Optical emission spectroscopy for time-resolved characterization of electron cyclotron resonance ion source plasma...

Optical emission spectroscopy is one of the few non-invasive methods for studying magnetically confined, highly charged plasma produced in an electron cyclotron resonance ion source (ECRIS). Analysis of the optical emission lines from the plasma allows for the determination of key plasma parameters, such as ion densities and temperatures. Many plasma processes are inherently dynamic, such as plasma breakdown and decay, highlighting the importance of time-resolved characterization methods. This work investigates the capabilities of the high-resolution visible-light spectrometer for time-resolved diagnostics of ECRIS plasma, using either a photomultiplier tube (PMT) or a camera as a light sensor. To achieve this, the emission line profile transients of Ar+ and Ar9+ ions were measured from the microwave-power-pulsed 14 GHz ECRIS argon plasma to extract the transients of emission intensity and ion temperature. Although the PMT is much faster than the camera, the temporal resolution of both is limited to ∼10 ms by the low plasma emission intensity. The spectroscopic setup requires modeling all relevant processes that influence the measured emission line profile to obtain reliable estimates of ion temperatures. This includes the splitting of the emission lines due to the Zeeman effect, caused by the magnetic field confining the plasma, which was found to significantly affect the determination of ion temperature. As a result, the temperature evolution of Ar+ and Ar9+ ions over a microwave pulse is presented, with the steady-state values of 3.5(4) and 4.2(9) eV, respectively.