EVALUATION OF QUADRUPOLE MAGNETS MISALIGNMENT IN THE
IFMIF PROTOTYPE ACCELERATOR USING THE BEAM BASED-ALIGNMENT METHOD
J. Hyun†, H. Usami, K. Hirosawa, S. Kwon, T. Akagi, A. Mizuno 1, K. Masuda, K. Kondo,
National Institutes for Quantum Science and Technology (QST), Rokkasho, Japan
M. Alonso, Institute for Plasmas and Nuclear Fusion (IPFN), Lisboa, Portugal
F. Scantamburlo, European Joint Undertaking for ITER and the Development of Fusion for Energy(F4E), Garching, Germany
I. Podadera, B. Brañas, The Center for Energy, Environmental and Technological Research(CIEMAT), Madrid, Spain1also Japan Synchrotron Radiation Research Institute (JASRI), Sayo, Japanin a collaboration between Japan and European Union institutes. The accelerator sub-systems were designed manuThe beam commissioning of the Linear IFMIF Prototype
factured and tested in Europe and are integrated as one acAccelerator (LIPAc) in what is called Phase B+
celerator system at the QST Rokkasho site.
configuration has started since July 2021 to confirm the
In July 2019, we succeeded in accelerating a 125 mA
performances of beam transport elements and beam
deuteron beam to 5 MeV at a low duty cycle of 0.1% using
diagnostic instrumentations for achieving the Radiothe RFQ, calling this beam campaign “Phase B” [1]. In
Frequency Quadrupole (RFQ) beam operation in CW. A“Phase B+”, we plan to accelerate a deuteron beam to 5
fine-tuning of the beam center to pass through the magnetic
MeV in the CW operation with the RFQ and also transport
centers of the quadrupole magnets in the beamline wasit to a beam dump located 15 m from the RFQ exit without
performed using a Beam-Based alignment (BBA) method.
unwanted particle losses to validate diagnostics perforTo gain confidence in the measurements, a comparison
mances and the beam dump commissioning toward highwith the measurement of positions performed with a laser
DC up to CW.
tracker was made. The BBA showed a good agreement of
For the Phase B+ campaign, the beamline was extended
misalignment of about 0.5 mm in the horizontal direction
temporarily from MEBT to High Energy Beam Transport
between the RFQ exit and the magnetic axis of the first(HEBT) sections, named as MEBT Extension Line (MEL),
quadrupole magnet of the Medium Energy Beam Transport
as shown in Fig. 1 where an SRF Linac is installed in thesection (MEBT) measured by the laser tracker. We
following Phase, and additional beam monitors were also
confirmed that the measurement accuracy of BBA wasinstalled along the beamline [2,3]. The components in theinsufficient to assess the quadrupole magnets'
MEBT sections were installed in 2017 within the required
misalignments in some sections of the beamline.
tolerance of alignment of +/-0.2 mm [4 - 6]. However, wefound a horizontal misalignment of 0.5 mm between the
INTRODUCTION
mechanical center of the RFQ exit and the magnetic axis
The LIPAc was designed and developed to validate the of the first quadruple magnet in MEBT, through the laser
PASJ2022
THP002of a 125 mA deuteron beam up to 9 MeV using
accelerating
tracker survey in 2020, whereas the other components were
October 18 - 21, 2022, Online (Kyushu University)an RFQ witha length of
9.8 m and a Superconducting Ra- aligned
within the requirement. We nevertheless decided
Proceedings of the 19th Annual Meeting of Particle Accelerator Societyof Japandio Frequency linac (SRF) in the CW operation for realiz- not to realign the MEBT component because particle siming the IFMIF project [1]. This activity has been promoted ulation with the TraceWin code [7] showed that particles

Abstract

Figure 1: The Phase B+ LIPAc beamline from the exit of RFQ to the entrance of the high-power Beam Dump (BD). Reds:
BPMs, blues: quadrupole magnets, purples: steering magnets, greens: bunchers and bending magnet.
____________________________________________† email address

hyun.jibong@qst.go.jp

would not be lost at the low beam currents in the primarybeam operation campaign.
In July 2021, we started the first stage of the Phase B+
operation. One of the major purposes of this stage was toconfirm the performances of beam diagnostic instrumentations using the low-current proton and deuteron beams in
preparation to the following stages targeting the nominal
beam current of 125 mA in CW. Beam position monitors(BPMs) [8] are useful to confirm the misalignment between the RFQ exit and the first quadrupole magnet (quad),using a Beam-Based Alignment (BBA) method [9] with aproton beam (10 mA, 2.5 MeV, 0.1 ms pulse). The beam
condition was chosen to suppress the radiation damage tothe components as low as possible due to the beam hit.
A fine-tuning of the beam center to pass through themagnetic centers of the quads was also performed using the
BBA method with a 5 MeV deuteron beam (20 mA, 5 MeV,
0.1 ms pulse). Moreover, from the steering kick angles andbeam positions at quads obtained by the BBA, we
examined whether the alignment of quads placed over a 10
m distance from the MEBT to the HEBT sections can beevaluated using a beam within several hours instead of alaser tracker-based alignment survey which for the LIPAc
in the present configuration takes a few days.

