Theory of EHD ion sources on PBFA II

Summary form only given. For an EHD (electrohydrodynamic) ion source to be successful on PBFA II (Particle Beam Fusion Accelerator II), there must be sufficient time for the EHD instability to produce an array of ion-emitting cusps before substantial electron loss to the anode. To estimate the emission time when the driving electric field has a finite risetime, an EHD ion emission code was written which allows a spectrum of unstable wavelengths to grow in a time-dependent electric field. The time-dependent electric field at the anode was obtained by numerical simulation using the 2.5-D electromagnetic PIC (particle-in-cell) code MAGIC. Unstable wavelengths between 0.07 and 7 μm were allowed to grow in the presence of the time-dependent electric field at the midplane. Conditions for ion emission were met for the 0.7-μm wavelength when the electric field achieved 10.5 MV/cm. In the MAGIC simulation, this field is achieved about 3 ns prior to electron loss to the anode