II-9. Instrumentation

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Thermo-mechanical simulation of high-power rotating target for
BigRIPS separator
K. Yoshida∗1 and Y. Yanagisawa∗1
Thermo-mechanical simulations have been performed
for the high-power rotating target system 1,2) of the BigRIPS separator in order to evaluate the stability of therotating target against high-power beam irradiation. A
2-mm-thick Be target rotating at 300 rpm is expected toheat up to 1230◦ C 3) with a 238 U beam at an energy of345 MeV/nucleon and intensity of 1 particle µA, whichmeets the target beam intensity of RIBF. The Be target does not melt in the heat of the beam, because themelting point of Be is 1287◦ C. However, it is not clear
whether the target is stable under thermal deformationor the destruction of the target at such a high temperature. Thus, the thermo-mechanical simulation of therotating target was performed to check its stability.
Coupled transient thermal-structural ﬁnite-element
analysis using the simulation code ansys 4) was utilizedfor the thermo-mechanical simulation. In the ﬁrst step,
the temperature distribution of the rotating target wasobtained through a transient thermal calculation withthe moving heat-source model described Ref. 3). The
simulation model consisted of the Be target with a diameter of 300 mm and thicknesses of 2, 3, 4 mm anda cooling disk with a diameter of 240 mm and a thickness of 25 mm in which a cooling water channel wasformed. The temperature dependence of thermal conductivity and heat capacity were taken into account in
the calculation. Heat transfer coeﬃcients of 10.5 and3 kW/m2 K were used for thermal contacts between thecooling water and cooling disk and between the cooling disk and Be target, respectively. The obtained timedependent temperature distribution was then transferredto the transient structural calculation with ansys under elastic and plastic deformation. The deformationand stress caused by the thermal expansion of the target at the given temperature distribution were calculated
in a time-dependent manner. The temperature dependence of the Young’s modulus, strain-stress curve (bilinear hardening is assumed), and thermal expansion coefﬁcient of the Be target were taken into account in thecalculation.
Figure 1 shows the calculated results for a 238 U beamat 345 MeV/nucleon and 1 particle µA with a size of
1 mm2 impinging on a 2-mm-thick Be target rotating at
300 rpm. In the ﬁgure, only half of the model is displayed in order to show the cross section of the target.
In Fig. 1(a), the temperature distribution is mapped incolor on the original model shape. The highest temperature is observed at the beam spot, and the hightemperature region is spread along the beam trajectory.
The Von Mises stress due to the thermal expansion ismapped on the deformed model shape in Fig. 1(b). The∗1

RIKEN Nishina CenterFig. 1. Results of thermo-mechanical calculation of the rotating target. Only half of the simulation model is displayedin the figure to show the cross section of the target. (a)Temperature distribution of the target displayed in color
on the original model shape (not deformed). (b) von
Mises stress distribution displayed in color on the deformed shape. Deformation was magnified by a factor
50 so that the deformation can be viewed easily.

deformation is magniﬁed by a factor 50 and shown inFig. 1(b). The Be target is enlarged by 0.6 mm in theradial direction and bent toward the cooling disk by
0.3 mm at the circumference. Thus, the deformationis very small compared with the 300-mm diameter of therotating target. A small but ﬁnite plastic deformation isobserved along the beam trajectory. This is why the vonMises stress at the beam trajectory decreases after thebeam passes. A plastic expansion occurs at the beamspot, and the expanded shape is retained even when thetemperature drops after the beam passes through.
The maximum von Mises stress of 260 MPa appearedat the contact region between the target and cooling disk.
The value is well below the ultimate tensile strength of440 MPa. The calculation results show that the rotatingtarget is stable under thermal deformation and destruction.
References

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) K. Yoshida et al., RIKEN Accel. Prog. Rep. 53, 103 (2020).
4) ansys. Inc Product Release 20.

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