John & Mark et al:
A little history may tell you most of what I know about the compact
particle accelerator that Bob S. is proposing.
Around 1965-66 I was responsible for supporting the scientific
staff at Varian Central Research. The
machine shop and the electronics shop people reported to me.
I also had, from time to time, research projects of my own.
Varian had recently acquired Eimac, a nearby company mostly engaged
in the manufacture of power grid vacuum tubes and magnetrons.
One of the end users of the magnetron lines was a company in the
potato chip and snack food business.
This company was also supplying the US Army with MREs, Meals Ready
To Eat. One of our VPs, Joe
Feinstein, proposed a system whereby a product line of various foods could
be sterilized within sealed plastic envelopes by means of free electron
bombardment. The high-energy
free electrons would pass through the plastic envelope and into the food,
sterilizing it. There was
sufficient experimental evidence to support the idea and if a practical
means could be found to generate an abundant supply of free electrons at
the right energy there seemed to be a ready market.
Accelerating charged atomic particles to a high energy is a matter
of keeping the particle in a strong electric field for an adequate length
of time. In the case of the
famous Stanford Linear Accelerator (SLAC) this is done by launching free
electrons (or perhaps other charged particles) at a low velocity into a
series of resonant cavities supporting axial electric fields of high
intensity. This sequence of cavities is excited using high power
klystrons designed for this specific application.
The phase of the electric fields, cavity to cavity, is arranged so
that the charged particles are always being accelerated. A very loose analogy is sometimes drawn between this effect
and that of a surfboard rider being pushed along on a moving ocean wave.
One of the primary functions at SLAC is to examine the particles
and waves scattered from various target substances placed at the end of
the accelerator, which is 2 miles long.
Feinstein’s idea was
to accelerate free electrons in a much more compact device, although to
much lower velocities than were routine at SLAC.
The electric field was to be established in a resonant cavity
consisting of a short length of shorted circular waveguide.
The TE11 resonant mode was to be used wherein the electric field is
perpendicular to the axis of the cavity and always normal to the circular
walls. This mode is easily
excited in any azimuthal orientation.
If the cavity is excited at 2 ports, 90 degrees apart (both spatial
and time-wise), the resulting electric field is rotating.
This is analogous to the rotating magnetic field in a 4-pole AC
motor where two pairs of windings 90 degrees apart spatially are excited
90 degrees apart in phase. The
rotating radial electric field in the cavity was to be excited by an Eimac
production magnetron in their San Carlos plant, some 10 miles down the
pike toward San Francisco from the Central Research facility where I
worked in Palo Alto.
Some free electrons were introduced along the axis of the cavity
from a simple thermionic cathode at a potential energy of perhaps 100
volts more or less. An axial
DC magnetic field was applied as well and the field strength could be
finely adjusted until the cyclotron frequency of free electrons in this
field was precisely the same as the frequency of the rotating electric
field. As soon as an electron
entering the cavity near the axis detected a radial electrical field, it
would start to move in the radial direction following the field.
The newly acquired radial velocity would interact with the magnetic
field and cause the electron to move in the azimuthal direction precisely
in step with the rotating electric field.
The net result was that the electron moved in an outward growing
spiral gaining energy at a more or less steady rate.
This spiral motion would be superimposed on some slight drift in
the axial direction due to the initial axial velocity upon entering the
cavity. It is worth noting
that the strength of the rotating radial electric field is a maximum
midway between the end hats of the cavity where the radial electric field
strength is zero.
One of the subtleties making a full understanding of such a device
difficult for some is the fact that all charged particles gain mass as
they gain energy following Einstein’s Law of Relativity.
And since the cyclotron frequency of a charged particle in a
magnetic field depends on the mass of the particle, it follows that there
is a limit to the amount of energy a particle can gain in such a simple
device in a fixed magnetic field driven at a fixed frequency.
Unless something is changed, the particle gaining energy will
simply fall out of phase with the exciting forces and eventually start
giving energy back to the driver.
The surfer analogy where the crest of the wave gets ahead of the
rider may (or may not) help one visualize this situation.
Dr. Howard Jory was the principal investigator in this project and
I was assigned to be his run-fetch-and-carry assistant, shuttling back and
forth between Palo Alto and San Carlos, as needed.
After several weeks of construction and cold testing the
experimental apparatus it was time to turn up the heat, activate the
cathode, draw some current, and apply power from the driving magnetron.
Preliminary calculations suggested that electron energies up to
100kv could be expected and the resulting X-Ray flux would need to be
monitored closely and shielded.
production of X-Rays results from the sudden impact of a high velocity
charged particle with a solid surface.
