II-8. Accelerator

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

High-intensity vanadium-beam production to search for a newsuper-heavy element with Z = 119†
T. Nagatomo,∗1 Y. Higurashi,∗1 J. Ohnishi,∗1 T. Nakagawa,∗1 and O. Kamigaito∗1In March 2020, we successfully accelerated theﬁrst beam (40 Ar13+ ) using several superconducting
quarter-wavelength resonators (SC-QWRs)2) installedin RIKEN heavy-ion linear accelerator (RILAC)1) toachieve enough energy to synthesize new super-heavyelements (SHEs) with an atomic number greater than118. To overcome the extremely small production
cross section of SHE with Z = 119, it was necessary to provide a highly charged vanadium (V)-ionbeam such as 51 V13+ with very high intensity. Thus,
we constructed a superconducting electron cyclotron
resonance ion source (SC-ECRIS) for RILAC, which
was named RIKEN 28-GHz SC-ECEIS “KURENAI”(R28G-K).3) R28G-K has essentially the same structure4) as another SC-ECRIS that is the only source ofheavy ions including uranium for RIBF, which is renamed RIKEN 28-GHz SC-ECEIS “SUI” (R28G-S).5,6)
When operating the SC-QWR, the particulate mattersputtered from the beam pipe irradiated by the beamis thought to signiﬁcantly reduce the gap voltage byincreasing the surface resistance of the cavity, thus wemust suppress the beam loss as much as possible. For
this purpose, we installed “slit triplet” in the low energy beam transport to limit the transverse emittance.3)
This indicates that only a portion of the beam extracted
from R28G-K is available despite the demand for an
unprecedented beam intensity. Therefore, we systematically studied the eﬀects of the amount of the V vapor and power of the microwaves, which heat up theplasma in the ion source, on the beam intensity, andthe optimal parameters that would allow long-term experiments with the highest possible beam intensity.
The upper ﬁgure in Fig. 1 shows the two high temperature ovens (HTOs)7) installed in the ion source. TheHTO was developed as an evaporator for high melting
point materials such as vanadium. The V-vapor amount
was equivalent to the sum of the consumption rates ofthe metallic V sample in each HTO crucible. The capacity of each crucible was approximately 2.2 gram of
the granular metallic V. The 51 V13+ -beam intensity extracted from R28G-S was obtained as a contour plot
in the lower ﬁgure in Fig. 1 as a function of the consumption rate of the V metal and the total power ofthe 18- and 28-GHz microwaves. As a consequence ofthe contour plot, it was deduced that a 400-electric µA
V13+ -beam can be produced at ∼6-mg/h consumption
and 2.5-kW microwaves. Because the total capacity ofthe two HTO crucibles is 4.4 gram, we can provide the†∗1high intense V beam for one month without interruption. Furthermore, at 24-mg/h consumption and 2.9kW microwaves, we also obtained the V-ion beam withan intensity of 600 electric µA that is suitable for essential development, for example, target development.

28-GHzwave guide

Crucible
HTO2

18-GHzwave guide

Biased disk

Crucible
HTO1

51V13+ beam intensity (electric µA)

0200

400600Supporting gas : 14N2
Acceleration voltage:12.6 kVConsumption rate (mg/h)
Fig. 1. Two HTO mounted on the injection flange of theplasma chamber of R28G-K (upper), and obtained contour plot of the 51 V13+ beam intensity as a function ofthe consumption rate and the microwave power (lower).

References

1) E. Ikezawa et al., in Proc. HIAT2015, (Yokohama, Japan,2015), p. 222.
2) N. Sakamoto et al., Proc. SRF2019, (Dresden, Germany,2019), p. WETEB1.
3) T. Nagatomo et al., Rev. Sci. Instrum. 91, 023318 (2020).
4) G. D. Alton et al., Rev. Sci. Instrum. 65, 775 (1994).
5) T. Nakagawa et al., Rev. Sci. Instrum. 81, 02A320 (2010).
6) Y. Higurashi et al., Rev. Sci. Instrum. 85, 02A953 (2014).
7) J. Ohnishi et al., Proc. ECRIS2018, (Catania, Italy,2018), p. 180.

Condensed from the article in the Proc. of 24th Int. Workshop on ECR Ion Sources (ECRIS’20), East Lansing, USA,
September 2020, in press
RIKEN Nishina Center- 75 -1