MAGNETRON H

ION SOURCE AT KEK

A. Takagi, K. Ito, Y. Mori ands. Fukumoto

National Laboratory for High Energy Physics (KEK)A negative hydrogen ion source of magnetron type has beendeveloped to increase the intensity of accelerated protons in theKEK 12 GeV synchrotron.
The source design is based on the magnetron source at FNALl).
H ions from the source are directly extracted into a sector focus
90° bending magnet which removes unwanted ions and electrons. The
sector focus magnet shapes the H- ions into a beam suitable forinjection into an accelerating column.The source must be capableof producing above 50 rnA of the beam with the maximum pulse lengthof 200 ~sec at a repetition rate of 20 Hz.
Fig.l shows the cross section of our magnetron source with anextraction system. The source anode and cathode parts are made ofmolybdenum. They are held by two thin insulators. The source bodymade of stainless steel contains the anode-cathode structure in it, and is covered with a titanium plate anode cover. The anode covercontains an anode aperture (lxlO mm). A thermal insulator is placed
between the source body and the base plate. The pulsed gas valve
which is popularly used in automobile as a fuel injector is mount-ed on the base plate. The hydrogen gas is directly introduced froma gas container lnto the source by th±s pulsed valve . The H- ionsare extracted from the ano~e aperture by the extraction electrodeand passed through an extraction aperture (lxl5 mm). The auxiliary
magnet pole produces the source magnet field. Any electrons ex~
tracted from the anode aperture are bent by the transverse magnetic
field and spiral back to the source.
The cesium vapor is introduced into the source through a hEt!at-edtube. The tube of about 40 em long connects with a valve to acesium
oven located outside of the vacuum chamber. To obtain the cesium
vapor in the source, the valve and the connecting tube must be
heated to 300~400 °C. The oven temperature is adjusted to 170~190°C during the normal operation. The cold box is necessary to trap
the cesium vapor from the source.
The arc power is supplied by the arc pulser. Output of a current pulse is regurated within a pulse duration by the negativelyfeedback circuit. In the hydrogen-cesium mode discharge, arc voltThe arc current can beages are 200"--'300 Vas shown in Fig.2.
adjusted up to 150 A. Fig.3 shows a typical waveform of the arcdischarge.
A typical result of the H-b~am is shown in Fig.4 together withsource parameters. 12~15 rnA of H beam is obtained with a shortened
extraction gap of 3 mm. Further high intensities could be extracted
by increasing the extraction e;perture width. The temperature control of the source and the cesium oven must be important for thestable operation of the source. We ha.ve continued experiments toobtain a high intensity of the l r beam in this ion source.
Reference
C.W. Schmidt and C.D. Curtis; IEEE Trans. Nucl. Sci.,NS-26,1)
4120 (1979).

-7 3-

H2 GAS+PULSED GAS VALVEHYDROGEN-CESIUM MCX:E
18003151

500400.......

200100100Iarc(A)

Fig.l

l1

H2 -Cs MODE DISCHARGE

Arc voltage vs arc
current.

Fig.2

KEK magnetron ion source

I il~: flEA'\ CPKREt'<T( 80062') )I B00315 I

5 mA/div.
50 tosec/div.

!'.\R.\~IETERS

rt'Pl'l it innlfl'<ltHHh•

H: SO J'"SBc/div.

CATHODE TEMP.
Cs OVEN TEMP.

50 A!50 ;.St't']50 nc
170 PC:!t•mp.

,.:nu rn· m;t<~.
,-~:rr;wtion

REPETITION RATE

270 \'

1r,- dural inn··at hnd,• t<.•mp.

U: Voce, 100 V/div.

L : !,, . 20 A/div.

20 Hzvnl ta~t·20 Hzf i (•j dvolt.

,,,.,.,. J,•r;H inn volt.
,.·.:t rot•·l ion .':ill'-450 °C•·:-;t r;H·t inn slitl•l'lld. Ill:\ g. f i<.· ld-190 °CI>Vt'll[<.•l'lj'.

r·:, ft·t·d ttllw U•mp.

Fig.3

Arc voltage and currentpulses.

Fig.4-7 4-]0 kV] mm
1·1 5 mm1470 Causs,J') ,·c/min.
170 °(g.t» 1· ln~o.· rat(t',.:920 Caussl 5 kV

Hlfl 4011 °C

12 rnA H beam after
90° bending magnet.