The 14th Symposium on Accelerator Science and Technology, Tsukuba, Japan, November 2003

INJECTION SYSTEM FOR THE J-PARC 3-GEV HIGH INTENSITYPROTON SYNCHROTRON
I. Sakai, T. Shimada*, T. Takayanagi*, K Yamamoto*, Y. Arakida, I. Sugai, Y. Takeda, S. Machida,
F. Noda*, K. Shigaki*, Y. Watanabe*, Y. Ishi **, T. Kawakubo, Y. Irie,KEK, Tsukuba, *JAERI, Tokai, ** MELCO, Kobe; JAPANAbstract
The J-PARC Project 3-GeV proton synchrotron isdesigned to accelerate 8.3x1013 protons per pulse at a25Hz repetition rate for the injection energy of 400MeV.
The incoming beam emittance of the 400-MeV linac is 4π mm mrad and the acceptance in the 3-GeV synchrotron
is 486π mm mrad in both the horizontal and verticalplanes. Painting injection system is designed to fit in theFODO structure, which has rather short drift space. Thebump orbit for painting injection is designed to have a fullacceptance of the circulating orbit through the injection
period. A full-acceptance bump orbit will enable bothcorrelated and anti-correlated painting injection.

INTRODUCTION .
The J-PARC Project accelerator complex comprises a50-GeV main synchrotron, a 3-GeV rapid-cycling
synchrotron, and 400-MeV Linac. The accelerators
provide high-intensity, high-energy proton beams forvarious scientific fields. The 3-GeV synchrotron isdesigned to accelerate 8.3x1013 protons per pulse at a 25
Hz repetition rate in the 400-MeV injection. The
hardware of the 3-GeV ring is designed to accept 400MeV injection beams.
The 3-GeV rapid cycling synchrotron (RCS) has athree-fold symmetric lattice. Each super-period consistsof 9DOFO modules, which are assigned to two 3DOFOmodules with a missing bend and 3DOFO modules ininsertion straights. These insertion straights are designed
to be dispersion free. The FODO structure requires
modest quadrupole gradients, and the alternatingtransverse beam amplitude easily accommodates
correction systems, but lacks a long uninterrupted drift
space for flexible injection.

H- Beamfrom Linac

MW2

MW1

MW3

SEP1

PSTR1

PARAMETERS FOR PAINTINGINJECTION
The machine acceptance of the linac and its transportline are designed to have 30π mm mrad, and that of 3GeV synchrotron has 486π mm mrad. The acceptablemomentum dispersion (∆p/p) in the transport line and 3GeV ring are ±0.3% and ±0.1%, respectively.
In the beam-transport line from the 180MeV Linac tothe 3-GeV RCS (L3BT); the transverse emittance of theH- beam is collimated to 4π mm mrad. In the momentum
direction, ∆p/p is ±0.1%.
In the case of 400 MeV injection, the painting
emittance in the ring is 216π mm mrad for the 3-GeV
facilities, and 144π mm mrad for 50-GeV ring injection.
The horizontal painting area is controlled by pulse
steering magnets located in the injection line and bumpmagnets in the ring by changing the excitation level in apulse-to-pulse mode. The vertical painting area can be

MW5

Foil Supply
Instrument
MW4PB-I
QDX

Q_dump

2nd foil B (H-->H+)
SEP3

1st Foil

SEP4

BPM

BPM

BPM+STR

MW8 To Beam Dump
(for H0,H-)

MW7

MW6
2nd foil A(H0->H+)

PSTR2
SEP2

Q_L3BT

The injection system for the J-PARC 3-GeV Proton
Synchrotron is designed to be constructed in the FODO
structure, which has rather short drift space. The injection
and collimator system will be in the same straight section.
The H- injection system uses the first whole cell and aquarter of the second cell. The collimator system islocated at the latter three quarters of the second cell andthe third cell. However, the system is designed to have afull acceptance for the injection bump orbit and to allow
independent lattice tuning to obtain a high-intensity beamand low-loss operation.
An outline of the injection system has already beenreported [1][2]. In this paper we mainly describe thechallenging issues about the H- injection line, disposallines for un-stripped H0 & H- ions and the structure of thebump magnets system.

SB-IIIIIIII

QFL

IV

BPM+STR

PB-IIIIV

QDL

QFM0.5m

MW*: Multi-W ire profile monitor
BPM : B eam Position Monitor-Fig.1 Outline of the H injection system

SEP : Septum magnet
STR : Se ering magnet
PSTR : Pulse steering magnet

01.0m

The 14th Symposium on Accelerator Science and Technology, Tsukuba, Japan, November 2003

controlled by changing the excitation level of verticalsteering magnets in the injection line.
The collimator acceptance in the 3-GeV ring is 324π
mm mrad and the whole ring will have 486π mm mradneeded for the scattered beam by the first collimator to becaught subsequently by the down-stream collimator. Thering will be filled with 308 turn H- foil-stripping chargeexchange injection. The 500µs pulses from the Linac
containing 8.3 x 1013 protons will be injected to twobunch RF buckets in the ring.

