Modern way of ECR multicharged ion sources development is connected with increasing of microwave frequency up to tens of GHz. Millimeter wave gyrotrons are used now at a few laboratories. Traditional mirror magnetic traps with min B configuration for suppressing of MHD instabilities became too expensive because very strong magnetic field is needed. So prospection of axisymmetric plasma trap with MHD stabilization is a quite relevant subject of modern plasma physics. The simplest trap of such kind is CUSP one. The zero level of magnetic field in the center of the trap doesn't allow to achieve a good confinement in classical regime. In a gasdynamic regime of plasma confinement was studied. The same regime may be realized in the CUSP geometry trap if plasma density is high enough. A small CUSP trap was designed for plasma creation by 37,5 GHz gyrotron radiation under ECR conditions. Temporal evolutions of plasma parameter in experiments were quite smooth and stable. Experimental ion charge state distribution corresponds with calculated one for optimal plasma conditions.