Dutt, P K

English

IACS Institutional Repository

1A  DEMOUNTABLE A LL M ETAL HOT-CATHODE VACUUM IONISATION G A U G E*Hy p . k . d u t tiNsTirt^ Tiv OK Nrn.KAK Pn\su\% Calcutta T vivkilsitv 92, riM'KK ClKCULVU RoU>, CALCUTTA\KeccivCii for Dccnubo 7, 195,3)ABSTRACT An all nietal dciiiountalik* hot-cathode vacuum ion-gauge has been c'UTstructcd whose filaincnt can l>e ('liaiigc 1 any nunibei of tinu's \vi<^ hout a change in the operational charaeterisfies The eliaraeteristie curves of the gauge have been given. vSome points towards the constructional improvements have been discussed wliich might account for better seii.sitiveiiessA hot-catliode deinountahlc type sturdy metal ion-gauge lias been developed, the filament of which can be changed within a short time any number of times aftei it is [loisoned or burnt out, without a change in the characteristics of the gauge oiieration. This gauge has been constructed out of the materials readily available in the laboratory store. Though not so sensitive like the modern glass envelope tyfies, it is suitable particularly for a dynamic metal vacuum system. It is well known that the greatest disadvantage for a hot-catliode ion-gauge is the life of the cathode. The cathode is likely to be poisoned, if not destroyed by gases like oxygen and hydro-carbon vapours, etc., (I)usliman, iqiq) which are very difficult to get rid of in a vacuum system ; many vacuum operations necessitate the intro­duction of air from time to time, each time the ion-gauge lias to be re­exhausted and the gases absorbed by the electrodes wliilo in presence of air have to be removed, which is usually done by increasing the electron emission from the cathode more than the normal rating for a little time. This also causes shortening of the cathode life.The average life of each filaincnt used in this gauge is of llic order of that of the tungsten filament of the commercial type ion-gauges with glass envelopes, e. g. R. C. A. 1950. So, economically it has one advantage over the commercial type, whose filament, if once loses its emissive properties has to be rejected permanently.Attempts have been made to incorporate the desirable features found in the previous designs (Buckley, 19 16 ; Dushtnan and Found, 1921 ; Morse & Bowie, i940j, e. g. reliability, high insulation for the ion-col lector, long filament life etc.The gauge envelope has been represented pictorially in figure i and figure 2 shows the photograph to the filament and the grid-structure.*  ConmnimVated b\ Prof. IT I). Nag.P. K . DuttIm(1. It)emountable All Metal Hot-Cathode Vacuum Gauge 3P. K . Duti'Hi. 1F ig . 2dem ou n tab le  A ll M etal H ot-C athode Vacuum  G auge 3V ia .  3P. K. Datt©s.1 mCOLLECTOJ^ .F k ;. tF ig . 5Demoantable A ll Meial Hot-Cathodc Vacuum GaugeF i g . 7The construction of the gauge can be understood from figure 3. The gauge body is made of brass. The portions A and B which are originally attached to each other when in operation with the Neoprene gasket 0  and nut bolts through the flanges X  and V can be separated whenever it is required to change the filament. Alignment between them during each assembly, is done by an 'index’ mark and the aligningP . K . Duttbusli W. Thu ^>auge is conneclfd to the vacuum system with the flange Z. The structures of tlie plate C, grid D and the filament have been shown separately in figure 4.The filament / is a 6 mil. tungsten wire, 2 inch in length, coiled on a 50 mil. mandrel, the coil length being about 3/4th inch- The two ends of the filament are spot-welded (via nickel medium) with two short tungsten wires a, h of 40 mil. diameter wdiich are inserted into two small brass-holders c, d and held by set screw’s. The \1pp2r holder c is brazed to the40 mil. tungsten wire support .s of the filament structure and the lower one d IS clamped to the terminal of the Kovar-glass seal o, soldered to the metal flange X . For a cliange of the filament the unit a h f  can be takenout as a whole by loosening the screws on c d and a new unit can be put in.For normal of)cration, as