TRAVELING WAVE TUBE FOR 6,000-MC RADIO RELAY 



1297 



at a later stage, an alignment cylinder is included in the gun at the time 

 of glazing (outer cathode alignment cylinder in Fig. 8) . When the gun is 

 ready to receive the cathode, the subassembly shown in Fig. 9 is slid 

 into the outer alignment cylinder. The cathode to beam forming electrode 

 spacing is set using a toolmakers microscope, and welds are made be- 

 tween the inner and outer aligmnent cylinders. 



Initially, we thought that the cathode should l)e completely shielded 

 from the magnetic field, and that the field should be introduced in the 

 region between the accelerator and the point at which the beam would 

 reach its minimum diameter in the absence of magnetic field. This ar- 



// 



/ra=l9i 



/ / 



/ / 



ACCELERATOR ; / > 



y//////////////////////////////^///^//y 



CATHODE 



\er r^ =192 >j 



(COATED DIAMETER) 



Fig. 7 — The electricall.y significant contours of the M1789 gun. All dimensions 

 are in mils. These contours were determined using an electrolytic tank and follow- 

 ing the procedure originated by Pierce. The measured potential at the beam boun- 

 dary in the tank was made to match the calculated value within ±j per cent of 

 the accelerator voltage to within 10 mils of the anode plane. The aperture in the 

 accelerator was made sufficiently large so that substantially no beam current is 

 intercepted on it. The significant parameters of this gun are: 



P = 0.3 X 10-« amps/volts3/2 rel<y 



fc/l-a =2.30 tr 



e = 12.67° 7-95 



VvIrFk = lM{Tk = 720°C) J 



= 3.50 lAt the beam mini- 

 = 4.80 mils [mum in absence of 

 = 20.5 milsj magnetic field 

 = 213 ma/cm2 



