Some questions about a simple high voltage circuit
This circuit is an example of a "boost" converter and usually has \$ R \$ missing or a small value so that you can measure the current.

This type of circuit is common in DC/DC converters where you want more output volts than input.  One very common use is in AC/DC switch mode power supplies to generate a 380V rail or similar while ensuring the input current follows the input voltage for power factor correction. A second converter then takes this to generate the required output voltage.

The switch is some kind of transistor, typically a N-channel MOSFET, and there are several switch mode control ICs you can use to control it.