As suggested by the reference to this page, it is essentially a vanity
project for Ecopulse's principal, Nino R. Pereira. It highlights his and
his co-authors' papers that stand out for one reason or another. Some
turned out to be useful, as qualitatively indicated by being referred to;
others represented an initial foray into a new scientific area or initiated
a new cooperative effort. In chronological order, they deal with solitons or
more generally nonlinear equations in the late 1970s, with intense, short
pulses of x-rays as needed to do nuclear weapons radiation test in the
laboratory up to the mid-1990s, and follow-on work in related areas that
continued for some time. At this writing (2022), ongoing are only the
high-resolution measurements with synchrotron radiation on bent crystals.
My 1976 thesis dealt with solitons, isolated structures that are
stable even though they are described by nonlinear equations, specifically
the nonlinear Schroedinger equation. The motivation was a creative
suggestion about plasma turbulence by Prof. Ravi Sudan. The only way to deal with
such equations was, and still is, numerically. Prof. Jack Denavit had developed
various codes that addressed one or another aspect of the problem. Most useful
turned to be a 1-D spectral code. In it, each small modification corresponds
to a slightly different nonlinear equation, all relevant to some physical
situation, and all led to interesting but minor papers. The exception is a paper
on the Benjamin-Ono equation, which connected
its solitons to the motion of corresponding poles in the complex plane.
In was done together with two superb mathematicians, who then continued
to do similar things elsewhere. Still, the most consequential paper presents an
exact soliton solution to the Ginzburg-Landau equation, which extends
the nonlinear Schroedinger equation to phenomena such as light pulses in
fibers. This so-called Pereira-Stenflo soliton is the standard soliton
in the nonlinear Schroedinger equation, but raised to a complex power.
For details see the Pereira-Stenflo
paper itself. It is still being referenced after more than 40 years.
After much fun with solitons and nonlinear equations, I found myself in
research that turned out to be really interesting and also better funded.
- Spectral softening by backscatter.
At the time it was
important to test all kinds of military equipment for its response to
radiation from a nuclear explosion. This is is mimicked in the laboratory
by various kinds of pulsed power machines known as nuclear weapons simulators.
One type makes longish pulses of MeV-like photons relevant to the equipment
on earth, another type makes much shorter pulses of keV-like x-rays relevant
to satellites. The most interesting regime is intermediate, around many
tens of keV x-rays, but this is difficult to achieve directly. Instead,
in a concept later known as flubber I had computed that
multiple Compton scattering would bring a photon's energy from an MeV or so
down substantially, and that this might work on the Aurora Pulsed Radiation Simulator
at the Army Research Laboratory (ARL), which was the largest pulsed power machine
ever built. Its history is on the web, just google for it.
At the time the facility's Director, F. J. Agee, was interested in facility
upgrades, and had enough funding. It didn't work exactly as predicted but
well enough as documented in later papers, and led to a most enjoyable
decades-long association with ARL.
- Megavolt pulsed power.
Agee's Aurora Upgrade program was
needed in part because the machine had not had the necessary tender loving care,
perhaps because some earlier upgrading attempts had failed
and it worked well enough for Government use. Still, the pulse to pulse variability
was a perennial problem, which was finally solved by symmetry arguments.
Initially, the idea was to improve
the so-called V/N
oil switch: it is a capacitive divider (1/N) that takes the 10 MV pulse down
to 1 MV, which can be handled by a large but otherwise more conventional
gas switch. The final result is perfectly reproducible
After this success Aurora was dismantled. The V/N swith papers have been
rarely referenced because no one uses a high-voltage blullein like Aurora
any more. In doing one better than the pulsed
power experts who designed the machine we benefited from better
instrumentation, from time to do the measurements, and better computers
(the computations are done by the second author Dr. Natalia A. Gondarenko).
In fact, the machine was to be dismantled, so we could try out various
ideas and no one feared that some non-standard intervention would
On the other end of the x-ray spectrum, not
MeV but keV, are z-pinches driven by low-impedance pulsers. First introduced
to the field by Prof. Norman Rostoker at Maxwell Labs, I ended up
organizing the second Dense Z-Pinch Conference, and the first one that
could be visited by Russian scientists. At the time I had written a
review of the topic, which
cold be distributed at the conference. It was much referenced at the
time, and it is still a useful introduction but now quite dated. A similar
paper is on plasma points ,
an update of a report by Konstantin Koshelev on localized radiation
emission within Z-pinches.
- Pulsed x-rays at NRL.
As nuclear weapons simulation
gradually lost its importance, and therefore Z-pinches and Aurora as well,
research on x-rays with a smaller pulsed power machine at the Naval Research
laboratory (NRL) increased. I fell in with the section of Bruce Weber. We showed
how to get some energy-selectivity in hard x-ray spectral measurement
with magnets ,
how to make a high power density bremsstrahlung diode
behave by removing hydrogen
from the tantalum anode by heating it to
2500 K or so (after cleaning it inside and out a second or so beforehand),
and made good use of the special environment in the Plasma-Filled Rod Pinch
(PFRP) to measure a tiny (10 eV)
change in a high-energy (63,287 eV) characteristic line (in Ir) caused by
rather modest ionization. The latter work led to many more papers with the
Polasik group in Torun, Poland.
- Nuclear Isomers
The reason to measure an energy shift in a characteristic x-ray line was
motivated by a project at ARL that tried to make some practical use of
the energy stored in nuclear isomers, perhaps a gamma ray laser. In this
project the latest accomplishment (as of 2022) is a paper in Nature
(by Chiara, Carroll, and others) that demonstrates a never before seen
electromagnetic interaction between an atom's nucleus and its electrons.
I think the project is scientifically interesting but completely
impractical: the energy in the nucleus is too well shielded by the
electrons, and in any case it's much too
expensive to put the energy into
the nuclei first. As the bomb people know, to get at nuclear energy you need
particles that don't see the electrons, like neutrons.
- Lithium for x-ray
The explosion that accompanies a radiation pulse is especially large for
softer x-rays, and it is difficult to make a window that stops the debris
from the explosion but still lets the x-rays through. For the purpose I
evaluated nitrogen-cooled lithium strengthened by powdered lithium hydride,
and lithium metal supported on a transparent grid: lithium is the most
transparent to keV-like x-rays of all solids, at least at room temperature.
Solid deuterium is better, but it must be kept at 10 K, cryogenic.
When the synchrotron community started to explore refractive lenses, our
lithium version attracted some attention.
Since then many publications have been done with people at the APS
synchrotron. Look for them in the section on bent crystals.
- Other papers.
Some are really good, some are insignificant, but
here they are.