Ⅱ-9. Instrumentation

RIKEN Accel. Prog. Rep. 51 (2018)

Surface temperature measurements of the high power beam dump ofthe BigRIPS separator
K. Yoshida,∗1 Y. Yanagisawa,∗1 Z. Korkulu,∗1 H. Takeda,∗1 K. Kusaka,∗1 N. Fukuda,∗1 and T. Kubo∗1,∗2
The surface temperatures of the high-power beam
dump1,2) of the BigRIPS separator were measured during the irradiation of the 48 Ca beam with a beam powerof 8.3 kW in order to evaluate the cooling power of thebeam dump. The beam dump consists of the side dumpand the exit dump. The two exit beam dumps with
1 mm and 3 mm wall thicknesses were designed to handle various ion beams up to 238 U with intensities of up
to 1 pµA.2) The exit beam dump with 3 mm wall thickness and the side dump were constructed in 2007. Since
then, they have been successfully operated with variousbeams. The design of the beam dumps was based on thesophisticated thermal model simulation;1,2) however, its
validity has not been well veriﬁed because of the limitation of available beam intensity. With the intense 48 Cabeam, which recently became available, temperatures of
the inner-side exit beam dump were measured by using the thermocouples mounted on the dump.3) The observed temperatures were consistent with the thermal
model simulations, indicating that the beam dump has
the expected cooling power. However, the results havesome ambiguity. The highest temperature in the beam
dump is expected at the beam impinging surface, but
the thermocouples measure temperatures 3 mm behindthe dump surface. In order to obtain clearer results,measurements of the surface temperature are highly desired.
The surface temperature of the outer-side exit dump
was measured with the compact thermo-viewer camera IP160 manufactured by OPTRIS. The camera wasplaced at the side window of the beam dump chamber,as shown in Fig. 1. A vacuum window made out ofBaF2 was used to observe the infrared image of the dump
surface, which was irradiated with the 48 Ca beam having an energy of 345 MeV/n and intensity of 500 pnA.
The beam size on the dump surface was estimated to be
20 mm (X) and 30 mm (Y) from the separately measured beam emittance. A BaF2 crystal with a thicknessof 13 cm was placed between the vacuum window andthe camera to reduce radiations (γ-rays and neutrons)from the beam dump. For further reduction of radiations, 20 cm thick concrete shielding blocks surrounded
the camera. Cooled water, with a temperature of 13◦ C,
pressure of 1.0 MPa, and ﬂow speed of 10 m/s, were supplied to the dump as the coolant. The temperatures werealso measured by using a thermocouple (TC) mounted
on the dump 3 mm behind the dump surface.
The observed thermal image is shown in Fig. 2. The
beam hitting portion of the beam dump is seen as a hotspot. Its size is about 30 mm (X) × 10 mm (Y), and the∗1∗2

RIKEN Nishina Center
FRIB/NSCL, Michigan State University

Fig. 1. Setup for the surface temperature measurement ofthe beam dump.

Fig. 2. Thermal image of the beam dump with 8.3 kW 48 Ca
beam irradiation.

temperatures are 62 and 23◦ C according to the beamon and oﬀ. The temperatures of the TC are 15.4 and13.6◦ C. The temperatures observed by the camera need
to be corrected for the emissivity and the attenuation of
the vacuum window and the BaF2 crystal. The calibration data was taken by changing the temperatures of thecooling water in oﬀ-line condition. The observed temperatures varied from 23 to 32◦ C when temperatures ofthe dump varied from 15 to 45◦ C. With the assumptionof the linear relation between both the temperatures,the observed temperature 65◦ C corresponds to an actual temperature of 147◦ C.
ANSYS4) simulation for this condition shows that thespot temperature is 170◦ C and the temperature at TC is46◦ C. Both temperatures are higher than the observed
ones. The observed temperatures can be reproduced bymodifying the beam size to 30 mm (X) and 22 mm (Y)and shifting the center of the beam 0.6 mm downward(this corresponds to 6 mm shift on the dump surface).
The observed spot size is also reproduced by the modiﬁcation.
References
1) N. Fukuda et al., RIKEN Accel. Prog. Rep. 41, 119(2008).
2) K. Yoshida et al., Nucl. Instrum. Methods B 317, 373(2013).
3) K. Yoshida et al., RIKEN Accel. Prog. Rep. 49, 159(2016).
4) ANSYS Inc. Product Release 18.0, USA.

- 171 -