The ion cyclotron resonance heating and acceleration in a magnetic nozzle are performed in a fast-flowing plasma in the HITOP linear device in order to investigate an advanced space propulsion system. When radio-frequency (RF) waves are excited by a helically-wound antenna, plasma thermal energy W[perpendicular] and ion temperature drastically increase during the RF pulse. Thermal energy of the heated ion is converted its flow energy when the ions pass through a diverging magnetic nozzle. The plasma thermal energy changes so as to keep the magnetic moment constant. The exhaust plasma flow energy can be controlled by changing an input RF power only.