US3284686A - Method of discharging a cloud - Google Patents

Description

Nov. 8, 1966 H. Moss-:s ETAL.

METHOD OF DISCHARGING A CLOUD 5 Sheets-Sheet l Filed May 5, 1964 mlm@ www Q www QN Il mvm H. MOSES ETAL METHOD OF DISCHARGIVNG A CLOUD Nov. 8, 1966 I5 Sheets-Sheet 2 Filed May 5, 1964 Nov. 8, 1966 H. MOSES ETAL 3,284,686

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.56 l INVENTORS United States Patent O 3,284,686 METHOD OF DISCHARGING A CLOUD Harry Moses, Park Forest, and Ronald L. Martin, La

Grange, Ill., assignors to the United States of America as represented by the United States Atomic Energy Commission Filed May 5, 1964, Ser. No. 365,223 3 Claims. (Cl. 317-262) The invention described herein was made in the course of, or under, a contract with the United States Atomic Energy Commission.

This invention relates to methods of discharging clouds and more particularly to a method of discharging a cloud using a charged particle beam.

A cloud in 'general is highly charged with respect to the earth, with respect to different regions of itself, and with respect to -other clouds nearby so that high electric fields exist therebetween. Under appropriate conditions, this charge or potential difference becomes so great that discharges occur spontaneously in the form lof lightning strokes. When lightning Istrokes occur to the ea-rth, large amounts of property damage may result therefrom. Moore, Vonnegut, Machado and Survilas, J. Geophys. Res., 67, 207 (1962), have observed increased radar echo development followed by heavy rainfall within a few minutes after a lightning flash occurred within a given region. These authors state that the lightning flash probably contributes to the formation of the rain gush, by greatly enhancing the rate of coalescene of rain droplets.

Thus,vunder certain conditions it is desirable to prevent the occurrence of lightning strokes either to stop attendant proper-ty damage or decrease the probability of rainfall. Conversely by initiating a lightning stroke from particular cloud formations, the probability of rainfall therefrom can be greatly enhanced in .a particular area.

It is therefore an object of the present invention to provide a method for discharging a cloud.

It is another object of the present invention to provide a method for dischar-ging a cloud whereby the prevention or initiation of a lightning stroke therefrom may be accomplished.

Other objects of the present invention will become more apparent as the detailed description proceeds.

In general, the present invention comprises generating a high energy particle beam, determining a charge center o'f a particular cloud and directing the high energy particle beam at the determined charge center of the cloud. The high energy particle beam creates `an ionized path in the atmosphere to provide a low resistance path wherethrough the cloud will discharge.

Further understanding of the presen-t invention will best be obtained by consideration of the accompanying drawings in which:

FIG. l is a graphical representation of the ver-tical profile of ionization concentration produced by the beam from the Argonne Zero Gradient Synchrotron.

FIG. 2 is a sketch of an apparatus for the practice of the present invention.

FIG. 3 is a sketch of the apparatus of FIG. 2 showing in detail the beam bending magnets and the control equipment associated therewith.

FIG. 4 is a cross section of the bending magnet of FIG. 3 taken along line 4-4 thereof.

For clarity of understanding of the method of the present invention, the proton ybeam of the Zero Gradient Synchrotron at Argonne National Laboratory willvbe usedvin the description thereof. It is to be understood that the pre-sent invention is not to be limited to the use of this beam and, as will later be set forth in the specifi- 3,284,686 Patented Nov. 8, 1966 ICC cation, other particle beams may be used to accomplish the method thereof.

The Argonne Zero Gradient Synchrotron is designed to produce a pulsed proton beam having 1013 protons per pulse of 10 micros-econd duration, once every four second-s. Protons with energies ranging to 12.5 bev. are possible. At the exit, the beam has a cross-sectional area of about 50 cm?. With suitable bending magnets, as will be shown later, it is possible to turn the accelerator beam into the atmosphere and -to aim it in a predetermined direction.

