Proceedings of the 5th Annual Meeting of Particle Accelerator Society of Japanand the 33rd Linear Accelerator Meeting in Japan (August 6-8, 2008, Higashihiroshima, Japan)

PREPARATION OF PAPERS FOR ACCELERATOR CONFERENCESA)

Tomonori Uesugi, A)Yoshihar. Mori, A)Yoshihiro Ishi, c)Makoto Inoue, A)Yasutoshi Kuriyama
A)
Kaichiro Mishima,B)Kota Okabe, A)Akihiro Osanai, A)Thomas Planche, B)Izumi Sakai, A)Seiji ShiroyaA)
Kyoto University Research Reactor Institute, OsakaB)
Fukui Universityc)
SLLS, Shiga, Japan
Abstract

In Kyoto University Research Reactor Institute (KURRI), we have FFAG accelerator complex for Accelerator
Driven Sub-critical reactor (ADS). The FFAG-ERIT has shown that the FFAG accelerator can be a high intensity
neutron source with internal target, because of its large energy acceptance. The FFAG accelerator complex
forADS has been already constructed and is under beam commissioning. In the main ring, proton beams will be
accelerated up to 100 MeV in this summer.

１．Introduction
Kumatori Accelerator driven Reactor Test(KART)project has been started at Kyoto University
ResearchReactor Institute (KURRI) from the fiscalyear of 2002, aiming to demonstrate the basicfeasibility of Accelerator.
Driven Sub-criticalsystem (ADS) and to develop and 150 MeV proton
FFAG accelerator complex as a neutron production
driver[1]. The accelerator complex is composed ofthree FFAG rings; injector, booster, and main ring[2].
The specifications of the each FFAG are summarizedin Table1. As a first stage, the accelerator complex has
been planned to output 100 MeV-0.1 nA proton beams
in this summer.

is 2.5 MeV in design. We have accomplished theacceleration of proton beams up to 1.5 MeV in theIONBETA. The average output current is about 10 nA.
Betatron tunes are also variable by the trim-coils. We
are experimentally investigating fast integer-resonancecrossing with the IONBETA. The first experimentshowed that the integer resonance was successfully
crossed when the crossing speed was high enough [3].

Table 1: Specification of FFAG complex forADS(design).

Focusing
Acceleration
Field index, kEnergy(MeV)
Pext/Pinj
Orbit radius(m)Injector Booster Main Ring
SpiralRadial Radial
8 cells 8 cells 12 cells
InductionRF
RF2.5
4.5
7.5
0.1-2.5 2.5-20 20-150
5.00(Max) 2.84
2.83
0.6-0.99 1.42-1.71 4.54-5.12

Figure 1: Photograph of FFAG-ADS accelerators

２．FFAG accelerator complex
The proton beams of 120 keV are
accelerated in the injector. FFAG betatron, called
IONBETA. The IONBETA is composed of eight spiralsector magnets, two acceleration gaps, and electric
septa for injection and extraction, respectively. The
field distribution in the radial direction can becontrolled by trim-coils, and which makes variableenergy acceleration possible. Maximum beam energy

The booster FFAG adopts multi-turn beam
injection using horizontal space, by a couple of bumpmagnets, an electrostatic septum (ES) and a pulsemagnetic septum (MS). Captured beam current isabout 1 3 nA with 59 Hz repetition rate. Fast
longitudinal matching with bunch rotation method [4]was tried. In a rapid-cycling accelerator, adiabatic
capture cannot be used, because it essentially requires
long capture time compared to the period of thesynchrotron oscillation. In the booster FFAG, theaccelerating time is about 7 ms, while the synchrotron
period is 0.1 msec. In the bunch rotation method, the-271-

Proceedings of the 5th Annual Meeting of Particle Accelerator Society of Japanand the 33rd Linear Accelerator Meeting in Japan (August 6-8, 2008, Higashihiroshima, Japan)

accelerating bucket was rapidly produced after 1/4
synchrotron oscillation in a waiting bucket. The bunch
length and the momentum spread after the rotation wascontrolled by the capture rf voltage. Saw-tooth rf wasemployed in order to minimize the filamentation. One
advantage of the method is that the longitudinal beamloss is suppressed. In addition, the longitudinalemittance is kept small and momentum spread of an
extracted beam is improved. With the bunch rotation,
the quadrupolar synchrotron oscillation could be
minimized as shown Fig. 3 and the extracted beam
intensity increased at least three times [5]. Final beamenergy was estimated to be 11.6 MeV by therevolution frequency and theright after injection is assumed to be caused byhorizontal aperture, which is limited by the ES. One
method to increase the intensity is the beam injection
without ES. In such case an additional kicker isnecessary.

