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Title Secondary Mechanism in Townsend Discharge Domain Sub Title Secondary mechanism in townsend discharge domain Sub Title Author 森, 為可(Mori, Tameyoshi) Publisher 慶應義塾大学藤原記念工学部 Publication year 1956 Jtitle Proceedings of the Fujihara Memorial Faculty of Engineering Keio University Vol.9, No.34 (1956. ) ,p.70(8)- 80(18) Abstract In the previous report, the author studied the relation between Townsend's and Streamer discharge domain and proved the fact that the both discharge domains are decided by the magnitudes of p(pressure), l(gap length) and Δ(overvoltage ratio). In this report, moreover, the author proceeds to the analysis of Townsend discharge domain itself, makes clear that Townsend's discharge domain is classified into two domains which are quite different in the secondary mechanism generally called γ mechanism by the measurement of the spark discharge formation time: i, e, the domain dominant γi action (the action of the electron emission caused by the collision of positive ions against the surface of the cathode as the secondary mechanism of the discharge), and the domain γp action (the action by the radiation of photons which are produced by the ionization or the excitation action of electrons). Notes Genre Departmental Bulletin Paper URL http://koara.lib.keio.ac.jp/xoonips/modules/xoonips/detail.php?koara_id=KO50001004-00090034 -0008 Powered by TCPDF (www.tcpdf.org) Secondary Mechanism in Townsend Discharge Domain. (Received November 15, 1956) by Tameyoshi MORI* Abstract In the previous report, the author studied the relation between Townsend's and Streamer discharge domain and proved the fact that the both discharge domains are decided by the magnitudes of p(pressure), l(gap length) and .:1 ( overvoltage ratio). In this report, moreover, the author proceeds to the analysis of Townsend discharge domain itself, makes clear that Townsend's discharge domain is classified into two domains which are quite different in the ~econdary mecha­ nism generally called 'Y mechanism by the measurement of the spark discharge formation time: i, e, the domain dominant 'Yi action (the action of the electron emission caused by the collision of positive ions against the surface of the cath­ ode as the secondary mechanism of the discharge), and the domain r 1) action (the action by the radiation of photons which are produced by the ionization or the excitation action of electrons). I. Introduction The original Townsend Spark Discharge Thory, that illustrated the ionization by collision (a action) of the electrons in a gas as the main mechanism and the ionization action by collision (/3 action) of the positive ions in a gas as the sec­ ondary mechanism, is obliged to be revised from the view points of the ionizing energy, the mobility, and the formative time lag of the positive ions. And, as the secondary mechanism an idea is adopted that the action of the electron emmission is caused by the collision of the positive ions against the surface of the cathode (r; action), and by the radiation of photons which are produced by the ionization or the excitation action of the electrons (rp action). In this secondary mechanism** (named r action generally) on the surface of the cathode takes an important role in the spark discharge formation, then a number of electron avalanches are necessary within the spark discharge formative time, for it is necessary for the discharge formation to be maintained by the continuous electron avalanches from the cathode. * ~ ~ PJ : As:;istant professor at Keio University ** In addition an electron emission action caused by the metastable atoms Crm action) is noticed, however, it is less important in the present study of the author judging from the difference between the a:bove spark discharge formative time and the velocity of the metastable atom. Therefore, in this report r action iS limitted to both r p action and t·i action. ( 8) Secondary Mechanism in Townsend Discoarge Domain 71 The theory that thus the spark discharge formation is accomplished by a number of electron avalanches, resembles the original Townsend Thory, though at present it takes 'Y action in place of fJ action. For this reason at present the spark discharge theory including a numder of electron avalanches from cathode is generally called Townsend Theory, and the domain of spark discharge condition applied to such a mechanism is called Townsend mechanism domain or Townsend discharge domain. On the contrary, when a satisfactory space charge electric field is produced by a single electron avalanches and spark discharge occured suddenly, it is hard to consider th;1t the secondary mechanism has any influence on this phenomenon. It is reasonable to consider this