A space-charge-neutralizing plasma for beam drift compression

Simultaneous radial focusing and longitudinal compression of intense ion beams are being studied to heat matter to the warm dense matter, or strongly coupled plasma regime. Higher compression ratios can be achieved if the beam compression takes place in a plasma-filled drift region in which the space-charge forces of the ion beam are neutralized. Recently, a system of four cathodic arc plasma sources has been fabricated and the axial plasma density has been measured. A movable plasma probe array has been developed to measure the radial and axial plasma distribution inside and outside of a ∼10-cm-long final focus solenoid (FFS). Measured data show that the plasma forms a thin column of diameter ∼5 mm along the solenoid axis when the FFS is powered with an 8 T field. Measured plasma density of ≥1×10¹³ cm^-3 meets the challenge of n_p/Zn_b>1, where n_p and n_b are the plasma and ion beam density, respectively, and Z is the mean ion charge state of the beam ions.