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(1)Experimental Studies on the Min. Potential for Formation of Lichtenberg Figures '. By ,. '. Bunji ARAI rnstttztte of Technology (Received Ap.ril 30, 1964). Abstraet It has been reported that the minimum electrical potentia! in which the Lichtenberg figures (positive and negative) appeared was 2 (kV) respectively. But these phenomena were limited to the cases in which photo dry plates were used. We discovered that both figures appeared when photo fiIMs were used, and even under 1,5 (kV). In our studies we found that the limit of the crest voltage was 1.4 (kV) for positive figure and 1.2 (kV) for pegative figure. It means that the surface corona discharge effected by the dielectric constant of an insulating substance inserted between the two electrodes and its thickness.. From this fact we get a suggestion to the extension of the range of measuring the impulse voltage by the KlydonograPh.. '. IIntroduction ' ･ '. , In the case of measuring the impulse voltage according to the size of the. Lichtenberg figures, the electric engineer's pocket-books published around 1930,. showed that the characteristic curves of the positive and negative went through zero in ehe diagram of the electric potential and the radius of the figures, respectively. But it was wrong. The fact is that the figures did not･ appear until the supplied voltage had attained some potential. This phenomenon is very interesting for us and taught us that certain min. electrical energy was needed to produce the Lichtenberg figures. In the later studies it was. found that the crest voltage of 2 (kV) was at least needed to record the figures, During our studies pn Lichtenberg figures taken in the low atmospheric pressure'), we observed that we could get Lichtenberg figures easily less than 2 (kV) by using photo films (color or black and white). Then at what (kV) (at least) did Lichtenberg figures appear ? To observe the minimum electrical potential which was necessary to make the positive and negative RCphetreinmbeenrtgedfiagsUrfeoSiioOwns,the PhOto fiims under the atmospheric pressure, we.

(2) B. ARAI. 22. 2. ' ' Experimental Apparatus and Procedure 2.1 Impulse circuit. The impulse circuit consisted of the three high tension condensors; C,,i C2, C3, three kinds of switches, Si, S2, S,, a static voltmeter V. ; and a resistance; R. It wiring wa3 shown in Fig. 1.. '. m-bu..-..-- Cl. i. '. '. -.. ¥ -ruLo or"-im. o. 9NILo pt.E L. o. S3. L･f,. Sz. R --. e3. -K. [gll. s･. Fig. 1. High tension impulse circuit. Cp C2, C3: High tension condensers (5ptF) respectively, Si, S2, S3: Combined knife switch. R: Fixed and variable resistance.. K: KlydonograPh camera. M: Hand driven Megger of 1 (kV). V.: Static voltmeter (YEW).. A KIydonograPh camera K was shunted with R. By the R, C and L in circuit, the wave shapes of impulse circuit were determined. We used the Megger M (1000 (V), hand driven) as a source of electricity. to charge these condensers with. The high tension condensers Were made in the Tokyo-Shibaura Electric ' Works, the capacity of which was 5 (ptF) respectively, containing Shibanoru, and its allowable voltage was 20 (kV). The range of static voltmeter which was made in the Yokogawa Electric Works was from O-2.0 (kV) to O-3.0 (kV). The resistance R, namely a fixed resistance 10 (k9) and the other variable resistance were connected in series, as an discharge-resistance for fix in 10.45 (k9), and both ends were connected in parallel with those of the KlydonograPh. The terininals of static voltmeter. V, were shunted by this KlydonograPh. Switch S, was a concurrently acting combined hand driven knife switch for shunting three condensers, and S2 was the same type switch for connecting the condensers in series. S3 was the switch to supply some impulse. voltagetotheKlydonograPhwith･ , ･ 2.2 Klydonogrmph camera and photo film ･ This camera was required not only to kept light tight but also to have enough dielectric strength for high tension. To use the roll films, we took.

