Condign volumes 1 to 3

Read from the scan by GLM-OCR; expect the odd misread word.

# UNCLASSIFIED

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23. Reflection If a rapid transition occurs, from free space to plasma (caused, for example, by the presence of large electrical/electromagnetic forces), the plasma will reflect. If the transition is diffuse, the plasma will reflect at a grazing angle. If the plasma transition gradient is too long, then the plasma patch will transmit (i.e. allow through) more energy than it reflects.

24. Absorption The absorption bandwidth depends on the collision rate and the plasma gradient. It is possible to generate a plasma absorber which is lightweight, has high attenuation per wavelength and can be switched on and off. Quite apart from any UAP-related properties, it is seen that there are potential military applications in the control of EM scattering and Low Observables.

25. The power requirements to sustain a plasma are dependent on the volume, the electron density required, the energy to generate electron-ion pairs and the lifetime required; and, of course the altitude (pressure) and the medium.

## INTERACTIONS

26. Plasma Interactions with Objects and Aircraft The interaction of plasmas alone, or when surrounding other objects are complex, since plasmas can act both as absorbers and reflectors. In addition, for transmitters, it has been shown in practice that the presence of a plasma can introduce an inductive reactance into an antenna mounted on a body, thus modifying its performance, causing an increase, for example, in radiated power. The change in radiated power is a function of the ratio of plasma frequency to signal frequency. In the UAP context it seems likely that the response of an impinging EM wave-front on reaching a plasma might be affected. If the radiation from a plasma is capable of modifying an

antenna on transmit, then presumably it will do so on receive hence it seems possible that the presence of a plasma in proximity to a radio receiver (especially at VHF/UHF) may modify the receiver front-end characteristics and even off tune or dampen normal reception. This may well be the cause of reports that receivers, in what could be termed the 'near field' of a UAP, suffer loss of function (receive and transmit) until the UAP and receiver are separated. Usually the UAP moves away or if the vehicle ignition is working, it is hurriedly driven off. In the context of radio transmission, the frequency dependence of this phenomenon also depends upon the inductive reactance introduced by the plasma layer improving the antenna towards resonance and reducing the resistive losses, such that the efficiency is maximised. [Apart from the UAP-related aspects, a factor of military importance may be that the antenna can be made smaller].

27. Interaction with Aircraft Because it is usually unclear as to what the entity comprises, coupled with the surprise factor, most encounters with what are clearly charged masses have been assumed to have been with ball lightning (Working Paper No 2). Whether this is the case and whether charged aerosols are a variation of the same physical realisation is not currently clear. The laws of motion of a plasma ball and the effects when in close proximity to an aircraft in flight are of special interest to MOD. It is assumed that the charge on the ball diminishes with time, due to the leakage, where the air layer is adjacent to the ball's surface. In effect it is likely to behave as a non-deformable solid sphere, in aerodynamic terms, in a flow of non-compressible fluid. The charged mass is likely to be 'captured' by the exhaust of aircraft engines and to follow the aircraft, maintaining both its shape and keeping a constant distance from the tail assembly. It is further assumed that the force required (which, if it were a solid ball would be required to overcome drag and stay behind the aircraft.