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)

PRESENT STATUS OF BEAM PHYSICS RESEARCH USINGACCELERATOR FACILITY OF ICR, KYOTO UNIVERSITY*Akira Noda#, Hikaru Souda, Hiromu Tongu, Masao Nakao, Akihisa Wakita , Mikio Tanabe†,
Takehiro Ishikawa&, ICR, Kyoto Univ. Uji-city, Kyoto Japan,Masahiro Ikegami, KPSI, JAEA, Kizugawa-city, Kyoto, Japan,Toshiyuki Shirai, Koji Noda, NIRS, Chiba-city, Chiba, Japan,Shinji Shibuya, Tetsuya Fujimoto, Soma Iwata, AEC, Chiba-city, Chiba, Japan,
Manfred Grieser, MPI-K, Heidelberg, Germany,Igor Meshkov, Alexander V. Smirnov, Evegeny Syresin, JINR, Dubna, Moscow Region, Russia
Abstract

GENERAL ACTIVITY WITH
ACCELERATOR FACILITY

Laser cooling has been applied to 24Mg+ beam withkinetic energy of 40 keV and equilibrium temperature in
the longitudinal direction has been found to be 3.6 Kelvinlimited by the heat transfer from transverse degrees offreedom due to an intra-beam scattering.
By themeasurements changing cooled beam numbers,
longitudinal temperature is found to depend linearly on
the transverse temperature as TL = 0.02T⊥ in thescheme of the present experiments. Bunched beamcooling has also been studied in order to approach to the 3
dimensional cooling, which indicated the capability ofheat transfer by synchro-betatron coupling. Applicationof electron cooling together with phase rotation and fast
extraction has realized provision of a very short proton
beam with duration 3.1 ns (2σ) for the proton number of
1.4x108.

Induction
Accelerator

RF Drift Tube

The layout of our accelerator facility is shown in Fig. 1.
After the first demonstration of 1 dimensional ordering of
7 MeV proton beam [1], our main efforts at S-LSR are
oriented for a laser cooling. In addition, such approach asutilizes an electron storage ring, KSR for the studies ofthe structure of nucleus trapped into an ion trap: SCRIT(Self-Confining Radioactive Isotope Ion Target) set in astraight section of KSR (Fig. 2) has been persuit in thesea few years by collaboration with the group at RIKEN
and recently the principle of such a scheme has beensafely demonstrated for stable ions as 133Cs, although thefinal aim of such a scheme is to be applied for unstable
nuclei [2]. The S-band electron linac with the maximum
energy of 100 MeV is also utilized for the calibration ofneutrino detectors to be used for T2K experiments.

CHORDIS Ion Source 24Mg+

7 MeV Proton Linac

Ion storage
Ring, S-LSR
Laser light (280 nm)
for Beam Cooling

5m
Figure 1 Layout of the accelerator facility of ICR, Kyoto University.

___________________________________________* This work is financially supported by Advanced Compact Accelerator
Development from MEXT of Japanese Government and the 21st COEof Kyoto University, Center for Diversity and Universality in Physics.
†Present Address: Nippon Hoso Kyokai, NHK&Present Address: Shimadzu Co. Ltd.
#noda@kyticr.kuicr.kyoto-u.ac.jp-52-

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)

condition to keep the beam crystal if it can be created [3].
In table 1, the main parameters of S-LSR are listed
up. .At first, laser cooling of 24Mg+ ion beam with thekinetic energy of 40 keV has been performed for thecoasting beam with simultaneous application of induction
deceleration voltage.
By application of frequency
doubled laser of the wavelength of 280 nm, which isequal to the level distance of the Mg ion, with the powerof ~50 mW, Mg ions with the initial number of 1x106 arecooled down to 3.6 Kelvin (1σ) reaching the equilibrium
between laser cooling force and heat transfer from thetransverse degrees of freedom. The momentum
distributions before and after the laser cooling are shownin Fig. 3.
The longitudinal equilibrium temperature has beenstudied changing the ion numbers to be cooled down,
which resulted in the variation of the strength of heattransfer from transverse to longitudinal directions due tochange of the strength of intra-beam scattering. In Fig. 4,
the experimentally observed dependence of thelongitudinal equilibrium temperature on the number ofFigure 2 An overall view of an electron storage ring,
KSR, in which the SCRIT is installed.

