The plasma density of a field reversed configuration (FRC) needs to be decreased below the present experimental regime in order to heat the plasma and sustain the configuration by a high energy neutral beam in an FRC reactor. However, as the plasma is produced in a linear vacuum vessel, there exists a severe breakdown limit at a low fill pressure as compared with a toroidal system. A method to form FRCs beyond the breakdown limit is proposed here. The preionized plasma is compressed by a strong bias field to enhance the plasma flow from the confinement region to the outside region and is then diluted before the start of the confinement field on the NUCTE device. The use of a diluted plasma enables the critical density of the FRC to be lowered from 1.1 × 1021 to 5.6 × 1020m-3 and the sum of the electron and ion temperatures to be increased from 0.35 to 0.81 keV.

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