From: mbk@hamilton (Matt Kennel)
Newsgroups: sci.physics.fusion,sci.physics
Subject: The H-Bomb secret is out
Date: 28 Sep 1992 17:08:42 GMT
Organization: Institute For Nonlinear Science, UCSD
NNTP-Posting-Host: hamilton.ucsd.edu
Followups-To: sci.physics.fusion
X-Newsreader: Tin 1.1 PL3


Today's New York Times, and this month's issue of Physics Today, (about
inertial confined fusion) reveal the 'secrets' of the hydrogen bomb.
They were declassified since other civilian scientists working in other
countries on inertial confined fusion already figured them out.

I'll get right down to it.

NYT:

  "The hydrogen bomb was invented in 1951 by Dr. Edward Teller and Dr. 
Stanislaw M. Ulam after Dr. Teller suggested that radiation from an
exploding atomic bomb could generate sufficient heat and pressure to
ignite fusion fuel.
   Dr Kidder{senior physicist at LANL} said Government officials thought
the concept of radiation implotsion was so novel that it would be
extremely difficult for foreign scientists to come up with it on
their own."

The essential idea is that they have a "hohlraum" (german for hollow
room) made out of an unspecified "high-Z" material (nudge nudge wink
wink say no more) which reradiates X-rays that implode the pellet.

So yes, it *is* radiation pressure, and X-rays that do it.

This is known as "indirect drive" in ICF.

Some quotes from Physics Today now...(This article is about ICF, but
they admit some details in the article have only recently been declassified.)

"High gain ICF targets have features similar to those shown in figure
1.{a round circle}  These capsules consist of a spherical shell filled with
low-density (<1.0 mg/cm^3) equimolar D-T *gas*. The shell is composed of an
ablator and an inner region of D-T which forms the main fuel.  Energy
from a driver is rapidly delivered to the ablator which heats up and expands.
As the ablator expands outward, the rest of the shell is forced inward to
conserve momentum.  The capsule behaves as a spherical, ablation-driven
rocket."

"The fusion fuel is imploded with typical efficiency of 5-15%.  That is,
5-15% of the total absorbed energy goes into the fuel.  In its final
configuration the fuel is nearly isobaric at pressures up to about 200
gigabars but consists of two effectively distinct regions: a central
hot spot, containing 2-5% of the fuel, and a dense main fuel region
(the "cold fuel pusher").  Fusion begins in the central hot spot, and
a thermonuclear burn front propagates rapidly outward into the main fuel,
producing high gain.

"The efficient arrangement of the fuel places stringent requirements on the
details of the driver coupling, including the time history of the irradiance
and the hydrodynamics of the implosion.  {goes on to talk about
Rayleigh-Taylor instabilities a bit}  The peak values of pressure and
irradiance during a pulse must reach about 100 megabars and 10^15 W/cm^2
respectively.   The required pressure depends on the required implosion
velocity, which is determined by the capsule size.  Minimum velocities
are in the range of 3-4 * 10^7 cm/sec. {!!!}
..
"In general only the charged particle reaction products are available to
heat the fuel because most of the neutrons escape the plasma."

{Which means of D+T -> 14.06Mev neutron + 3.52 Mev alpha, only the alpha
counts}

"The fuel compression is energetically efficient if the D-T remains nearly
Fermi degenerate.  Only 6.5*10^4 J is required to compress 5 mg of fuel to
400 g/cm^3 in this case, but the fuel remains too cold to burn during
the inertial confinement time.  Thus high-gain also requires hot-spot
ignition.

..

"Direct drive is more efficient in transporting driver energy to the fusion
capsule but is sensitive to the spatial quality of the illuminating
radiation.  Inderect drive has the advantage of being less sensitive
to the details of the irradiating beams.  In addition, implosins using
x-ray driven ablation are more stable hydrodynamically."  {Than what?
I guess compared to ion beams...}

"As discussed above, to efficiently compress D-T to several hudred g/cm^3,
the compression must be near Fermi degenerate.  To ensure this, the entropy
generated in the main fuel must be limited to that which would be generated
by a 1-Mbar shock passing through solid density D-T.  Because the peak
pressures in the implosion must be about 100 Mbar, the pressure in the shell
must be increased from an initial shock of 1 Mbar to 100 Mbar in such a way
that little additional entropy is generated.  {A nice trick!} Various types
of irradiating pulse shapes can accomplish this objective. {I.e. how you
make the A-bomb part of an H-bomb makes a big difference in detail}"


The article goes on alot longer.  One thing was conspicious by its absence,
lithium was never mentioned.

--
-Matt Kennel  		mbk@inls1.ucsd.edu
-Institute for Nonlinear Science, University of California, San Diego
-*** AD: Archive for nonlinear dynamics papers & programs: FTP to
-***     lyapunov.ucsd.edu, username "anonymous".
Newsgroups: sci.physics.fusion