Ⅱ-8. Accelerator

RIKEN Accel. Prog. Rep. 53

Revaluation of beam orbit calculation method for the injection line ofAVF cyclotron after tuning pepper-pot emittance monitor
Y. Kotaka,∗1 Y. Ohshiro,∗1 H. Yamaguchi,∗1 N. Imai,∗1 Y. Sakemi,∗1 T. Nagatomo,∗2 T. Nakagawa,∗2 M. Kase,∗2J. Ohnishi,∗2 A. Goto,∗2 K. Hatanaka,∗3 H. Muto,∗4 and S. Shimoura∗1
We developed a calculation method for the beam orbit from the Hyper ECR ion source to the AVF cyclotron
using the 4D emittance measured by a pepper-pot emittance monitor1) named PEM_IH102,3) and evaluated itwith the degree of ﬁt, which is χ2 divided by the degree of freedom (DOF) between two projections to anarbitrary coordinate axis made from both the measurement of other diagnostics and the beam orbit calculation.
However, the dispersion of χ2 is assumed to be the squareof 10% of the highest value of the measurement. Subsequently, the method of processing the beam image on
the ﬂuorescent plate of PEM_IH10 recorded by a digital camera was improved.4) This report is a summary ofRef. 4).
This year, as it was found that the degree of ﬁt varied
at diﬀerent thicknesses of the ﬂuorescent agent, the variation of the degree of ﬁt was examined while varying thecombination of the exposure time and gain and the thickness. The results of beam orbit calculations are compared with the beam proﬁle monitor (BPM), which measures 3 axes of proﬁles set 867 mm behind PEM_IH10
using the 23.6-keV 4 He2+ ion beam of 100 eµA. In thistest, the degree of ﬁt is deﬁned by dividing the sum of 3axes of χ2 by the sum of 3 axes of DOF. The thickness isdeﬁned by dividing the weight by the area and density.
The upper and lower tables of Fig. 1 show the degree ofﬁt obtained from thickness of 1.9 and 34.6 µm, respectively. From these results, irrespective of the thickness,the measurement of PEM_IH10 can be homogenized if
the gain and exposure time are optimized.
In order to revalue the beam orbit calculation method
after the optimization with respect to the thickness of thehe ﬂuorescent agent, the degree of ﬁt is examined using 4
beam intensities (124, 187, 196, and 308 eµA) of 15.4 keV

Fig. 1. Degree of ﬁt compared with BPM when the thicknessof the ﬂuorescence agent and the exposure time and gainof the digital camera are varied. (top) thickness = 1.9 µm;(bottom) thickness = 34.6 µm.
∗1
∗2
∗3
∗4

Center for Nuclear Study, University of Tokyo
RIKEN Nishina Center
RCNP, Osaka University
Center of General Education, Tokyo University of Science,Suwa

Fig. 2. Scatter plots showing the degree of ﬁt of (left) (u, u’)and (right) (w, w’) compared with EM_I36.

Fig. 3. Scatter plot showing the degree of ﬁt of (u, w) compared with a BPM set 107.5 mm behind EM_I36.

He2+ , 100 eµA of 12.6 keV 2 H+ , and 214 eµA of 12.8 keV
H+ by comparing the measurement of a 2D emittancemonitor5) (EM_I36) set 6.2 m behind PEM_IH10 withu and w coordinate axes perpendicular to the beam direction. The angles of u and w are indicated by u’ andw’, respectively. The left and right of Fig. 2 show thescatter plot of the degree of ﬁt of (u, u’) and (w, w’)of EM_I36, respectively. The u or w values of all samples are less than 4. However, 3 samples showed u’ orw’ values are greater than 6, and their widths of angular distributions from the beam orbit calculations were
all smaller than those from the measurements for both uand w.
On the contrary, Fig. 3 shows the scatter plot of degreeof ﬁt of (u, w) of BPM set 107.5 mm behind EM_I36.
It is found that all the degrees of ﬁt are less than 4.2.
This reason is not clear yet. We will check the tendencywith more data. On the whole, the results of beam orbit
calculation using 4D emittance measured by PEM_IH10
agree with real beam orbit so that they are useful for
analysing real beam orbits.
42References

1) T. Hoﬀmann et al., AIP Conf. Proc. 546, 432 (2000).
2) Y. Kotaka et al., Proc. 13th Annual Meeting of PASJ,(2016), pp. 1072–1075.
3) Y. Kotaka et al., Proc. 14th Annual Meeting of PASJ,(2017), pp. 1118–1122.
4) Y. Kotaka et al., Proc. 16th Annual Meeting of PASJ,(2019), pp. 1109–1113.
5) Y. Kotaka et al., RIKEN Accel. Prog. Rep. 41, 96 (2008).

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