The ion source for along pulse operating diagnostic neutral beam injector has been developed. The ion source has to form an 8 A, 60 keV hydrogen ion beam. The ion source consists of an RF-plasma driver and a four grids ion-optical system. Both ion-optical system and plasma driver have an augmented water-cooling system. Geometry of the ion-optical system was optimized by the numerical simulations in order to achieve the minimal beam angular divergence. The performance of the developed water-cooling system of the ion source was numerically simulated. Design of the developed ion source and experimental and numerical simulations results are presented in the paper.