24aD22P
磁場揺動計測を目指した原子磁力計の設計検討
Design of Atomic Magnetometer for Application in Fusion Plasmas
清永浩之1), 山田淑宣1), 福田武司1)
Hiroyuki KIYONAGA1), Yoshinobu YAMADA1), Takeshi FUKUDA1)
大阪大学大学院工学研究科
1)
Graduated School of Engineering, Osaka Univ.
1. Introduction
The detailed magnetic field measurement is verysignificant in fusion research and various methods suchas the Faraday rotation and motional stark
spectroscopy techniques have been developed.
An atomic magnetometer, especially amplitude
modulated atomic magnetometer (AM-AOM) [1],allows spatially resolved magnetic field measurementseven inside the fusion plasma, and Helium atoms
suggested as probing targets in this work are produced
from the D-T fusion reaction. Accordingly neither
heating beam nor impurity species are necessary.
Aiming at investigating the proposed AM-AOM, wedeveloped the prototype and conducted rudimentary
experiments: measuring small magnetic fields (about afew microtesla). In a poster session, the possibility ofAM-AOM application in fusion plasmas is discussed.
2. Design of the prototype AM-AOM
Our prototype of AM-AOM is shown in Fig.1. Forsimplifying the setup, single beam configuration wasadapted, with which amplitude of magnetic field on thebeam pass can be measured. The beam of which
wavelength is 1083nm (He D1 line), are injected into a
He discharge cell. This beam is amplitude modulated
at frequency fpump and circularly polarized for the spinpolarization of the He atoms. When fpump equals theLarmor frequency fL(=γB), the resonant property isdetected in the transmittance rate, and magnitude of themagnetic field at the cell is evaluated. Here, γ is thegyromagnetic ratio; 28[GHz/T] for He. The transmitted
light intensity is detected by a photo diode amplifier
circuit. Furthermore, the signal is amplified with
Rock-in amp whose reference is synchronized the AM
frequency. The direction of generated magnetic field isperpendicular to the beam direction, since thisconfiguration maximizes resonant signal [2].

Fig.1 Schematic of Experimental setup

3. Property of the developed light source
As a light source for our prototype AM-AOM, ahollow-cathode type He discharge lamp has beendeveloped in the lab. In order to produce amplitude
modulated light emission, its power supply has also
been designed and built. This power supply can
produce tunable frequency AC voltage with DC
voltage offset which is high enough to discharge thelamp. Fig.2 shows AM emission intensity of this lightsource measured in the optical system shown in Fig.1.
Though the intensity decreases in high frequency
region possibly due to the parasitic capacitance of thelamp, frequency tunable AM He D1 emission wassuccessfully obtained.
4. Status of the experimentWith the developed AM-AOM, we have performed an
exploratory experiment of test magnetic field (5 [μT])
measurement. Fig.3 shows the transmittance rateversus AM frequency. The transmittance rate seems tohave its peak around 130 [kHz] corresponding to4.6[μT], which is possibly sign of magnetic field
detection. Intensive effort for defining the peak is inunderway.

Fig.2 AC emission intensity VS frequency (left).
Fig.3 Transmittance rate VS frequency (right).
Around 130 [kHz], transmittance rate seems tohave its peak, and this corresponds to 4.6[uT]
which roughly equals to the amplitude of test
magnetic field (5 [μT]).
Reference[1]W.E.Bell and H.L.Bloom, Phy.Rev.Lett.6, 280.
[2]Volkmar Schultze et al., Optics
Express20,13,14201