LASER COOLING AT S-LSR
Laser Cooling of Coasting Beam
S-LSR is an ion storage and cooler ring, thecircumference of which is 22.56 m and has 6-foldsymmetry in order to satisfy the so-called maintenance

Figure 4 Relation between the number of cooled ionsand the equilibrium longitudinal temperature [4].
cooled ions is shown [4].

Laser Cooling of Bunched Beam
In order to cool down the transverse temperature by alaser cooling, such a scheme as couples the transverse
degrees of freedom
with the longitudinal
one actively with theuse of “Synchrobetaron coupling” isrequired. [5]. For
thispurpose,bunchedbeamcooling has been
applied at S-LSR
with the operationtune of (νx, νy, Figure 5 A drift tube for RFνs)=(2.064, 0.814, acceleration of 40 keV 24Mg+.
0.065),
which
satisfies the relation;
ν x − ν s = m(int eger ) .
(1)

Figure 3 Momentum distributions before and afterlaser cooling for coasting beam [4].
Table 1 Main parameters of S-LSR
Circumference
22.557 m
Average radius
3.59 mLength of straight section
1.86 mNumber of periods
6
Betatron Tune Horizontal
2.07
Vertical
1.07-53-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)

The newly fabricated two-gap drift tube for RF
acceleration as shown in Fig. 5 is set at the finite
dispersion (~1 m) position indicated in Fig. 1. The
equilibrium momentum after laser cooling is plotted forvarious synchrotron tunes in Fig. 6, which indicates theheat transfer into the longitudinal direction forsynchrotron tunes satisfying Eq. (1). So as to establish
the realization of transverse laser cooling, it is desirable toobserve the reduction of horizontal beam size. As our
optical measurement system of spontaneous emitted lightby 24Mg+ ion is capable of observation of only thevertical beam size limited by the available viewing port, it
is not possible to measure the horizontal beam size at themoment.

Figure 6 Relation between the equilibrium momentum
spread and synchrotron tune for the case of application ofa laser cooling.

SHORT BUNCH FORMATION WITH
ELECTRON COOLING

leaded by Dr. M. Wakasugi
collaborations presented here.

For the investigation of free radicals, short bunchformation with the use of an electron cooling has beenstudied. Such a short bunch 7 MeV proton beam is fast
extracted by an excitation a fast kicker magnet together
with bump magnets, which creates orbit bump with muchslower time constant than a kicker magnet. For proton
beam with the intensity of 1.4x108 , phase rotation withthe applied RF voltage of 800 V after application of anelectron cooling compressing the fractional momentum
spread to ±0.015 %, has attained a very short pulse withthe duration of 3.1 ns (2σ) (Fig. 7 (a)) although its
intensity is rather limited due to cut of beam filamentation.
On the other hand, bunched beam electron cooling canprovide higher intensity beam with ~100 % beam delivery
to the extraction channel resulting a longer beam durationof 15.7 ns (2σ) (Fig.7 (b)) [6].

ACKNOWLDGEMENTS
The authors would like to present their sincere thanks
for all the members of detector calibration of T2K
experiments guided by Dr. T. Nakaya and SCRIT groupfortheirfruitful

REFERENCES[1] T. Shirai et al, “One-Dimensional Beam Ordering ofProtons in a Storage Ring”, Phys. Rev. Lett. 98(2007) 204801.
[2] M. Wakasugi et al., “Novel Internal Target forElectron Scattering off Unstable Nuclei”, Phys. Rev.
Lett. 100 (2008) 164801.
[3] J. Wei, H. Okamoto and A.M. Sessler, “Necessaryconditions for attaining a crystalline beam”, Phys.
Rev. Lett. 80 (1998), pp2606-2609.
[4] M. Tanabe et al., “Longitudinal and Transverse
Coupling of the Beam Temperature Caused by theLaser Cooling of 24Mg+ “, Applied Physics Express, 1(2008) 204801.
[5] H. Okamoto, “Transverse laser cooling induced
through dispersion at an rf cavity”, Phys. Rev. E50(1994) pp4982-4996.
[6] T. Fujimoto et al., “Formation and fast extraction of avery short-bunched proton beam for the investigationof free radicals”, Nucl. Instr. And Meth. In Phys. Res.
A588 (2008) pp330-335.

Figure 7 Short bunch of 7 MeV formed by phase rotation with 800 V after electron cooling (a) and bunched beamelectron cooling (b)-54-