Accelerator design report for
3-GeV Next-Generation
Synchrotron Radiation Facility

September 2020
National Institutes for Quantum and Radiological
Science and Technology (QST)
Institute for Advanced Synchrotron Light Source

This design report outlines the current accelerator design of 3NGSR (3-GeV
Next-Generation Synchrotron Radiation) facility at the Aobayama new campus of
Tohoku University. This facility is expected to form a National photon science
platform together with SPring-8, which covers a wide spectral range from UV tohard X-rays. The 3NGSR facility mainly provides long-wavelength lights ranging
from UV to tender X-rays. The 3NGSR facility is therefore required to be a practical
SX (Soft-X-ray) light source with high performance, stability and reliability.
As another aspect, the 3NGSR construction project has faced a quite tightbudget, human resources, and time schedule. In order to fit the severe conditions,
we have designed the accelerator complex with strong supports from RIKEN,JASRI, and KEK accelerator-groups and have extensively introduced outcomesfrom R&D and design studies for SPring-8-II.
The accelerator design has the following features:
1. target emittance set around 1nm.rad giving a high coherence at SX
wavelengths
2. compact ring design based on quintet bend achromat with combined bends
3. 3-GeV C-band full-energy linac injector enabling a future extension to SX FEL(Free Electron Laser)
At last, we would like to express grateful thanks to all the collaborators from
QST, RIKEN, JASRI, and KEK accelerator groups for their tremendous contributions,and also to give appreciations to directors, administrative staffs, and all the
involved persons in the above laboratories.
Representatives of QST Accelerator Group
Nobuyuki Nishimori, Takahiro Watanabe, and Hitoshi Tanaka

1Contents
1. Lattice ............................................................................................................... 4
1.1 Storage ring lattice ...................................................................................... 4
1.2 Electron beam dynamics in storage ring ..................................................... 9
1.2.1 Optimization of sextupole magnetic field strengths to expand dynamic
aperture ......................................................................................................... 9
1.2.2 Momentum aperture and Touschek lifetime ....................................... 11
2. Magnet system ............................................................................................... 14
2.1 Magnet ...................................................................................................... 14
2.1.1 Quadrupole magnets .......................................................................... 15
2.1.2 Sextupole magnets ............................................................................. 15
2.1.3 BQ combined magnets ....................................................................... 16
2.1.4 Steering magnets ................................................................................ 16
2.1.5 Girders................................................................................................. 172.2. Power supplies .......................................................................................... 17
2.3 Alignment .................................................................................................. 18
2.3.1 Alignment in straight sections ............................................................ 18
3. Vacuum system ............................................................................................... 21
3.1 Outline of vacuum system ......................................................................... 21
3.2 Structure and function of vacuum system ................................................. 22
3.2.1 Straight section chamber .................................................................... 22
3.2.2 Bending section chamber ................................................................... 23
3.2.3 Photon absorber ................................................................................. 24
3.2.4 Vacuum chamber parts ....................................................................... 25
3.2.5 Pumping system ................................................................................. 26
3.3 Gas scattering lifetime and pressure ......................................................... 26
3.3.1 Gas scattering lifetime ........................................................................ 26
3.3.2 Amount of outgassing ........................................................................ 26
3.3.3 Pressure distribution ........................................................................... 27
4. RF acceleration system .................................................................................... 28
4.1 Overview ................................................................................................... 28
4.2 High-power RF source and transmission system....................................... 30
4.3 RF accelerating cavity ................................................................................ 30
4.4 Low-level RF control system ...................................................................... 32
5. Beam diagnostic system ................................................................................. 35
5.1 Outline of beam diagnostic system ........................................................... 35
5.2 Beam position monitor .............................................................................. 362

5.3 Beam size monitor using synchrotron radiation........................................ 38
5.4 Control of beam instability ........................................................................ 38
6. Beam injection system .................................................................................... 40
6.1 Outline of beam injection system.............................................................. 40
6.2 Parameters for beam injection .................................................................. 40
6.3 Magnets for beam injection ...................................................................... 42
7. Beam injector linac .......................................................................................... 44
7.1 Overview ................................................................................................... 44
7.2 Electron beam injector .............................................................................. 47
7.3 Main accelerator ........................................................................................ 50
7.4 Beam transport line ................................................................................... 52
7.5 Low-level RF system .................................................................................. 54
8. Accelerator Control System............................................................................. 57
8.1 Overview ................................................................................................... 57
8.2 Framework of the Control System ............................................................. 58
8.2.1 Database System and Data Acquisition .............................................. 58
8.2.2 Data Acquisition Process ..................................................................... 59
8.2.3 Messaging Server................................................................................ 59
8.2.4 Equipment Control Process（Equipment Manager：EM／Equipment
Manager Agent：EMA） ............................................................................. 59
8.3 Equipment Control .................................................................................... 59
8.3.1 Equipment Control Platform ............................................................... 59
8.3.2 Vacuum Equipment Control System.................................................... 60
8.3.3 RF Acceleration Control System .......................................................... 60
8.3.4 Magnet Power Supply Control System................................................ 60
8.3.5 Beam Diagnostic System ..................................................................... 60
8.3.6 Device Interlock System ...................................................................... 60

3

1. Lattice
1.1 Storage ring lattice
When MAX Laboratory of Sweden introduced a so-called multi-bend achromat
lattice with seven bending magnets per cell for the new 3 GeV light source, MAX IV,
in pursuit of low-emittance rings with the emittance of lower than 1 nm rad, it wasnothing short of an epoch-making undertaking. Natural or horizontal emittance istheoretically reduced in inverse proportion to the cube of the number of bending
magnets, which makes multi-bend configuration is essential for lowering theemittance. This, however, makes the packing factor of the magnet arrangement
extremely high, making it difficult to arrange other accelerator components such as
gate valves, beam diagnostic instruments, and so on. Lowering the emittance also
demands multipole (quadrupole and sextupole) magnetic fields that are significantly
stronger than the conventional levels. It inevitably requires decreasing a bore
diameter of each multipole magnet that makes the beam duct narrower, andconductance smaller, causing difficulties in designing the vacuum system. Despite
these difficulties, most of the upgrading plans for existing synchrotron radiation
facilities use this multi-bend lattice, and it is bound to become even more common
in the light source ring lattice.
The storage ring has also employed a type of multi-bend lattice called double
double-bend achromat (DDBA) lattice, which has 4 bending magnets per cell. With
its 16 cells, the designed storage ring has a horizontal emittance of 1.14 nm rad anda circumference of 349 m. While DDBA is a type of multi-bend lattice, the number of
its bending magnets is not extremely large as with MAX IV's 3 GeV ring, and theresulting emittance is therefore not as small. Even so, the design allows for a compact
cell structure, making it possible to achieve the lower emittance than that of a current
third-generation light source with a relatively short circumference.
Table 1.1 shows the key parameters of the storage ring. A DDBA unit cell iscomprised of four bending magnets, ten quadrupole magnets, ten sextupole
magnets used for the linear chromaticity correction and the nonlinearity suppression,and orbit-correction dipole magnets. Each cell is 21.8-m long. Of the sixteen 5.4-mlong straight sections, fourteen are for installing undulators and the remaining two
are for beam injection systems and radiofrequency (RF) accelerating cavities. As forthe 1.6-m short straight sections, fourteen have multipole wigglers (MPWs) thatgenerate high-intensity white-light hard X-rays in lieu of bending magnets, and theother two have a beam instability suppression system, beam diagnostic instruments,a beam current monitor (DCCTs), beam collimators, and so on.
4Table 1.1 Key parameters of the storage ring
Beam energy

E

2.998 GeV
Double Double-Bend Achromat

Lattice structure
CircumferenceC

348.843 m

Number of cells (bends)

Ncell

16 (64)

Long straight section

LSS

5.44 m × 16

Short straight section

SSS

1.64 m × 16

Betatron tune

(x, y)(28.17, 9.23)

Natural chromaticity(x, y)(-60.50, -40.99)

Natural horizontal emittancex

1.14 nmrad

Momentum compaction factor

00.00043

Natural energy spread

E/E

0.0843 %Lattice function at LSS(x, y, x)(13.0, 3.0, 0.0) m

Lattice function at SSS(x, y, x)(4.1, 3.0, 0.05) m

Damping partition number(Jx, Jy, Je)(1.389, 1.0, 1.611)

Damping time

(x, y, e)(8.1, 11.2, 7.0) ms

Energy loss in bends

U0

0.621 MeV/turnRF accelerating frequency

fRF

508.759 MHz

RF accelerating voltage

VRF

3.6 MV

Harmonic numberh592

Natural bunch lengthb2.92 mm (9.74 ps)

5The linear optics is an achromatic design with an energy-dispersion function ofzero for each long straight section. Figure 1.1 shows the distribution of latticefunctions along the unit cell.

Figure 1.1 Distribution of lattice functions along the unit cell. The red and blue lines
represent horizontal and vertical  functions, respectively, and the green line represents
the horizontal energy dispersion function.

As a bending magnet, a combined-function-type electromagnet that combines the
dipole magnetic field with the quadrupole one is used in order to make the ring small
and reduce the horizontal emittance. The dipole magnetic field is 0.87 T to reduce
the radiation loss per turn, so that the power consumption by the RF cavities isreduced. The combined quadrupole field is 7.06 T/m. For the quadrupole andsextupole magnets the maximum strengths are 49 T/m and 1541 T/m2, respectively,
which are achievable with a realistic bore diameter and the effective length is 20 cm
for all these magnets. Table 1.2 shows the specifications of these electromagnets andfigure 1.2 shows the magnet lattice of the unit cell.

6Table 1.2 Specifications of main electromagnets
MagnetName

Length (m)Strength (T, T/m, T/m2)

Combined Dipole

B

1.13

Quadrupole

Q1

0.20

+32.6151

Q2

0.20-2.6278Q3

0.20+49.1523

Q4

0.20+5.4300Q5

0.20+44.6423

S1

0.20+949.50S2

0.20-1124.87

SD1

0.20

-472.34SF

0.20+1061.73

SD2

0.20

-1540.68

Sextupole

0.8688,7.06

Although the drift spaces between Q3 and B and between Q4 and B are relatively
large in the magnet lattice shown in Fig. 2.2, this is intended to make the dispersion
peak larger in the dispersion arc and reduce the SF strength (no phase matching iscarried out for the purpose of making the sextupole magnetic fields transparent,
however). Beta function distortions caused by MPWs installed in the short straightsections, along with the tune shifts, are corrected using trim coils attached to
upstream Q1 and downstream Q5 in combination with main power supplies.

