Explosively formed projectiles (EFP) are a major problem in terrorism and asymmetrical warfare. EFPs are
often triggered by ordinary infrared motion detectors. A potential weak link is that such electronics are not
hardened to ionizing radiation and can latch-up or enter other inoperative states after exposure to a single
short event of ionizing radiation. While these can often be repaired with a power restart, they also can
produce shorts and permanent damage. A problem of course is that we do not want to add radiation
exposure to the long list of war related hazards. Biological systems are highly sensitive to integrated dosage
but show no particular sensitivity to short pulses. There may be a way to generate short pulsed subsoil
radiation to deactivate concealed electronics without introducing radiation hazards to military personnel
and civilian bystanders. Electron beams of 30 MeV that can be produced by portable linear accelerators
(linacs) propagate >20 m in air and 10-12 cm in soil. X-radiation is produced by bremsstrahlung and occurs
subsoil beneath the point of impact and is mostly forward directed. Linacs 1.5 m long can produce 66
MWatt pulses of subsoil x-radiation 1 microsecond or less in duration. Untested as yet, such a device could
be mounted on a robotic vehicle that precedes a military convoy and deactivates any concealed electronics
within 10-20 meters on either side of the road.
Why is it so difficult to detect concealed shallow buried landmines while it is relatively easy to image and detect cancers within the human body? One reason is that in medical x-ray imaging, the source is on one side of the body and the detectors are on the other. This is back-illumination, the optimal orientation for x-ray imaging. Can back-illumination be used in landmine detection? That is, is it possible to generate sufficient xrays 10 or more cm below the soil surface so that suitable detectors above ground could be used to image shallow buried objects including landmines? In an x-ray tube, high voltage electron beams produce x-rays by electron deceleration (bremsstrahlung) and induced orbital transitions. It may be possible to produce 1000 amp short pulses of electrons at 30 MeV using an electron gun with multiple field emitters. (This is a section of an antiballistic missile device proposed at SPIE Defense and Security 2004.) Electron beams of such energy have range of approximately 100 m in air and 10-15 cm in soil. This 5-10 m tall device could be carried by balloon, helicopter or land vehicle. X-ray production efficiency at 30 MeV is over 50 fold higher compared to medical x-ray tube efficiency. Such a device would produce a bright isotropic source of x-rays in a subsurface plume that might be usable in landmine detection.
Mutual repulsion of discrete charged particles or Coulomb repulsion is widely considered to be an ultimate hard limit in charged particle optics. It prevents the ability to finely focus high current beams into small spots at large distances from defining apertures. A classic example is the 1970s era “Star Wars” study of an electron beam directed energy weapon as an orbiting antiballistic missile device. After much analysis, it was considered physically impossible to focus a 1000-amp 1-GeV beam into a 1-cm diameter spot 1000-km from the beam generator. The main reason was that a 1-cm diameter beam would spread to 5-m diameter at 1000-km due to Coulomb repulsion. Since this could not be overcome, the idea was abandoned. But is this true? What if the rays were reversed? That is, start with a 5-m beam converging slightly with the same nonuniform angular and energy distribution as the electrons from the original problem were spreading at 1000-km distance. Could Coulomb repulsion be overcome? Looking at the terms in computational studies, some are reversible while others are not. Based on estimates, the nonreversible terms should be small - of the order of 0.1 mm. If this is true, it is possible to design a practical electron beam directed weapon not limited by Coulomb repulsion.
Mutual repulsion of discrete charged particles or Coulomb repulsion is widely considered to be an ultimate hard limit in charged particle optics. It prevents the ability to finely focus high current beams into a small spots at large distances from the defining apertures. A classic example is the 1970s era “Star Wars” study of an electron beam directed energy weapon as an orbiting antiballistic missile device. After much analysis, it was considered physically impossible to focus a 1000-amp 1-GeV beam into a 1-cm diameter spot 1000-km from the beam generator. The main reason was that a 1-cm diameter beam would spread to 5-m diameter at 1000-km due to Coulomb repulsion. Since this could not be overcome, the idea was abandoned. But is this true? What if the rays were reversed? That is, start with a 5-m beam converging slightly with the same nonuniform angular and energy distribution as the electrons from the original problem were spreading at 1000-km distance. Could Coulomb repulsion be overcome? Looking at the terms in computational studies, some are reversible while others are not. Since the nonreversible terms should be small, it might be possible to construct an electron beam directed energy weapon.
While not obvious, deflection aberration is a key aberration in Cathode Ray Tube (CRT) design. A new concept in electron beam deflection with electric fields, originally proposed in 1997, is now being tested in the laboratory. Using a beam injected off the axis of symmetry, deflection aberrations are predicted to be 10 fold reduced compared to symmetrical injection. This would be less than magnetic deflection aberrations. If the invention proves to be valid, important improvements are possible in CRT brightness, resolution, energy consumption, and footprint reduction. As one example, reducing deflection aberrations allows larger beam diameters in the deflection plane as well as large deflection angles. This will reduce space charge spread, allowing larger beam currents and/or smaller focused spot size. Improved medical imaging displays could be built. For another example, much of the energy consumed in a magnetically deflected CRT display is associated with deflection. Electric deflection has a significant advantage in energy consumed compared to magnetic deflection. With 400 million CRTs in daily use in the US consuming 0.54 quads, there is a large incentive to reduce power consumption in CRTs particularly so since excess heat produced adds to office air conditioning loads.
Magnetic rather than electric fields are usually used to deflect charged particle streams into large angles primarily because electrostatic deflection aberrations are 2 - 3 times larger. This very mature subject has been reexamined using a ray trace program. Traditionally, beams are injected centered between deflection plates to avoid the fringe fields and scanned symmetrically. Analysis produced a simple and surprising result. Injecting the beam asymmetrically significantly reduces aberrations. This very far-off-axis solution is only effective if the beam is deflected toward the near plate. Electrostatic deflection aberrations can be reduced over 10-fold by (1) injecting the beam into the deflection plate gap with a specific off-center displacement located at the inflection point of the beam landing at the target versus injection offset curve, (2) asymmetrical scan, and (3) quadrupole upstream. These results have been partially confirmed. One application has been studied -- a 4000 by 5000 pixel CRT for digital mammography workstations. By dynamically adjusting the injection offset, the beam can be scanned 61.0 degrees with undetectable (greater than 13 fold reduction) deflection aberrations. With static offset, (offset 42% toward the attracting plate) the beam can be scanned 38.1 degrees toward and 9.5 degrees away from the near plate. Multiple discrete beams are possible.
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