The physics was explained to me in a college physics course as
follows: All charged
particles exert a force on all other charged particles and physicists
explain this in terms of an electric field.
A “field” may be defined as a region in space each point of
which has associated with it a physical quantity.
A force field describes a force, having both magnitude and
direction, on an object placed within the field.
Thus the gravity field of the Sun causes the Earth and all other
massive bodies, moons and planets, etc., to experience a force toward the
Sun. The closer to the Sun,
the greater the force of gravity, although objects far beyond the outer
planets may safely ignore the gravitational field of the Sun as compared
with other effects. Charged
particles such as electrons and protons exert strong electric forces on
all other charged particles in their near proximity. If all of the charged particles are stationery the
forces are all directed along the axis between them.
If, however, one particle is in rapid motion with respect to a
stationery particle, the stationery particle may be imagined to “see”
the moving particle as being where it was a bit earlier. The “bit” of time earlier referred to is a function of
the velocity of light and the distance.
A complete picture of the physics (Einstein’s Relativity) leads
to a description of the magnetic field around a moving charge (an electric
current) and the increase in mass referred to earlier.
When an energetic charged particle is stopped suddenly by collision
with a “solid” surface the normal electric field associated with the
charge is suddenly disrupted. A
mathematical analysis of the situation based on all of the physics we know
shows that one of the required components is a radiating electromagnetic
wave… an X-Ray. The higher
the energy at impact, the higher the energy (and the shorter the
wavelength) of the X-Ray. Likewise,
the more dense the target the stronger the X-Rays.
Thus a Tungsten target results in higher energy X-Rays than does an
case of the device we started testing at Eimac, the X-Ray flux was much
higher than expected and was decidedly a safety hazard for people in the
vicinity. The operation was
shut down while all available scientific minds studied the matter.
I was kept busy driving the forklift to a nearby warehouse to
retrieve several pallets of lead bricks left over as shielding from some
other high-energy experiment. By
the time I had completed a lead brick enclosure for our experiment, the
physicists had analyzed the situation as best they could in the short time
When the experiment was fired up again the X-Ray flux leaking out
between the inevitable gaps between the lead bricks was still far too high
for safe operation. Nor did
anyone on the physics side have any explanation.
Another supply of lead bricks was found and I went to great pains
to stack the new ones so as to cover the regions of contact between the
bricks in the first layer. When
the experiment was turned on again the X-Ray flux was almost as high as
ever and we began looking for other effects… such as electro-magnetic
cross talk between the X-Ray detector and the magnetron power supply.
An alternate X-Ray detector operating on a different principal from
the first was brought to bear. The
X-Ray flux indicated was still intolerable.
I began making plans to cast a solid lead housing around the
experiment, but before I got very far I was told that the project was
suspended until further notice and I was given other assignments.
As far as I know it was never revived and I never heard an
explanation of the unexpected high energies that were apparently observed.
My first experience with X-Ray emission from a high voltage device
was in 1957. I was working on
a vacuum tube capable of producing short pulses of microwave power in the
1-meggawatt range. This was
an electron beam device operating in the range of 100 kv.
The collector for the spent beam electrons was made of copper to
facilitate the disbursal of heat and was enclosed in a lead shield to
protect people from X-Rays. Several
pinhole cameras were always on hand and taking X-Ray photographs of the
tube and its surroundings was routine.
These cameras were simple lead boxes with a tapered pinhole in one
side and X-Ray sensitive film on the inside wall opposite the pinhole.
A certain degree of skill and experience was required to get the
right exposure and the right view. The
lone technician I knew who was endowed with the right stuff could not be
found when he was needed for the project in 1965 and no one I asked knew
where he was. Good pinhole exposures can be very useful indeed giving
incontrovertible evidence as to what is going on inside a high voltage
device showing precisely where high-energy charged particles are striking
the inner surfaces. In the
case of the vacuum tube I was working on in 1957 such exposures told us
that the beam electrons were striking surfaces other than those intended
and we were able to implement a simple fix.
In the case at hand in 1965 we never had this opportunity while I
The next time I had serious occasion to revisit the Feinstein-Jory
experiment I was working at Litton Electron Devices in San Carlos, CA in
the mid 1990s. A related
company, part of Litton Industries, was in the oil well business and my
boss, Bob S., became aware of a need for an alternate source of hard
X-Rays used by this company for “logging” an oil well.
Logging, as he explained it to me, was an operation whereby a
highly radioactive source, in this case a pellet of an isotope of Cesium
(or so I believe), was lowered into an oil well casing along with some
auxiliary instrumentation. The radiation from the pellet passes through the casing walls
and into the surrounding rock, causing these rocks to fluoresce and send
back secondary radiation. The
instrumentation associated with the Cesium pellet is able to analyze the
reflected florescence and determine the elements making up the surrounding
rocks. This information
enables geologists to construct a geologic model of the region and assess
the probability of finding oil or natural gas and perhaps just where those
deposits might be found.
