Ⅱ-9. Instrumentation

RIKEN Accel. Prog. Rep. 49 (2016)

ANSYS code calculations for measuring beam spot temperature
Z. Korkulu,∗1 K. Yoshida,∗1 Y. Yanagisawa∗1, and T. Kubo∗1
RIBF cyclotrons can accelerate very heavy ions suchas uranium up to 345 MeV/nucleon. The goal beam intensity is expected to be 1 particle µA (6.2×1012 pps),
which corresponds to a beam power of 82 kW in thecase of 238 U1) . An important aspect in increasing beam
intensity is limiting the maximal temperature due tobeam energy loss in the material. Controlling this absorbed power is a key challenge. Therefore, a highpower production target system2,3) was designed andconstructed in 2007 for the BigRIPS separator4,5). The
water-cooled rotational disk targets and ladder-shaped
fixed targets are currently in operation.
As the fixed ladder-shaped target, a Be taper of
3-mm thickness was irratiated by a 238 U beam of
345 MeV/nucleon, up to 38 pnA with a beam spot sizeof 1.5-mm diameter. This target was tightly mounted
on a water-cooled target holder using a 5-mm thickaluminum fixing plate. Although the present primarybeam intensity is much lower than the goal value, thebeam spot temperature at various conditions was measured and compared with thermal simulations to examine the beam power tolerance and to evaluate thecooling capacity of the high-power production target.
The finite element thermal analysis code, ANSYS6) ,was used to model thermal distributions in the targets.
Figure 1 shows the quarter model of the laddershaped target and the result of the temperature distribution calculated by the steady-state thermal analysis.
The mesh of the target body is generated using threedimensional hexahedral elements 0.2 mm in size. The
input power was given as the heat generation, which isapproximately 87 W/mm3 . In addition, the total absorbed power in the whole Be target, not the quartermodel, is approximately 460 W for 35 pnA intensity.
Owing to the high energy deposition in the target, thetarget system is cooled using a forced convection mode.
For forced convection, the heat transfer coefficient of
the cooling channel was calculated (using JAERI formula7) ) and used in the simulation. For this simulation, the cooling water (25◦ C) flowed at 3.5 l/min
through the cooling channel. To ensure efficient heattransfer, the temperature-dependent thermal conductivity of Be and Al were used at temperatures between
25 and 750◦C. As shown in Fig. 1, the maximum temperature of the target center was approximately 650◦ C
under the above mentioned conditions. Figure 2 shows
the calculated and measured beam spot temperature
on a Be target as a function of the primary beam intensity of 48 Ca, 78 Kr, and 238 U. For all primary beams,
the temperature is always below the melting temperature (1278◦ C) of the Be target for beam intensities∗1RIKEN Nishina Center- 157 -Fig. 1. Quarter finite element analysis model and the calculated temperature distrubiton in the Be target.

Fig. 2. Calculated and measured beam spot temperature
on a Be target as the function of a different primarybeam intensity.

used in the simulation. In order to reach the goal intensity, it is recommended to use a water-cooled rotating disk target with a suitable velocity so that different
parts of the target are irradiated by bunches.
Presently, the beam spot temperature calculated using the ANSYS code is higher than the measured beam
spot temperature8) . Discrepancy between the measured temperature and the simulation can be caused by
the suboptimal spatial resolution of the thermal camera system. Since the spatial resolution of the thermal
camera is approximately 2 mm, some improvements toachieve a more accurate measurement will be necessary.
References
1) Y. Yano, Nucl. Instr. Meth. B 261, 1009 (2007).
2) A. Yoshida et. al., Nucl. Instr. Meth. A 521, 65 (2004).
3) A. Yoshida et. al., Nucl. Instr. Meth. A 590, 204 (2008).
4) T. Kubo, Nucl. Instr. Meth. B 204, 97 (2003).
5) T. Kubo et al., IEEE Trans. Appl. Sup. 17, 1069 (2007).
6) ANSYS, Inc. Product Release 16.0, USA.
7) J. Boscary et al., Fusion Eng. Des. 43, 147 (1998).
8) Y. Yanagisawa et al.: In this report.