7th Asia-Pacific Conference on Plasma Physics, 12-17 Nov, 2023 at Port Messe Nagoya

Numerical Study for Influence of Different Gap Length on Nanoparticles
Synthesis by Tandem-Modulated Induction Thermal Plasma
Jingqian Peng1, Rio Okano1, Yasunori Tanaka1, Yusuke Nakano1, Tatsuo Ishijima1,Shiori Sueyasu2, Shu Watanabe2, Keitaro Nakamura2
1
Kanazawa University, 2Nisshin Seifun Group Inc.
e-mail (speaker): pengjingqian@stu.kanazawa-u.ac.jp

We have so far developed the pulse-modulatedinduction thermal plasma (PMITP) and time-controlledfeedstock feeding (TCFF) method to produce large
amounts of nanoparticles. For the improvement of themethod, a numerical simulation model has beendeveloped, which could calculate the temperature
distribution, flow velocity, nucleation frequency, average
nanoparticle size and so on for different experimental
conditions [1]. Furthermore, we developed the two-coiltandem-type modulated induction thermal plasma(Tandem-MITP) to prevent destabilization of plasma due
to raw material injection [2]. In this paper, the gap length
g between the two coils were studied, and a suitable gap
length could benefit the generation of nanoparticles.
The developed numerical model solves the momentum
conservation equations, energy conservation equations,mass conservation equations and Poisson’s equations to
get the distributions of multiphysics fields. As calculation
conditions, the Ar was supplied as sheath gas and carriergas with 90 L/min and 4 L/min, respectively. The chamberpressure was 300 torr. The Si feedstock powder wassupplied with 1.0 g/min/rad intermittently, synchronizing
with the coil current. For the upper and lower coils, theaverage powers were set to both 10 kW. The upper coilcurrent frequency is 420 kHz, while the lower one is 210
kHz. The shimmer current level (SCL) for the upper coilcurrent is 70%, while it is 10% for lower coils. The
modulation cycle was 20 ms, in which there is 10 ms forhigh-current state, while there is 10 ms for low-current
state. As comparison, the gap length (g) was set as 20 mm,40 mm, 60 mm, 80 mm and 100 mm.
Fig. 1 shows the calculated particle size distributions.
As shown, the sum of the nanoparticle counts for the gaplength of 100 mm is the largest, while the cumulative
fractions are similar for different g’s. Thus, the change in
g causes the change in nanoparticle amount, while hardly
influencing the ratio of particles with different diameters.
For the distributions of multiphysics fields, thesimulation shows that the maximum of the temperature in
the torch would be higher for longer g, as shown in the left
panels in Fig. 2. The area where a higher nucleation
frequency could be achieved near the coil would be larger
with a longer g, as depicted in the right panels in Fig.2.
The higher temperature field would result in more
efficient evaporation of silicon feedstock, which would
help to nucleate more frequently. At the same time, thehigher temperature causes a higher gas flow velocity. This
would result nucleated particles transported more broadly.
As the gap length g increases, Si vapor is produced at
higher concentrations and nucleated at higher frequencies,
which would transport them downstream to produce alarge number of nanoparticles.

References[1] R. Furukawa, et al. J. Phys. D: App. Phys.
55.4,044001 (2021).
[2] R. Furukawa, et al. Plasma Chem. & Plasma Process.
42.3, 435-463 (2022).

(a) g=20 mm(b) g=60 mm(b) g=100 mm
Figure 1 Particle diameter distribution
for g=20, 60, and 100 mm.

(a) g=20 mm(b) g=60 mm(c) g=100 mm
Figure 2 Two-dimensional gas temperature
distributions(left) and nucleation frequency
distributions(right) for different gap lengths
at t=2.5 ms during off-time.