Ⅱ-9. Instrumentation

RIKEN Accel. Prog. Rep. 52 (2019)

Thermal model simulation of high-power rotating target for BigRIPSseparator
Z. Korkulu,∗1 K. Yoshida,∗1 Y. Yanagisawa,∗1 and T. Kubo∗1,∗2
Since 2007, a water-cooled high-power rotating disktarget made of beryllium or tungsten has been used as
the production target at the in-ﬂight radioactive-isotope(RI) beam separator BigRIPS.1,2) The diameter of therotational disk is 30 cm while the thickness can be optimized according to the atomic number and the energyof the selected projectile. To obtain a variety in thickness, the circumference edge of each disk has two steps
to realize less thicknesses. The rotational disk target
system was designed to withstand the maximum beam
intensity of 238 U at 345 MeV/nucleon and 1 particle µA.
Although only about 20% of the goal beam intensity of
82 kW has been achieved, the high-power rotating target system has been successfully operated with variousbeams. Because the present primary beam intensity ismuch lower than the goal value, the requirement that Be
could withstand the goal intensity cannot be experimentally commissioned. Therefore, we started to develop
simulations based on ANSYS Parametric Design Language (APDL)3) to calculate the beam spot temperature
at various conditions. Earlier, a prototype target system
was designed and constructed using the same simulation
code.4,5)
In the analysis, a complete model built by APDL wasused. The primary beam was focused at a diameter of
1 mm (FWHM) with Gaussian beam distribution. The
power deposition in beryllium material was calculatedwith the LISE++ simulation code.6) To include the effect of radiation cooling, the emissivity of 0.57 was used
for the surface of the Be disk.5) The target disk wastightly ﬁxed with screws on the water-cooled aluminum
plate (see Fig. 1) and the boundary temperature for theFig. 2. A 48 Ca primary beam at 345 MeV/nucleon with
470 pnA (7.8 kW in beam power) onto the beryllium target of 10 mm thickness. The heat deposited in the target
was 0.96 kW for a beam spot size with a diameter and rotation speed of 1 mm and 10 rpm, respectively. The maximum beam spot temperature is approximately 118◦ C.

cooling water was ﬁxed at 25◦ C. The heat transfer coefﬁcient, calculated by JAERI formula,7) was found to be
10.5 kW/m2 K at 25◦ C. Because the beam spot temperature varied with time, the temperature-dependent thermal conductivity of Be and Al was used for temperatures
between 25 and 1200◦ C and 25 and 700◦ C, respectively.
In our simulations, the heat source was ﬁxed and thetarget model moved across it based on the mass transport option of ANSYS. To capture the eﬀect of temperature variation occurring in the model, the applied meshsize must be small enough. Although the beam spot temperature became constant after several rotations, thiscomplex model required a few hours of the CPU time.
The initial analysis was performed with low rotational
speed, from 1 to 10 rotations per minute (rpm), in several
steps to conﬁrm the reliability of our simulation code.
The present status of simulated heat distribution with
10 rpm is reported in Fig. 2. Further simulation studies
are under way to optimize a small mesh size that canincrease the rotation speed of the disk target up to therequired velocity of 100 to 1000 rpm.
References

Fig. 1. Cooling-water is introduced to the aluminum disk
through a double-piped shaft.
∗1∗2

RIKEN Nishina Center
Facility for Rare Isotope Beams, Michigan State University

1) A. Yoshida et al., Nucl. Instrum. Methods Phys. Res. A
521, 65 (2004).
2) A. Yoshida et al., Nucl. Instrum. Methods Phys. Res. A
590, 204 (2008).
3) ANSYS, Inc. Product Release 19.0, USA.
4) A. Yoshida et al., RIKEN Accel. Prog. Rep. 35, 152 (2002).
5) A. Yoshida et al., RIKEN Accel. Prog. Rep. 37, 295 (2004).
6) O. Tarasov et al., Nucl. Instrum. Methods Phys. Res. B
266, 4657 (2008).
7) J. Boscary et al., Fusion Eng. Des. 43, 147 (1998).

- 132 -