THE LIPAc BEAMLINE

BEAM POSITION MEASUREMENT WITHQUADRUPLE SCAN METHOD
A beam passing off the center of a quad is kicked by adipole field of the quad, which causes the beam to be displaced downstream of the quad. Let us consider a caseshown in Fig. 2 where the quad Q0 is scanned while Q1
and Q2 are fixed at their nominal strengths, and their centers are aligned. When the beam positions in phase spaceat each magnet and a BPM are (x0, x′0), (x1, x′1), (x2, x′2),and (xB, x′B), respectively, the relation between them can be
written as
𝑥 = (𝑥 + 𝐿 𝑥 ′ ) + 𝐿 𝑘 𝑥 ,(1)𝑥′ = 𝑘 𝑥 + 𝑥 ,𝑥 = (𝑥 + 𝐿 𝑥 ′ ) + 𝐿 𝑘 𝑥 ,(2)𝑥′ = 𝑘 𝑥 + 𝑥 ,𝑥 = (𝑥 + 𝐿 𝑥 ′ ) + 𝐿 𝑘 𝑥 ,(3)𝑥′ = 𝑘 𝑥 + 𝑥 ,where L0, L1, and L2 denote distances between components
and k0, k1 and k2 denote the normalized magnetic strengthof the quad, as shown in Fig. 2.
When the strength k0 of quad Q0 is changed by dk0, induced beam displacement dxB at the BPM can be obtained
by
′
𝑑𝑥 =
𝑑𝑘 + 𝐿𝑑𝑘 + 𝐿 𝑘
𝑑𝑘 . (4)From the Eqns. (2) and (3), we have
The LIPAc consists of an ion source that can generate a= 𝑥 (𝐿 + 𝐿 + 𝐿 𝐿 𝑘 ),(5)
proton or a deuteron beam, a Low Energy Beam Transport′(LEBT) section to guide the beam from the ion source to= 𝑥 (𝑘 𝐿 + 1) .
the next section, an RFQ with a length of 9.8 m to accelerate the beam, a MEBT section, a MEL, a HEBT section By substituting Eqn. (5) into Eqn. (4), the beam displacement dxB at a BPM for a triplet quad is written as[2,3] with a bending magnet, and a Beam dump (BD).
𝑑𝑥 = 𝑥 𝑑𝑘 [(𝐿 + 𝐿 + 𝐿 ) + (𝐿 + 𝐿 )𝑘 𝐿 +A 50 keV/u deuteron (proton) beam generated at the ion(𝐿 + 𝐿 + 𝐿 𝐿 𝑘 )𝑘 𝐿 ].
(6)source is accelerated up to 2.5 MeV/u in the RFQ. Then the
Therefore,thebeam
positionfromthemagnetic
centerofbeam matched transversely by a triplet and a doublet of
the
quad
is
quads in the MEBT section [10] is transported to the MEL
𝑥 =
. (7)
section with two sets of doublets of quad magnets. In the
[(
) (
)
(
)
]
HEBT section, the beam delivered from MEL is focused Then, the error 𝜎 of the beam position is given by an erby a triplet and a doublet of quads and then is bent by a ror in dx /dk , 𝜎, as follows.
B0
dipole magnet with a bending angle of 20 degrees to the
PASJ2022 THP002
October 18 - 21, 2022, Online (Kyushu University)BD.
𝜎 of=Japan𝜎.
Proceedings of the 19th Annual Meeting of Particle Accelerator Society
) (
)
(
)
|(
|
Figure 1 shows the LIPAc beamline with the component(8)
names from the middle of the RFQ to the BD. The first
triplet quad is placed close to the exit of the RFQ because In a doublet case, k2=0 (or k1=0) reduces Eqn. (8) as,
the beam needs to be focused to suppress the effect by the
𝑥 =
,
(9)
[(
) (
)
]
strong space charge force.
𝜎 =𝜎.
BPMs in the MEBT section are placed at the middle po) ()|(|
sitions of each quad, while BPMs in the MEL and HEBTIn a singlet magnet case, k1 = k2 = 0. Therefore, it is resections are placed separately from the quads. The first andduced further as,
the last quads of triplets are equipped with steering mag𝑥 =.
(10)nets in the MEBT and HEBT sections, and with all the[()]
quads in doublets. In the MEL section, two steering mag𝜎 =𝜎.
)||(
nets are placed separately from the quads.

