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Investigation on Operating Parameters of the
Homemade Penning-Type Ion Source for
Cyclotron
Silakhuddin, S. Santosa
Center for Accelerator Science and Technology ,National Nuclear Energy Agency
Jl. Babarsari, Yogyakarta 55281, Indonesia
ARTICLE INFO
ABSTRACT
AIJ use only:
Received date
Revised date
Accepted date
A Penning-type ion source for a cyclotron producing PET radioisotopes has been
Keywords:
Ion source
Cyclotron
Parameters
Puller voltage
Magnetic field
Cathode current
investigation was carried out by experiments on an ion source test device. The
made. To determine the performance of the ion source for further developments,
the investigation has been conducted on the operating parameters.
The
investigated operating parameters are the puller voltage, the magnetic field, the
hydrogen gas flow rate and the cathode current. The results showed that the
puller voltage is the most sensitive parameter to change ion beam current, and at
a voltage of 8 kV an ion beam current of 35 µA was obtained, and this parameter
is still likely to be raised if the current beam will enlarge.Change in the magnetic
field showed saturation the ion beam current after the magnitude of magnetic
field is approximately 450 gauss. It was obtained a moderate range of gas flow
rate on the value of 5-10 cc/min, producing a high beam current without effect to
the significant decrease of vacuum. The increase of the cathode current gives
significant effect until 1 mA and then does not affect to the increase of ion beam
current.
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INTRODUCTION
construction phase to create an ion source is to be
Development activities to make a cyclotron are
installed at the cyclotron. With the recent testing of
currently being done in the Center for Accelerator
the ion source resulting an H- ion beam current of
Science and Technology BATAN, and one of the
35 µA, it was tested on a homemade ion source
activities is the development of a Penning-type ion
testing device with a puller voltage of 8 kV DC.
source. Currently, an ion source development has
Testing on a similar ion source was done at the
already been up on the end stage of the
Institute of Fluid Pysics, China Academy of
experimental phase and will be continued on the
Engineering Physics China, with result of ion beam
current was 200 µA at a puller voltage of 2 kV [1].

Corresponding author.
E-mail address:[email protected]
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Another testing in Sungkyunkwan University of
Korea obtained a H- ion beam current of 1 mA at a
puller voltage of 1 kV [2].
Compared with other
experimental results, the homemade ion source has
not been on a standard performance. It is important
to investigate the characteristics of operating
parameters in order to get methods to increase the
ion source performance.
Operating parameters in a Penning type ion source
consist of cathode voltage, puller voltage, gas flow
rate
and
intensity
of
the magnetic
Figure 1. Scheme of the ion source and the testing
field. Investigations of the ion source parameters
were carried out by experiments to study the
influence of the operating parameters on the end
product of the ion beam current. The experiments
were executed on an ion
source
testing device. Through the investigations, it would
be to get data for determining further research
and development of ion source design for DECY-13
cyclotron, which the goal
will
be obtaining
negative hydrogen ion beam current by several
hundreds of µA.
device
Plasma is produced in the anode cavity caused by a
hydrogen gas ionization discharge between cathode
and anode those are connected to 0-3 kV DC
source. Intensity of ionization is amplified by the
magnetic field existence of 0-1000 gauss. Negative
hydrogen ions are pulled by puller that is applied 010 DC voltage compared to the anode. The ion
beams are measured by a collector and a current
meter. Existing geometry of the ion source,
especially surface of the anode and the puller follow
the shape of common H- ion source [1,3].
The
EXPERIMENTAL METHOD
distance between the anode aperture (slit) and the
The Penning Source and Its Testing Device
puller aperture is 0.5 cm and the distance between
The Penning ion source for a cyclotron and scheme
the puller aperture and collector is 3 cm. The
of testing device is shown in Figure 1.
material of the anode is W-Cu alloy, the cathode is
tantalum and the puller is graphite. The magnet was
generated by electric current winding of 0-15 A.
Experimental Procedures
The main operating parameters of ion source are:
-
Cathode electric current, referred to as
electron current that ionizing gas on the
anode cavity.
-
Magnetic field strength of electro-magnet
that affect the intensity of ionization on the
anode cavity.
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-
-
Hydrogen gas flow that affects on the
5×10-5 Torr. After cathode voltage was raised to
plasma pressure.
slightly over 1800 V and electro-magnet current
Puller voltage that affects on extracted ion
was raised to 10 A (based on the calibration this
beam current out of the anode cavity.
value is equivalent to 465 gauss magnetic field), a
Experiments were
done by
making the
highest
visible glow can be observed on the anode slit. It is
vacuum conditions be reached. The next steps are
an indication that a plasma has been occurred. The
observation an ionization on the anode cavity by
occurrence of ionization also was ensured by the
following steps:
cathode current of 5 mA. After the occurrence of
1. Hydrogen
gas was
piped into
the head
until approximately some cc/minute.
the parameters on the ion beam current are as
2. Cathode voltage was raised to over 1800 V; this
is
the voltage that
the tantalum
ionization, the observed results of the influence of
allows electrons from
cathode surface escape
follows.
Measurement data results of the influence the puller
voltage on the beam current is shown in Figure 2.
toward anode cavity.
3. Electrical current generating magnetic field was
raised to observe a glow on the anode slit, as a
sign that glow discharge ionization has occurred.
After ionization is observed, the next step is
observing the influence of ion beam current by ion
source operating parameters by following steps:
1. Observing of influence of puller voltage change
against ion beam current.
