i tried to simulate the circuit but it says unknown subcircuit as seen in the attached photo

 

You have a symbol on your schematic labeled VR1 which calls out a subcircuit file for a potentiometer. Unfortunately your system does not have a potentiometer subcircuit where it is expected to be. Since I can't be there to look over your shoulder I can't easily tell you where to look for one.

One problem that does come up is custom symbols with hard coded paths to the subcircuit. When you move them to another machine the hard coded paths become invalid. If you post your schematic file (.asc) to your message I will try to debug it for you, and give you back something that is machine independent.

 

If you're on Win10 then LTspice looks for its files, by default, in your Documents path.

 

i tried to simulate the circuit but it says unknown subcircuit as seen in the attached photo
View attachment 255902

Since you are using a pot configured as a variable resistor, you could use an ordinary resistor for VR1 instead, then substitute a stepped parameter as the value of VR1. That is the functionality a standard LTspice potentiometer would provide anyway.

 

Also, the circuit is useless without the part number of the Mosfet to see how only one with "typical" specs works.
The important pulse voltage is not shown.

 

Also, the circuit is useless without the part number of the Mosfet to see how only one with "typical" specs works.
The important pulse voltage is not shown.

YAGBATS - Yet Another Ghosting By A TS