Builders may have used Type III superconductors,
which (AFAIK) are not yet known here.

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Dr John Stockton <spam.RemoveThis@merlyn.demon.co.uk> wrote in message news:<gjNEE1DXtqSBFwob.RemoveThis@merlyn.demon.co.uk>...
 > JRS: In article <8b42afac.0409162023.7fc62a07.RemoveThis@posting.google.com>,
 > dated Thu, 16 Sep 2004 21:23:28, seen in news:alt.books.larry-niven,
 > James Kuyper <kuyper.RemoveThis@wizard.net> posted :
 >
  > > Our real world superconductors are rather
  > >finicky about magnetic fields. They don't allow magnetic fields to
  > >penetrate them.
 >
 > How about Type II superconductors, then? It is those which are of
 > greatest technological use.
 >
 > Of course, the Ring-Builders may have used Type III superconductors,
 > which (AFAIK) are not yet known here.

I suspect you know a lot more about superconductors than I do. Are
type II superconductors unaffected by strong magnetic fields, or are
they simply less easily disrupted by them than type I superconductors?<!-- ~MESSAGE_AFTER~ -->
 >> Stay informed about: Significance of the solar wind 

JRS: In article <8b42afac.0409172027.31ffa79a.TakeThisOut@posting.google.com>,
dated Fri, 17 Sep 2004 21:27:48, seen in news:alt.books.larry-niven,
James Kuyper <kuyper.TakeThisOut@wizard.net> posted :
 >Dr John Stockton <spam.TakeThisOut@merlyn.demon.co.uk> wrote in message news:<gjNEE1DXtqSBFw
 >ob@merlyn.demon.co.uk>...
  >> JRS: In article <8b42afac.0409162023.7fc62a07.TakeThisOut@posting.google.com>,
  >> dated Thu, 16 Sep 2004 21:23:28, seen in news:alt.books.larry-niven,
  >> James Kuyper <kuyper.TakeThisOut@wizard.net> posted :
  >>
   >> > Our real world superconductors are rather
   >> >finicky about magnetic fields. They don't allow magnetic fields to
   >> >penetrate them.
  >>
  >> How about Type II superconductors, then? It is those which are of
  >> greatest technological use.
  >>
  >> Of course, the Ring-Builders may have used Type III superconductors,
  >> which (AFAIK) are not yet known here.
 >
 >I suspect you know a lot more about superconductors than I do. Are
 >type II superconductors unaffected by strong magnetic fields, or are
 >they simply less easily disrupted by them than type I superconductors?

I've not worked on the topic for some while; you'd do better to consult
books by reputable authors.

Type II superconductors are penetrated by magnetic fields between Hc1 &
Hc2, the first and second critical fields, while remaining able to carry
current without resistance. The difference between Hc1 & Hc2, and their
ratio, can be large. Think of it as quantum flux lines threading
through lossless material, and resisting E x B type forces by being
pinned to irregularities in the material.

It is Type II which carry current in high magnetic fields, and so are
used in magnets, motors, etc.

--
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 >> Stay informed about: Significance of the solar wind 

In article <8b42afac.0409161951.51f9d65a.DeleteThis@posting.google.com>,
kuyper.DeleteThis@wizard.net (James Kuyper) wrote:

 > Dark2112 <Dark2112.DeleteThis@FakeEmail.com> wrote in message
  > > news:<t2djk0dbvaftkd02dl755hf6rr7a3v4m9o.DeleteThis@4ax.com>...
  > > On Thu, 16 Sep 2004 00:14 +0100 (BST),
  > > steve.DeleteThis@antispam.sforbesa.cix.co.uk (Stephen Forbes) wrote:
 > ...
  > > From what I've seen of this lengthy debate, it basically breaks down
  > > into a few points.
  > >
  > > Some of you say that Ringworld's atmosphere is unstable, and needs
  > > some sort of protection that's not mentioned in the novels. This may
  > > or may not be true.
 >
 > We all agree that the Ringworld's atmosphere is unstable. Some of us
 > believe that it's roughly as unstable as the Earth's atmosphere;
 > others of us believe that it's far less stable than that.

Actually I've come across a couple of sites which bear directly to this
debate. On one site it shows that the Earth always has a magnetic field,
even during a pole reversal, and another site which says that Venus
actually does have a magnetic field. I have started a new topic which
lists these sites and others so I won't repeat them here.
Keeping it fairly simple.
UV light from the sun ionises the upper atmosphere. The solar wind creates
a bow shock where it hits the ionosphere and a tail where it leaves. The
solar wind also carries with it a magnetic field from the sun. Its called
the interplanetary magnetic field (IMF) and it integrates itself into the
ionosphere. This keeps the ionosphere intact under the constant
bombardment of the solar wind.
This happens on Venus all the time and on Earth when our main field fails
during a reversal.

On the Ringworld however, there may be a bow shock but there is no stable
flow of plasma into a tail. As far as I can see there is only the
equivalent of a bow shock and if the magnetic field does somehow integrate
into the ionolayer, then it will make my scenario more likely as the
plasma will become a cohesive whole separate from the air below.

In fact, the situations are so different that comparing the stability of a
planet's atmosphere to the Ringworld is like comparing chalk with cheese.
The Ringworld needs to be modelled from scratch without referring back to
planets, which is what I have been doing.

Stephen

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 >> Stay informed about: Significance of the solar wind 

In article <414A1B75.9BA4B788 DeleteThis @alcyone.com>, max DeleteThis @alcyone.com (Erik Max
Francis) wrote:

 > Stephen Forbes wrote:
 >
  > > I went back over Erik's posts, which I have reproduced below, and he
  > > never
  > > once mentions Earth's magnetic field. He keeps saying that Earth has
  > > no
  > > rim walls (obvious) and that is the reason that the Ringworld's
  > > atmosphere
  > > is stable.
 >
 > So you're admitting that that children's teaching page doesn't
 > contradict me, then?

Looks like you cannot read, try again but sober this time.

 >
  > > His argument is that Earth would have a problem long before the
  > > Ringworld, and that argument completely ignores the contribution of
  > > Earth's magnetic field.
 >
 > 1. That page doesn't say that Venus is losing its atmosphere because of
 > a lack of a magnetic field. It says it lost the WATER IN ITS ATMOSPHERE
 > because of a lack of magnetic field.

Actually Venus does have a magnetic field, transfered from the solar wind
and integrated into the ionosphere. Its on another site I found.

 >
 > 2. The Ringworld has a superconductor grid and is perfectly capable of
 > creating a magnetic field around itself similar at least in vague detail
 > to Earth's. That you refuse to acknowledge this doesn't really change
 > anything.

I don't refuse to acknowledge it, I just don't think James is using the
correct arrangement for generating that field. Please note that it hasn't
stopped me discussing it with him in detail.

 >
 > 3. If you're right, and Ringworld would lose its atmosphere in 100 yr
 > due to its lack of a magnetic field, why has Venus managed to retain its
 > atmosphere for billions of years?
 >

See above and my post of interesting links.

Stephen

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