BEAM BASED ALIGNMENT METHOD
The BBA is used to determine the optimum current of asteering magnet placed upstream of the target quad so thatthe beam at the downstream BPM is not displaced by a scanFigure 2: Special configuration of Q0 quad scan for the firstone of three quads with a BPM at downstream.

Figure 3: Conceptual plots to be measured by BBA.

mentioned before. To confirm such a misalignment, wemeasured the beam positions with the BPMs at the middleof MMA01 and MMA03 (the first and the third quads in
MEBT, see Fig. 1), using the quad scan method with a 2.5
MeV proton beam and the BBA script. Under the assumption that centers of BPMs are well aligned, the beam position at the RFQ exit was estimated by solving transfer matrix equations between MMA01&3 and MMA01& RFQ
exit.
Figure 4 shows the results of quad scans for MMA01
and MMA03. For the MMA01 scan, the beam displacements were measured with MBP02 at the condition of
MMA02 OFF (see Fig. 1). For the MMA03 scan, MMA01
and 02 were set to the nominal currents, and MBP03 wasused to monitor the beam displacements. The quad scans
were carried out twice at different days to confirm the reproducibility of the beam positions measured using the
BPMs. From Eq. (10), beam positions can be obtained withslopes and distances between the target quad and BPM. Table 1 shows the beam positions and divergences at the RFQ
exit, MMA01, and MMA03. The beam angles x’, y’ required to estimate the beam position at the RFQ exit werecomputed with the beam positions and the transfer matrix
between MMA01 and MMA03. As a result, it is found thatthe beam passed through at around -1 mm and 0.1 mm in
the horizontal and vertical planes, respectively, from theirmagnetic centers.
Figure 5 shows the positions of the RFQ exit, MMA01,
and MMA03 to compare the misalignments measured withthe proton beam and the laser tracker system. As a baseline(zero positions in the vertical axes) to compare them, wechose a line passing through the magnetic centers of
MMA01 and MMA03. Here we assume that the beam
comes out of the center of the RFQ exit. In the horizontal
plane in Fig.4, the RFQ exit is found to be at around -0.5mm with respect to the magnetic centers of the two quads.
For the vertical plane, they are found aligned well. The
misalignments in both planes measured with the proton
beam are consistent with those surveyed with the laser
tracker. Hence, we could confirm a 0.5 mm horizontalof the quad. As explained in the previous section, we
should determine a steering magnet current so as to be
dx0=0 in Eqn. (10).
We made a script to optimize steering currents via BBA
for LIPAc. Below is the procedure implemented to thescript:
1. Set a steering magnet current, I1.
2. Scan the quad strength (current), k0, and measure
beam position using the BPM at each step of thequad scan, see Fig a).
3. Repeat 1 and 2 for various Im, see Fig.3 a), b), c).
4. Fit the measured beam positions at the BPM as afunction of quad strength (current) using linear fitting. Get slopes (corresponding to dxB/dk0’s in Eqn.
(10)) for each steering current.
5. Fit the steering current as a function of the slopes
PASJ2022 THP002
with linear fitting, see Fig. 3 d).
October 18 - 21, 2022, Online (Kyushu University)
Table
1: Beam Positions and Divergences at the RFQ Exit
6. Set thesteering
where
the slopeequalszero. Society
Proceedingsof current
the 19th Annual
Meetingof Particle
Acceleratorof Japan
MMA01
and MMA03
Table 2: Beam positions and beam angles at M M A01 and M M A03 in mm and mrad.

MISALIGNMENT BETWEEN RFQ EXIT
AND MEBT QUADSThe laser tracker-based alignment survey showed a horizontal misalignment of -0.5 mm between the exit of the
RFQ and the magnetic axis of the first quad in MEBT, as

Name
RFQ exit
M M A01M M A03

Date
Thu.
Fri.
Thu.
Fri.
Thu.
Fri.

(x ± σx , x ′ ± σx ′ )(-0.47± 0.08, -3.06± 0.22)(-0.59± 0.06, -2.98± 0.21)(-1.01± 0.07, -3.06± 0.22)(-1.09± 0.05, -2.98± 0.21)(-1.13± 0.15, -2.16± 0.64)(-0.97± 0.15, -1.57± 0.56)(y ± σy , y′ ± σy ′ )(0.15± 0.12, 0.22± 0.48)(0.04± 0.13, 0.05± 0.56)(0.19± 0.08, 0.22± 0.48)(0.05± 0.09, 0.05± 0.56)(0.24± 0.10, -1.43± 0.65)(0.06± 0.12, -0.37± 1.41)

Figure 4: The plots of quad scans for MMA01(left two plots) and MMA03 (right two plots). a) and c): the horizontal
plane and b) and d): the vertical plane. Blue and red colors show the results carried out at different days.