domain as streamer Theory domain which adopts a photo-ionization action in gas. In the previous report Cl) the author studied such relations between Townsend discharge domain and Streamer discharge domain with the analysis of discharge voltage wave-form and the calculation of discharge energy, and proved the fact that the discharge mechanism is affected by the magnitude of pressure p (mmHg), gap length l (em), and overvoltage ratio A (%). In this report, moreover, the author will proceed to the analysis of Townsend discharge domain itself, and will make clear the relation between two domains which are mainly represented by 'Yt mechanism and 'Y11 mechanism respectively from the measurment of spark discharge formation time principally, i. e. it is explained that in the air bordering p l (few mmHg em) and A (few %) corresponding the vicinity of p l of the minimum spark discharge voltage, 'Yt domain is at lower p, /,A, and the breakdown of 'Yv mechanism domain is at higher p, l, L1. II. Theory When a voltage V higher than static bre~k down voltage Vs is applied to the electrodes impulsively, the time from voltage application to voltage-sudden drop, i. e. (i) statistical time lag Ts which is dependent on the existence of the originally­ present electron useful to the spark discharge formation. (ii) formative time lag Tr. i. e. the time that the present electron takes in ac- complishing the spark discharge by the effect of the electric field. That is, T!l = Ts + T1 (1) hL7fil,.. __ Within the time lag 11 the electric field of space charge of electron avalanches grows up to a satis­ _j--Tg---, factory value and supperposing with the applied --t electric field promote the ionization action all over Fig. 1. Voltage wave-form of the the gap with acceleration and finally the figure of electric discharge. the discharge advance is changed abruptly. 1) Tameyoshi Mori:].I.E.E.J. Vol. 2 No.2 P. 54, (1956): J.I.E.E.J. (Home Edition) Vol. 75, P. 1156 (1955) (9) 72 Tameyoshi MORI Briefly speaking, formative time lag T1 is the advancing time of electron ava­ lanche, and at the end of the formative time lag it is considered that the streamer begins to start at high p, 1, J, condition. On the other hand, at low p, 1, L1, condition glow discharge is observed. The formative time lag condition in the streamer discharge domain is in principle as follows: Applied electric field = space charge electric field. This was refered to in the previous report 1). In the Townsend discharge domain it is presumed that " the discharge current grows up to the degree of glow discharge current," and then "the density ncs of the electrons and positive ions just before the surface of the 10 3 positive plate increases to nearly 10 (number /cm ), the level of the density of glow discharge." Tracing back to the negative plate, if the number of the emitted electrons (Nos) from it is considered, it will be Nos= j ncsdvfexp. a!::::10 4--101:i v Now, the basis of the calculation of NuJ can be explained as follows : If the space occupied by positive ions from a single electron avalanchel shows a spheric at its top like the case of the calculations of Meek or Reather, and if multi- electron avalanches occur at the same point, the equation V= j_7t;3 3 2 L=l ;= v' 6D{:. =~./0.4~~< ) v_ are presented. When calculated with the assumption of the uniformity of the ion density among v, Nus is showed as in diagram 1 (J=2.5%). p/(mmHgcm) t_ (sec) I r (em) v ( cm3) [ al erxl I Nos ; 1 1.3x1o-s 0.316 o 132 1 5. n 299 I 4.7x106 I I 1.8x1o-s 1 2.5 0.200 I o. 0335 6. 87 955 I 2.5 X 105 5 [2.1 x 1o-s[ o. 141 ! 2981 I 3.4xl04 i ~~~~~---~~-- 8.00 ----------- Diagram 1. Calcu]ation of Nos (Ll=2.5%) From this point of view, the formative time lag T1 under both "'t and 'Yv mecha­ nisms, can be calculated as follows. If an electron Nu=l emitted from the negative plate at the begining (Fig.1. t= Ts) grows to Nos right after the formative time lag (Fig. 1. Tg= Ts+ T1 ) with the contin- · uance of n times of electron avalanches, the following relation can be obtained. (10) Secondary Mechanism in Townsend Discharge Domain 73 Cry( ea,t-1 )J" ~ rynenU,t =Nus (2) n= (o_gNas_ log(ryea.l) (3) If L and t+ are the transit times of the electrons and postive ions respectively between electrodes, the im1ization process time accompanied by a single electron avalanche containing secondary mechanism is for "'t action L+t+~t+ for y v action L (neglecting the transit time of photon) Hence, the formative time lag can be explained as follow. for "'t action Trt=nt+ (4a) for "tv action Trv=nL (4b) The transit time in these eqs. is explained as l L=-­ v_ (5) And the direction velocities v_ and v+ of electrons and positive- ions in eqs.
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