The two diodes are connected back-to-back to simulate a diac (the diac device is not available on everycircuit).
The current through the 10 Ohm load resistor shows the positive and negative half-cycle current spikes similar to those produced in diac circuits.
These 'spikes' can be used to trigger devices such as the Thyristor.
By adjusting the values of the 6 Ohm resistor and the 300uF capacitor the 'diac' spike angle can be adjusted.
Waveforms:
Orange = AC supply Voltage
Blue = Phase Shifted 'Diac' Voltage
Green = 'Diac' output current
