Gaw
The next step is to display the file produced by spice. The command used by ngspice is the 'write' command (i.e. write volt.raw v(1) v(2) v(3)). I use gaw Link to gaw, which is a gwave replacement. This viewer is used to display the nodes that were written with spice. Please see the documentation at the link location provided.
Please notice the classic voltage doubler wave form(s). All is well, so there is no need to change parameters and re-run. Notice the it did not double the voltage. This is due to the voltage drop across the diodes. About (~.64) volts each in the case of silicon.