The negatively charged Nitrogen-Vacancy (NV) center in diamond is one of the most versatile and robust quantum sensors suitable for quantum technologies, including magnetic field and temperature sensors. For precision sensing applications, densely packed NV centers within a small volume are preferable due to benefiting from 1/ sensitivity enhancement ( is the number of sensing NV centers) and efficient excitation of NV centers. However, methods for quickly and efficiently forming high concentrations of NV centers are in the development stage. We report an efficient method for creating high-density NV centers production from a relatively low nitrogen concentration based on high-energy photons generated from Ar plasma source. This study was done on type-IIa, single crystal, chemical vapor deposition (CVD)-grown diamond substrates with an as-grown nitrogen concentration of 1 × 10 cm. We created high NV density (~20,000 NVs over the diffraction limited sample volume) distributed homogeneously over 150–200 μm deep from the diamond surface. The plasma-created NVs in CVD diamond have a spin-lattice relaxation time (T) of 5 ms and a spin-spin coherence time (T) of 4 μs. We measure a DC magnetic field sensitivity of ∼104 nT Hz, an AC magnetic field sensitivity of ∼0.12 pT Hz and demonstrate real-time magnetic field sensing at a rate over 10 mT s using the diffraction limited sample volume.