CHARACTERISTICS OF ECR ION SOURCE FOR OPTICAL PUMPING
TYPE POLARIZED ION SOURCE
Akira TAKAGI, Yoshiharu MORI, Kiyoshi IKEGAMI and Sadayoshi FUKUMOTO
KEK, National Laboratory for High Energy Physics
Abstract
An optical pumping type polarized ion source has been developed at KEK.
A 16.5 GHz ECR ion source was adopted as an H+ ion source. The properties ofECR ion source i.e. ion beam intensities, proton ratios, plasma electron
temperature and plasma densities were measured.
Fig. 1 shows a schematic setup of polarized ion source using the 16.5 GHzECR (Electron Cyclotron Resonance) ion source. The ECR ion source consists ofa cylindrical plasma chamber and three solenoid coils. 1 ~ 2 kW microwave
power was produced by a coaxial magnetron (JRC, Ml408), which was modified fortolerating long pulse width (~ 1 msec) and high repetition rate (20 Hz) operations. The microwave power was fed into the plasma chamber through a thin
microwave window for vacuum sealing. The plasma chamber is made of stainlesssteel. Three solenoid coils form magnetic mirrors (mirror ratio ~ 2) and thefield at the beam extraction and Na cell region is 0.9 T. Low energy (2 ~ 5keV) H+ ion beam was extracted by multi-slit electrodes forming accel.-decel.
system. Total extracted ion current was 220 rnA at 3.7 keV and the beam current of 50 ~ 60 rnA was measured at the exit of Na cell (10 em away from extractor) by a 1 em~ Faraday cup as shown Fig. 2.
Measured proton ratio was more than 60 % at the distance of 40 em aparting from the multi-slit electrodes. Hydrogen pressure in the plasma chamber
was less than 1 x 10- 4 Torr in normal operation. It affected strongly proton
ratio. Fig. 3 shows the measured values of proton ratio as a function of thehydrogen gas pressure.which was measured at the head of a turbomolecular pump.
As the pressure increased, the proton ratio decreased. A higher proton ratioof 70 % was obtained by optimising the source parameters.
Langmiur probe for the measurement of plasma parameters of the ECR ion
source was placed at 10 mm separated for axis of plasma chamber. The electron
temperatures and the plasma densities were measured for the two types of theplasma chamber; one is of introducing the microwave transversely to the magnetic field and the other of longitudinally. The results are summarized inFigs. 4 and 5. Hydrogen pressure in Fig. 4 was measured at the plasma chamber
and that in Fig. 5 was at the head of the turbomolecular pump. The plasma
densities in these figures were separately calculated from the electron saturated current (Ies) and the ion current (Ii). As seen in figures, the electron temperature decreased abruptly as the hydrogen pressure increased. In
normal operation, the electron temperature and the plasma density were 23 eV
and 10 12 n/cm 3 respectively.

-227-WIEN FILTER

16GHz MICROWAVEI

Ht GASECR ION

SOURCE

1!100 4/s

2500 1/s

Fig.l. Schematic setup of polarized H ion source.
100r---------------~

Vacc=l..1 kV
S1 =420 A0;:::~500 1~~2,-~3.-74--~5--67-~7~Fig.2. Ion beam current of
ECR ion source.
Hv

T. M.P. PRESSURE (x10-6Torr)

Fig. 3. Proton ratio of ion beam-::as a functionof hydrogenpressure

50 11s/div.
10 mA/div.

30,-------------------~

40

No.2 Cavity
S1=500 A

No.1 Cavity
S1=500 A
30Te201013>

5-~20'"">(j}~Uesl

1tf~_.o-"'IEu

ne /c{ ---a--~~10--=a:------D------ ---- ---o--- ----'J" ___ , ---o--( i ;)·
neT,\nesv' /IEu10......

.-a-( Iil5

Lr

010-5

1()'110_,

2P1 (Torr)
Fig.4. Electron temperature and plasma
density versus hydrogen pressure forNo.1 plasma chamder.
-228-

010·6

P2 (Torr J
Fig. 5. Electron tempera tm;e andplasma density versus hydrogenpressure, for No.2 plasma chamber.