7

Figure 1.2 Magnet lattice of the unit cell. Blue: bending magnets (1 family); red:quadrupole magnets (5 families); yellow: sextupole magnets (5 families).

8

1.2 Electron beam dynamics in storage ring
1.2.1 Optimization of sextupole magnetic field strengths to expand dynamic
aperture
As expected from the lattice of the storage ring, the linear chromaticity is correctedwith SF, SD1 and SD2. Because the dynamic aperture (DA) of the ring varies
depending on the SD1-SD2 balance, and the optimization of the distribution of
sextupole magnetic strengths was carried out to maximize the dynamic aperture,including the strengths of S1 and S2.
The target chromaticity was set at (+1, +1); 3.6-MV RF accelerating voltage wasapplied in order to take account of a synchrotron oscillation of tracking particles withenergy deviations (off-momentum particles). Figure 1.3 shows the DAs obtained at
the center of the long straight section. Even with energy deviations of ±3%, ahorizontal aperture of approximately -15 mm is secured, which is large enough forthe stable beam injection. In the vertical direction, an aperture of 7 mm is obtained
and this value is smaller compared with the horizontal one. However, it is not a serious
problem because the minimum operating gaps of the in-vacuum undulators areplanned to be around 5 mm.

Figure 1.3 DAs for on-momentum particles at the center of the 5.4-m long straightsection and for off-momentum particles with energy deviations of ±3%. Operating
point: (x, y) = (28.17, 9.23).

9

The maximum value of sextupole magnetic field strengths is 1541 T/m2 , a levelattainable using a bore diameter of 40 mm. Figure 1.4 shows the dependence of tunes
on the momentum deviation (a) and the horizontal and vertical oscillation amplitudes(b, c).

(

(a)

(b)

(c)
Figure 1.4 (a) Nonlinear chromaticity(momentum dependent tune shift), (b)horizontal amplitude dependent tune
shift, and (c) vertical amplitudedependent tune shift, where operating
point: (x, y) = (28.17, 9.23). For (b) and(c), the horizontal axes show theamplitude at the center of the longstraight section.

(c)
In a range where a normalized momentum deviation changes form -3% to +3%
the tune shift is kept approximately less than 0.1. This shows that the nonlinear
chromaticity is well suppressed by the optimization in this range. On the other hand,as seen in Fig. 1.4, the amplitude dependent tune shift seems to be rather large evenin the required amplitude range. However, under the condition that the excitation ofseveral resonance lines nearby the operating point is properly controlled by the
optics correction procedures and magnet error tolerances, the amplitude dependent
tune shifts obtained do not affect the stable beam operation.

101.2.2 Momentum aperture and Touschek lifetime
Momentum aperture (MA) can be kept sufficiently by applying establishedcorrection procedures, such as COD, tune, and beta function corrections, underallowable magnetic errors. To evaluate the Touschek lifetime, the local MA
distribution in a regular cell was calculated conservatively, using the following
conditions: (1) 31 points at the edge of bending and quadrupole magnets are
selected as evaluation points for each cell; (2) random alignment errors of sextupole
magnets ( = 25 m with a cut-off at 2) are assumed; (3) an RF accelerating voltage
is 3.6 MV; (4) synchrotron oscillation is taken into account without radiation losses;and (5) insertion devices are not considered in the simulation model. Figure 1.5 shows
the simulation result. Absolute MAs are between 3% and 5% in terms of normalized
momentum deviation (Δp/p), and it strongly correlates with the horizontal dispersion.
Mean MA values are +4.1% for the positive p/p side and -4.4% for the negative
p/p side.

Figure 1.5 Momentum aperture distribution in a cell.

Touschek lifetime was evaluated by numerical calculations with the MA distribution
shown in Figure 1.5 and the lattice functions distributed along the ring. The following
conditions were assumed: (1) an RF accelerating voltage is 3.6 MV; (2) radiation loss
from the bending magnets is only taken into consideration; (3) the smallest apertureamong MA, physical aperture, and bucket height determines the beam loss; and (4)electron beam density is adjusted changing the coupling ratio and bunch length.
Figure 1.6 shows the dependence of Touschek lifetime on the bunch current. The

11

calculation was performed for four different conditions combining two coupling
ratios with two bunch lengths. Coupling ratios of 0.2% and 1% are a normal value
and enhanced one by a coupling control, respectively. Two bunch lengths are aminimum length at a zero current (zero current limit) and longer bunch length at a
normal operation current (twice as long as the zero current limit).
Assuming that the target beam current, 400 mA, is stored in about two-thirds ofthe 592 buckets, the averaged bunch current is 1 mA (a charge of 1.16 nC). In thiscondition, it is clear that the coupling needs to be increased to approximately 1% tokeep a beam lifetime of 5-10 h, which is a rough target value. The bunch length, on
the other hand, is longer than the zero current limit due to the effects of ring
impedance, particularly potential well distortion. By combining this fact with theeffect of the coupling increase, the beam lifetime is expected to be at around 10 hwith a stored current of 400 mA and a bunch current of 1 mA.

Figure 1.6 Dependence of Touschek lifetime of beam on bunch current calculated using
bunch length and coupling as parameters.

Intra-beam scattering (IBS) in the bunch increases beam emittance in the three
axial directions. This effect is caused by a small angle scattering, of which energy
transfer is too small to cause beam losses. By taking small angle scatterings into
account, a dynamic equilibrium where the emittance excitation including thescattering contribution balances radiation damping in the three axes, namely

12horizontal, vertical, and energy axes, can be numerically calculated in a self-consistentmanner [1.1].

Figure 1.7 Bunch current dependent degradation in horizontal emittance (left) andenergy spread (right) caused by IBS.

Figure 1.7 shows increases in the horizontal emittance and energy spread as afunction of bunch current. The same calculation conditions were used as those forthe numerical calculation of the Touschek lifetime. These results show that theincreases in both the horizontal emittance and energy spread are at negligible levels
with a coupling ratio of 1% and a bunch current of 1 mA. This condition gives a
Touschek lifetime of approximately 10 h.
Reference[1.1] K.L.F. Bane et al., PRST-AB 5, 084403 (2002).

13

2. Magnet system
2.1 Magnet
Figure 2.1 shows a magnet configuration in a unit cell. The storage ring consistsof 16 unit cells, each of which has four BQ combined, ten quadrupole, and ten
sextupole magnets that fold back at the short straight section (indicated as “SS” in
the figure) at the center of the cell. The BQ combined magnets provide bending anddefocusing functions in a single magnet. Thus, there are a total of one type of BQ
combined, five types of quadrupoles, and five types of sextupole magnets. Each typeof quadrupole and sextupole magnets are powered in series by a common power
supply as a family, while all the BQ combined magnets from a single family poweredby a single power supply. A variation of the integrated magnetic fields of magnets ineach family needs to be controlled within ±0.2 % for the BQ combined magnets and± 0.4 % for the quadrupole and sextupole magnets. All the magnets areelectromagnets, and all the coils for the magnets are hollow conductor types. To
accommodate to the high packing factor lattice, the magnets need to be designed
as short as possible by carefully designing compact coil configurations. Anotherimportant criterion is power consumption. For that, and also for suppressing thermal
deformations of magnets, we set the limit of the current density in the coils below
3.2 A/mm2. The temperature rise of cooling water under a pressure drop of 0.6 MPashould be less than 5 K to suppress deformation of the magnets.
Measurements of integrated magnetic fields, excitation curves, and fieldharmonics will be carried out for all the magnets. The excitation curves and flux
density distributions in the transverse and longitudinal directions will be measured
by a Hall probe, and the field harmonics will be resolved by making use of so-called
the single stretched wire (SSW). In the SSW setup, a single wire is rotating or moving
according to some rule inside a magnet so that the field harmonics can be analyzed
for verifying the field quality of the magnet.

Figure 2.1 Configuration of magnets in a unit cell.

14

2.1.1 Quadrupole magnets
Specifications of the quadrupole magnets are described in Table 2.1 The core ismade with laminated silicon sheets with a thickness of 0.5 mm. The bore diameter is
34 mm and the maximum excitation current is 352 A, which results in the maximum
magnetic field gradient of 53 T/m. The effective magnetic length is all 200 mm. For abeam-based alignment and a local correction of the lattice, an auxiliary power supply
is connected to an individual quadrupole magnet so that we can independently andfinely adjust the magnetic field of each magnet in the same family.
Table 2.1 Specifications of quadrupole magnets.
Q1
Bore diameter [mm]34

Maximum excitation current [A]352

Number of turns in a pole [T/Pole] 17
Effective magnetic length [mm]200

Total length of magnet [mm]≤248

Homogeneity of field gradient [%](x≤±8 mm)
Number of magnets

Q2

Q3

Q4

Q5

12

20

20

20

≤230

≤248

≤248

≤266

32

32

32

32

≤ ±0.132

2.1.2 Sextupole magnets
Specifications of the sextupole magnets are described in Table 2.2. The core is thelaminated silicon sheets with the same thickness as quadrupoles, i.e., 0.5 mm, but thebore diameter is 40 mm with a maximum excitation current of 250 A. It corresponds
to the field gradient of 2120 T/m2. The effective magnetic length is all 200 mm. The
sextupole magnets are equipped with auxiliary air-cooling coils as it can work as asteering magnet as well. The auxiliary coils are also used for independent tuning of
the sextupole field in case of the beam-based alignment. For the purposes, all thethree pairs of coils, each of which are connected to a facing pair of poles, can betuned independently.
Table 2.2 Specifications of sextupole magnets.
S1
Bore diameter [mm]40

Maximum excitation current [A]250

Number of turns in a pole [T/Pole]

9

15

S2

S3

S4

S5

9

9

5

9

Effective magnetic length [mm]200

Total length of magnet [mm]≤259

Homogeneity of Field gradient

[%]

≤259

≤259

≤309

≤259

48

48

48

20

48

32

32

32

32

32

≤ ±0.1(x≤±6 mm)
Maximum excitation current for20

auxiliary coil [A]
Number of turns in a pole for
auxiliary coil [T/Pole]
Number of magnets

2.1.3 BQ combined magnets
Specifications of the BQ combined magnets are shown in Table 2.3. The crosssectional shape of the pole comes in a truncated hyperbolic curve. A gap length ofthe magnetic poles is 28 mm along the beam trajectory. We set the maximum
excitation current at 650 A for generating a bending field of 0.9 T and a quadrupole
field of -7.3 T/m. The effective magnetic length is 1130 mm.