2. Observing of influence of magnetic field against
ion beam current, and the calibration to
determine the relationship between electrical
Figure 2. The influence of the puller voltage on the
current and magnetic field was done before.
ion beam current;
3. Observing of influence of gas flow rate change
against ion beam current.
:measurement data,
:
calculation data using the least square fit method
by I ~ const. V3/2
4. Observing of influence of cathode current
change against ion beam current.
The data were acquired for puller voltage up to 8
kV, above this value the excessive spark was
occurring in the space between the anode and
puller, so the ion beam current was difficult to be
measured. The excessive spark due to the vacuum
being less high and that is because a less powerful
RESULTS AND DISCUSSION
of vacuum pump. At the 8 kV puller voltage an ion
After the flow of hydrogen gas was raised to 2
-6
cc/min, the vacuum came down from 5×10 Torr to
beam current of 35 μA is obtained.
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In the theoretical approach, the influence of
increased by using increasing the magnetic field.
puller voltage is expected to comply with the Child-
But this phenomena is actually still to be examined
Langmuir equation, i.e. the ion beam current is
further because some references mentioned that
proportional to power 3/2 of the extraction (puller)
testing of this type of ion source generally is done at
voltage, which is 𝐼~𝑐𝑜𝑛𝑠𝑡 × 𝑉
3⁄
2
[4]. In Figure 3
several kilogauss magnetic field [1,2].
are shown curves of measured and theoretically
As the puller voltage of 7 kV and electro-magnet
calculated ion beam current, and two curves are
electric current of 10 A, the influence of the gas
seemed to coincide with each other. From these two
flow rate on the ion beam current is shown in
curves there are two things that can be concluded
Figure 4.
that firstly optics of an anode-puller functions
properly for extracting ion beam and secondly the
space charge effect of ion beam does not affect on
ion beam current.
The observation was done on the gas flow rate of
the same as the earlier observation, but the
puller voltage was reduced to 7 kV (so that the
excessive spark effect can be reduced).When the
electric current of electro-magnet was varied, the
effect of variation of magnetic field on the ion beam
current is shown in the Figure 3.
Figure 4. Influence of gas flow rate on ion beam
current at puller voltage of 7 kV and electro-magnet
electric current of 10 A
There is a minimum flow rate of value of 2 cc/min
and no optimum value until 10 cc/min. The ion
beam increase is not too sharp compared with the
influence of the puller voltage.
A result of
simulation study using Fluent 6 showed that the gas
flow rate will affect linearly to gas pressure in the
Figure 3. Effect of magnetic field on the ion beam
anode cavity [5], and the gas pressure affects
current.
linearly to the intensity of the ionization [6]. The
From above results seem to be a constancy of the
linearity in that experiment didn’t happen, it can be
ion beam current even if the magnetic field is
caused by no linear effect of gas flow rate on the
increased. So up to 700 gauss magnetic field, it can
gas pressure because not all of the molecules will
be concluded that the ion beam current cannot be
be ionized after entry into the anode cavity but part
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of them out of the cavity as neutral molecules. It
electrons from the cathode surface in thermionic
was obtained a moderate range of flow rate on the
mode. Technically, this can be done by enlarging
value of 5-10 cc/min, which producing a high beam
the cathode current up to several hundreds of mA.
current but does not affect on the decrease of
vacuum. This, according to Penning-type ion source
operation on cyclotron in general [7,8]. In the
CONCLUSION
experiment, the cathode current rising from
The potential of the puller or the puller voltage is
originally 6 mA to 10 mA at gas flow rate of 2
the most substantial role in giving effect to changes
cc/min and 10 cc/min respectively.
in ion beam current, and this parameter is still likely
The influence of cathode current on the ion beam
to be raised if the current beam will enlarge. But
current at the gas flow rate of 2 cc/min, the puller
the excessive spark is a constraint to raise the puller
voltage of 6 kV and electric current of electro-
voltage, and this can be overcome when the vacuum
magnet of 10.5 A (concurrent with 465 gauss
is to be higher than before. Change in the magnetic
magnetic field) is shown in Figure 5.
field showed saturation the ion beam current after
the magnitude of magnetic field is approximately
450
gauss,
this
uncommon
phenomenon
is
necessary for the next research object. It was
obtained a moderate range of gas flow rate on the
value of 5-10 cc/min, which producing a high beam
current without effect on the significant decrease of
vacuum. The increase of the cathode current gives
significant effect until 1 mA and then does not
affect on the increase of ion beam current. So it
should be tried in further experiments on several
tens or hundreds mA cathode current. As a final
Figure 5. The influence of the cathode current on
conclusion is that in order to increase the ion beam
the ion beam current
current, it is necessary to do two things, first is an
increase in the vacuum of experiment chamber and
The influence of cathode current on the ion beam
the second is an increase in cathode current source
current at the gas flow rate of 2 cc/min, the puller
operation up to several hundred miliamper.
voltage of 6 kV and electric current of electromagnet of 10.5 A (concurrent with 465 gauss
ACKNOWLEDGMENT
magnetic field) is shown in Figure 6. To increase
This experiment was funded by an annual R&D
program of Center for Accelerator Science and
Technology, the National Nuclear Energy Agency of
Indonesia, so the authors would like to thank the head of
the center. The authors also would like to thank Mr.
Sunarto for his support throughout the experiments and
measurements.
the ion beam current into the larger amount it
requires a change in the ionization from the glow
discharge state to the arc discharge state, which can
be done by making the process of the release of
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5. Silakhuddin, “Influence of a Geometry of
Circulated Chamber on Distribution of Gas
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