1960 Mancebo: The Livermore Multibeam Cathode-Ray Tube 555

For n =odd, 11 -I2, so that E0= 0, i.e., odd harmonics i.e., the circuit does not function without bias. For*are not detected. For n=even, a-->0, i.e., R>>r,

ao/2 Eo=E-s CSfX(2Io = l 2 E Esn cos (nwt - 0') a E8COcos) (12)

27rrJ-a/2 n even a-0 n even

- Io(R + 2Ro)] dt,, For a= 90', second-harmonic signal with distortioni,4 Es nr

so that, as before, for Ro-c>x, = - s sin cOs9n2 where n = 2, 4, 690o 7r n 4

2 En na0 =- n

sin coseve () Assume that the signal is phased for maximunm output,

=..0)=. Then,For a=1800, i.e., C=0 e., 42

Eo = 2 sin cos kn = 0, Eo= 2 -/COS 06+- COS -'* (13)180° 7r n even n 2 9o -c 3 5

The Livermore Multibeam Cathode-Ray Tube*LLOYD MANCEBOt

INTRODUCTION THEORY

,f< ATHODE-RAY tubes with dual guns are com- The Common Focusing and Deflection Systemmon, and a few special purpose tubes, with as A single lens with low aberrations and little bulk hasmany as ten guns, are commercially available. been described by Schagen, et al.' The lens is essen-

Still, for shockwave studies, in which a hundred signals tially two concentric spheres, but since the image pro-are compared, a cathode-ray tube with many more guns duced by this system is virtual a small hole is providedis desirable. But a tube of formidable dimensions is pro- i I

in the smaller sphere (anode). In this lens, as adaptedduced when forty or fifty of the standard commercial in our tube, an electron emitted at the cathode dishguns, each with its own focusing and deflection systems, arrives at the anode and passes through the hole. As itare stacked side bv side. Scaling a standard gun to a

passes through, it experiences the divergent lens effectdiminutive size is also impractical because of the at- pt of the aperture and crosses through a point slightly be-

incrastredufcuty of maictrontbeainingtechi,ani tol- yond the geometrical center. All the beams from theelectron injectors, which are located along a segmiieniterances. Actually, all that is required for shockwave of the cathode dish, pass through this crossover point,

studies is a bar graph display with an on-off, time-s it is here that the deflection plates have been located.dependent trace. In the actual tube only that portion of the cathode

From these considerations evolved a common,In th acua tue'fl htprino h ahdFrom these considerations evolved a common,~~dish radially opposite the anode hole iS useful, but re-

spherical lens system that focuses the beams from mul- ming the unuse tiodi he sercl feltiple injectors and affords a common crossover point Neve lsthe fiedportion dbstorts the spherical field.

permitting a single pair of deflection plates to sweep all ofvfield-shaping felectd betweethe cathod dishnf tii h,qmzAtI)Anf ilzll ITIC! I-1CO-111 of field-shaping electrodes between the cathode dishof the beams. A tube of reasonable size was possible, n h nd.Ti lcrd ofgrto sda

only~.afe tehiqe weredevlope tht alowe th grammed in Fig. 1. The electrode voltages can be veryfabrication of a miniature, grid-controlled electron in- coeydtrie natn ihawdesae

jector. ~~~~~~~~~~~~electrolyte.* Received by the PGI, May 3, 1960. Presented at the Fourth

IRE Instrumentation Conference, Atlanta, Ga., November 9-11,1959. The work was done under the auspices of the Atomic EnergyCommission. 1 p. Schagen, H. Bruining, and J. C. Francken, "A simple elec-

t Lawrence Radiation Lab., University of Californlia, Livermore, trostatic electron-optical system with only one voltage," PhilipsCalif. Res. Repts., vol. 7, pp. 119-130; April, 1952.

356 IRE TRANSACTIONS ON INSTRUMENTATION December

The Injectors CATHODE DISHAn injector in this tube is an indirectly heated elec-

tron emitter spaced behind an aperture in the grid can. BEAM TRACEIt is mounted on the outside of the cathode dish byspot welding the grid can to the dish. This permits thegrids to be electrically grounded through a low com-mon impedance, thereby shielding the individual cath- PHOSPHOR SCREEN

odes and decreasing the cross talk. The cathode-to-grid FIELECTRODESspacinig is large (0.020 inch rather thani the more usual FOCUSING ANODE DEFLECTION PLATES0.005 inch) to insure a good mechanical tolerance in Fig. 1-Configuration of electrodes.such a small assembly and to provide a good cutoffcharacteristic. The aperture in the grid can focuses theelectron beami approximately 1/10 inch iniside thecathode dish radius. It is this crossover that the lensfocuses on the screen. Because these electronis at thecathode dish have such small components of velocitytangential to the cathode dish, the circle of confusionon the screen is small, despite their high energy.

DESIGN

Description of the TubeThe tube (Fig. 1) consists of a vacuum envelope, 39

electron injectors, a set of field-forming electrodeswithin a spherical lens, a pair of horizontal deflectionplates, and a phosphorescent screen. It is 24 inchesover all, and has a maximum diameter (that of thescreen) of 9 inches. The total weight is about 100 Fig. 2-Assembled tube on test stand.pounds. Fig. 2 is a picture of the assembled tube on atest stand.

The EnvelopeThe vacuum envelope is glass and Kovar assembled

with demountable steel flanges and copper gaskets to Lpermit disassembly without extensive rebuilding. In thefuture, these flanges may be eliminated to reduce thesize and weight.

The ScreenP-11 (zinc sulfide with a silver activator) settled Fig. 3-Actual construction of the lens.

phosphor forms the screen. The first screen employedwas an evaporated P-5 (calcium tungstate) phosphorthat had better resolution and less halation than theP-11. The settled phosphor, however, has a greaterluminescent efficiency. An aluminum film, approxi-mately IOOOA thick, was evaporated over the phosphorto prevent electron sticking and to complete the shield-ing for the field-free region between the focusing anodeand the screen.

