I am having trouble coming up with a solution to a problem engineering a DC circuit that can take a single line input (Vin) and split into two outputs (Vout1 & Vout2). 

The goal of the circuit is to take a high voltage line and supply two parallel electrodes connected to Vout1 and Vout2. By changing the potentiometer setting (R1) one should be able to adjust |Vout1-Vout2| between 0-9V or 0-18V depending on the switch (SW1) settings. The circuit should be able to handle high voltage inputs (Vin: 0-4000 VDC, 1000 VDC typically). The electrodes are floating in ultrahigh vacuum.

The current circuit setup is shown below; however, this circuit does not perform as desired. 

![schematic](https://i.stack.imgur.com/fadAJ.png)

[simulate this circuit](/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2ffadAJ.png) – Schematic created using [CircuitLab](https://www.circuitlab.com/)

The current configuration allows one to change electrode voltages (Vout1 & Vout2) 0-9V or 0-18V by adjusting the potentiometer; however the potential difference between the two electrodes (|Vout1-Vout2|) is always constant (either 9V or 18V depending on SW1 settings). I would like to be able to use the potentiometer to "tune" one electrode relatively. For example, I might wish to use a 1000 VDC input voltage (Vin) and get output voltages of: Vout1= 1000 VDC, Vout2= 1005 VDC.

Does anyone know of a way to modify this circuit or adapt a simple design to implement this idea?