A. Nishizawa

E. Asano

K. Tsukada

M. "Nishiura

S. Kato

T. Ido

Y. Kawasumi

Y." Hamada

National Institute for Fusion Science (NIFS-Repository)

§ 17. Development of Au-Ion Sou rce for aHeavy Ion Beam Probe of LH DNishiura, M., Kawasumi, Y., Nishizawa, A., Asano,E., Tsukada, K., Kato, S., Ido, T., Hamada, Y.2a ,-----,-'---1,----.-1-----,',----.-, ----.15 I- -10 ....-5f- -605040302010OL.-----'-__-L--__...L...-_---JL.-_---'-__---'o5Fig. 2 Dependence of Au- beam current as a function oftarget voltage.a '---__.1....-1 __..<.-..1_--'-1__...£.'__-1.1__---"a 100 200 300 400 500 600Target current VI [V]Time [min]Fig. 3 Temporal Au- beam current by use of residualcesium. The ion source is operated under the conditionsthat the discharge voltage is 60 Y, the discharge currentis 5 A, the target voltage is --400Y, and the beam energyis 10 keY.1 10of 2 keY. As the target voltage is increased, Au- beamcurrent monotonically goes up.Next day the residual cesium was made use ofwithout heating the cesium oven. At 10 minute operationthe Au- beam current reached at the maximum of 17.5 /-lAoAfter 22 minute operation the Au-beam current wassuddenly decreased. This is considered that the residualcesium inside the ion source was consumed beyond theoptimum thickness of cesium layer on the gold target.The filaments were broken after a several hours operation.In order to obtain more Au- beam current stably,the input power should be increased by use of a LaB6 orbigger diameter ofRe-W filament. The ion species, energyspread, and emittance should be measured for theoptimization of the ion source.For the purpose of understanding of plasmabehaviors it is essential to measure the potential profileand density fluctuation in a fusion device. A heavy ionbeam probe(HIBP) system is a candidate and has beenbuilt to diagnose LHD plasmas. The development of agold negative ion source, which is one of maincomponents of LHD-HIBP system, becomes a key issue torealize the system. We adopted the sputter typemulticusp ion source with cesium added in argon plasma.The ion source for diagnostic beams requires thefollowing conditions. If the potential in plasma is assumedto be a few percent of the plasma temperature of a fewkeY, the energy spread of diagnostic beam should be lessthan 10 eY. Taking into consideration the attenuation bypassing through the LHD plasma, we require at least 100/-lA of gold negative ion beam current.The size of the cylindrical ion source is 8 cm indiameter and 9 cm in length. The electrostatic extractionsystem consists of an electrode with the 5-mm-diam. hole.The source body is connected to a potential of theacceleration power supply, Yaw which varies over 0 - 20kY, while the voltage of the Einzel lens electrode, YL, isadjusted to the optimum beam current, measured by aFaraday cup located at the beam down stream.The beam current is measured at about 50 cm downstream from the plasma electrode by using a Faraday cupFull beam enters into the Faraday cup. After adding thecesium vapor into the ion source, the ion source wasoperated for a few hours.The Au- beam current is plotted in Fig. 2 as afunction of the target voltage, Yt. The Au- beam current of12 /-lA(61 /-lA/cm2) is yielded at Yt=500Y at beam energyFig. 1 Photograph of sputter type gold negative ionsource for LHD-HIBP system.166

Development of Au-Ion Source for a Heavy Ion Beam Probe of LHD

Development of Au-Ion Source for a Heavy Ion Beam Probe of LHD

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