(3) Min. Potential of Lichtenberg Figures 23 off the photographing lens from a MALcAFLEx camera (Brownie reflex camera) which we happened to have fortunately. And in place of the removed lens we set an ebonite bushing screwed there. We scooped out the upper side in the shape of a cup to prevent this surface leakage. The ebonite bushing was screwed with a brass rod electrode (3 mm ip) through the half of the upper part. We made the lower end as a semi-sphere, and the other side had the terminal screwed for connecting a leading wire.- Details of this camera were shown in Fig. 2. We used a plate electrode with a Al-plate to hold the films of this camera for the rod electrode. Accordingly we set the other electrode on the body of the camera itself.. f /. fi. 2 ,l. t]･1'. -t tt. g-. llr -'. l'. s･. 3. 5:://g:tt;g/i･･. 64. rr. Fig. 2. Details of KlydohograPh camera.. Rebuilded from the MALcAFLEx. 1: High tension terminaL 2; Ebonite bushing. 3: Terminal for the other side. 4: Fuji X-ray indirect photographing films (l"luorograPlp). 5: Ring of lock nut for ebonite bushing. 6: Brass bar electrode (3 mm ￠).. 7: Peep window for number of films. 8: Al-plate for a plate electrode (6.0cmx6.0cm). 9: Wind up side for films.. ' We took a Brownie size roll (6.0cmx80cm) for 12 exposure of the Fuji X-ray indirect photographing film (FluorograPhy) on which we tried to apply the impulse voltage 24 times or more than that and get Lichtenberg figures. The reasons why we took this film were that it was suitable for the photo sensitive range to record Lichtenberg figures (it meant that the film could catch all phenomena exactly), and that we could get both figures, in it for this. experiment, and that moreover, no tax was paid for it.. 2.3 Procedure We set the Fuji X-ray indirect photographing Brownie roll film in the state of the rod electrode of Klydonograph camera raised by the handle of controling a focusing surface. We wound up'this film by the number in the.

(4) 24 B. ARAI '. peep window of back of the body and by several marks printed on the back･. paper of the film. After the film was set, the brass rod electrode which was lifted up was got down to the lowest position. By this operation, the part of semi-sphere in the rod electrode was in contaCft with the emulsion surface of. the film, and the camera was ready, Then we shunted it to both ends of R in Fig. 1. 0n the other hand we kept the switches S2, S, off and the combination switch Si on. Then we charged the parallel connection in three high tension condensers (Ci, C,, C3) with the hand driven Megger of 1 (kV). If we turned off Si and S2 here, these condensers were changed up in series and both sides of these condensers gave us about 3 (kV). So we used this for the source of impulse voltage circuit. We could measure this voltage by the static voltmeter V,. As this valtage was going down because of leakage of the circuit, we had to switch S, on, when V. showed the voltage which we wanted. At this time theimpulse voltage was supplied among both terminals of the KtydonograPh camera. Here crest voltage was given by V.,and the waves of the impulse voltage was able to be controled by the parallei resistance R.. In this experiment various V. were offered against constant R changing the positions on the films in a series. We gave the directed photographing treatment to them.. 3 Experimental Result and Discussion We kept the rod electrode in positive or negative polarity and got Lichtenberg figures one after another lowering the valtage little by･little. As the. figures were smaller comparatively we measured each maximum radius en-. 3.0 '･ '. -e-. i. s￠hFe-. g9ts. N Vb'. S zo N >o. scLSQ .ILWC)"b-. F--------O-------. H-----,--O-------l. F-----O-------. ,}ot. F------cFL----- g,%ese5. F---o----. -F--. va. y U v .9. Nq' I-O. 6. readiqs. ofmarktouchin3a 6areteetrode. O' 1.0 20 3.0 4.o･50 6.0 7･O ･ Max.radiusoffisures-[mml. Fig. 3. Relation between the crest voltage and the max. radius of both ,figures..

(5) Min. Potential of Lichtenberg Figures 25 larging five times as large as them. But about the size of each figure we observed some fiuctuations .compared with the higher crest voltage. The relation between these maximum radius of figures and the supplied crest voltage were shown in Fig. 3. Besides, the cases in which the negative polarity was tried were also shown in Fig. 3 tha' t the fluctuation of the negative figures were smaller than the positive one, and the typical figures in a. series were shown in Photo.1 and 2. The expanse of the negative figure was smal!er than of the positive one, but the density marked on the films was far. deeper than the latter. Fig.4 was the diagram explaining about this by comparing quantitatively by the microphotometer. As a result of these experiments we found that the threshold electrical potential was 1.4 (kV) where the positive figure's appeared or did not, and that the one of the negative figures was 1.2 (kV). Moreover, we found that the negative figures appeared at the lower voltage. Anyhow this fact suggested us that the figures would not appeare till it took certain potential and certain discontinuous work function required for the figures to be formed. And also it was suggested that the fact that there was some difference of the lowest voltage in the appearance of positive and negative figures was connected with the energy particles working to produce figures with the difference of the mechanism of the process producing figures. If you thought of the Lichtenberg figures as a record of corona discharged on the emulsion surface of the photo films, the figures should be thought as a record of the extending state of the pole brush corona from its electrode, or a mark of the direct actions of the charged particles, MtiLLER-HiLLEBRAND reported that in the atmospheric pressure the lowest voltage in which pole brush corona could appear was 2.5 (kV) in the use of the KlydonograPh2'. PRAEToRius described that he got 3.8 (kV) using the 1.4 (mm) thick of photo dry plate in the some conditions3).. ToEpLER`) gave us the following formulas which showed the relations betweeri the radius of figures of the pole brush corona R (cm) and the sup-. plied voltage V (kV):-. incaseofpositivefigures V=5.9R" . (1) in case of negative figures V=11.5R- (2) Those formulas suggested us that the ratio of expanses of the negative and positive pole brush corona was. V=5.9R+=11.5R-, R--/R+==5.9:11,5!Fl:2 (3) This was the phenomenon in the atmospheric pressure and the thickness of the photo dry plate was 1.6tv5.5 (mm). Also- ToEpLER gave us the foliowing formulas which showed the relations between the maximum length of the positive and negative pole brush corona R....(cm) and the thickness of the dielectric substance d (cm),. t.