Table 2.3 Specifications of BQ combined magnets.
Gap length along the beam trajectory [mm]28

Maximum excitation current [A]650

Number of turns in a pole [T/pole]

16

Effective magnetic length [mm]1130

Total length of magnet [mm]≤ 1315

Number of magnets

64

2.1.4 Steering magnets
Six sextupole magnets, i.e., S1, S3, S5, S6, S8, S10, in each cell are equipped with
auxiliary coils for steering functions. All the six magnets can provide both horizontal
and vertical kicks with the kick angle of up to 0.4 mrad. Besides, a pair of independent
steering magnets with the maximum kick angle of 0.3 mrad in both horizontal andvertical planes will be placed at both ends of a multi-pole wiggler (MPW) in the shortstraight section. Also, another pair of independent steering magnets will be preparedat both ends of an undulator in the long straight section as well.
16

2.1.5 Girders
There are six common girders in each cell as shown in Figure 2.1. The common
girders are labeled A to F from the upstream to the downstream in each cell. Due tothe line symmetry of the magnet configuration in the cell, the common girders arealso symmetric in such a way that the girder A and F, that B and E, and C and D havethe same structure with the opposite direction. Each girder is supported at four
positions on a floor, aiming at the suppression of the girder deformation in a longtime as well as the easy height adjustment. The girders are designed to keep thedeformation due to the magnet weights less than 0.05 mm and the eigenfrequencyof the girder vibration larger than 110 Hz. Portions of the accelerator hall floor
supporting the common girders are coated by epoxy resin to readily secure thesurface flatness and to mitigate the vibration transfer from the floor to the girders.

2.2. Power supplies
The specifications for power supplies are summarized in Table 2.4. These power
supplies are controlled by taking advantage of digital feedback control based on an
FPGA (Field Programmable Gate Array). In order to suppress the quantum noises inanalog-digital conversion, the power supplies have the DCCT-ADC circuits with 24bit high-resolution converters. There are 11 power supply families for main magnets;
one for BQ combined, five for quadrupole, and five for sextupole magnets. In orderto reduce development efforts and costs, these power supplies are designed to share
most specifications. As a result, there are only two types of quadrupole and one typeof sextupole power supplies in addition to BQ combined power supply. These main
power supplies for the BQ combined, quadrupole, and sextupole magnets are
required to stabilize the ripple and long-term drift of the current within 20 ppm(peak-to-peak). The current control utilizes the chopper-switching scheme based on
the PWM (Pulse Width Modulation), of which conversion efficiency is larger than 0.85.
Every type of power supply has one backup for a quick replacement in case of thepower supply failure.
The independent steering magnets at short straight sections and the ones
combined with the sextupoles are driven by the same type of switching power supply,
and those at long straight sections are driven by smaller ones as shown in Table 2.4.
These are bipolar power supplies that utilize full-bridge switching with the current
stability of better than 50 ppm including ripples and long-term drift. We need tosynchronize the three power supplies for each pair of steering coils equipped in the
sextupole for applying it to the beam-based alignment and other purposes.
17Electromagnetic interference between power supplies via magnet poles should also
be considered in the design. Auxiliary power supplies connected to individual
quadrupole magnets are bipolar type both in current and voltage. The required
stability should be better than 50 ppm including ripples and long-term drift.
We run power cables for the family magnets clockwise along the ring and run
them back counter clockwise for avoiding to make a current loop along the ring.
Table 2.4 Specifications of electric power supplies
Type
BQ combined

Load
BQ

OutputUnipolarMaximum

Maximum

RippleCurrent

Voltage

Drift

650 A

400 V

20 ppmQuantity1

20 ppm/8 h
Quadrupole

Q1, Q3, Q5

Unipolar

350 A

200 V

Type1
Quadrupole

3

20 ppm/8 h
Q2, Q4

Unipolar

50 A

50 V

Type2
Sextupole

20 ppm50 ppm2

50 ppm/8 h
S1 ‒ S5

Unipolar

250 A

110 V

20 ppm5

20 ppm/8 h
Steering

Sext. mag.

Bipolar

±16 A

±8 V

Mag at SSS
Steering

Mag at LSS

50 ppm384

50 ppm/8 h
Bipolar

±5 A

±4 V

50 ppm96

50 ppm/8 h
Auxiliary

Quadrupole

Bipolar

±18 A

±10 V

50 ppm96

50 ppm/8 h

2.3 Alignment
The alignment procedure is classified into two stages. One is to align magnets inthe straight section between BQ combined magnets, and another is to do thealignment between the straight sections. Alignment tolerances for the two stages arelisted in Table 2.5.

2.3.1 Alignment in straight sections
At the first step of alignment, magnets are aligned on a common girder on thestraight. As is shown in Table 2.5, the tolerance is ±0.05 mm, but we aim to achieveeven smaller alignment errors for obtaining adequate dynamic aperture. For the
purpose, we apply the vibrating wire technique that we assume is effective to a18

precise magnet alignment on the straight. In the scheme, a tensioned wire, excitedwith an AC current, is placed along the longitudinal axis in a series of magnets andeach magnet is powered one by one. Then the field profile of the magnet near its
magnetic center is measured by detecting the wire vibration at its resonancefrequency. Thus we can directly determine the magnetic centers and do thealignment on the straight without relying on any fiducials [2.1]. On girders A, B, E,
and F, magnets are subject to this alignment scheme except for the BQ combined
magnets, while on girders C and D, where we only have a BQ combined and a single
quadrupole magnet, magnets are aligned based on the conventional laser tracker
measurement. Once the magnets are aligned on the straight, we set fiducial points
on the magnets at both ends of the straight for preparing for the alignment between
the straights. There is one more procedure before proceeding to the alignment
between the straights. The magnets on the common girder need to be moved into
the accelerator tunnel after finishing the magnet alignment in a straight section.
Before moving, we measure with high precision each magnet position by using a
newly developed system, called “Wire Alignment Monitoring System (WAMS)”. Here,
we set a wire position sensor on the SMR (Spherically Mounted Retroreflector) target
pedestal on the top of each magnet, and run another wire along with them. We thenrecord the relative magnet positions deduced from the wire positions measured ateach wire position sensor. The WAMS is useful when (i) a drift of magnet position
upon the move needs to be identified, and (ii) a precise magnet position
measurement is necessary with a vacuum chamber already sitting in the magnet. This
monitor is expected to give us information on a long-term drift of the magnet
position due to the deformation of the girder and others in years.
Table 2.5 Alignment tolerances.
x, yYaw, Pitch, Roll

On straight±0.05 mm±0.1 mrad

Between straights±0.09 mm±0.1 mrad

The next step is to do the alignment between the straights after moving themagnets aligned on the girder into the accelerator tunnel. Inside the tunnel, girders
are aligned using a laser tracker and an alignment level tool. Important criteria forthis step are to keep the relative position between adjacent girders within thetolerance (see Table 2.5). Beyond the wavelength of betatron oscillation of electrons,
the alignment requirement between girders is rather relaxed. Only we have to do is19

to smoothly align girders without a sudden jump of the girder position within the
betatron oscillation wavelength. The alignment tolerance for girders is not extremely
challenging, so it can be achieved by rather conventional ways based on the network
measurement by the laser tracker.
In addition to the above alignment steps, there are other critical issues that wehave to consider in carrying out the precise alignment. The temperature drift ofambient air may affect the precision of the alignment. Magnets need to bedisassembled by half when the vacuum chambers are installed into the magnets,
where the precision of physical repeatability of the magnet yokes may distort the
precise alignment. Most of the effects can be monitored by using the WAMS system,
but still the careful treatment is the key to reliable alignment works.
Reference[2.1] K. Fukami et al., “Performance verification of a precise vibrating-wire magnet
alignment technique for next-generation light sources”, Rev. Sci. Instrum. 90,
054703 (2019).

20

3. Vacuum system
3.1 Outline of vacuum system
The vacuum system was designed targeting 20 h of the gas scattering lifetime ata stored electron beam current of 400 mA, which required the pressure of 1 × 10-7 Pa
equivalent to CO. Figure 3.1 shows the layout of magnets, vacuum chambers, andphoton absorbers for a unit cell. The vacuum system of each cell (unit cell) consistsof six straight section chambers and four bending section chambers. The longstraight section, where an insertion device (ID) is installed, can be isolated from thestraight section 5 (the previous cell) and the straight section 1 by sector gate valve 2(SGV 2) and sector gate valve 1 (SGV 1), respectively. An ID-dummy chamber isinserted into the long straight section until an ID is installed. In addition, a chamber
for a multi-pole wiggler (MPW) is inserted into the center of the straight section 3(the short straight section). For the material of the vacuum chamber, stainless steel
was chosen. Stainless steel CF flanges connect the vacuum chambers.

Figure 3.1 Layout of magnets, vacuum chambers and photon absorbers for a unit
cell. Bending magnet (B), quadrupole magnet (Q), sextupole magnet (S), photon
absorber (CR1, 2, AB1 to 10, and SAB1 to 4).

21

The 12 photon absorbers (CR1, 2 and AB1 to 10) and four supplemental photon
absorbers (SAB 1 to 4) are discretely arranged so that the synchrotron radiation fromthe bending magnets may not irradiate the chamber wall. By concentrating thevacuum pumps at the photon absorbers, photon stimulated desorption (PSD) gas will
be locally evacuated to maintain low pressure even during the beam operations. To
protect the stainless steel walls of the vacuum chambers from the collision of theelectron beam on the occasion of beam dumps, the AB8 chamber in each cell isequipped with an electron beam absorber made of graphite to spread and absorb
the dumped electron beam.
In-situ baking of the vacuum chamber and non-evaporable getter pump (NEG)
activation is carried out after installation in the ring tunnel.

