Speaker
Description
A strong spontaneous-focusing of low energy ion beam (~150 eV) having the high current density (~3 mA/cm$^{2}$) was observed using three sets of concave electrodes with nominal focal length of 350 mm [1-5], where the ion and electron current density profiles were measured by Faraday cups in an ion beam propagation chamber, to which the ion beam is injected from the ion source [6]. To study the mechanism of this focusing phenomenon, a pair of electrostatic double probes with a unique structure have been installed. Two pairs of double probes compose totally 4 tungsten tips which are installed in perpendicular and parallel directions to the ion beam, respectively. It was found that this combination enables to measure slow ions and fast beam ions components by using the probes. During the focusing phenomenon, large amounts of slow ions were produced. It is also possible to measure radial profiles of those components by sweeping the probe up and down perpendicular to the ion beam direction. Moreover, by inserting an extremely high impedance resistance between the tungsten tip and ground line in the system, it became possible to measure the space potential before and after the focusing phenomenon.
At the conference, we will present these probe measurement techniques for estimating the slow and fast ion components, and for measuring the radial profiles of space potential. Possible mechanism of the focusing phenomena will be discussed by using these results together with the results obtained by the Faraday cups.
References
[1] H. Sakakita, et. al., Rev. Sci. Instrum. 83, 02B708 (2012) 1-3.
[2] Y. Hirano, et. al., J. J. Appl. Phys. 52, 066001 (2013) 1-6.
[3] Y. Hirano, et. al., Rev. Sci. Instrum. 85, 02A728 (2014) 1-3.
[4] Y. Fujiwara, et. al., Rev. Sci. Instrum. 87, 02B930, (2015) 1-3.
[5] Y. Hirano, et. al., Rev. Sci. Instrum. 86, 113303 (2015) 1-9.
[6] Y. Fujiwara, et. al., Rev. Sci. Instrum. 85, 02A726 (2014) 1-3.
