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A COMPACT 2.45 GHz MICROWAVE ION SOURCE BASED HIGH
FLUENCE FACILITY AT IUAC
Narender Kumar*, P. S. Lakshmy, G. Rodrigues, Y. Mathur, R. Ahuja, R. N. Dutt and D. Kanjilal
Inter University Accelerator Centre, New Delhi-110067, India
when the rings were separated by a distance of 140 mm.
Abstract
A compact 2.45 GHz microwave ion source has been
designed and developed for production of low energy,
high current singly charged ions at Inter University
Accelerator Centre (IUAC), New Delhi [1, 2]. The heart
of this facility consists of a permanent magnet based 2.45
GHz microwave ion source. The facility is used for ion
implantation, phase formation, etching and surface
patterning experiments. The ion source consists of a
compact cavity with two movable permanent magnetic
rings and 2kW microwave generator along with water
cooled magnetron-head. It is designed to generate various
ion beams of singly charged ions having energy up to 30
keV. A description of the design of 2.45 GHz microwave
ion source and associated LEBT and few experimental
results are presented.
INTRODUCTION
Figure 1: View of 2.45 GHz compact microwave ion
source.
Microwave ion sources are well known for their
stability, ruggedness and for their long lifetime due to
absence of electrodes. Microwave ion sources operating
at 2.45 GHz in the off-resonance mode are being utilized
for various applications in many laboratories, viz., for
industrial applications [3], high current ion implanters [3],
and ion beam deposition [4]. Depending upon the plasma
density, ion beam intensities extracted for the singly
charged ions can be very intense. A microwave ion source
operating at frequency 2.45 GHz has been designed and
developed at IUAC, New Delhi [1, 2]. This ion source is
able to deliver relatively intense beams of lower mass
singly charged ions that is used for ion implantation and
ion deposition experiments.
DESIGN AND INSALLATION OF 2.45 GHz
MICROWAVE ION SOURCE BASED
HIGH FLUENCE FACILITY
At IUAC, we have designed and developed a 2.45 GHz
microwave ion source based, high flux facility. The ion
source consists of a non-magnetic stainless steel cavity
designed for operation in the TE111 mode. The ion source
constitutes of two NdFeB permanent magnet rings, each
of the permanent magnet ring consists of 6 wedge shaped
sectors having dimensions of 45 mm × 35 mm as shown
in figure 1. The pole tip field of each sector is
approximately 1 T. They are arranged in a non-magnetic
stainless steel jig such that their magnetization is in the
radial direction. The axial magnetic field generated by
these two magnetic rings can be tuned by changing the
distance between the magnetic rings with respect to each
other. Figure 2 shows the measured axial magnetic field
*
[email protected]
Figure 2: Measured axial magnetic field using two
permanent magnet rings separated by distance of 140 mm.
The calculated ECR surface at the operational
frequency of 2.45 GHz using TRAPCAD [5] is shown in
figure 3.Standard 900 bend, WR340 waveguides have
been used for microwave coupling between the 2.45 GHz,
2 kW water cooled magnetron and the cavity. A quartz
window is used for vacuum isolation between plasma
chamber and waveguides. The high voltage DC break
which consists of a thin teflon sheet, is used for high
voltage isolation of ion source from ground potential and
at the same time allowing the propagation of microwave
energy.
In order to minimize the reflection of microwave
power, a ‘three-stub’ tuner is coupled between the
magnetron and plasma chamber. The cooling of the
plasma chamber and the microwave window is
maintained by using compressed air all along the length
of the plasma chamber
Figure 3: Calculated ECR surface at 2.45 GHz.
EXPERIMENTAL RESULTS
After installation of ion source, it was integrated with
the low energy beam transport system as shown in figure
5. The operation of the source and LEBT parameters is
controlled and monitored using LabView interface [6]
with wireless control.