Figure 3: Output signal from current transformer (CT)right after the ion-source (yellow), and Booster bunchmonitor (blue); 100 ms/div

Figure 2: Input accelerating
accelerators;4 ms/div.

voltagesofthecircumference.
Horizontal and vertical betatron tunes weremeasured in the booster FFAG. Horizontal coherent
betatron oscillations were excited by rf-modulation,and vertical ones were excited by a perturbator
electrode. The measured tunes agreed the designed
ones. A rapidlotted as functio beam loss was observed
when the current of defocusing magnets was increased,
as shown in Fig. 4. It is assumed that the beam loss
was caused by the coupling resonanceνx + 3νy=6.
Proton beam of 11.6 MeV was injected in the mainring. The main ring is composed of 12 return-yoke freemagnets. A magnetic material in the straight section
gathers the fringing field near by, and thus distorts theclosed orbit. The main source of the closed orbit
distortion (COD) is the rf cavity, which is covered by amagnetic shield to protect the core from the fringing
field. In order to correct the COD, a couple ofcorrection magnet is put on both sides of theaccelerating gap. The injected beam is kicked into theclosed orbit by an electrostatic septum (ES) and amagnetic kicker (KCRI). Figure 5 shows thecirculating beam picked up by an electrostatic bunchmonitor (BMON) in the main ring.[6,7] The beam loss

The betatron-phase advance between thekickers is 550 deg, so that the kickers work on phase.
This means that the strengths of them iscomplementary.
The beam was accelerated with the rf gapvoltage of 2.5 kV and the synchronous phase of 30
degree. A rapid beam-loss was observed at 4 ms at
20 25 MeV. The beamloss is related to νx − 2ν
y=1. The beam-loss will be cured by putting locally
additional yokes at the orbit.
Accelerated beams
after the beam-loss were observed by a radial probewith high-sensitivity fluorescent screen at its head.
Beam energy can be estimated by the revolution
frequency or the orbit radius, using scaling rule with

Figure 4: Measured betatron tunes in the booster-272-

Proceedings of the 5th Annual Meeting of Particle Accelerator Society of Japanand the 33rd Linear Accelerator Meeting in Japan (August 6-8, 2008, Higashihiroshima, Japan)

bunch monitor.

FFAG.

k=7.5. The injected beam energy was 11.6MeV,capture frequency 1591.84 kHz, and measured beam
position was 4430 mm at injection energy. Figure 6shows the relation between the revolution frequency,
the beam energy and the orbit radius measured at thecenter of straight section.
Figure 7 shows the beam
intensity in the main ring.

３．SummaryFigure 5: Output signals from bunch monitor of themain ring (yellow) and the booster (magenta); 40
us/div.

The FFAG complex for ADS project was successfully
accelerated proton beams up to 100 MeV, with therepetition rate of 59/2 Hz.
After the optimization of
the beam behaviors such as beam intensity iscompleted, the extraction of the beam from the main
ring will be tried.
The first trial for ADSR
experiment with the reactor (KUCA) will be scheduledin this year.
REFERNECES[1] K. Kawase and M. Inoue, “ Neutron Factory Project at
KURRI ”, APAC 1998, Tsukuba, Japan, 104-106 (1998).
[2] M. Tanigaki et al., Construction of FFAG Accelerators inKURRI for ADS Study, EPAC 2004, Lucerne, 517-519(2004).
[3] A. Osanai, FFAG’06, Osaka, November 2006 (2007). .
[4] M. Aiba, FFAG workshop 2001.
[5] H. Horii, FFAG’06, Osaka, November 2006 (2007).
[6] Y. Mori, presentation at the Internal Workshop of the FFAG
Accelerators (FFAG03), Tsukuba, 2003.
[7] Y. Mori, Nucl. Instr. Meth., PRS, A563 (2006) 591-595.

Figure 6: Calculated (A) beam energy and (B) radius ata center of a straight section as functions of revolution
frequency; Symbols show the measured values.

Figure 7: Beam in the main ring measured by a beam-273-