Ⅱ-9. Instrumentation
RIKEN
Accel. Prog. Rep. 56 (2023)

RIKEN Accel. Prog. Rep. 56 (2023)

Conceptual design of new high-power beam dump for BigRIPS
Y. Togano,∗1 N. Fukuda,∗1 H. Suzuki,∗1 Y. Shimizu,∗1 H. Takeda,∗1 M. Yoshimoto,∗1 and K. Yoshida∗1A new high-power beam dump situated at the exitof the ﬁrst dipole magnet (D1) in the BigRIPS separator has been designed to absorb a 2 particle µA 238 U
beam at 345 MeV/nucleon. The BigRIPS separator isequipped with beam dumps located both inside and at
the exit of the D1 magnet to intercept unreacted beams
resulting from primary beam + production target reactions at the focal plane F0. In the near future, theRIBF intends to utilize a 2 particle µA 238 U primarybeam, which is 30 times more intense than the current 238 U beam, in order to produce a greater varietyof exotic nuclei. However, the existing beam dump at
the exit of the D1 magnet (hereafter referred to as theexit-beam dump) is incapable of safely absorbing suchan intense beam due to insuﬃcient cooling power. For
performing experiments with 2 particle µA 238 U beam,
a new high-power exit-beam dump, that utilizes a rotating water-cooled copper drum, has been designed.
The schematic depiction of the newly proposed exitbeam dump is illustrated in Fig. 1. The drum-shaped
beam dump, measuring 300 mm in diameter and
350 mm in depth, rotates about its central axis to
distribute heat and improve radiation damage resulting from the intense beam. The dump is made of acopper alloy, speciﬁcally Cu-Cr-Zr, and is equippedwith 72 screw tubes (M8 tapped) to serve as watercooling channels.1) The water ﬂowed in the coolingchannels is pressurized at 1 MPa and runs at a velocity of 10 m/s, ensuring a high rate of heat transfer between the cooling water and the copper alloy. This M8
tapped cooling channels have already been equipped
for the present exit beam dump.2) The distance fromthe surface of the dump to the center of each coolingchannel is 14 mm, and the pitch of the cooling channels
is 12.2 mm. The rotational frequency of the dump isassumed to be suﬃcient to achieve a uniform temperature distribution along the circumference of the dump.
The cooling capacity of the dump is evaluatedthrough ﬁnite element method simulation utilizing theANSYS code. The results of the simulation are appraised against the following criteria:2) the maximum
temperature of the dump should be less than 350◦ C tomaintain the radiation hardness of the dump, and theheat ﬂux at the surface of the cooling channels mustbe less than the critical heat ﬂux (55 MW/m2 ) for stable cooling of the dump. It is known that copper alloy
keeps good radiation hardness at temperatures below
400◦ C. Above the critical heat ﬂux, the heat transfer
rate at the cooling channel abruptly decreases as thesurface of the cooling channel becomes covered withvapor generated by vigorously boiling cooling water.
In the simulation, it is assumed that a 2 particle µA
238
U beam (Q = 86+ ) at 345 MeV/nucleon is directly
impinged on the dump as illustrated in Fig. 1a). The
beam spot on the dump is of an elliptical shape due
to overfocus by the D1 magnet. The ratio of magnetic
rigidities between the 238 U beam and a beam following the central trajectory of the D1 magnet is assumed
to be 0.85. The range of the 345 MeV/nucleon 238 U
beam in copper alloy is 3.2 mm.
Figure 1b) illustrates the calculated temperature
distribution on the surface of the dump upon the impingement of the 2 particle µA 238 U beam. The maximum temperature of the dump is 159◦ C and the maximum heat ﬂux at the surface of the cooling channel
is 5.4 MW/m2 . These values are below the allowabletemperature and the critical heat ﬂux, indicating thatthe new dump can safely absorb the 2 particle µA 238 Ubeam. The detailed design of the new exit beam dump
is currently underway.
References
1) J. Boscary et al., Fusion Eng. Des. 43, 147 (1998).
2) K. Yoshida et al., Nucl. Instrum. Methods Phys. Res. B
317, 373 (2013).

Fig. 1. a) Schematic view of the new exit beam dump. b)
Caluculated temperature distribution on the surface ofdump impinged by a 2 particle µA 238 U primary beam.
∗1RIKEN Nishina Center- 79 -