For hydrogen plasma working with a gas pressure of
1.4 × 10-5 mbar, microwave power 250 W and extraction
voltage 20 kV, the measured total beam current, was 1.8
mA. In the case of nitrogen plasma, we obtained 760 µA
of beam current at a working gas pressure of 8.4 × 10-6
mbar, microwave power of 250 W, and extraction voltage
20 kV. The variation of total beam current of hydrogen
and nitrogen with extraction voltage is shown in figure 6.
The tendency shows that still higher intensities can be
extracted at higher voltages.
Figure 4: View of the microwave ion source coupled to
the microwave and extraction systems.
Figure 6: Measured total beam current with variation of
extraction voltage for hydrogen and nitrogen plasmas.
The extraction system is a standard ‘three-electrode’
system working in the ‘accel-decel’ mode and mounted
inside a vacuum chamber pumped by a 1000 l/s turbomolecular pump shown in figure 4. Gas is bled inside the
plasma chamber through a capillary tube and flow rate is
controlled by a gas valve controller. Taking into account
the experimental conditions, the maximum voltage for ion
source and the ‘accel-decel’ system is 30 kV and 15 kV
respectively. A schematic view of the low energy beam
transport section coupled to the microwave ion source is
shown in figure 5.
We also observe that there are two ring marks on the
inner wall of the plasma chamber pertaining to the
injection ring and the extraction ring as per the
simulations.
FUTURE PLANS
A new compact LEBT system is planned for this
system. The design and development of the new compact
LEBT system is in progress. A new multi-electrode
extraction system is designed for extracting intense
beams. It consists of four electrodes having an aperture
Figure 5: Schematic view of the low beam energy transport (LEBT) section coupled to the microwave ion source.
of 10 mm & total length of 60 mm. The beam optics for
this system is designed using IGUN [7] and is shown in
figure 7. The 3d model based on the multi-electrode
design is shown in figure 8.
Figure 10: View of the new 2.45 GHz Microwave ion
source plasma chamber.
Figure 7: Calculated optics for transporting 10 mA of
protons in newly designed multi-electrode.
CONCLUSIONS
A 2.45 GHz microwave source together with the low
energy beam transport has been successfully designed,
developed and commissioned at IUAC, New Delhi. In the
near future, a compact LEBT system is found to be
essential to minimise beam losses. The design and
development of the compact LEBT is under progress.
ACKNOWLEDGEMENT
One of the authors (N. Kumar) is grateful to University
Grant Commission (UGC), India for financial support
through Junior Research Fellowship (JRF). The Authors
would like to thank the workshop personnel and other
staff members for their help.
Figure 8: (a) Schematic view of the new multi-electrode
extraction system and (b) cross sectional view.
A new compact, water cooled plasma chamber is
designed and is shown in figure 9. The fabricated new
compact, water cooled plasma chamber is shown in
figure10. In the new designed ion source, the advantages
are better plasma chamber cooling, additional ports for
Langmuir probes/diagnostics, better microwave coupling
through the ridge waveguide.
Figure 9: Schematic view of the new 2.45 GHz
Microwave ion source’s plasma chamber.
REFERENCES
[1] Y. Mathur, G. Rodrigues, R. Ahuja, U. K. Rao, N.
Kumar, P. S. Lakshmy, D. Kanjilal & A. Roy, Indian
Particle Accel. Conf. INPAC, IUAC Delhi, Feb. 1518, 3B 60 (2011).
[2] Narender Kumar, G. Rodrigues, Y. Mathur, R. Ahuja
and D. Kanjilal, Workshop on Highly Charged Ions
and Atomic Collisions 2012 (WHCI 2012), TIFR,
Mumbai, India, Mar. 28-31, pp 16 (2012).
[3] N. Sakudo, Rev. Sci. Instrum. 49,940 (1978).
[4] Y. Gotoh, H. Kubo, H. Tsuji and J. Ishikawa, Rev.
Sci. Instrum. 71, 1160(2000).
[5] S. Biri, A. Deszsi, E. Fekete and I. Ivan, 2007 High
Energy Phys. Nucl. Phys. 31, 165.
[6] ni.com/labview/
[7] R. Becker and W. B. Herrmannsfeldt, Rev. Sci.
Instrum. 63, 2756 (1992).