Figure 6: Beam center positions at each quadruple magnet
after the BBA.

Figure 5: The positions of the RFQ exit, MMA01, andMMA03. a) and b) are the horizontal and vertical positions,
respectively. Zero positions in the vertical axes is a line
passing through the magnetic centers of MMA01 andMMA03.
misalignment between the RFQ exit and MEBT quads exit
and also the validity of the BBA procedure implemented tothe script.

BEAM-BASED ALIGNMENT OF BEAMSTO QUADS

because we did not tune the bending magnet due to the limited beam commissioning time, and the horizontal steering
magnet between the bending magnet and HMA07 was notstrong enough to adjust the beam. The vertical errors at thelast triplet quads of HEBT are larger than the other ones.
One of the reasons is that HEBT BPMs were unstable due
to a hardware problem similarly to the MEBT one mentioned above [11,12]. Currently, efforts are being made fora better stability in BPM signals [11,12].
Since we confirmed that the beam was transported to themagnetic centers of most quads within +/-0.2 mm by the
BBA, we will calibrate each BPM by setting the electricaloffset so that the electrical center of the BPM matches withthe magnetic center of the nearest quad in the next beam
campaign.

QUAD POSITIONS MEASURED BY BBAAND LASER TRACKER SYSTEM

Figure 7 shows relative quad positions from the baselinefrom the MMA03 to the last quad HMA05 measured by
We carried out the BBA with a 5 MeV deuteron beam BBA and the laser tracker system. The last triplet magnets
for the last quads of the doublet and triplet magnets and in the HEBT section are excluded since the coordinate systhen scanned all the quads except for MMA01&02 to iden- tem are different before and after the bending magnet. In
tify the beam center positions with respect to the magnetic order to compare quad positions measured by the twocenters. Figure 6 shows the beam center positions at each methods, we chose a line passing through the magnetic
quad obtained by the BBA. The vertical axis in Fig. 6 rep- centers of MMA05 and LMA01 as a baseline. Here, thePASJ2022 THP002
resents the horizontal or vertical distance from the mag- beam divergencesof MMA05 and LMA01 were calculated
October 18 - 21, 2022, Online (Kyushu University)
netic centerProceedingsof each ofquad.
Note
that
the
beam
positionsby solving
the 19th Annual Meeting of Particle Accelerator Societyof Japan a transfer matrix equation using the beam posiplotted in Fig. 6 were calculated with Eqns. (7)-(9) since tions of MMA05 and LMA01, and then the relative quadthe other quads were set to the nominal currents while the positions were evaluated using each local beam position at
BBA for a target quad was performed. From Fig.6, it is each quad and steering kick angle obtained by BBA. The
concluded that the beam could pass through within +/-0.2 errors were also estimated with
mm from the magnetic centers of all quads except for
𝜎 { } = 𝑚 𝜎 +𝑚 𝜎 ,(11)
MMA04 and HMA07 after the BBA.
The vertical beam position at MMA04 in Fig.6 is far where m11 and m12 represent elements of a transfer matrix
from the magnetic center, and the error is also larger than between target quads.
the other ones. The reasons are that the distance between
Regarding the beam-based horizontal quad positions in
MMA04 and the used BPM (MBP04) was close (L=0.23 Fig. 7, we can see, unlike the laser-tracker-based ones,m) and also the measured signal of MBP04 was not stable large misalignments with respect to the baseline (x=0)[11,12] both of which are seen in Eqn. (10) to contribute to from the last MEL quad to the last HEBT quad. We cona large 𝜎 . One of the simple methods to reduce the error firmed after the beam campaign that the alignment suris to choose a BPM long away from the quad such as veyed by the laser tracker system has a reproducibility.
LBP01 downstream of MBP04 (see Fig. 1).
Possible causes for the discrepancy beyond the assumed
In the HEBT section, the horizontal beam center position errors can be some systematic errors in the present beamat HMA07 is far from the magnetic center. This is simply

Figure 7: Comparisons of quad positions measured with a 5 MeV beam and the laser tracker system. The left and rightplots show the horizontal and the vertical planes. Note that the vertical scales are different in the two plots. Blue andorange colors stand for the results measured by the BBA method and laser tracker system, respectively.
based measurements. However, the cause of the large disREFERENCES
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deuteron beam, and the beam could be transported throughOf IBIC 2019, WEPP013.
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ited to a shorter distance unless errors in beam positions in
the individual quads are made smaller in the future.

DISCLAIMER
This work was undertaken under the Broader Approach
Agreement between the European Atomic Energy Community and the Government of Japan. The views and opinions
expressed herein do not necessarily state or reflect those of
the Parties to this Agreement.