My half wave rectifier graphic is wrong
From memory, the GK junction of an SCR, in reverse mode, acts as a Zener diode of 7V or so (much like the BE junction of a transistor). A current flows through RL, this GK zener diode, and R1, creating the voltage across RL observed. The zener thresold explains why there are two periods with almost no current during a cycle.

If that effect is undesirable, inserting a diode in series with R1 (cathode connected to G, anode to R1) should reduce it (but the SCR will turn on a little later).