According to Aron, Hoffman, and Williams, Range Energy Curves, ABOU-663, TID, Oak Ridge, Tennessee, l950,a beam of 3 bev. protons loses roughly 2 mev. per gram per square centimeter of dry air. This energy loss is referred to as the specific rate of energy loss; and if it is multiplied by the density of air (l.25 lO3 grams per cubic centimeter), the actual rate of energy loss for particles of that ener-gy value is obtained. That is, protons having an energy of 3 bev. will lose 2.5 103 mev. per centimeter (or 0.25 mev. per meter) of air traversed. Assuming normal temperature and pressure conditions, the proton beam will pass through about 8 meters of atmosphere before losing 2 mev. of energy. This assumes no cataclysmic condi-tions are involved. Since a homogeneous atmoshpere at common ambient temperatures has a height of about 8 kilometers and taking into consideration the gyrations of a high energy proton beam around the earths magnetic lines of force, a proton beam having energy greater than 3 bev. will pass through most of the vertical extent of the atmoshpere and continue along the geomagnetic lines of force toward the conjugate point on earth. In other words, if a beam of protons having an initial energy of 3 bev. is directed vertically, i-t will pass through the atmosphere losing approximately 2 bev. (0.25 mev. per meter 8 kilometersX 1000 meters per kilometer), and have a residual energy of 1 bev., whereby the protons will still be traveling at relativistic velocity since their rest energy is 0.938 bev.

The-flux of particles, F, may be represented as:

where Nozthe number of particles emitted at the exit of the accelerator,

T :the time in seconds of the pluse duration, and

A=the cross-sectional area in cm.2 of the beam.

At the accelerator exit of the Argonne Zero Gradient Synchrontron, the flux is therefore 2 1016 particles per square centimeter per second. Since the ionization potential of air may be taken as 35 electron volts per ion pair, the Argonne proton lbeam will generate 57,000 ion pairs per particle for every gram of air per cm.2 (8 meters) traversed, which is approximately 7l ion pairs formed per cm.3 per particles at normal temperature and pressure. The energy of each particle, as noted above, will be reduced by 2.5 103 mev. for each centimeter of air it tranverses as long as the particle is travelling at relativistic velocity. This energy is spent almost en tirely on ionizing air molecules in its path. Therefore, the total number of free charge carries produced by the beam is substantial considering that 71 ion pairs (2.5 10-3 mev. per cm. 1/35 ion-pair per electron volts) are generated by each particle as it travels a centimeter and that there are 1013 particles transmitted per pulse.

At any instant, the number of ion pairs present per cm.3 can be determined by the equation:

where n=the number of ion pairs per cm,

q=the ion pair production rate per second per cm,

a=the recombination coehcient in cm.3 per ion pair per second and taken as equal to 1.6 l*6.

The computation of the ionization as a function of height in the atmosphere is complex even when secondary ionizations resulting from nuclear interaction-s are disregarded. However, an approximate semiquantitative calculation is used to indicate the order of magnitude of ion concentration produced by a high energy proton beam.

As the proton beam'of the Argonne accelerator exits therefrom, it is divergent with an angle of approximately 0.4 milliradian and disperses further due t-o multiple scattering. It also becomes attenuated due to nuclear interactions. The ionization produced per unit volume therefore decreases with increasing heights. The rate of ionization production is expressed by the equation:

where p0=air density at NTP which equals l.293 103 grams per cm,

p=air density in grams per cm,

Z=height above ground in centimeters,

k=distance from beam exit to a virtual point source,

6=angular spread of the beam upon exit and equal to 0.4 milliradian,

71 :ion pair production per centimeter per particle as set forth supra,

L=absorption thickness, taken as 120 grams per cm?,

P0=atmospheric pressure at the surface taken in dynes per cm?,

P=atmospheric pressure at height Z in dynes per cm?,

g=acceleration of gravity taken as 980 cm. per sec?.

Integrating yields:

(exp. 21A/Ig) .1 1

This equation applies for a given height during the time required for the beam to pass. After the beam has passed the given height, the ionization production falls to zero .and the number of ions may be expressed by the equation:

"D 1 -l-cmpt where np represents the number of ions due to electronic collision just after the tail of the proton beam has passed. FIGURE 1 illustrates the vertical profiles of ionization concentration based -on the above equations with NACA standard atmosphere assumed. Graphs 10, 12, 14, 16 and 18 are Iplots of the ionization concentration at times, 10, 20, 30, 40 and 80 microseconds respectively after transmission of the beam from the accelerator exit. Ionization due to vmeson production and other spallation reactions may yield total ionizations which are several times greater than that indicated in the graphs of FIGURE l. However, this would be counteracted by multiple scattering of the beam. Thus, the proton beam from the Argonne Zero Gradient Synchrotron may 'be used to produce a highly ionized beam or column from the surface of the earth to heights well above the tropopause.