shown in the calibration curve (figure 5), the filament re<iuires about 3,0 amps, of current at 6 5 volts.The grid ^ is a ic) turn spiral of 15 mil. molybdenum wire (wound on a i  inch, cylindrical mandrel), liacli turn of the spiral being spot-welded to the two supporting .40 mil. nickel wires. The nickel wires were again spot-welded to the Kovar-glass seal terminals p  and q on the metal flange X . The coil length of the grid spiral was ijj inch and the relative distance between each turn of the spiral was i inch.The ion collector /, was a hollow silver cylinder 6 mil. thick, l i  inch, in length, its inside diameter being 1 inch. It was suppoiteci by a Geiman silver wire r bo mil. thick lead in through the Kovar-glav^ s^ seal F, as shown in figure 3, soldered to the gauge metal wall.In the present design outgassing of the electrodes was difficult, and required longer time than that required for the commercial types of gauges, e.g., RCA 1050, complete outgassing being hardly possible. The only means of degassing the plate and grid structures in this i)re.senl gauge is by electron boiii bard men t. Moreover, the inner wall of the metal gauge-body was a constant source of gassing. vSo another metal demountable type of gauge with a glass envelope round the inner wall of the gauge l>ody to minimize the metal surface exposed to the oiicration as far as possible, has been designed. It has a thin ion collecting electrode made of nickel, and the grid structure is helical ; provision has been made to he.d the giid to sufficient teniperatuie for better outgassing by passing current through it.With ‘ TCxternal Contror’ type circuit arrangement the observed characteristic curves have been given in figures 5, 6, and 7.For comparison, the characteristics of a commercial type ion-gauge with glass envelope, RCA 1950 are given along with it. in figure 8, taken fioni the R C A  Tube Manual—9205—6818.Kelly (1950) has described an all metal ion-gauge, on which he has used water coils for cooling the gauge body. In this present gauge no such cooling device has been used, as it was thought that it would make it complicated and inconvenient to use. The gauge, though worked at atcMiipeiature z to 3°C higlior than tlu- room temperature due to the heat dissipated from the filament and tlie othei electrodes, gave consistent readingsDemountable All Metal Hot-Cathode Vacuum Gauge 7CALtaeAT/ON Ci//?\f£S fa g  6AU6E fC A .  f 9SO.when compared and calibrated against the gauge KCA 1050. on different occasions under different conditions for a pressure range of i x lo ’  mm. to 8 X io“ “ mill. Hg.It can conveniently be used for hunting leaks without any great care for the safety of the filament, as it can be replaced readily and easily without dismantling the gauge envelope. The gauge has been tested on the vacuum sy.stem of the 38 inch cyclotron of the Institute of Nuclear Physics, Calcutta University. It has the added advantage that it has practically no r.f. pick up from the cyclotron oscillator without any extra shieldingarrangement.8 P, K. DuttA C K N 0  W Iv E 1) G M E N T SThe author js indebted to Prof. M . N . Saha, P . R . S ., D irector of the Institute of N uclear P h ysics, C alcutta U n iversity  for his kind interest and encouragem ent in the work and wishes to thank P rof. B . D. N ag for help fu l su ggestion s and guidance.R F E R E N C EHuckley. 0 . E. igi6, Proc Nat. Acad. Sci V. S 2, 683.Du,simian, S. ‘ Scientitic foundation of Wacuurn Terhnitiue”, John Wiley Hi vSons.Inc, New York, p p 344Dushman, vS and C (J., ig.y, Pliya. krv.  ^ 17, 7.Kelly, F, M. 1950, Rev Sci. Jnstr , 21, 675.Morse, k. S and Rowie R. M. 1040, Rev. Sci, Jnstt.y 11, qi.

A Demountable All Metal Hot-Cathode Vacuum Ionisation Gauge

http://arxiv.iacs.res.in:8080/jspui/bitstream/10821/1798/1/A%20demountable%20a%20ll%20m%20etal%20hot-cathode%20vacuum%20ionisation%20gauge_P%20K%20dutt.pdf

A Demountable All Metal Hot-Cathode Vacuum Ionisation Gauge

Abstract

Similar works

Full text

Available Versions

IACS Institutional Repository