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. 

The 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 Aluminum target.

In the 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 they had.

            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 was involved.

            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 here.

            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. 

The idea 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. 

I claim 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.

The idea 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. 

One 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.