Fig. 4. An Applegate diagram for the photoklystron showing electron energy loss to the rf field over successive cycles. This is a plot of electron distance from the photocathode vs time for 10 electrons which leave the photocathode at equal time intervals and with 0 initial energy. ultimate quantum efficiency of 25%, we estimate an overall efficiency of about 10% under AMO solar illumination. Furthermore, we wish to emphasize that this is the first photoklystron ever built and no attempt has been made to optimize the design. III. THEORETICAL ANALYSIS Since the strongest modes were those not attributable to conventional reflex klystron theory, we initiated a program of computer simulation to attempt to understand these modes. This computer code models the instantaneous electric field within the photoklystron and plots the resulting electron trajectories vs time. Based on this, we found a set of allowed conditions under which electrons leaving the photocathode at certain times and with certain energies can undergo multiple oscillations between the grids losing energy to the rf electric field all the while. Some electrons eventually fall out of phase with the rf field, however, after about five such oscillations 90% of these electrons have hit the grids. Figure 4 illustrates such trajectory calculations. It is evident from these trajectory calculations that a selection process takes place. Electrons which take energy from the rf field on the first pass are quickly eliminated by collision with the cathode. The remaining electrons transfer a portion of their kinetic energy to the rf field over a period of several cycles. The heart of our present photoklystron theory is the condition that the “favorable” electrons stay in phase with the rf field. To illustrate how this is possible, we calculate the total time required for an electron to perform a single cycle. We define an electron cycle as the sum of the times required for two grid crossings and the two turnaround times. We then set the period of an electron cycle equal to an integral number of rf periods. We have:
RkJQdWJsaXNoZXIy MTU5NjU0Mg==