Ⅱ-8. Accelerator

RIKEN Accel. Prog. Rep. 52 (2019)

Operation of high-temperature oven for 28-GHz superconducting ECR
ion source
J. Ohnishi,∗1 Y. Higurashi,∗1 and T. Nakagawa∗1Table 1. Summary of MT using HTO.

∗1

RIKEN Nishina Centermaterial

consumption
rate (mg/h)

34

UO2

2.4

35

UO2

3.2

UO2

4.0, 4.2, 12

periodU35+

10–11/2016

100–120

U35+

5–6/2017

60–120U35+

10–11/2017

80–1207 + 27 + 10

U35+

10–12/2018

110–140

27.5 + 30

UO2

2.4, 2.4

V13+

1–2/2018

100–210

20 + 13

metal V

2.2, 4.1

V13+

6–7/2018

100–230

23 + 9metal V

2.0, 3.8V13+9/2018

90–11010metal V

2.4

890

U35+ beam current
oven current
power

160
140

860
830

120

800

100

770

80

740

60

710

40

680

20

650

0

10/7

10/17

10/27

11/6

11/16
date

11/26

12/6

Current (A) / Power (W)18062012/16

Fig. 2. Operational trend of HTO in U-MT of 2018.

beams are not supplied to the accelerators and change
according to the width of the slits located upstream.
This trend shows that uranium beams of 120 μA ormore could be supplied stably except during the last two
weeks mentioned below. The power of heat generationof the crucible was obtained by subtracting the Jouleloss on the support pipes from the total electric power.
The operation of the ion source was interrupted because
the crucible was changed to a new one for replenishment
of UO2 on Nov. 9. Although stable operation was performed, we had to increase the current and power of theHTO after the end of November, as can be seen in theﬁgure. The reason was because a vapor-ejection hole ofthe crucible was blocked by a pileup of UO2 and thebeam intensity decreased. The ﬁrst blockage that happened on December 6 was resolved naturally and the MT
ended as scheduled even though the second blockage occurred. It was found that blockage tends to occur when
the amount of vapor is large. This problem is serious,
but it has not been solved yet. Details of this article areshown in Ref. 3).
References

Fig. 1. Schematic of the tungsten crucibles.

beam
operation
current (PA) time (d)ion

U35+ (μ A)

Uranium beams, which are accelerated at the RI-beam
Factory (RIBF), are extracted from a 28-GHz superconducting ECR ion source (SC-ECRIS)1) by using ahigh-temperature oven (HTO). Our HTO uses a tungsten crucible, which is joule-heated with a DC current of600–700 A. Figure 1 shows the dimensions of two typesof crucibles. The crucible is heated to approximately
2000◦ C in order to achieve a UO2 vapor pressure of 0.1–
1 Pa. The HTO, which has been under development
since 2013,2) was ﬁrst used to operate the ion source forthe RIBF experiments in the autumn of 2016.
The HTO was also used to produce high-intensity
vanadium beams in the 28-GHz SC-ECRIS. V13+ beams
with a current of 100 μA or more were supplied tothe beam time for experiments on super heavy element
synthesis from 2018. For the production of vanadium
beams, we placed a yttria crucible into a tungsten crucible and ﬁlled it with metal vanadium (vapor pressure:
1 Pa at 1827◦ C) because the metal vanadium should beelectrically insulated from the crucible.
Table 1 lists a summary of the machine-time (MT),whose beams were supplied from the 28-GHz SC-ECRIS
using the HTO. Four uranium-MT (U-MT) and threevanadium-MT have been performed so far. During normal operation, the average currents of U35+ and V13+
were both approximately 100–120 μA. The HTO can be
operated continuously for at least three weeks because
the ﬁllable amount of the R692 type, which was used forthese MTs, was approximately 2 and 4 g for vanadiumand UO2 , respectively.
Figure 2 shows the trend of the beam current of U35+ ,the electric current, and the power of heat generation of
the crucible during the U-MT in the autumn of 2018.
The beam current of U35+ was measured with a Faraday cup positioned down-stream of the analyzing magnet. The beam current can only be measured when the1) Y. Higurashi et al., Rev. Sci. Instrum. 85, 02A953 (2014).
2) J. Ohnishi et al., Rev. Sci. Instrum. 87, 02A709 (2016).
3) J. Ohnishi et al., Proc. 23rd Int. Workshop on ECR ion
sources, Catania Italy, Sep. 2018, to be published in JACOW Web site.

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