3.2 Structure and function of vacuum system
3.2.1 Straight section chamber
Figure 3.2 shows the cross-section of the straight section chamber. The chamberconsists of a beam chamber, an antechamber, and a slot that connects both chambers.
The height of the beam chamber is set at 16 mm by considering the vertical size ofthe stored electron beam and the area where the dynamical stability of the electron
beam can be secured. The width is set at ±15 mm to secure enough margins for the
injection beam orbit. The 5 mm height slot enables the passage of synchrotron
radiation from the bending magnets. The inner wall of the antechamber is set at 73mm from the beam center in the horizontal direction. The discrete photon absorbers
are located to prevent the irradiation of synchrotron radiation from the bending
magnets to the inner wall of the antechamber.
The chamber is made of stainless steel, which has excellent corrosion resistanceand high nonmagnetic stability. The inner top and bottom surfaces of the beamchamber are plated with copper more than 0.1 mm thick to reduce resistive-wall
impedance. The vacuum chamber has cooling channels for stabilizing chamber
temperature.

22

antechamber

48

16

3

13

22

13

beam chamber

15

56
71

60
137

Figure 3.2 Cross-section of straight section chamber. The unit is mm.

3.2.2 Bending section chamber
Figure 3.3 shows the cross-section of the bending section chamber downstream
part. The bending section chamber consists of a beam chamber and an antechamberequipped with a supplemental photon absorber at the most downstream. Theinternal dimension of the chamber is determined to fit in a narrow gap of the bending
magnet poles without significant cross section deformation at atmospheric pressure
and to extract all ±4.0 mrad synchrotron radiation from the MPW. The chamber isalso made of stainless steel. The stainless steel plates formed by bending are cut inaccordance with the bending radius, and connected by laser beam welding (LBW) tobuild the chamber. The inner top and bottom surfaces of the beam chamber are also
plated with copper more than 0.1 mm thick to reduce resistive-wall impedance.
antechamber

24

20

5

16
2

5

20

2

beam chamber

4.5

21

4.5 10

15

20

28

73
103

Figure 3.3 Cross-section of the bending section chamber downstream part. The unit
is mm.

23

3.2.3 Photon absorber
The photon absorbers should be positioned properly with an appropriate light cut
position in the horizontal direction, taking into account the need to prevent theunwanted radiation to the vacuum chamber walls, to prevent the radiation power
allocated to each photon absorber from being excessively large, and to extract thelight with a required divergence angle to the beamline (see Figure 3.1). The unit cellhas two crotch absorbers (CRs), ten absorbers (ABs) and four supplemental photon
absorbers (SABs). The difference between a CR and an AB is the presence or absenceof a window for extracting the light to the beamline. The CRs and ABs with propercooling ability are supposed to be attached to dedicated chambers by flangeinterface with no gap, which intends to accurately position the irradiation body. The
CRs and ABs have structures for confining scattered radiation in the absorber as muchas possible. CR1 and CR2 located at the downstream of the ID and the MPW havewindows for extracting light with a horizontal divergence angle of ±1.5 mrad and±4.0 mrad, respectively. SAB is located at the most downstream of the bending
section chamber.
Table 3.1 shows a list of power distribution on each photon absorber at the stored
beam current of 400 mA. The CRs and ABs are designed based on the results ofthermal and thermomechanical analyses and are made of GLIDCOP that has highmechanical strength at higher temperatures [3.1]. The heat-absorbing part isdesigned with simple grazing angle configuration to have a peak power density of
about 200 W/mm2 (normal incidence equivalent). The SABs are made of oxygen-freecopper (OFC) because the maximum temperature and equivalent stress do not
exceed 200°C and the yield point. In the design of the cooling mechanism, it is crucial
to not only incorporate flow passage structure adaptable to miniaturization but also
prevent the corrosion of the heat-absorbing part [3.2] caused by the interaction
between the cooling water and synchrotron radiation. In addition, it is also importantto keep the flow rate as low as possible to prevent a vibration problem.

24

Table 3.1 List of absorbed total power (TP) on each photon absorber with peak
power density (PPD) at normal incidence.

3.2.4 Vacuum chamber parts
CF flanges made of stainless steel connect the vacuum chambers. Beryllium copper
RF contacts are inserted to fill the gap between the flanges.
Two types of welded stainless-steel-bellows are designed to efficiently fit in the
narrow space between multi-pole magnets. The short-stroke bellows absorbs themisalignment of the chambers. The long-stroke bellows is retracted when the vacuum
chamber is inserted in the storage ring, or absorbs thermal expansion of thechambers during baking. Inside the bellows, RF shield made of Beryllium copper isinstalled to maintain the RF continuity between adjacent chambers. Due to the severe
packing factor, it is important to make bellows parts as small as possible. In addition,
there is a need to suppress the increase in impedance carefully taking into accountthe small cross-sectional dimensions of the beam chamber. In order to connect thecross-sections of the vacuum chamber and parts continuously, steps and gaps of thecross-sections must be minimized.
All-metal sector gate valves with RF shields are installed on each side of an ID
vacuum chamber to facilitate vacuum maintenance when the chamber is vented toatmospheric pressure. If the pressure deteriorates in any section, these sector gate
valves are closed and the section is isolated.

25

The pressure is monitored by cold cathode gauges, which do not require
maintenance because there is no filament to burn out. Signals from the cold cathodegauges and ion pumps are used for the interlock closing the sector gate valves.

3.2.5 Pumping system
In the 3-GeV storage ring, since most of the synchrotron radiation from thebending magnets is received by photon absorbers, outgas due to PSD is localizedaround the photon absorbers. As a small cross-sectional area of the vacuum chamber
makes it difficult to ensure sufficient conductance in the longitudinal direction, alumped pumping system comprised of a cartridge NEG pump and ion pump isinstalled near the photon absorbers. The effective pumping speed required for thepumping system is about 0.1m3/s for CO.
3.3 Gas scattering lifetime and pressure
3.3.1 Gas scattering lifetime
The lifetime of the stored electron beam is mainly determined by the quantum
lifetime resulted from the emission of synchrotron radiation, Touschek lifetime
decided by Intra-beam scattering inside the bunch, and the gas scattering lifetime
caused by the collision with residual gas. Taking into account the RF voltage of 3 MV,
the quantum lifetime is adequately long. However, the Touschek lifetime is about 15
h. To prevent the gas scattering lifetime from having significant effects on the beam
lifetime, it is required to ensure the gas scattering lifetime of approximately 20 h at
the stored beam current of 400 mA. Considering the minimum gap of the insertion
device and optical lattice function in the vertical direction, the required ultimate
pressure is estimated to be approximately 1 × 10-7 Pa (converted to CO pressure).
3.3.2 Amount of outgassing
The outgassing in the vacuum system of a dedicated light source storage ring is
caused by thermal desorption and PSD. In the pressure distribution calculation shown
below, the thermal desorption yields of H2 and CO of stainless steel were set to 2.8 ×
10-9 and 7 × 10-10 Pa·m3 / s / m2, respectively, and the outgassing was allocatedaccording to the surface area of the vacuum chamber. The outgassing due to the PSD
was allocated to each photon absorber according to the number of photons and thenumber of integrated photons, based on the parameter [3.3] used in the vacuum
system design at SPring-8-II.

26

3.3.3 Pressure distribution
Figure 3.4 shows the calculated vacuum pressure distribution in a unit cell at 400
mA operation after 1500 Ah conditioning. In the figure, S = 0 is the position of thesector gate valve 1 at the downstream end of the ID section. An ID-dummy chamber
is inserted in the ID section. As a result of the calculation, the average pressure of CO
was 6 × 10−8 Pa, the gas scattering lifetime was about 22 hours, and the beam lifetime
was 9 hours.

Figure 3.4 Calculated vacuum pressure profile in a unit cell at 400 mA after 1500 Ah
conditioning.
References[3.1] S. Takahashi, et al., J. Synchrotron Rad. 15, 144 (2008).
[3.2] M. Shoji, et al., Vacuum 84, 738 (2010).
[3.3] M. Oishi, et al., Proc. of IPAC2016 THPMY001, Busan, Korea, 3651 (2016).

27

4. RF acceleration system
4.1 Overview
The role of the RF acceleration system in the storage ring is to compensate for theenergy loss of the electron beam due to the generation of synchrotron radiation(radiation loss) at the bending magnets and the insertion devices. This radiation loss
is estimated to be up to 1.26 MeV per turn. An RF power of approximately 1 MW
must be continuously supplied to the RF cavities to compensate for the radiation loss
at a beam current of 400 mA and to generate an acceleration voltage of more than
3.6 MV ensuring a beam lifetime of more than 5 hours. About 500 kW of RF power isconsumed over the walls in the RF cavities. To supply such high power with highstability, we will build an acceleration system using the 500 MHz band RF acceleration
technology. This frequency band is selected because many pieces of RF equipment
have been developed in this band and utilized for accelerators for high-energy
physics experiments and synchrotron radiation sources [4.1][4.2]. The equipment has
high stability, high power-efficiency, and is relatively inexpensive.
When a high current beam passes through a cavity, parasitic higher-order modes(HOMs) of the cavity are strongly excited. The HOMs are harmful because they force
the beam to start unstable motion. This instability is called coupled-bunch instability(CBI). It degrades the emittance and finally leads to beam loss. A TM020-mode RF
accelerating cavity with built-in HOM absorbers [4.3][4.4] was designed to damp the
HOMs and to suppress the CBIs. The cavity can generate high accelerating electricfields required for high current beam acceleration efficiently.
Table 4.1 and Figure 4.1 show the design parameters and the configuration of the RF
acceleration system. The acceleration system consists of (1) an RF source including
its driving power supply and a power-transmission system, (2) four acceleration
cavities, and (3) a low-level RF control system, each of which is described in thefollowing sections.

