Ivconic, welcome!
Some considerations: the 555-oscillator requires work with voltage regulator. I think 8 volts is fine. So, two 9 V alkaline batteries needed for mantain large time in operation.
Now the transistor is connected to 18 V, no in regulator part for to prevent inestabilities.
Also replace the common 555 by 7555 wich drain less current. Cx is for calculate the desire frequency, believe 100 between 400 Hz is good. The key command another diode for detect positive ions. Dish polarizate negative = attract positive ions. Dish polarizate positive = attract negative ions. The batteries must be independent to this stage of the sensor-amplifier stage.
Any idea? Is correct this?