CHARACTERISTICS OF AN ECR-EB HYBRID-TYPE
MULTIPLY-CHARGED ION SOURCE
Keiji ODA, Yusuke MORIGUCHI, Takayoshi YAMAMOTO and Masaharu KAWANISHI

The Institute of Saientifia and Industrial Research
Osaka University, Suita, Osaka 565

1. Introductio n

An ECR plasma can be applied to a multiply-ch arged qeavy ion source. It
has been pointed out by the authors that a high electron temperature would benecessary in addition to a high electron density and a long confinement timeof ions, in order to obtain high-yield multiply-ch arged ions with an ECR
plasma-type ion source [1,2].

The electron temperature easily becomes several tens of keV in an ECR
plasma. However, it is difficult to produce a homogeneous hot-plasma at ahigh gas pressure only by the microwave supply. The operating pressure of an
ECR plasma-type ion source will depend on the microwave frequency, the microwave power, the magnetic configulati on, the magnetic field strength, theshape of the cavity, etc.
In this report, a plasma heating has been performed by the injection of anelectron beam into an ECR plasma. It is the purpose to ·investigate a new
hybrid-type ion source in combination of the ECR heating and the electron
beam injection.
2. Experimenta l apparatus
The schematic .diagram of the experimenta l apparatus is shown in Fig. 1.
An ECR plasma is generated in the cavity chamber of 16 em long and 17 em indiameter. The magnetic field by two coils forms a mirror configulatio n witha mirror ratio of 3.7 and the maximum field strength of 1.1 kG. The 2.45 GHz
microwave power is supplied by a magnetron (1.3 kW).
A magnetron injection gun, ofwhich cathod is made of 0.5 mm¢
W wire, is placed on the opposite
side of the chamber to ion extraction electrodes. The electron beam of 520 eV and 1.3 A is
injected into the cavity chamber.

Micro Wove--~~"~'~·~ ~ [8J~:;~[8J~~~0~f:.mIons produced in a plasma areextracted into a drift tube, andtheir charge states are analyzed
by a mass spectromete r [1]. Xrays emitted from the plasma canbe measured by a pure Ge solidstate detector, which is placed
about 150 em apart from the chamber.

MagneticColiFig. 1.

-69-Jl XI

IXICavl tv
Chanber

Experimenta l apparatus.

Electrode3. Results and discuss.ionThe density and the temperature of hot
Ar100·~·--·
electrons in plasma can be estimated from the500•>
measurement of the bremsstrahlung X-ray spec.....--.~
10 3trum. Figure 2 shows the gas-pressure and the 75 1o'O
microwave-power dependences of these plasma.A:>parameters, where argon plasma was generated
....
>ffi
only by the microwave. As is shown in this~~figure, both parameters of the ECR plasma deffi 10.
2 ....
10••• _"zcrease as the gas pressure exceeds about 1.0~x lo-4 Torr. On the other hand, the intensity tt
ratio of Ar2+ ions to Ar+ ions extracted fromiil~To.... 300
the plasma became larger than 1.0, in the gas
100
pressure region of 4. 5 'V 6. 0 x lQ-5 Torr. But
2101
10.
10- 410- 5at the gas pressure of 2. 6 x lo-4 Torr, the( Torr )GAS PRESSUR.E
ratio was smaller than 0.1.
Fig. 2. Pressure- andThese experimental results may be attribpower-dependences of electronuted to that the plasma heating takes placedensity and temperature in anonly in the surface region at a high gas pres- ECR plasma.
sure. Namely, this unhomogeneity would cause
the decrease of average electron density andtemperature.

.

·-·-~

~'\.
0~""·~

1~~--~n:~::.: ~;::::::~~~~:~~::~:~~:=:::l:.

-..

..
.
..

In order to restrain the decrease of the density and temperature, an electron beam was injected into the ECR plasma. The electron-beam-injection experiments were carried out with a xenon gas at first. The temperature variation in the range of 10 'V 30 keV can be clearly observed by the intensity ofKa line (29.6 keV). Typical X-ray spectra are shown in Fig. 3, where the notations "ECR" and "ECR-EB" represent the X-ray spectrum from the plasma produced only by the microwave and by both the microwave and the electron beam,respectively.

. a.o.
.

Xenon

1. 8 " 10- 41 TorrGas Presuure...c
It is recognized that the elecMicrowave Input Powertron density increases by the elec6.0250"' 350 "'itron beam injection, because the xElectron BeiUIII
ray intensity nearly correspcnds to520 eVEnergy
the electron density. The fact that ffi
Current (peak) l.lA
the characteristic X-ray intensity"'ilof "ECR-EB" is much higher than that z 2.0
of "ECR" means a remarkable increase ~iEin the electron temperature. From
the X-ray spectra, the temperature20•• 60 80 100 120 uo
was estimated to be 13 keV in case
( keV )
PHOTON ENERGYof "ECR", and 23 keVin case ofFig. 3.
X-ray spectra emitted from
"ECR-EB". It has been also conECR plasma and EB-injected ECR .plasma.
vinced that the temperature could
increase up to 20 keV at the gaspressure of 2. 4 x lo-4 Torr, where the temperature of "ECR" was so low that Xrays could not be emitted.

.. ...
0

It is expected that a higher current of multiply-charged ions can be obtained by a hybrid-type ion source in combination of ECR heating and electron
beam injection.
References[1] N. Abe, K. Oda, T. Yamamoto, M. Kawanishi[2] K. Oda, N. Abe, T. Yamamoto, M. Kawanishi-7 0-Jpn. J. Appl. Phys. 19 (1980) 149.
Proc. 4thSymp. ISAT(l980), p.l9.