0000000000275918
AUTHOR
M. Marttinen
Plasma diagnostic tools for ECR ion sources : What can we learn from these experiments for the next generation sources
International audience; The order-of-magnitude performance leaps of ECR ion sources over the past decades result from improvements to the magnetic plasma confinement, increases in the microwave heating frequency, and techniques to stabilize the plasma at high densities. Parallel to the technical development of the ion sources themselves, significant effort has been directed into the development of their plasma diagnostic tools. We review the recent results of Electron Cyclotron Resonance Ion Source (ECRIS) plasma diagnostics highlighting a number of selected examples of plasma density, electron energy distribution, and ion confinement time measurements, obtained mostly with the second-gener…
Charge breeding at GANIL: Improvements, results, and comparison with the other facilities
International audience; The 1+/n+ method, based on an ECRIS charge breeder (CB) originally developed at the LPSC laboratory, is now implemented at GANIL for the production of Radioactive Ion Beams (RIBs). Prior to its installation in the middle of the low energy beam line of the SPIRAL1 facility, the 1+/n+ system CB has been modified based on the experiments performed on the CARIBU Facility at Argone National Laboratory. Later, it has been tested at the 1+/n+ LPSC test bench to validate its operation performances. Charge breeding efficiencies as well as charge breeding times have been measured for noble gases and alkali elements. The commissioning phase started at GANIL in the second half-y…
Experimental evidence on photo-assisted O− ion production from Al2O3 cathode in cesium sputter negative ion source
The production of negative ions in cesium sputter ion sources is generally considered to be a pure surface process. It has been recently proposed that ion pair production could explain the higher-than-expected beam currents extracted from these ion sources, therefore opening the door for laser-assisted enhancement of the negative ion yield. We have tested this hypothesis by measuring the effect of various pulsed diode lasers on the O − beam current produced from Al 2O 3 cathode of a cesium sputter ion source. It is expected that the ion pair production of O − requires populating the 5d electronic states of neutral cesium, thus implying that the process should be provoked only with specific …
Experimental evidence on photo-assisted O$^-$ ion production from Al$_2$O$_3$ cathode in cesium sputter negative ion source
The production of negative ions in cesium sputter ion sources is generally considered to be a pure surface process. It has been recently proposed that ion pair production could explain the higher-than-expected beam currents extracted from these ion sources, therefore opening the door for laser-assisted enhancement of the negative ion yield. We have tested this hypothesis by measuring the effect of various pulsed diode lasers on the O$^-$ beam current produced from Al$_2$O$_3$ cathode of a cesium sputter ion source. It is expected that the ion pair production of O$^-$ requires populating the 5d electronic states of neutral cesium, thus implying that the process should be provoked only with s…
Estimating ion confinement times from beam current transients in conventional and charge breeder ECRIS
International audience; Cumulative ion confinement times are probed by measuring decaying ion current transients in pulsed material injection mode. The method is applied in a charge breeder and conventional ECRIS yielding mutually corroborative results. The cumulative confinement time estimates vary from approximately 2 ms–60 ms with a clear dependence on the ion charge-to-mass ratio—higher charges having longer residence times. The long cumulative confinement times are proposed as a partial explanation to recently observed unexpectedly high ion temperatures. The results are relevant for rare ion beam (RIB) production as the confinement time and the lifetime of stable isotopes can be used f…
Spectroscopic study of ion temperature in minimum-B ECRIS plasma
Experimentally determined ion temperatures of different charge states and elements in minimum-B confined electron cyclotron resonance ion source (ECRIS) plasma are reported. It is demonstrated with optical emission spectroscopy, complemented by the energy spread measurements of the extracted ion beams, that the ion temperature in the JYFL 14 GHz ECRIS is 5–28 eV depending on the plasma species and charge state. The reported ion temperatures are an order of magnitude higher than previously deduced from indirect diagnostics and used in simulations, but agree with those reported for a quadrupole mirror fusion experiment. The diagnostics setup and data interpretation are discussed in detail to …
A new 18 GHz room temperature electron cyclotron resonance ion source for highly charged ion beams
An innovative 18 GHz HIISI (Heavy Ion Ion Source Injector) room temperature Electron Cyclotron Resonance (ECR) ion source (ECRIS) has been designed and constructed at the Department of Physics, University of Jyväskylä (JYFL), for the nuclear physics program of the JYFL Accelerator Laboratory. The primary objective of HIISI is to increase the intensities of medium charge states (M/Q ≅ 5) by a factor of 10 in comparison with the JYFL 14 GHz ECRIS and to increase the maximum usable xenon charge state from 35+ to 44+ to serve the space electronics irradiation testing program. HIISI is equipped with a refrigerated permanent magnet hexapole and a noncylindrical plasma chamber to achieve very stro…
Photo-assisted O− and Al− production with a cesium sputter ion source
It has been recently proposed that the production of negative ions with cesium sputter ion sources could be enhanced by laser-assisted resonant ion pair production. We have tested this hypothesis by measuring the effect of pulsed diode lasers at various wavelengths on the O− and Al− beam current produced from Al2O3 cathode of a cesium sputter ion source. The experimental results provide evidence for the existence of a wavelength-dependent photo-assisted enhancement of negative ion currents but cast doubt on its alleged resonant nature as the effect is observed for both O− and Al− ions at laser energies above a certain threshold. The beam current transients observed during the laser pulses s…
ECRIS plasma spectroscopy with a high resolution spectrometer
Electron Cyclotron Resonance Ion Source (ECRIS) plasmas contain high-energy electrons and highly charged ions implying that only noninvasive methods such as optical emission spectroscopy are reliable in their characterization. A high-resolution spectrometer (10 pm FWHM at 632 nm) enabling the detection of weak emission lines has been developed at University of Jyväskylä, Department of Physics (JYFL) for this purpose. Diagnostics results probing the densities of ions, neutral atoms, and the temperature of the cold electron population in the JYFL 14 GHz ECRIS are described. For example, it has been observed that the cold electron temperature drops from 40 eV to 20 eV when the extraction volta…