Laser cooling of one-component plasma and drive of troidal flow

• Project/Area Number: 15540472
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Single-year Grants
• Section: 一般
• Research Field: Plasma science
• Research Institution: Nagoya University
• Principal Investigator: SAKAWA Youichi Nagoya University, Graduate school of Engineering, Research Associate, 工学研究科, 助手 (70242881)
• Co-Investigator(Kenkyū-buntansha): SHOJI Tatsuo Nagoya University, Graduate school of Engineering, Associate Professor, 工学研究科, 助教授 (50115581) ; HAYASAKA Kazuhiro Communication Research Laboratory, Chief Researcher, 主任研究員 ; ARAMAKI Mitsutoshi Nagoya University, Graduate school of Engineering, Research Associate, 工学研究科, 助手 (50335072)
• Project Period (FY): 2003 – 2004
• Project Status: Completed (Fiscal Year 2004)
• Budget Amount: ¥3,200,000 (Direct Cost: ¥3,200,000); Fiscal Year 2004: ¥1,200,000 (Direct Cost: ¥1,200,000); Fiscal Year 2003: ¥2,000,000 (Direct Cost: ¥2,000,000)
• Keywords: laser cooling / one-component plasma / troidal flow / troidal RF trap / non-linear resonance / 一成分プラズマ

Research Abstract

The purpose of this experiment is (1)to confine Ca^+ ions in a toroidal rf trap (the major radius is 40 mm) and achieve Coulomb coupling parameter Γ>1 by laser cooling and (2)to control a potential of the rf trap in a troidal direction to drive laser-cooled Ca^+ ions in the troidal direction.
In order to cool Ca^+ ions, 397 nm and 866 nm radiation were produced by diode lasers with a grating-laser-stabilization systems, in which feedback stabilization from holographic grating in the Littrow configuration was used. The 397 nm laser light was produced by doubling the 794 nm light of a diode laser. For this purpose, an external enhancement cavity containing the nonlinear crystal (LBO) was used. The 397 nm and 866 nm laser beams were collinearly overlapped and focused tangentially on the trapped ions. The optical feedback phase and the frequency of the grating-stabilized 397 nm laser were simultaneously controlled by 1f and 3f electric feedbacks, respectively, using a proportional and integ ral(PI) feedback method. The frequency scan of nearly 5 GHz was achieved. The laser-induced fluorescence (LIF) of the 397 nm radiation was used for the detection of Ca^+ ions.
We improved confinement of Ca^+ ions by changing an one-side-grounded(OG) rf trap to a center-grounded(CG) rf trap. When the OG rf trap was used, possibly due to a residual electric field caused by the charging of the rf trap, Ca^+ ions were confined in narrow regions of rf voltage(V_<RF>) and current(I_b) of electron-gun, by which Ca^+ ions are ionized. When the CG rf trap was used, the residual electric field was removed and confinement of Ca^+ ions were achieved in wide regions of V_<RF> and I_b. As a result, we have observed the reduction of both the number of confined ions and confinement time caused by the nonlinear-resonance effect. However, laser cooling of Ca^+ ions was not achieved since the confinement time at high vacuum, which is necessary in laser cooling, was short and ions were lost during the wavelength-scan of the 397 nm laser. Further improvement of rf trap is required.