28

Table 4.1 Specification of the storage ring RF acceleration system
Items

Specification

Beam energy

3 GeV

Beam current

400 mA

Beam revolution frequency

859.4 kHzRF frequency

508.759 MHz

Energy loss

1.26 MeV/turn max.

Bending magnet

0.62 MeV/turnInsertion device

0.64 MeV/turn max.

RF cavity voltage

3.6 MV (900 kV per cavity)

Synchronous phase

160 - 170°(depends on energy loss)

Synchrotron frequency

6.0 kHz

Number of RF cavities

4 cavities

Heat dissipation at cavity

119 kW per cavity

Input RF power

245 kW per cavity max.

Figure 4.1 Configuration of RF acceleration system29

4.2 High-power RF source and transmission system
When RF power exceeds 1 MW, the solid-state amplifier is still too expensive andimpractical. Therefore, we adopt a 1.2 MW continuous-wave klystron with a highdegree of efficiency [4.5][4.6], which has been used for more than 30 years. This
klystron is a triode tube with an anode electrode enabling a high power-efficiency of
60-70% by adjusting its voltage according to the output power. Because a gain of the
klystron is over 50 dB, the klystron can provide 1.2 MW power with an input powerof approximately 10 W from a driver amplifier. The klystron output power is controlled
by the input power and the anode voltage while the cathode voltage is kept at 90 kV.
A simple 12-phase full-wave rectifier is used as the power supply to apply a high DC
voltage of 90 kV and a current of 20 A in maximum to the cathode of the klystron.
In order to transmit the high-power RF generated by the klystron to the accelerating
cavities, a high-power transmission system is constructed using a waveguide of WR1800 and WR-1500 standards. A circulator [4.7] with a rated forward power of 1.2
MW and a rated reverse power of 650 kW is installed directly downstream of the
klystron to protect the klystron from the reflected power. A dummy load with a rated
power of 300 kW (maximum allowable power of 3 MW at 20 ms) is connected to thethird port of the circulator to absorb the reflected power. After passing through thehigh-power phase shifters, the RF power flows into the four accelerating cavities. We
use special waveguides with cross-sectional dimensions of 381 mm × 100 mm fromthe through-holes of the storage ring tunnel to the cavities in order to reduceradiation leakage from the holes.
4.3 RF accelerating cavity
We employ the compact TM020-mode RF accelerating cavities developed at
SPring-8 to generate a high accelerating voltage, to install four cavities in the 5-m
straight section and to suppress the CBI at the high storage current. Figure 4.2 showsa photograph of a prototype of the cavity. The figure also indicates the distributionsof the electric and magnetic fields from 3-D RF simulation. The estimated shunt
impedance is 6.8 M and the unloaded Q value is 60,300 with the cavity material ofoxygen-free copper. The cavity has two slots inside the body along the nodes of themagnetic fields of the TM 020-mode to prevent the TM020-mode from entering theslots. On the other hand, the fields of the HOMs pass through the slot and areattenuated by the ferrite absorbers installed in the slots. Figure 4.3 shows the
impedance distributions of the monopole and dipole HOMs obtained from thesimulation. Black and red dots indicate the impedances with and without the30

absorbers, respectively. The impedance of the beam accelerating mode is notdegraded by the absorbers though the HOM impedances can be attenuated to below
the CBI thresholds.
For the connection between the cavity and the waveguide, we use a special coupler
and adjust the coupling according to the beam loading in high-power operation [4.8].
A variable length copper plunger (coupling tuner) is installed in front of the iris of thecavity, and the coupling value can be varied from 1 to 4 or more by changing theinsertion length of the plunger. In this way, the reflected power from the cavity canbe reduced and the RF power can be used effectively by keeping the optimum
coupling in accordance with the beam current (400 mA max.).
In order to evacuate the cavity and feeding an RF power into the cavity, a ceramic
window is installed in the waveguide [4.3]. The window is made from a low-loss
alumina-ceramics (dielectric loss < 0.0001), which is bonded to a copper plate with
an iris shaped into a racetrack. If damage to the ceramics happens, the window canbe easily replaced.
In order to confirm the RF performance of the designed cavity and to conduct
high-power RF operation tests, a prototype cavity was fabricated (Figure 4.2). Whenthe cavity has the HOM absorbers made of ferrite, Q-values of major HOMs such as
TM110 and TM011 were less than 1,000 sufficient for damping. On the other hand, adecrease in Q-value of the TM020 mode was only 1.4%, as expected. A high-power
test was carried out at a test stand of the SPring-8. An RF power of 120 kW was fed
into the cavity to generate a voltage of 900 kV for the designed beam acceleration,and there were no serious problems [4.4].

31

Figure 4.2 Photographs of the TM020-mode RF cavity and the HOM absorber (left),and distribution of electric and magnetic fields by a simulation

Figure 4.3 Impedance map of monopole mode (left) and dipole mode (right). The
blue circle indicates the beam acceleration mode.

4.4 Low-level RF control system
One of the main functions of a low-level RF control system is to stabilize theamplitude and the phase of the acceleration voltage. A digital control system basedon the MicroTCA.4 standard [4.9] will be adopted. The merits of this system are to
reduce the size and cost of the system by using highly integrated modules and to32

improve the control functions. A similar system was introduced in the SPring-8
storage ring in 2017 and has been working stably.
Figure 4.4 shows the configuration of the digital control system. The RF signals
from the waveguide or accelerating cavity pickup are fed to a signal processing RTM(Rear Transition Module). The processed signals are fed to a 10-channel digitizer AMC(Advanced Mezzanine Card) capable of sampling at 16 bits and 370 MHz. The Digital
Down Conversion is performed by the firmware running on the FPGA in AMC and theamplitude and the phase of the RF signal are obtained. To generate the drive RF signalof the klystron, two channels of DACs on the AMC are used. These signals are fed to
the RTM to control the vector modulated RF output. Advanced functions, such as
vector summation of the signals from several cavities, RF phase rotation, andnumerical operation of feedback control, are realized by the firmware running on the
FPGA in AMC.
The acceleration voltage and phase are stabilized by a two-loop feedback
controller: the klystron loop and the cavity loop. The klystron loop has a control
bandwidth of a few kHz and suppresses the fast output fluctuations caused by thehigh voltage ripple of the klystron power supply. The cavity loop suppresses slow
variations in the order of a few Hz, such as changes in beam load, environmental
temperature, and cooling water temperature.
The resonant frequency of the acceleration cavity is adjusted by a motorizedplunger (frequency tuner) installed in the cavity. The position of the frequency tuner
is controlled so as to keep the phase difference between the input RF signal to thecavity and the pickup RF signal of the cavity constant.
The coupling strength between the waveguide and the cavity is controlled byadjusting the coupling tuner to suppress the power reflection from the cavity since
the optimum coupling strength depends on the beam load.
The system also has a function to monitor the operating status of RF devices andabnormal conditions, such as arcing at the ceramics windows, high reflection powerfrom cavities, and so on. If the system detects an abnormal event, the RF switch is cut
off immediately and the operation of the klystron is stopped to protect the RF
equipment.

33

Figure 4.4 Schematic of the digital low-level RF system
References[4.1]

http://www-superkekb.kek.jp//[4.2]

Y. Kawashima et al., Proc. of EPAC08, Genoa, p. 1485 (2008).

[4.3]

H. Ego et al., Proc. of 11th PASJ meeting, Aomori Japan, p237 (2014).

[4.4]

H. Ego et al., Proc. of 16th PASJ meeting, Kyoto Japan, p17 (2019).

[4.5]

S. Isagawa et al., Proc. of PAC87, Washington D.C., p. 1934 (1987).

[4.6]

M. Hara et al., J. Synchrotron Rad.5, 379 (1998).

[4.7]

H. Ego et al., Proc. of EPAC94, London, p. 1865 (1994).

[4.8]

H. Ego, Nucl. Instr. Meth. A564, p. 74 (2006).

[4.9]

T. Ohshima et al., Proc. of IPAC17, Copenhagen, p. 3996 (2017).

34

5. Beam diagnostic system
5.1 Outline of beam diagnostic system
The beam diagnostic system is important to generate high-quality synchrotron
radiation by monitoring and controlling the electron beam. This chapter describes
the beam diagnostic instruments in the storage ring and the injection beam transportline near the storage ring.
The diagnostic instruments in the beam transport line near the injection point tothe storage ring are listed in Table 5.1. To inject the electron beam stably andefficiently with the beam injection system in Chapter 6, both the beam profile andthe injection beam orbit have to be adjusted to fit the dynamic aperture of thestorage ring. Sufficient clearance between the injected beam and the septum walland small amplitude betatron oscillation of the injected beam should be realized byadjusting the injection beam orbit and the optics of the beam transport line. We
install an OTR-based beam profile monitor to measure the injection beam size andtwo beam-position monitors (BPMs) to determine the injection beam orbit. We also
install a current transformer (CT) to evaluate the beam injection efficiency bycomparing the injection beam charge from this CT and the increase in the stored
beam current of the ring measured by with a DCCT (described later).
The diagnostic instruments in the storage ring are summarized in Table 5.2. BPMs
are installed along the whole storage ring to monitor both the single-pass beam
trajectory of the injected beam and the equilibrium orbit of the stored beam. A DCCT
is used for the stored beam current measurement and a stripline BPM is employed
to monitor the current and the longitudinal phase of each electron bunch and todiagnose the orbit fluctuations etc.
To provide stable x-rays to users, a reliable x-ray beam-position monitor (XBPM) tomonitor the optical axis precisely is essential. A conventional blade-type XBPM is notgood enough for this purpose since the position reading of this XBPM depends onthe gap of the insertion device. The blade-type XBPM detects not the core center ofthe X-ray beam but just the tail part of the x-ray beam profile that changes with thegap movement of the insertion device. Therefore, we need to develop a new XBPM
sensitive to the center of the core of the x-ray beam according to the latest researches
for the SPring-8-II, etc.
The beam size at the source point for each beamline is estimated from the emittanceand the x-y coupling ratio obtained at one location with the information from theorbit response matrix measurement by the BPMs. The emittance and x-y coupling35

ratio are measured by a beam size monitor, which detects the X-ray synchrotron
radiation from a 3-pole wiggler.
A real-time betatron tune monitor is also equipped for the evaluation of the beam
optics and the automatic compensation of the tune shift due to the gap change of
insertion devices. To save the installation space for the instruments and to realize areal-time measurement capability, the tune monitor is implemented in the bunch-bybunch feedback (BBF) system described later.
The beam diagnostic instruments in the storage ring, except for the BPMs and
XBPMs, are installed into two short straight sections dedicated to beam
instrumentation.
Table 5.1 Beam diagnostic instruments for the injection beam transport line
Instrument

