The plasma density in ECR sources is limited by the cutoff plasma frequency, which prevents producing multicharged ions if one uses for plasma heating such low frequency microwaves as 2.45 GHz. In order to overcome this limitation a device consisting of two cavities located symmetrically in mirror regions was investigated. The ECR heating took place in the cavities and the plasma was accumulated in the zero microwave field space between the cavities. The cavities were fed with microwave power of 2.2 kW at 2.45 GHz. At an argon pressure of 0.04 mTorr, the plasma density of 2.4×1012 cm -3 in the central region of the trap was about 30 times higher than the cutoff value. A significant improvement in performance was found in comparison with the HELIOS-12. The expression for the lifetime of ions trapped into an electrostatic pit was defined. The charge state distributions both for the plasma and the extracted ion beam was calculated.