A control valve assembly for a downhole wellbore including a body formed partially from a magnetic material. A plunger is moveably mounted in the body. A portion of the plunger is formed from a magnetic material. A magnetic circuit having a gap is arranged within the control valve assembly. The portion of the body formed from a magnetic material defines a first portion of the magnetic circuit and the portion of the plunger formed from magnetic material forms another portion of the magnetic circuit. A solenoid is mounted at the body and is selectively activated to create a magnetic field across the gap in the magnetic circuit causing the plunger to move thereby narrowing the gap to produce a pressure pulse in the wellbore.