Active Sintered Controlled Porosity Dispenser (CPD) Cathode A.K. Singh * , M. Ravi * , M.S. Bisht * , R.K. Barik * , S.K. Shukla * , R. Prajesh * , T.P. Singh * , S.K. Saini * , Ashish Kumar * , Rajesh Kumar * , and R.S. Raju * * CSIR-Central Electronics Engineering Research Institute, Pilani, INDIA Microwave Tubes Research Development Centre (MTRDC), Bangalore, INDIA E-mail: raju.ceeri@gmail.com Abstract—CPD cathode, made out of tungsten wire, using active sintering resulted in uniform and two-fold emission as compared to B-type cathode. Studies on wire diameter using MATLAB code suggests that 20 μm diameter provides optimum barium coverage. Detailed experimental results will be presented. A conventional dispenser cathode has an emitting button, made out of porous tungsten. The pores are distributed in random sizes and shapes across the surface. As a result the barium diffusion from bulk to the pore end and the subsequent migration into the inter-pore region are not uniform all across the surface, due to which the emission uniformity is affected. Figure 1. SEM image of CP pellet A cathode wherein the distribution and size of the pores can be directly controlled would represent a controlled porosity dispenser (CPD) cathode. One of the techniques to fabricate a CPD cathode pellet is by slicing a pellet out of sintered bunch of tungsten (W) wires [1]. A simple technique has been developed by us [2] to fabricate the pellet out of “activated sintered bunch of tungsten (W) wires”. In this approach the activation energy for sintering is lowered by an addition of a small amount of active material - thereby avoiding the need to reach elevated temperatures. A compression fixture has been designed and fabricated to carry out sintering operation under pressure. The fabrication of CPD cathode assembly, mainly, involved: (a) making bunch, out of bits of W-wire of diameter 50 μm and compressing under hot condition, (b) machining of bunch using wire cutting to obtain pellets, (c) vacuum firing of pellets to remove the excess active material, (d) impregnating the pellets with barium-calcium-aluminates in the ratio of 4:1:1, and (e) integration of the impregnated pellets with potted heater assembly using laser tagging. Figure 2. Pulsed I-V characteristics of CPD Cathode The SEM image the cathode pellet is shown in Fig. 1.The pores have a triangular geometry with hexagonal distribution 978-1-4799-5772-9/14/$31.00 ©2014 IEEE