We discussed the technical aspects and the start-up experiments of the KAIST tokamak. The original machine was the PRETEXT. It was recommissioned with the help of Fusion Research Center of The Univ. of Texas at Austin. Its basic design parameters are : $R_0=53 cm$, a=15 cm, $B_T=10 kG,\; I_p=60 kA,\; T_e=200 eV,\; n_e=10^{13} cm^{-3}$. Tokamak main body was constructed through the test of vacuum vessel and coils. The vacuum system for a ultra high vacuum was installed. A 2.2 kHz, 30 kW RF discharge cleaning power supply system was constructed for the removal of the impurities in the vacuum vessel. We obtained the $\sim10^{-7}$ Torr with the help of this system. The power crowbar system for the large current supply to the toroidal magnetic field coils was designed and built through the proper combinations of ignitrons, thyristors, and capacitors. In this configuration, we obtained 5 kG toroidal magnetic field. For the plasma production, simplified Ohmic heating circuit was constructed. Loop voltage and main pulse width can be varied easily through this scheme. A DC magnetic field control system for the additional poloidal magnetic field using IGBTs was developed for the plasma position control. We developed the diagnostic apparatus and techniques. The magnetic pickup coils, electrostatic probes, microwave interferometer, and spectroscopic apparatus were installed for the diagnosis of the tokamak plasma. Especially, we demonstrated the relation between the plasma flow velocity and the ion collections in Mach probes. We developed a 0-D code for the understanding of the physics of the start-up phase of the KAIST tokamak. The physical parameters were volume averaged quantities. The results showed that the influences of the energy confinement time, loop voltage, and impurity effect on the start-up phase. We performed the start-up experiments. They were performed by varying the hydrogen pressure, and the vertical magnetic field. We could get a 7 kA of plasma current, and pulse width of 8 ms maximum. Almost fully ionized plasma could be obtained in this condition. To achieve the design parameters of plasma current, more precise control of the plasma density and vertical magnetic field is required.