As noted above, a proton having an energy of 3 bev. looses approximately 2.5:10-3 mev. per centimeter of dry .air traversed. This ligure representing the actual rate of energy los-s, is a function `of the particular energy state of the particle, as is well known in the art. However, it can =be generally stated that the specific rate of energy loss remains nearly constant .as long as the particle is of an energy at least as great as its rest energy, or in other words, is relativistic. Thus, t-he ion-pair generation will also be constant at 71 ion pairs generated. per centimeter traversed per proton for all energies above the rest energy. The rest energy of proton is '938 mev. For electrons, the corresponding value of rest energy is 0.51 mev. (or approximately 1/1850 of the rest energy for a proton whichl is approximately the ratio of their respective masses).

While the actual rate of energy loss of changed particles is relatively constant for energies greater than the rest energy of the particle, it increases 'appreciably for lower energies. This is well known in the art, as indicated in the graph on page 168 of Nuclear lPhysics, A.E.S. Green, McGraw-Hill Book Company, Inc., 1955. In this graph, the specific rate of energy loss :for protons is indicated for particular energies up to about 9 bev.; however, as a rst approximation, the curve may be extended to the 12.5 bev. energy value of the present example by simple linear extrapolation as is indicated in the work of Aron, Hoffman and Williams, ibid.

As noted above, it is desirable (for maximum ionization of the air) that the particles be travelling at relativistic velocity after traversing 8 kilometers of atmosphere. The actual rate of energy loss for all relativistic particles indicated. on the graph on page 168 of Green, ibid., except the alpha particle, is approximately 2.5 l0-3 mev. per cm., as used in the .above example for protons. Hence, all such particles will lose approximately 2 bev. of energy in traversing 8 kilometers of atmosphere; and, therefore, for maximum ionization, the particles should have an initial energy at least .as great as their rest energy plus 2 bev. in order that they still be relativistic after they have traversed the 8 kiolmeters of atmosphere. However, it is noted that cloud discharge will `occur even if the particles are not relativistic at the end of eight kilometers of travel as long as there exists a continuous path of ionized particles between the cloud and the earth. The word discharge is used in the sense of reducing, and not necessarily removing, the charge of the cloud.

Turning now to FIGURE 2 wherein is shown an apparatus for the practice of the present invention using a highly ionized beam generated lby the Argonne Zero Gradient Synchrotron as hereinbe-fore described. Every cloud has at least two charge centers and for the purposes of the present invention it is desirable that the lowest charge center of the cloud with respect to ground level be selected.

A network of electric eld meters 20 `are disposed symmetrically around the accelerator 22. Assuming a cloud 24 has two charge centers, at least eight eld meters should be used so that discrimination -between the charge centers may be achieved. Electric eld meters and their use in measuring charge centers of clouds are well known in the art and hence a detailed description thereof will not be presented herein. Reference is made to Some Theoretical Aspects of the Relation of Surface Electric Field `Observations to Cloud Chargel Distribution by D. R. Fitzgerald, Journal of Meteorology, pp. 505-512, Decem- 'ber 1957, and The Distribution and Discharge of Thunderstorm Charge-Centers lby Reynolds and Weill, Journal of Meteorology, pp. 1-12, February 1955. The electric field Imeters 20 are placed in an essentially square arrangement with the accelerator 22 at the center thereof. Each field meter 20 is positioned so that the -measurement thereof is vertical, thereby giving a 2 1r Igeometry measurement.Y The output of each meter 20 is an A.-C. signal which is a function of the potential gradient in the region between the cloud 24 and lground level at the iield meter position.

The output of each field meter 20 is fed to a computer 26 located adjacent the accelerator 22. The computer is preprogrammed to solve the simultaneous equations which may be written for the output of each of the field meters 20 whereby the X, Y and H coordinates and the charge value of the charge centers of the cloud 24 are obtained. For a detailed discussion of these equations and their solution see D. R. Fitzgerald, ibid., pages 505 and 506. Though Fitzgerald illustrates only four field meters in monopole detection, it is to be understood that the same techniques and equations are used for a dipole or other arrangement, the only variance bein-g in the number of simultaneous equations requiring solution. Thus, by preprogramming the computer 26, the output therefrom is a signal which is a measure of the spatial coordinates of the charge center of cloud 24 with respect to the accelerator 22. This signal is then used in a manner hereinafter described to position the beam from the accelerator 22 so that it is directed at the determined charge center of the cloud 24.