Number of units

Beam size monitor

1

Beam position monitor (BPM)

2

Beam charge monitor (current transformer, CT)

1

Table 5.2 Beam diagnostic instruments for the storage ring
Instrument

Number of units

Beam position monitor (BPM)

112 (7 per cell)Stored beam current monitor (DCCT)

1

Stripline BPM

1Photon beam position monitor

1 per beamline

Beam size monitor

1

Betatron tune monitor

1 (implemented in BBF)

Beam instability control system (BBF)

1

5.2 Beam position monitor
As described in Table 5.2, 7 BPMs are installed in each unit cell. The signal of thebeam is picked up by button-type electrodes developed for the SPring-8-II. This
electrode was carefully designed to suppress the impedance and heat generation[5.1]. The BPM vacuum chamber (BPM block) is shown in Figure 5.1. The chamber hasa bulk stainless steel part to mount button electrodes and a water cooling channel toreduce temperature rise. For the geometry of the BPM block, the beam position
sensitivity factor is estimated to be approximately 7 mm for both x and y directions,with which sufficient precision of the beam position can be obtained. The BPM block36

has precise fiducial planes on the outer surface to survey the BPM block with respect
to adjacent quadrupole and sextupole magnets.
The BPM readout electronics are required to have both the single-pass detection
and the equilibrium orbit monitor functions with sufficient precision, accuracy, andstability. The single-pass trajectory data of the injected beam is essential for the beamcommissioning of the ring. The precise equilibrium orbit data is crucial for stable user
operation. Furthermore, an interlocking logic to abort the beam storage is needed
for the BPMs adjacent to the insertion devices in case of an abnormal beam orbit
shift since the intense radiation from the insertion devices can damage the vacuum
chamber of the storage ring. The transient beam orbit fluctuation measurement
function on beam loss events etc. is also demanded. To implement all these functions,
the BPM electronics must be operated with several data rates in parallel, such as turnby-turn, 10 kHz, and 10 Hz. As a sufficient solution, we employ a BPM electronics
system based on the MicroTCA.4 standard [5.2], which was developed for the SPring8-II.
Reverse polarity
SMA connector
Welding

Fiducial plane

Water cooling channel
Flange(stainless steel)

BPM block(stainless steel)

Ceramic (Al2O3)
e-beamElectrode (Mo)  7mm

Pin (Mo)

Figure 5.1 Cross-section of the vacuum chamber with BPM electrodes (BPM block).
To deliver stable synchrotron radiation to users, the beam orbit stability is quite
important. The BPM block and its girder should be designed to suppress the thermal
deformation. The signal cables are required to have low loss, small reflection, andradiation-resistance for long-term stability and good temperature tolerance. The
readout electronics are also demanded to be highly stable and the temperature of
the electronics should be regulated to reduce the thermal variations.

37

The calibration procedures of the BPM system before the beam commissioning will
be investigated based on the required position accuracy and the commissioning
strategy. After the success of beam storage, the BPM offset will be calibrated by using
an electron beam (beam-based alignment). The BPM offset with respect to the field
center of an adjacent quadrupole or sextupole magnet is demanded to be measured
with an accuracy of better than 10 μm.

5.3 Beam size monitor using synchrotron radiation
A 3-pole wiggler is installed to one of the short straight sections of the ring tomeasure the beam emittance and the x-y coupling ratio. The wiggler radiation isdetected by an x-ray pinhole camera, which is designed by improving the one
operating at the SPring-8 storage ring [5.3]. The spatial resolution of the pinhole
camera is expected to be a few μm. Visible radiation from the 3-pole wiggler is also
extracted to evaluate the bunch length, etc. The x-ray pinhole camera is installedinside the storage ring tunnel and the darkroom for the visible light detection is built
in the experimental hall.
5.4 Control of beam instability
The suppression of beam instability is necessary to stably circulate the highcurrent electron beam of 400 mA within the narrow vacuum chamber described in
Section 3. Since the storage ring will be operated with the top-up injection, thechromaticity has to be small enough to minimize the loss of the injected beam.
Therefore, a bunch-by-bunch feedback (BBF) system to control the beam instability
is utilized from the early stage of the operation. The schematic diagram of the BBF
system is shown in Figure 5.2. Beam position signals are picked up by striplineelectrodes, the counter kick signal is calculated by an FPGA-based electronics, andstripline kickers manipulate the beam orbit. The FPGA-based BBF electronics arewidely used in other facilities and the stripline electrodes and the wide-band
amplifiers are already developed in SPring-8. The BBF system is designed according
to these successful experiences.
As mentioned in Section 5.1, the BBF system is also utilized for the real-time
betatron tune monitor.

38

Figure 5.2 Block diagram of the transverse BBF system.
References[5.1]

M. Masaki, et al., Proc. of IBIC16, Barcelona, TUPG18 (2016).

[5.2]

H. Maesaka, et al., Proc. of IBIC19, Malmo, WEBO03 (2019).

[5.3]

S. Takano, et al., Proc. of IBIC15, Melbourne, TUCLA02 (2015).

39

6. Beam injection system
6.1 Outline of beam injection system
We adopt an off-axis beam injection system to the storage ring. The highperformance linear accelerator described in Section 7 is used as a full energy injectorof low-emittance beams to enable a compact, highly efficient and stable beam
injection system. The beams are injected from the inside of the ring to a position
shifted horizontally from the stored beam orbit. Septum electromagnets to deflect
the injected beam and four kicker magnets for the injection orbit bump are installedin the 5.4m long straight section of the cell 4.

Figure 6.1 Schematic of the beam injection system. Numbers without units in the
figure represent millimeters.
Figure 6.1 shows an overview of the beam injection system. The injection system
consists of four kicker magnets (BP1 to BP4) and three septum magnets (DC SEP1,
DC SEP2, Pulse SEP). A differential pumping system is installed upstream of the
septum magnet (DC SEP1) to connect the beam transport vacuum to the ultra-highvacuum of the storage ring without a Be window that deteriorates the emittance of
the injected beam. Non-linear magnets such as sextuple magnets are not included
inside the injection orbit bump so that the beam fluctuation at the moment of beam
injection does not affect the experimental users.

6.2 Parameters for beam injection
The beam parameters at the injection point into the storage ring assumed for thedesign of the beam injection system are shown in Table 6.1. The positional
relationship between the injected beam and the stored beam orbit is illustrated in
Figure 6.2. The effective beam size (r.m.s.) of the injected beam and the accumulated40

beam at the injection point are 245 m and 114 m, respectively. The pulsed septum
electromagnet (Pulse SEP) is of in-vacuum type, and the effective thickness of the
septum wall, the total thickness of the eddy current shield plate and the magnetic
field shield, is 1 mm including the manufacturing accuracy. The orbit bump heightrequired for beam injection depends on the size of the physical aperture at the
injection point. The smaller this aperture is, the easier the design of the kicker
magnets for the orbit bump. A smaller aperture, on the other hand, means smaller
distances from the stationary ring orbit and the bumped orbit, respectively, to theseptum wall of the pulsed septum magnet. It could potentially cause the beam
instability, the beam loss, and tuning difficulties of the storage ring as well. Here, thedistance from the stored beam orbit to the septum wall is set to 8.5 mm, and theheight of the pulsed orbit bump to 6 mm. In the startup of the storage ring operation,
we assume the position of the injected beam in the range of 2 mm to 4 mm from theseptum wall. We would aim to reduce the maximum amplitude of beam injection
down to about 6 mm by adjusting the injection beam position as close as 2 mm fromthe septum wall. When an on-axis beam injection is required for the commissioningof the ring and the beam tuning later on, an auxiliary DC orbit bump should becreated with the steering electromagnets on both sides of the beam injection section
and superimposed on the pulsed orbit bump generated by the kicker magnets.
Table 6.1 Stored beam and injected beam parameters at the beam injection point
Parameters

SymbolInjected beamStored beam

Horizontal emittanceεx

3nm rad

1nm radEnergy dispersion

σE/E

0.1%

0.084 %

Betatron and dispersion

βx、Dx

20m, 0m

13m, 0m

σx

245m

114m

functions
Beam size (σ)

41Figure 6.2 The positional relationship between the injected beam and the stored
beam orbit. Numbers without units in the figure represent millimeters.

6.3 Magnets for beam injection
The specifications of the electromagnets for beam injection are given in Table 6.2.
The kicker magnets (BP1 to BP4) have C-shaped laminated cores of 0.1 mm thicksilicon steel sheet. To assure the closed orbit bumps free of beam fluctuation at the
moment of the injection disturbing the experimental users, the identity of themagnetic field waveform of the four kicker magnets is the key. For a better magnetic
field identity, each pair of the two upstream (BP1, BP2) and the two downstream (BP3,
BP4) kickers are driven respectively by one high-precision pulsed power supply withsolid-state switching devices. The vacuum chambers for the kicker magnets are madeof ceramics. The inner surfaces are coated with a metal like Ti to reduce the coupling
impedance. The shape and thickness of the coating are designed considering theinfluence of the eddy current on the magnetic field waveform. The DC septum
electromagnets (DC SEP1 and DC SEP2) are installed in the air. They have iron cores
made of silicon steel plate or electromagnetic soft iron with water-cooled coils. The
in-vacuum pulsed septum electromagnet (Pulse SEP) is of an eddy current type. It has
a laminated core of 0.1 mm thick silicon steel sheet placed in an ultra-high vacuum
chamber made of stainless steel.

