Long pulse electron beam extraction from a plasma edge cathode

Summary form only given. In the plasma edge cathode scheme, a nearly stationary plasma cathode is formed by partially intercepting a plasma jet with a material edge. By extracting a space-charge-limited flow of electrons in a direction transverse to the plasma flow behind the edge, gap closure can be avoided. An electron current density in excess of 100 A/cm² is theoretically possible from a plasma with density n=5×10¹³ cm^-3 and kT_e=1 eV. Experimental investigation of the plasma edge cathode has resulted in an achieved electron current density in excess of 20 A/cm² for several microseconds. Geometric gap spacings between 0.4 cm and 1.5 cm were typically used with closure rates of less than 0.1 cm/μs. The space-charge-limited behavior of the extracted current density was verified by varying the gap potential and spacing. A multipinhole imaging technique has been employed to infer the shape of the effective plasma boundary and to measure the intrinsic divergence of the electron beam. In addition, the electron temperature both in and downstream of the extraction region has been measured via a double Langmuir probe