Development of a new ion-guide with use of magnetic field

点击翻译按钮获取中文摘要

The ion-guide is a novel technique which has been used for nuclear spectroscopy combined with an on-line isotope separator. The principle of the technique is that reaction products recoiling out of the target are stopped and thermalized in a He gas cell while keeping a singly charged state, the ions are carried by gas flow to vacuum, and then accelerated and mass separated by a separator. The advantages of the ion-guide are chemical-property independence and fast separation. There are, however, major drawbacks, i.e., 1) limited yield, 2) poor beam quality, 3) "plasma effect" (presence of primary beam in the cell traps ions). For the point 2), we have developed a cooling device, SPIG (RF sextupole ion beam guide), which has become a standard technique.The aim of the present work is at the points 1) and 3). The origin of the point 1) is in the size of gas cell, which is about 1cm in thickness, and corresponding stopping capability of 10 keV/u. Since the transport is carried only by the g … More as flow, it is hard to increase the size. We have proposed to apply an electric field of a superposition of DC and RF into the cell (RF ion-guide) where ions are totally under control of the field. It allows to use a large cell, e.g., 2 m in length which corresponds to a stopping capability of 5 MeV/u, since the DC electric field keeps fast extraction and the RF electric field protects from diffusion loss to the wall. This large stopping capability also effective to the point 3). The RF ion-guide can be coupled with a projectile fragment separator where the primary beams do not irradiate the gas cell.The present work showed effective transport of ions in a large He gas cell by the RF ion-guide technique. We have also fabricated a funnel structure of RF electrodes with very fine pitch, as fine as 0.3 mm, which allows to use a relatively high pressure of 150 Torr. Though the use of a magnetic field was not tested in the present work, we are certain that it will effective for further increase of effective stopping capability of the cell. Less