42

Table 6.2 Specifications of magnets for beam injection
KickerDC septum

Pulsed septum

electromagnets

electromagnets

electromagnet(BP1、BP2、(DC SEP1、DC(Pulse SEP)

BP3、BP4)

SEP2)

Type

C shaped

Direct drive

Eddy current

Shape

Rectangular

Sector

Sector

B(T)

0.22

1.2

1.4

Length (m)

0.22

0.4

0.5

Pulse width（s）

3 (half-sine)DC

10（half-sine）

Repetition (Hz)

1

DC

1

Core material

0.1mm-thicksilicon steel or

0.1mm-thicksilicon steel

electromagnetic

silicon steel

soft ironChamber

Ceramic chamber

Stainless steel
chamber

43

In-vacuum7. Beam injector linac
7.1 Overview
There are two types of electron beam injectors into the storage ring, the linac(linear accelerator) and the synchrotron. We choose the linac, because the power cost
during operation is lower, a free electron laser (FEL) can be installed in the future, andTable 7.1 Required specifications of the beam injector linac.
Items

Requirement

Beam energy

E

3 GeV

Energy spread

ΔE/E

0.16％ (FWHM)

Energy stability

E/E< 0.2%

Bunch chargeQ

0.3 nC/bunch

Normalized emittanceβγε< 10 mmmrad

Bunch lengthσz< 5 ps (FWHM)

Pulse repetition rate

frep

1 Hz (beam injector)
25 Hz (RF conditioning)

the use of the high-precision, highly stable linac has been proven in SACLA [7.1] of
RIKEN.
A stable beam injection into a narrow dynamic aperture of a low emittance storage
ring requires a highly stable low emittance beam. The required beam performance isshown in Table 7.2. A low emittance electron gun and a C-band accelerator are used
to meet the requirements and to reduce the size of the linac. Figure 7.1 shows thearrangement of the linac and beam transport line [7.2]. The 112 m long 3-GeV linac
consists of a 30 MeV electron injector, a chicane section (BC1) for beam energy
measurements after the injector, and 20 C-band accelerator units, which generate ahigh electric field of 42 MV/m using a 50-MW klystron, an RF pulse compressor, andtwo 2 m long C-band accelerating structures [7.3]. A space was provided downstreamof the third and fifth C-band acceleration units so that the bending magnets for themagnetic bunch compression chicane (BC2) could be installed in the future.
For stable operation of the top-up beam injection, it is important to reduce theprobability of failure of the components. Especially for high-power components, we
use reliable and proven components, providing sufficient margin for performance,

44

Figure 7.1 Layout of the 3 GeV linac and the beam transport line.
and allow for easy replacement in the case of failure. For usual operation, we use 18
C-band accelerator units for the beam acceleration, keeping two units as “standby”.
If a certain trouble happens at one of the active units, the beam operation isimmediately resumed by switching the failed unit to the standby unit.
Since the maximum repetition rate of beam injection is 1 Hz, the repetition rate of
the klystrons and modulators should also be 1 Hz, for usual operation. Only the casefor the RF conditioning, we operate them at 25 Hz for effective conditioning.
Accordingly, the electric power system and cooling water system are designed tocover 25 Hz operation, but optimized for 1 Hz operation. For the cooling water
system, heat dissipation and thermal gradient at the RF cavity are negligibly small for
1 Hz operation. Therefore, we omit an individual water temperature regulation system
for the RF cavity. All the accelerating structures and SLED cavities are tuned at 28 ℃
and the common cooling water system circulates the cooling water with atemperature of 28 0.1 ℃. The RF amplitude and phase fluctuations caused by
disturbances are highly stabilized by RF amplitude and phase feedback control of alow-power RF system using MicroTCA.4.
The magnets used at the linac are 6 magnetic lenses in the injection section, 23
quadrupole magnets for beam transport in the C-band main acceleration section, 19
steering magnets, and four bending magnets in the chicane section. The power
supply for these electromagnets is the same as the digital power supply used in thestorage ring to streamline the list of the backup equipment.
The beam diagnostics system consists mainly of nondestructive monitors such as
current transformer (CT) and beam position monitor (BPM). All the acquired data are
analyzed by the MicroTCA.4 control system and managed by the database system.

45

The basic lattice of the beam transport in the 3 GeV linac is FODO. Figure 7.2 shows
β function, energy dispersion, and beam size. Several quadrupole magnets are
installed behind the 30-MeV injector (before and after the chicane section) and in thearea where BC2 is expected to be installed, for beam optics matching. In the C-band
main accelerating section, quadrupole magnets are installed in every four C-band
acceleration units (18 m). Figure 7.3 shows the beam profile at the end of the 3 GeV
linac, estimated using a beam tracking code. The beam emittance is estimated to beless than 2 nm rad with the beam charge of 0.4 nC, and an energy spread of 0.1%.

Figure 7.2  function, energy dispersion function, and beam size in theinjector linac.

46

Figure 7.3 Beam size and energy-time distribution at the end of 3 GeV linac.

7.2 Electron beam injector
Figure 7.4 shows the layout of the 30-MeV injector section. The electron gun
requires a charge of 0.6 nC with a normalized emittance of 5 mmmrad. A gridded
thermionic cathode (EIMAC Y-845, CPI), which is used in many accelerator facilities,
is adopted as the electron source. To achieve a low emittance, the 50-kV electron gun
is connected to a 238-MHz RF cavity with a minimum distance, which immediately
accelerates the beam energy to 500 keV [7.4].
A low emittance 500 keV beam of 2 mmmrad (normalized) and 0.6 nC is generated
by passing through a beam collimator installed at the RF cavity exit. Subsequently,
the 500 keV beam pulse is compressed by a 476 MHz subharmonic buncher (SHB)
and injected into a 2 m long S-band accelerating structure. Figure 7.5 shows theresults of the simulation code PARMELA for the beam performance at the exit of the
S-band accelerating structure. The result shows the bunch length is compressed to
2.3 ps (FWHM) and the beam energy reaches 36 MeV.
The beam focusing system is composed of six magnetic lenses (MLs). The
magnetic field strength of the magnetic lenses is adjusted to keep the optimum beam
diameter and to suppress the emittance growth due to the nonlinear space charge
effect.

47

Figure 7.6 shows the results of the normalized emittance calculation in the injector.
The normalized emittance at the exit of the injector is 8 mmmrad and the charge is
0.4 nC. The beam charge can be adjusted by the physical aperture of the beamcollimator placed between the 476 MHz SHB and the S-band accelerating structure.

Figure 7.4 Layout of the 30-MeV injector section.

Figure 7.5 Beam size and energy-time distributions at exit of the 30-MeV
injector.

48

Figure 7.6 Normalized emittance and beam charge, as a function of thelongitudinal position from the cathode.

49

7.3 Main accelerator
For the effective beam acceleration from 30 MeV to 3 GeV, we use 20 C-band
acceleration units. Figure 7.7 shows the configuration of the C-band accelerator unit,
and Table 7.2 shows the parameters of the main components [7.5], which is similar to
the C-band accelerator system used in SACLA [7.6]. The RF power of up to 50 MW
and 2.5 μs from the pulse klystron will be increased by a factor of about four by a
low-loss cavity-type RF pulse compressor (SLED), and then fed into two travelingwave-type acceleration structures. They consist of a disk-loaded structure, quasiconstant gradient type with a total length of about 2 m. It is designed to produce anaverage accelerating gradient of 42 MV/m when 80 MW of RF power is supplied [7.7].
The electron beam is accelerated by 168 MeV with the nominal accelerating gradientof 42 MV/m. Each klystron is driven with 350 kV, 310 A pulse power supplied by amodulator, and 300 W RF input supplied by a driver amplifier. They are remotely
controlled from the upper control system through a MicroTCA.4 based low-level RF
system and PLC control system installed in the control rack. A sputter ion pump isused to maintain an ultra-high vacuum inside the accelerator, RF pulse compressor,
and waveguide. In addition, a ceramic waveguide vacuum window is installed
between the klystron and the SLED to maintain a vacuum in the accelerator during
klystron replacement. A quadrupole magnet to focus the electron beam, a steering
magnet to control the orbit, a beam position monitor (BPM), and a gate valve (GV) to
separate the ultra-high vacuum area is installed in each of four acceleration units(about 18 m).
Since the normal repetition frequency of the linac is only 1 Hz, the heat generated
by the accelerator and RF pulse compressor is small, and the temperature fluctuations
when switching between operations are negligible. The temperature of the common
cooling water is controlled within 280.1°C. Therefore, the precise temperature
regulation system of cooling water for each unit is not adopted. The temperature
coefficients of the accelerator and RF pulse compressor are shown in Table 7.2. Since
the main accelerator is used at the crest phase, the effect of phase change is small as
long as the cooling water temperature is stable within 0.1 °C.

50

Figure 7.7 Schematic of C-band accelerator unit.

51

Table 7.2 Main parameters of the C-band accelerator unit
Devices

Items

Specifications

Klystron

RF frequency

5.712 GHz

RF output power

50 MW max.

RF pulse width

2.5 μsRF pulse compressor

Unloaded Q-value

185,000(SLED)

Coupling constant11

Power magnification factor Pout/Pin(average of filling time ~300 ns

4.0
Amplitude: 0.06%/0.1 K

Thermal constantPhase: 1.7/0.1 K
2π/3 mode,

Acceleration
structure

Quali-constrant-

RF modegradient type travelingwave structures
Regular cell 112

Number of cells

Coupler cell 2

Effective accelerator length

1.994 mAttenuation parameter τ

0.604

Filling time tF

300 nsShunt impedance Rsh

63 MΩ/mNominal accelerating gradient

42 MV/mTemperature coefficient

Phase: 1.1/0.1 K

7.4 Beam transport line
The electron beam accelerated to 3 GeV in the injector linac is transported to thestorage ring through an 80 m-long transport line. As shown in Figure 7.8, the electron
beam is horizontally deflected toward the storage ring by 42 degrees after the linac.
Then the transport line goes through a radiation shield wall and crosses a photon
beamline and the storage ring. Before reaching the beam injection point of the52storage ring, the electron beam is horizontally deflected twice (30 and 19.7 degrees)again and injected to the ring from the inner side using septum magnets.
The floor height of the electron beam is 800 mm at the linac and 1200 mm at thestorage ring. The floor level is elevated by 200 mm at the shield wall, so the beamheight of the transport line is 800 mm before the wall and 600 mm after the wall.
After crossing under the photon beamline and the storage ring, whose heights are
1200 mm, the transport line is lifted up by 600 mm using two vertical bending
magnets. There is a drift space of 5 m between the vertical bending magnets for thetransport route of an insertion device.
Figure 7.9 shows the beam optics of the transport line. All the bending magnets
have water-cooled coils, and each horizontal deflection is made by a four-bend
achromatic lattice. The quadrupole magnets have air-cooled coils except for the threemagnets used in the achromatic lattice. The electron beam dump is installed
downstream of the linac, and the beam is dumped by exciting only the first bending
magnet. As beam diagnostics, 8 beam position monitors, 4 screens and 3 current
monitors are installed along the transport line. 11 steering magnets, which are x-y
combined type, are installed to adjust the beam orbit. In order to reduce thehysteresis of the steering magnets, permalloy is used for the yoke.

