In this paper, a continuous wave (CW) low-voltage fundamental harmonic W-band gyrotron has been designed and simulated with the help of a particle-in-cell (PIC) software CHIPIC. The output power of 33.4 kW with an electron efficiency 37.1% in the PIC simulation is obtained by the designed conventional gyrotron employing a 30-kV, 3-A electron beam which is produced by a triode magnetron injection gun. In addition, a high-power capacity collector being one of the key components of CW gyrotrons has been evaluated and tested. The peak power density on the collector wall using the spreading electron system is about 390 ${\rm W}/{\rm cm}^{2}$ in the hot test. The CW output power of 15.8 kW is achieved with the condition of a 29-kV, 1.8-A electron beam in the hot-test experiment of the designed prototype.