(6) 26 ' B.Al<Al inpositivefigure Rm...'=8VEP (4) innegativefigure R....-==4.2V'an (5) f'. Combining these formulas, the voltage in which the positive and negative pole brush corona (V.+, Vp-') appeared was follows respectively,. V,+=47.2Va (6) V. -' =48.3Vd (7) V.=K'vid', :.V.oc'Vff (8) It was studied before that those formula's factors were changed by the kind of the dielectric substance, that is, the dielectric constant e. On the other hand it was known that the relations between the static capacity C of the dielectric substance and R.... were shown in the following formula.. V-. Rmax.=kp v"c- (9). Here kp was constant in the stage on the pole brush corona. With these phenomena in view, let us examine the fact that the figures were recorded at the lower voltage than that shown before in their experiments,. First of all we supposed that e of the photo dry plates and the photo films were in same order and the value was about 5rv9:5.5rv6. The chief difference was its thickness and that of the dry plate was O.13 (cm), while. the film was about O.O13 (cm). In the experiments the back paper of the Brownie films existed in the unequal electrical field. But as a result of measurement we found that its thickness O.O12 (cm) was nearly same as that of films. The e of the back paper was assumed to be in the same order as that of the glass or films. Namely, it was estimated 2rv2.5.. The decrease of this thickness d meanstheincrease of capacity C. From these formulas (4) to (9), the increase of C means the decrease of Rm.x.. But Rmax. or Vp is proportional to v!aT, From the fact we thought that the great. decrease of d (tvl/5) was the most dominant reason in these case. It was thought that even' the same Vp, gave longer Rmax, and even the lower Vp. gave R..... This fact suggested that the range of measurement was expanded not by･the photo dry plates, but by the thinner films,. We are going to measure E of the photo films and that of the back. papers, Apri1 27, 1964. Acknowledgements. The writer wishes to expresses his hearty thanks to Dr. T. AsAHiNA and. Dr. C. MAGoNo who made suggestions to him throughout this work. The writer also thanks Mr. M. TAKANo (the Research Laboratory of Fuji Photo Film Ltd.) and Mr. K. SAKAyANAGi for his cooperation in 'this research,.

(7) Min. Potential of Lichtenberg Figures. 27. References 1) B. ARAi: Japan. J. Appl. Phys. 30-3 (1961), 201.. B. ARAi: ``Low Pressure Klydonograph" (Japanese) Natural Science and Museums, 28 (1961) (=No. 3-4). B. ARAi: Science Reports of the Yokohama National 2) MULLER-HiLLEBRAND: Siemens Zeitschrift, 7 (1927), 3) G. PRAEToRius: Arch. Elektrotech. 34 (1940), 83. 4) M. ToEpLER: Ann. Physik. 53 (1917), 217.. Univ. Sec. 1-8 (1961), 547.. 1. 31..

(8) Plate I. CkV). CkV]. f.4. 2. 4 1･ 6. Mss. 1, g. 2. 6. uD N. 2. 0. Q ts.. 2. 8. Z2. D Q. Photo. 1. Series of posittve Lichtenberg figures with varlous crest voltage.. 1.

(9) Plate II. [kV]. [kV]. 1.2. Z2 1. 3. Z4. f. 4. t. 1. 6. `. 2. 6. 1. 8. Z8. zo. O5 tO. Cm m]. Photo. 2. Series of negatlve Lichtenberg figures with various crest voltage.. }. o. 1. 2. 3. 4 [m rn). O 2 4 6 8[mm]. ,. :. Fig. 4.. Diagram of comparing density of both figures by the microphotometer. Crest voltage: V.=1.6 [kV].. (upper: negative, lower: positive)..

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