As described supra the ionized column created by the beam provides a low resistance path wherethrough the charge of the cloud 24 may be dissipated. The ionized column derived from the beam of accelerator 22 causes considera-ble deformation of the electric eld which, if the charge is high enough, will increase the potential gradient to values exceeding those necessary to create a spark discharge whereby the discharge of cloud 24 via the beam from accelerator 22 will be in the nature of `a lightning stroke.

As shown in FIGURE 3, the output from the accelerator 22 is connected to a bending magnet 28. The bending magnet 28 is fixedly mounted and curved so that the emerging beam from the accelerator 22 is caused to bend whereby it is directed vertically into the atmosphere. A second bending magnet 30 is mounted on top of the bending magnet 2S so as to be rotatable with respect thereto. The magnet 28 causes the beam to be bent into a vertical direction and the magnet 30 by rotation and variation of the field thereof causes the beam to change direction in a region bounded by a cone.

The bending magnet 28 to effect bending of the beam has a radius of `67 feet and produces a field of 21,000 gauss. A cross-sectional view along lines 4 4 of the magnet 28 is shown in FIGURE 4. The outer shell 32 is iron with the coil 34 being placed within interior spaces 3 5 and 36. The beam aperture 38 has a cross section of approximately 6 X 15".

Turning back to FIGURE 3, as previously stated, the bending magnet 30 is mounted so that it is rotatable with respect to magnet 28. To effect this rotation the magnet 30 is fixedly mounted on a base plate 40. The periphery of the ibase plate has teeth 42 cut therein. The base plate 40 is spaced from the bending magnet 28 by roller bearing supports 44 which permit rotation of the base plate 40. The base plate 40 an-d the bending magnet 30 both have apertures 46 therein to permit the passage of the beam therethrough. The size of the apertures 46 is the same as that in the bending magnet 28, namely, 6" x 15 The cross section of the magnet 30 is the same as that shown in FIGURE 4 for magnet 28. The bending magnet 30 has a height of approximately 72" and produces a maximum field of approximately 20,000 gauss, thereby .giving the beam a conical sweep having a half angle of 5.4 degrees.

As described supra, the output from the computer 26 is a signal which is a measure of the spatial coordinates of the charge center of cloud 24 with respect to the accelerat-or 22. This output is fed through an amplifier 47 to a motor 48. Motor 48 in turn drives a spur gear 50 engaged with the Igear teeth 42 cut into the periphery of the base plate 40. The diameter of the spur gear 50 is small With respect to the diameter of the base plate 40 so as to permit incremental m-ovements of the base plate 40. Connected to the shaft of motor 48 via reduction gearing 51 is a synchro 52. The gearing S1 has a gear reduction such that the shaft -of synchro 52 has a positional movement the same as base plate 40 for rotation of the shaft of motor 48. The stator of the synchro 52 is excited from a power source 53 and the output voltage taken from the rotor of the synchro is proportional to the rotative position of the base plate 40. The output of the synchro is fed back vto an error sensing device 54 to provide a closed loop servo system for the positional control of the base plate 40 responsive to the output of the computer 26. f

The -output of the computer 26 is also fed to a regulator 56 which in turn controls the output of a power supply 57 supplying the coils `of-magnet 30. By varying the power to the coils of magnet 30, the field developed therefrom is varied as is the angle through which Vthe beam is bent. Thus, the output from the computer 26 controls the angle through which the beam is bent and the rotation of the base plate 40 which determines the direction of the bending.

It is to 'be noted that the Argonne Zero Gradient Synchrotron has duplicate outputs through which the beam may be ext-racted. Thus, when no beam out-put is required for the present invention, the accelerator beam output yis diverted thro-ugh the second output.

