Ⅱ-8. Accelerator
RIKEN
Accel. Prog. Rep. 56 (2023)

RIKEN Accel. Prog. Rep. 56 (2023)

Development of auto-tuning system using Bayesian optimization
for ion optics in primary beam line with 26 electric nA Kr beam
T. Nishi,∗1 N. Fukuda,∗1 E. Iwai,∗2,∗3 H. Maesaka,∗2 Y. Shimizu,∗1 T. Sugimoto,∗2,∗3 T. Sumikama,∗1 andA. Uchiyama∗1∗1∗2∗315F3Y [mm]80σh: 1.5 mm

1070σv: 0.7 mm

560
5004030−520−10−15−1510−10−505F3X [mm]1015Beam width (rms) [mm]H2_F3XY0864200RIKEN Nishina Center
RIKEN SPring-8 Center
Japan Synchrotron Radiation Research Institute- 71 -220200σv: 0.8 mm

1801601400120100−58060−104020−15−15−10−505F3X [mm]4681010150DMT2 DMT3DMT1Beam width (rms) [mm]240σh: 1.1 mm

52location number with PF

1510DMT2 DMT3DMT110H2_F3XYF3Y [mm]We started the project to introduce the auto-tuning
system of the accelerator facility to RIBF as reportedlast year.1) As a ﬁrst step in this project, we adopt anauto-tuning program using sequential learning based on
Bayesian optimization2) to the beam line optics from theSRC to BigRIPS ﬁrst production target F0, so-called TCourse.
A test experiment for the project was conducted inMay 2022 with Kr36+ beam to develop a new method tomeasure beam intensity and beam spot simultaneouslyfor high-intensity beams. In the method, the phase ellipse and intensity of the primary beam are measured
using BigRIPS nominal detectors. Because the direct
measurement with these detectors limits the intensity ofthe primary beam, the charge-converted particles created by the 1 mm-thick Be target at F0 are measured
by downstream detectors. This method enables to measure, for example, approximately 10 kcps Kr34+ beamat F3 as an indicator of a primary 30 electric nA Kr36+
beam.
In the experiment, Kr34+ was selected by the F1 slit
and measured by PPACs and a scintillator at F3. The
beam intensity was set to approximately 0.001 electric nA for the 5 diﬀerent optical conditions to compare with the nominal method, and spot images wereacquired with the viewer target at F0. As a result, they
showed good agreement and we conﬁrmed the measured
values by F3 detectors were good indicators for the primary beam. Next step, we adjusted the optics of theT-course using the developed indicators. In the opticalsystem tuning, it was necessary to ﬁnish the measurement and evaluation in a few tens of seconds for each parameter sets. We converted PPAC data into trajectories
and beam widths within a few seconds using the newly
developed BYACO3) system and passed the data to theoptimization program via EPICS. Finally, we optimizedthe currents of doublet quadrupole magnets QDT11ab and QDT12a-b with 26 electric nA Kr36+ primarybeam to maximize the scintillator count rate and minimize the beam widths at F3. Left panel of Fig. 1 shows
beam spot measured by F3 PPACs before (left top) andafter (left bottom) optimization. As shown in the ﬁgures, the horizontal beam widths are reduced from 1.5
to 1.1 mm (rms) at F3. The transmission eﬃciency wasalso measured for each optics with the Faraday cup atG01 and beam dump inside the D1 magnet, and it conﬁrmed that both values agree within the errors. Graphs
in the right panel of Fig. 1 show measured and calculated beam widths at the location of proﬁle monitors in

108642002468location number with PF

10Fig. 1. (Top) Before optimization. (Bottom) After optimization. (Left) beam spot of Kr34+ measured by F3 PPACs.
(Right) Beam widths at the location of proﬁle monitors. Red (blue) marks correspond to horizontal (vertical) beam widths, and circle (square) marks correspondto the data measured by proﬁle monitors (calculated bythe simulation).

T-Course. The location 10 indicates F0. The calculation is based on the measured beam phase ellipse at F3.
As shown in the ﬁgures, the measured and calculated
values are in good agreement, except the vertical beamwidths between DMT1 and DMT2. These calculations
also show the optimized ion optics realized the smaller
beam spot at F0.
In conclusion, we developed a new method to measure beam spot and intensity simultaneously with highintensity primary beam. With the method we optimized
ion optics in T-Course and reduce beam spot size at F0,keeping beam transmission eﬃciency. This new method
using BYACO opens the possibility of optimizing theparameters of the beam lines using not only the beamspot, but also the signal of any downstream detector(e.g., the signal-to-noise ratio of secondary particles) as
an indicator. We are developing a new algorithm withsafe regions to apply this method for the higher intense
primary beam.
References
1) T. Nishi et al., RIKEN Accel. Prog. Rep. 55, 66 (2021).
2) E. Iwai et al., Proc. PASJ2021, WEOB02 (2021).
3) T. Sumikama et al., RIKEN Accel. Prog. Rep. 54, 82(2020).