Ⅱ-9. Instrumentation

RIKEN Accel. Prog. Rep. 53

Thermal model simulation of high-power rotating target for BigRIPS
separator
K. Yoshida,∗1 Z. Korkulu,∗1 Y. Yanagisawa,∗1 and T. Kubo∗1
A realistic thermal-model simulation is particularly
important to evaluate the beam-power tolerance of thehigh-power rotating target system of BigRIPS separator,1,2) which has been successfully operating at RIBF
since 2007. The target system was designed to withstanda beam power of 82 kW, which corresponds to the goal
beam intensity of 1 particle µA (pµA) for a 238 U beam at345 MeV/nucleon. The available beam intensity at RIBF
was 13 kW so far, less than 20% of the goal. Therefore,
thermal-model simulations were utilized to estimate thethermal behavior of the target system for high-intensity
beams from the observation at lower beam intensities.
Many eﬀorts1–5) have been devoted to the thermal
model simulations of the target systems with ﬁniteelement ANSYS code. In the simulations, the rotating target was modeled using a mass transport optionof ANSYS6) to describe the rotating motion. The model
worked ﬁne at the design stage4) but has been less usable because a recent version of ANSYS limits the use ofmass transport only for motion slower than the thermal
diﬀusion speed. Since the rotating target distributes theheat load by a fast rotating motion, the restriction prevents the simulation in the operational condition of therotating target.
A new model of the rotating target was developed to
avoid the restrictions. In the new model, the target itself
is ﬁxed, and a heat source moves along the circumferenceof the target. As shown in Fig. 1, many heat sources witha square shape of 1 mm by 1 mm were deﬁned along thecircle of the beam trajectory, and each source was excited by a heat load at a slightly diﬀerent timing along
the trajectory. Thus, the rotation of the heat source was
successfully accounted for in the transient thermal calculation of ANSYS. In order to obtain the temperature distribution of a rotating target at the steady state, we haveFig. 2. Temperature distribution of the rotating target forirradiation with a 238 U beam at 345 MeV/nucleon, 1 pµA.

to simulate whole thermal equilibration process startingwith the room-temperature target. More than 400 rotations of a spot heat source were necessary to obtainthe saturation of the temperature. This process can beshortened by starting with the temperature distributionof a time-averaged heat source, which was calculated bysteady-state thermal calculations with a time-averaged
circular heat source. A nearly steady temperature distribution was obtained after 3–4 rotations of the spot
heat source in this case.
A simulation for the case of a 238 U beam at an energyof 345 MeV/n and 1 pµA impinging on a 2-mm-thick
Be target was performed, and the resulting temperature
distribution is shown in Fig. 2. Heat transfer coeﬃcientsof 10.5 and 3 kW/m2 K were used for thermal contacts
between the cooling water and cooling disk and between
the cooling disk and Be target, respectively. As shown inFig. 2, the highest temperature of 1230◦ C indicated by
the “Max” label was obtained at the beam spot. Starting at the beam spot, the high-temperature region wasspread along the beam trajectory. The calculation showsthat the Be target does not melt in the heat of the beam
since the melting point of Be is 1287◦ C. The maximum
temperature of the calculation for 238 U beam at 30 pnA
was 66◦ C, which is consistent with the measured temperature of 63.6◦ C at RIBF. Thermo-mechanical calculations are in progress to check the thermal deformation
or destruction of the target.
References

Fig. 1. Model of the rotating target. Graphs are the time
structure of heat loads applied to heat source cells.
∗1RIKEN Nishina Center1) 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) A. Yoshida et al., RIKEN Accel. Prog. Rep. 35, 152 (2002).
4) A. Yoshida et al., RIKEN Accel. Prog. Rep. 37, 295 (2004).
5) Z. Korkulu et al., RIKEN Accel. Prog. Rep. 52, 132 (2019).
6) ANSYS. Inc Product Release 19.

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