Ⅰ. HIGHLIGHTS OF THE YEARRIKEN Accel. Prog. Rep. 56 (2023)
RIKEN
Accel. Prog. Rep. 56 (2023)

Energy measurement of beam from SRC for GUINNESS WORLD
RECORDSTM registration
H. Okuno,∗1 N. Fukuda,∗1 H. Haba,∗1 H. Hasebe,∗1 Y. Higurashi,∗1 H. Imao,∗1 H. Otsu,∗1 H. Sakurai,∗1Y. Shimizu,∗1 T. Sumikama,∗1 D. Suzuki,∗1 H. Suzuki,∗1 H. Takeda,∗1 K. Yoshida,∗1 and M. Yoshimoto∗1The SRC (Superconducting Ring Cyclotron) wasregistered into GUINNESS WORLD RECORDSTM asthe highest beam energy cyclotron on April 11 2022.1)
The energy of the beam from the SRC was measured
mainly using BigRIPS prior to the registration. Theacceleration of 238 U up to 345 MeV/nucleon was chosen to maximize the energy of the extracted beam.
The energy ET of the beam extracted from the SRC
is expressed as√
ET = (M0 c2 )2 + (pc)2 − M0 c2(1)
pc = Q × ecBρ(2)
M ∼ M0 /Mamu(3)
where M0 , M , Mamu , p, c, Q, e, and Bρ express therest ion mass, mass number, uniﬁed atomic mass unit,
momentum, speed of light, charge state, elementarycharge, and magnetic rigidity, respectively. Therefore,M , Q, and Bρ must be measured or deﬁned. Z is also
required to be deﬁned in the measurement.
Firstly we must show that the accelerated particle is238
U (Z = 92, M = 238). Mass spectra were measured
in the ion source plasma used in the RIBF accelerator
complex. Measurements were taken at 2 kV and 22 kV
extraction voltages. M/Q was calibrated using the two
peaks of m/q = 1 and m/q = 2 at 22 kV. The obtained
data show that the mass of the heaviest element in thesource is approximately 236. The only nuclei that arestable in nature at these mass numbers are 232 Th or238
U. The color of the sample in the ion source wasdark brown, a typical color of UO2 , while the color ofThO2 is white. From these reasons, it can be deduced
that the Z and M of the accelerated ion beam are 92
and 238, respectively. The accelerated ion, therefore,
is 238 U.
Secondly, the beam energy is roughly measured.
This measurement helps us to deﬁne charge state of theaccelerated beam in the succeeding measurement. Atarget of Be is placed at F0 in BigRIPS, and the energyof the particles in full strip (Q = Z = 92) is measured.
Three target thicknesses are prepared: 0.5 mm, 1 mm,and 2 mm. The obtained data are plotted as shown inFig. 1 together with linear regression. When the thickness of the target is zero, the approximation indicatesthe beam’s original energy. Because the energy loss is
not proportional to the thickness of the target, it is alittle oﬀ from the correct answer but is still accurateenough to identify Q in the next process.
Thirdly, magnetic rigidity Bρ of the accelerated∗1RIKEN Nishina Center- S22 -Fig. 1. Energy of 238 U92+ versus the target thickness withlinear regression.

beam is measured through the BigRIPS without thetarget. Because the charge is still undetermined, theblue dots in Fig. 2 show that the energy can jumpfrom one value to another under a constant Bρ condition. In contrast, from the results obtained previously,
we know that the energy is approximately around theorange line, so thus we determined Q to be 86. We
deduced the extracted energy of 82400 MeV by combining the measured Bρ value with Q = 86.

Fig. 2. Beam energy converted from the measured Bρ as afunction of assumed Q values of the accelerated ion.

Reference1) https://www.guinnessworldrecords.com/world-records/
675272-highest-beam-energy-cyclotron .