The Lens SystemThe actual construction of the lens is shown in cross

section in Fig. 3. A photograph of the lens and mountedelectron injectors, before enveloping, is presented inFig. 4. The anode and the cathode dish radii are 1 and8 inches, respectively. The hole in the anode is ap-proximately 4 inch in diameter, and is located 10.6 Fig. 4-Lens and electron injectors before enveloping.

1960 Mancebo: The Livermore Multibeam Cathode-Ray Tube 357

-----GRID CAN

------CATHODEGRID CATHODE

INSULATOR

0L X HEATER

Fig. 6-Components of electron injector.

HEATER LEAD SUPPLY

W 1 u | , SuKs ~~~~~~~~~~~~~~~~~~~~~~~-rMCONTRO ln n v- - 1 1L r -- ---1

INSULATOR- j A 7t 7\IOElO_t § U CA->OOt ~~~~~~~~~~~~~~TOS9 O;.=21 l SUPPLIES

HEATER LEADS SlO CATOE i O 0

Fig. 5-Cross section of electron inijector.TOW TO CT]DS < SWEEP

- I - _

inches from the screen. The injectors are mounited LThJ s SYNCradially oni A--inch centers along a 4-inch segmeiit ofthe cathode dish. Fig. 7-Schematic diagram of tube ani(d associate(1 eqoipmeit.

i'he InjectorsT.eelectro.iiiectorsareoil 1 iiicli inleithe trace is proportional to the duration of the event,The electron injectors arc only 2 inch i1 length and anld is measured witlh timiie marks superinmposed on the

0.110 inchi in diamiieter. The assembly is sketched in trace. The tube can be used in one-shot, on-off ap-Fig. 5, and the actual components are shown beside the plications or it can be electrically or meclhanicallycompleted injector in Fig. 6. The emitting surface is abarium-stronitium-calcium oxide. It is indirectly heated The cathode heaters are operate in parallel at 5withi a bifilar winding of 3-mi tungsten wire spray volts, and draw a total current of 15 amperes. Thecoated with 2 mils of RCA Alundum for insulationi. The cathode bias, approximately 1 volt, is adjusted for eachalumina insulators are cast in carbon molds, and thenickel cathode and grid are electroform1ed. The focall gun1 so that each trace is equally bright on the screeniiickel cathoe aA sweep length of 8 inches requires that a push-pulllength of the aperture is approximately 0.100 inch, sawtooth of 2 kv be applied to the deflection plates.neglecting space-charge effects. In future tubes, the The deflection sensitivity is approximately 500 voltscathode emission surface will be made concave, to in- per inch. The anode voltage is 10 kv An astigmatismcrease the beaim current and to prefocus the electrons in correction is applied in the direct-current positioningthe gun. The beam current in the present model is circuitapproximately 5 microamperes.

Presentation QualityPERFORMANCEC The lens system yields a trace with extremely good

Operation depth of focus with minor aberrations, a small pin cush-The start of an event to be measured triggers the ion distortion being the most prominent. Fig. 8 is a

sweep generator and turns on the beams. (Fig. 7 is a photograph of the raster with a square pulse appliedschematic of the external test circuitry.) Some time to one of the guns (see arrow). This picture shows alater, a positive pulse, applied to the cathode of the time resolution of one part in a thousand or 0.1 perindividual injector, shuts off the trace. The length of cent. The spot size is 0.015 inch.

358 IRE TRANSACTIONS ON INSTRUMENTATION December

Exploding Gas ExperimentThe tube and the attendant circuitry were tested

with an exploding gas contained in a cylindricalchamber. A cross section of the chamber and the cir-cuit for the middle pin is shown schematically in Fig. 9.Each of the other pins was similarly tied to an injectorbut not to the gate-time mark generator. A sparkignited a mixture of oxygen and propane and a com-

Fig. 8--Tube raster with a square pulse applied to one gun. One pression wave was generated by the burning gas. Thetrace is interrupted at the arrow for about 5X10-8 sec. expanding wave front pressed an aluminum foil against

NOTE; the row of projecting pins, thereby grounding them.EACH ELECTRON GUN The center pin, slightly longer than the rest, acted as

the sweep and time mark generator trigger. As succes-sive pins were grounded, the corresponding guns were

. =_VOL-TAGE / turned off. A typical raster photographed in this ex-periment is shown in Fig. 10.

[3ULEE]--- \ It,_O_IMFD. DISCUSSION

This tube, although designed for shockwave diag-EXPLODING 150 ~~~~~~nostic work, will finid applicationi in any field where

. _ Afi; _ amplitudes can be presented as time durations. Forexample, the simultaneous monitoring of temperatures

ALUMINUMxJ7IL----/ (in engines, chemical reactions, or furnaces); rates ofOGTE-TIM _SWEEP flow (in pipes or over aerodynamic surfaces); mechan-MARK GEN GEN ical strains (induced by motion or under dynamic

Fig. 9-Cross section of exploding gas chamber loading); and complex wave functions (in pretunedand circuit for middle pin. filters or cavities). A bar graph display and good resolu-

tion make the tube a valuable tool in many fields ofresearch.

ACKNOWLEDGMENTThe author wishes to acknowledge the skills and

patience of the technicians who constructed and testedthe tube: D. Stewart, W. Tindall and A. Maddux. IHealso wishes to thank H. M. Owren for his ideas andencouragement, and E. Sikorsky, for his design of thetest circuitry. This report was prepared by G. A.

Fig. 10-Raster from exploding gas experiment. Leavitt.