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RESEARCH PRODUCT

Electron heating with broadband microwave radiation: A new method for improving the performances of conventional B-minimum electron cyclotron resonance ion sources

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Abstract The charge-state enhancing effects of broadband microwave radiation are demonstrated by comparing the charge-state distributions and intensities of Arq+ ion beams, extracted from a conventional B-minimum geometry, 6.4 GHz ECR ion source, when operated with traveling-wave-tube (TWT) amplified microwave signals generated, respectively, from a “white” noise generator (WNG, bandwidth: 200 MHz) and a conventional narrow-bandwidth local oscillator (LO, bandwidth: ∼1.5 MHz). Clear enhancement (factors > 2) is obtained for high-charge-state Ar ion beam intensities, produced with broadband radiation, over those obtained with narrow-bandwidth radiation at the same power level. The high-charge-states (q > 9) exhibit an anomalous, abrupt increase in intensity at an optimum pressure while the total X-ray count and plasma potential suddenly dip at approximately the same pressure, seemingly in correlation. These effects are not understood in terms of rf adsorption or principal charge-state limiting atomic physics phenomena. Future experiments are proposed for evaluating the full potential of the broadband heating method enhancing the high-charge-state ion beam capabilities of conventional minimum-B ECR ion sources.