In the present invention, therefore, the eld meters 20 furnish information to the computer 26, which according to the solution of prepro-grammed simultaneous equations lgives a continuous output on the spatial location and charge value of a lcharge center within a cloud. The output 'from the computer 26 controls bending magnet 30, so that when the output proton beam from accelerator 22 passes therethrough it is directed at the charge center of the cloud. The proton beam creates an ionized column extending from the accelerator to the charge center, through which the charge center discharges. As previously set forth, if the charge center in the cloud has a sufficient-ly high potential, then the discharge will be effected via an arc, or lightning discharge. If the potential of the charge center of the cloud is not sufficiently high, then the charge bleeds off to discharge the cloud. Thus, by monitoring t'he measurement of the charge in the charge center obtained from the computer 26 and electric field meters 20, t'he time of emitting the beam from the accelerator may be controlled to prevent lightning by early discharge of the bleeding type or to initiate lightning by discharge when the charge of the charge center is high.

Since the discharge of the cloud is effected down the ionized path created by the accelerator beam, the accelerator 22 must be protected from the effects thereof. A Faraday cage 58 havin-g an aluminum structure is mounted so that it surrounds the accelerator 22. The cage 58 is grounded. Since the cage 58 is of a thin aluminum construction, it does not impede the transmission of the beam therethrough.

The above description was directed towards the use of the Argonne Zero Gradient Synchrotron and apparatus compatible therewith to effect the method of the present invention. It is to be understood that the present invention lis not limited to such apparatus, but other accelerators may be used as may other apparatus for controlling and directing the beam. Nor is it necessary that the ionizing beam be a proton beam. For instance, an electron beam may be used. Electrons have an advantage over protons in that they remain relativistic to much lower energies; however, they also scat-ter more than protons.

Persons skilled in t'he alt will, of course, read-ily adapt the teachings of the present invention to methods far different than those illustrated. Accordingly, the scope of the protection afforded the invention should not be limited to the methods ishown -in the drawings and descri-bed above, but should be determined only in accordance `with the appended claims.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A method of discharging to a predetermined location lon earth a charge-bearing cloud which is located Igenerally above said predetermined location and at an altitude of not more than eight kilometers comprising determining the spatial position of a charge center of said cloud relative to said predetermined discharge location, generating a beam of charged nuclear particles originating at said predetermined discharge location to form a column of ionized air extending a length suicient to reach from said predetermined location to said charge center, and directing said column at said charge center, whereby a continuous path of increased conductivity extends between said charge center and said predetermined disohange location.

2. The method of claim 1 wherein said step of generating a beam of charged nuclear particles comprises 8 transmitting a pulse of approximately 1013 protons hav-ing an energy of at least 3 bev., said pulse having a crosssectional area of approximately 50 square centimeters and duration of approximately 10 microseconds.

3. The meth-od of claim 2 wherein said step of determining the charge center of the cloud comprises defining a pluraiirty -of ground positions relative to said predetermined discharge location, measuring the potential gradients of each of said ground positions, and obtaining coordinates of a charge center of said cloud relative to said predetermined discharge location from said potential ygradient measurements.

References Cited by the Examiner UNITED STATES PATENTS 3,019,989 2/1962 Vonnegut 317-262 X MILTON `O. HIRSHFIELD, Primary Examiner.

LEE T. HIX, Examiner.

I. A. SILVERMAN, Assistant Examiner.

Claims (1)

1. A METHOD OF DISCHARGING TO A PREDETERMINED LOCATION ON EARTH A CHARGE-BEARING CLOUD WHICH IS LOCATED GENERALLY ABOVE SAID PREDETERMINED LOCATION AND AT AN ALTITUDE OF NOT MORE THAN EIGHT KILOMETERS COMPRISING DETERMINING THE SPATIAL POSITION OF A CHARGE CENTER OF SAID CLOUD RELATIVE TO SAID PREDETERMINED DISCHARGE LOCATION, GENERATING A BEAM OF CHARGED NUCLEAR PARTICLES ORIGINATING AT SAID PREDETERMINED DISCHARGE LOCATION TO FORM A COLUMN OF IONIZED AIR EXTENDING A LENGTH SUFFICIENT TO REACH FROM SAID PREDETERMINED LOCATION TO SAID CHARGE CENTER, AND DIRECTING SAID COLUMN AT SAID CHARGE CENTER, WHEREBY A CONTINUOUS PATH OF INCREASED CONDUCTIVITY EXTENDS BETWEEN SAID CHARGE CENTER AND SAID PREDETERMINED DISCHARGE LOCATION.

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