Magnet power supplies

30°

Ring injection section

19.7°

Space for undulator installation
Vertical bending magnets

Shield wall

Photon beamline
42°
Quadrupole magnets
Bending magnets
Linac end

Beam dump

Figure 7.8 Schematic layout of beam transport line.
53

Beta functions (m)

100

(a)

80

Horizontal

60

Vertical40200Dispersion (m)

0

20

40

60

80

Distance from linac end (m)

(b)

1.0

Horizontal

0.5
0.0

Vertical

-0.5
-1.0
0

20

40

60

Distance from linac end (m)80

Figure 7.9 Beam optics of the beam transport line, (a)beta functions,(b)dispersion functions.

7.5 Low-level RF system
The main task of the injector linac is to inject the electron beam into the aimed
bucket of the storage ring with high efficiency. It requires a high timing accuracy
better than the bunch length of the ring, 6 ps, and stable beam energy better than
0.1%. To satisfy these requirements, we build a Low-Level RF system with MicroTCA.4
based modules [7.7]. The reference 238 MHz signal of the linac is generated bymultiplying a rational number to the frequency of the reference 508.76 MHz signalof the storage ring. This reference 238 MHz signal is delivered to each accelerating
unit through an optical link. A master trigger signal synchronized to both the 238
MHz signal and the bucket timing signal of the ring is generated using a
synchronization Rear Transition Module (RTM). The master trigger is delivered
through an optical link of the trigger AMC. Figure 7.10 shows a block diagram togenerate the reference 238 MHz signal and the master trigger signal of the linac. At
each accelerating unit, an rf signal to drive a high power amplifier or a klystron is54generated by multiplying the frequency of the 238 MHz linac reference signal. Figure
7.11 shows a block diagram of the LLRF control system for the C-band accelerating
structure. The 5712 MHz signal is generated at the LO/CLK module. The 5712 MHz
signal for the klystron is generated by a vector modulator (VM) to have the aimed
pulse width, amplitude and phase by using a 5712 MHz RTM [7.8]. The VM signal isamplified to 800 W by using a GaN amplifier and is fed to a klystron. The pickup
signals from the accelerating structure are down-converted by the RTM and are
detected by a 10 channel digitizer AMC.
References[7.1] T. Ishikawa et al., Nature Photonics 6, 540 (2012).
[7.2] T. Asaka et al., Proc. of 16th PASJ meeting, Kyoto Japan, p771, (2019)[7.3] T. Sakurai et al., Phys. Rev. Accel. Beams 20, 042003 (2017).
[7.4] T. Asaka et al., Proc. of 29th Linea accelerator Conf, Beijing, China, p949, (2018)[7.5] T. Inagaki et al., Proc. of 16th PASJ meeting, Kyoto Japan, p766, (2019)[7.6] T. Inagaki et al., Phys. Rev. ST Accel. Beams 17, 080702 (2014).
[7.7] T. Ohshima et al., Proc. of 15th PASJ meeting, Nagaoka Japan, p55, (2018)[7.8] E. Iwai et al., Proc. of 16th PASJ meeting, Kyoto Japan, p130, (2019)55

Figure 7.10 A block diagram to generate the reference 238 MHz signal andthe master trigger signal of the linac.

Figure 7.11 A block diagram of the LLRF control system for the C-band
accelerating structure.

56

8. Accelerator Control System
8.1 Overview
The control framework developed by SACLA/SPring-8 is adopted as the software
for the accelerator control. The framework is distributed control architecture, as
characterized in the following list.


By providing SVOC as a human-readable abstract instruction, the GUI
developer does not need to know the detail of the device, and can promote
the upper-level design by assembling the logic using the abstracted
instructions.



It is a control framework based on RDBMS (Relational DataBase Management
System) and can maintain data integrity by managing online, archive, andparameter databases.

Asynchronous processing using messages and network hiding can reduce theload of GUI production.



Data collection is possible if the control system and the data collection system
can be controlled by the common functions of the control system and the datacollection system.



We can visualize the data using web services.
These features ensure reliability, repeatability, stable operation and flexible control

using a parameter database. The upper-level computer system used as a terminal for
operation uses Linux as the operating system and provides GUI Builder and graphic
libraries. The control device that controls the interlock is composed of PLC(Programmable Logic Controller) to ensure the same safety level as the hard wire. In
addition, the introduction of a wiring-saving system is aimed at shortening theconstruction time and improving maintenance.
APIs (Application Programming Interface) are provided to obtain the operation
status of the accelerator and to set the parameters of the light source to enable theuser to operate from the experimental control system. The network consists of acontrol network and an experimental network, and the control network is separated
from other networks by a firewall and constructed as an independent network. Each
network will be connected to the backbone, 10G Ethernet and branch line, 1G
Ethernet. The experimental network can be upgraded to the high-speed Ethernet
standard (10G Ethernet for branch lines and 40G or 100 G for backbone lines)
according to the future experiments. The control and experimental networks are

57

operated under different security policies, and communication is controlled by
firewalls.

8.2 Framework of the Control System
Figure 8.1 shows a schematic view of the control system.

Figure 8.1 A schematic view of the control system

8.2.1 Database System and Data Acquisition
One of the features of RDBMS is that the relationship between data is maintained
so that data inconsistency is difficult to occur. Another feature is the use of a language
called SQL which allows for flexible searching. This is an effective tool for correlating
multiple signals against archived data, for example. On the other hand, it adopts the
NoSQL system database specialized in writing performance as an online database.
RDBMS is adopted for the archive and parameters, and the configuration makes thebest use of the features of each database. As for the parameters, the operation
parameters and calibration data are handled in a unified manner, and the structure isdesigned to be portable and predictable by eliminating the labor for operation in
text files and maintenance of hard-coded programs.
58

8.2.2 Data Acquisition Process
The data acquisition process (MDAQ in Figure 8.1) provides processes for periodic,
synchronous and waveform data acquisition. For waveform data collection, two typesof process are prepared: one that can monitor waveforms by periodically collecting
them, and one that detects abnormalities and collects the waveforms before and after
them. Each process is run on a host for device control (such as a PC server orMicroTCA.4) and written to the database server. Considering the delay caused by the
network, the data collection process has a buffer so that the time series of the data
does not change.
8.2.3 Messaging Server
Use a global message server for the exchange of messages between processes.
MQTT [8.3] is adopted as the protocol for exchanging messages. This protocol wasdeveloped by IBM and standardized by ISO, etc. It is a lightweight and bidirectional
protocol, and adopts the Publish/Subscribe model without queues. In case of
hardware failure, it is assumed that fault-tolerant hardware or software failover will
be used to minimize downtime.
8.2.4 Equipment Control Process（Equipment Manager：EM／Equipment Manager
Agent：EMA）
The EM exchanges messages with the GUI for operation and operates one process
on each host to control the device. For software control, we assume a latency of 100
msec or more, and for 10 msec or less, we are considering hardware support. 10 to
100 msec will be supported in consideration of process characteristics.
EMA is forked from EM for complex feedback control. The parameters used for
feedback are managed by using the database management.
8.3 Equipment Control
The equipment control system controls, monitors, and collects data for vacuum
equipment, RF acceleration system, magnet power supplies, beam diagnostic
equipment, beam injection system, and front ends.

8.3.1 Equipment Control Platform
We plan to use MicroTCA.4 for the parts of the equipment control platform that
require high-speed control (beam diagnostic system and RF acceleration control

59system). MicroTCA.4, the PC servers, and network devices are monitored and tracked
using standard remote management protocols such as SNMP, IPMI, etc.

8.3.2 Vacuum Equipment Control System
In the vacuum equipment control system, the PLC controls and monitors thevacuum pumps and gate valves, etc., and acquires the vacuum gauge data. In addition,
each PLC is equipped with a touch panel. It can be remotely monitored to operate
the equipment and monitor its condition within the storage tunnel.
8.3.3 RF Acceleration Control System
In the control system of the RF acceleration control system, the voltage, phase,frequency, temperature, timing, etc. of the acceleration cavity are set, automaticallycontrolled and monitored by the MicroTCA.4. The high power and cooling systems
are controlled by PLCs and data and other information is exchanged with theMicroTCA.4 computer via a wiring-saving system.
8.3.4 Magnet Power Supply Control System
In the magnetic power supply control system, the start/stop, current setting, andvarious status monitoring of the magnet power supplies are controlled by a PLC.
EtherCAT [8.4] is used to control the electromagnetic power supply as a wiring-saving
system.
8.3.5 Beam Diagnostic System
The beam diagnostics system controls the beam current monitor, the beam
position monitor, the beam size analyzer, and the beam instability suppressor. For
monitoring the beam position, MicroTCA.4, which is used in the RF acceleration
system, is used for signal processing. The beam size measurement using thesynchrotron radiation is carried out by capturing images acquired by a camera to a
PC (or MicroTCA.4) and processing the images.
8.3.6 Device Interlock System
The device interlock system receives equipment protection interlock signals fromthe accelerator equipment, the insertion device and the beamline interlock system tofast beam abort the stored beam, stop the electron gun trigger for protecting thevacuum equipment.

60

Reference[8.1] T. Fukui, et al., “Status of the Control System for the SACLA/SPring-8 Accelerator
Complex”, Proceedings of ICALEPCS 2017, FRAPL03, Barcelona, Spain, 2017[8.2] T. Sugimoto, et al., “Status of the Control System for Fully Integrating
SACLA/SPring-8 Accelerator Complex and New 3 GeV Light Source Constructing at
North Region in Japan”, Proceedings of ICALEPCS 2019, WECPL01, New York, NY,
2019[8.3] http://mqtt.org[8.4] https://www.ethercat.org/default.htm

61