This logging process, well established over a long period of time,
had come under question due to environmental concerns in case the Cesium
pellet should ever be lost at the bottom of the well.
The rules for handling such radioactive substances mandated that
the pellet must be found and retrieved… regardless of cost or effort…
or so someone up the chain of command believed.
As ridiculous as this proposition may seem to a novice such as
myself, it was sufficiently grave to inspire at least some modest search
for an alternate source of high energy radiation that would present no
environmental concerns should the device be lost down the well.
Bob S. vaguely recalled the Feinstein-Jory experiment and asked me
what I could tell him about it. He
also dug in the published records he could find and made a few
calculations of his own. He
thought that the whole experiment, magnetron, power supply, and all, could
probably be assembled in a single compact vacuum package comparable in
size to the instrument package already in use to analyze the induced
fluorescence. After thinking
about the matter off and on for a period of time, he came to believe that
a way could be found to keep a charged particle, steadily growing in mass
and energy, always in an accelerating field for an extended period of
time. The effect of
increasing the mass is to reduce the cyclotron frequency for a given
magnetic field. If the axial
magnetic field is to remain constant then the frequency of the driving
electric field must be reduced accordingly.
The resonant frequency of the cavity must also be altered
appropriately. I do not
know the details of Bob’s final concept, but I suppose that he has found
a way to have the particles being accelerated drift from one cavity to
another, in linear sequence, always finding the right conditions in each
appropriate to the increased mass. Electromagnetic
cross talk between adjacent cavities is a concern in my thinking, but I
have worked with Bob S. long enough to know that he has not neglected such
matters and probably has a solution in mind if, indeed, there is a problem
Common sense apparently reared its ugly head somewhere along the
way and the search for an alternate to a Cesium source was abandoned. By this time, however, Bob had decided that he had found a
way to accelerate charged particles to extraordinary high energy in a
compact device. And, being a
generalist, he immediately saw at least one practical use for such a
device… the Transmutation of Plutonium.
of transmutation has been kicking around for many years, but the
accelerator necessary to produce the high energy protons was too
cumbersome and expensive to be practical.
If Bob S.’s cyclotron accelerator can be made to work, the cost
and convenience should be minimal making it practical to install an
“afterburner” on the premises of any nuclear power plant.
absolutely no expertise in atomic or nuclear physics, but the
transmutation proposition has been explained to me in the following
layman’s terms. Plutonium,
it seems, is one of the products of the radioactive decay of Uranium and
is found in spent fuel rods in a conventional nuclear power plant.
The Plutonium atom stores a great deal of energy and when it
happens to decay, on rare occasions, one or more very energetic particles
is emitted. Living tissue in
the path of such particles is apt to be damaged severely.
Other Plutonium atoms in the path of these particles are likely to
be excited into an unstable state where they will be induced to decay as
well. If enough Plutonium is
concentrated in a critical mass the result is a Plutonium Bomb chain
reaction… a fearsome object indeed.
In a world full of terrorists willing to kill themselves in order
to bring chaos and destruction to the rest of mankind, having a lot of
loose and poorly guarded Plutonium lying about would seem to be a wholly
intolerable situation. Yet that seems to be the situation around the world wherever
nuclear power plants are in operation.
of transmutation has 2 laudable goals… 1) to provide an abundant source
of clean energy as an alternative to fossil fuel and 2) to keep the
Plutonium out of the hands of terrorists.
There is very good reason to believe that if a sub-critical mass of
Plutonium was to be bombarded by Protons (the Hydrogen Nucleus) of
sufficiently high energy, the Plutonium would decay in an orderly fashion,
one atom at a time, giving up a great deal of heat to its surroundings and
leaving behind a benign ash. This
heat would be in an ideal form to make steam for the generation of
electric power and, perhaps, to disassociate water, H2O, or Methane, CH4,
to produce Hydrogen. The
economic value of this energy should be sufficient to make inventory
control a high priority for the operators of the facility.
obvious hurdle is the knee-jerk reaction of many people at the very
mention of the word “nuclear” (or, as some would have it, “nucular”). There is also the small matter of a presidential order left
behind by Jimmy Carter… a nuclear engineer… forbidding the
re-processing of spent fuel rods in the USA.
Of course, other countries are not bound by this order and we can
gather from the news that a lot of reprocessing is going on all over the
world… a cause of great concern in this troubled world.