lMHz PULSED DUOPLASMATRON
S . I was a k i , K. 0 node r a , R. Sa kam ot o ,M.Fujisaw a, M.Baba, S.Itagaki

I. Abe ,Fast Neutron Laborator y, Departmen t of Nuclear
Engineerin g, Tohoku University , Sendai
Abstract
The high speed arc pulsing system has been developped
for Duoplasma tron ion source in our 4.5 [MV] Dynamitron
accelerato r.
In this study, we have improved the arc pulsing system(which was previously reported*) synchroniz ed with a nanosecond pulsing system.
In this report, we will describe the system and theperformanc e of the lMHz arc pulser which is synchroniz ed witha nanosecond pulsing system using a photo fiber isolatvr.
System and Performanc e
A system of lMHz arc pulsed duoplasma tron synchroniz ed
with a nanosecond pulsing system is illustrate d schematic allyin Fig;l.
The duoplasma tron ion
Sweepsource has been operating inRetrace
Buncherawheneven
the D.C. mode,
nanosecond pulsing system wasrunning between 7.8KHz and
2MHz of repetition rate.
The ion source is at 40[KV] potential by extractor
The triggerpower supply.
signal from a nanosecond pulsing
system to the arc pulser istransmitte d by the photo fiber
isolator in the terminal.
It is also possible to control the frequency and the pulse
width of the arc pulser fromoutside of the SF6 pressurize dF1bertank through the 4.5 [MV] photo
PRESS. TANK
EIO
fiber isolator.

L_~..:::::::'-o----1

Initially we had someproblems and care was taken in
the first stage of the instalAt the present time,lation.
the fiber itself operates very
reliably,b ut the PD receiver
has problems from time to time.

-6 7-

Arc pulsed duoplasma tron
synchroniz ed with a nanosecond pulsing system.
Fig-1

The measured wave forms of arc current and voltage areshown in Fig~2.arid Fig.3.
The voltage across the pulser
is 50 [V], and the arc current is 2 [A].
50 [nS] of risetime and 60 [nS] of fall time was observed at 2 [A] of the arc
current.
High speed, high voltage MOS FET (2SK135) is employed
as a switching device in the arc pulser to improve the riseand fall time.
The duoplasmatron needs D.C. bias current (at least 100[rnA] to 300 [rnA] ) of the arc in the pulsed mode operation ofhigh frequency.
The D.C. bias current improves rise time of the arc
current .
The ratio of D.C. bias current and pulsed current
is up to 50 in the case of our duoplasmatron.
The system can be operated successfully uP to lMHz
repetition rate in the present stage, and now it is expectedthat the life of the barium oxide coating filament and theeizel grid wire will run much longer.
That is a majoradvantage of this system.
The arc pulser is also expected to get more beam current.
The current measured is 2 times to 6 times as much as theD.C. ion source current.
It was also noticed in our experiment that the energy
spread of accelerated beam was improved.
The author would like to thank Mr.D.Okihara of the
Optical Communication Section, Transmission Department of OKICo,. and also Mr. Sato and Mr.Akama of the workshop of Nuc~~arEngineering Dept. for their cooperation.

Fig.3 the arc current wave form
0.6[A]/div. 0.5[pS]/div.
Fig.2 the switching voltage
wave form.
lO[V]/div. 0.5[~S]/div.

*) I.Abe,et al. ,"Arc pulsing system of a duoplasmatron ionsource". 2nd Symp. on Accelerator Science and Technology
1978. p.l7-68-