DESIGN OF THE MAGNETIC FIELD
The magnetic field must be carefully chosen so as toprevent the Lorentz stripping of H- and to minimize thestripping of excited H0.
In the upstream of the stripping foil, the H- beam willpass through septum magnets, quadrupole magnet andclosed orbit bump magnets. The maximum magnetic fieldis estimated to be 0.55 T for 400-MeV H- beams. Thebeam loss rate is less than 10-6 for the above magnets.
Because the injection beam power is 133 kW, and its
losses by Lorentz stripping is less than 0.13 W.
After the H- beam passes through charge-exchange foil
made of 290µg/cm2 thick carbon, a H0 beam of 0.4 kW isproduced. When a 1MW output is attained, it becomesvery important to control the loss of the excited H0 [3]. Inthe case that the magnetic field of the bump magnet is set
to be about 0.2 T, the excited H0 with a principal quantum
number of n ≥ 6 becomes the uncontrolled beam loss.
Because of the yield of n ≥ 6 is 0.0136 and the total H0
beam power is 0.4 kW, the maximum uncontrolled beamloss is about 6 W. On the other hand, the excited H0 under
the condition of n ≤ 5 reaches second foil without decay
and stripped to H+, and is led to the beam dump.
The magnetic field at the foil position is designed to beless than the value at which the bending radius of thestripped electrons is larger than 100mm, which enables aelectron catcher to be settled outside of the foil. The foil
position is at a distance of 350 mm from the end of thebump magnet SB-III. The trajectory of stripped electrons
at the foil is traced by solving 3D differential equations
with the Runge Kutta method [4]. The bending radius isestimated to be about 120 mm in the given magnetic field
distribution.

The incoming beams are injected at the entranceof ”SB-I” to obtain a full acceptance for the injection
bump orbit. The injection angle of the incoming beams
with the circulating beam orbit is expanded by themagnetic field of the upper-stream F quadrupole. The
angle of the disposal beam line of un-stripped H0 and Hare also expanded by a downstream D quadrupole magnet.
The field of the quadrupole magnets may be changed tomeet varieties of operating point of the ring. The injection
angles and positions at the quadrupole magnet are
adjustable by steering magnets at the up-stream points ofthe injection line.
Horizontal painting injection is performed by an orbit
shift in horizontal plane. Two additional sets of bumpmagnet pairs for the horizontal painting, named “PB-I,PB-II”and “PB-III, PB-IV”, are located in the up-streamof the F quadrupole magnet and downstream of the Dquadrupole magnet, respectively.
For vertical painting, two small vertical steering
magnets, which are not shown in Fig.1 are placed in thetransport line at a betatron phase of nearly π up-stream ofthe stripping foil to vary the injection angle and position.
Painting injection in the vertical phase plane is performedby sweeping the injection angle. The phase difference will
be compensated by those two vertical steering magnets.
Both correlated and anti-correlated painting injections
are available by changing the excitation pattern of thevertical painting magnet

DESIGN OF THE H-INJECTION LINEAND H-, H0 DISPOSAL LINES
As can be seen in the Fig.1, injection area is socongested that any other focusing magnets can not beinserted in the injection area which has a length of 20 m.
Furthermore, the beam needs to be injected vertically offcenter for vertical painting. The corner of the F and D
quadrupole magnets are thus required to have additional
aperture for the injection/disposal beam lines
The beam optics of beam transport line from the Linacto RCS is designed to be insensitive to space charge effect.
Space-charge effects have been analyzed by simulation on

CONSTRUCTION OF THE INJECTIONSYSTEM IN THE FODO STRUCTURE
An outline of the injection system is shown in Fig.1.
The injection system in the horizontal plane is composedof four main orbit shift bump magnets named “SB” tomerge the injection beam with the circulating beam, andfour other orbit paint bump magnets named “PB” forpainting injection. The “SB” have a split-type structure toinsert the second foil for H0 stripping. Also the vertical
painting is performed by vertical steering magnets in theinjection beam line.
Fig.2 Beam envelope of the injection beam line

The 14th Symposium on Accelerator Science and Technology, Tsukuba, Japan, November 2003

THE MAIN BUMP MAGNETS
Four dipole bump magnets named (SB-I~SB-IV), areidentical in construction and are powered in series to givea symmetrical beam bump within the straight in an
uninterrupted drift space between the focusing magnet
and the defocusing one.
A cross-sectional view of the bump magnet is shown in
Fig.4. The dipoles are out of the vacuum and a ceramicvacuum chamber is included in the magnet gap. The
structure of the magnet is composed of two-turn coils andwindow frame core made by laminated silicon steel coresof which the thickness is 0.1 mm. The electrical insulationof the coil is achieved by air gap and a ceramic insulator.
The waveform of the magnetic field is trapezoid. A falltime of 100 µs is decided by the hitting probability of
proton beams on the stripping foil and the temperature of
the foil heated by the beam hit. The maximum
temperature of the foil is estimated to be 1500ºC at the tipof the foil.[5]The excitation current is supplied in the middle of thecore through the split to form a symmetrical distributionof magnetic field along the longitudinal direction.

320

540

BUHS

586
930

Fig.3 A cross-sectional view of the main bumpmagnet

290

BUHP

580

this optical design. The results estimate that the spacecharge effect is not much of a problem under the designed
bunch lengthes of 400 MeV and 180 MeV injection.
Separation of THE H0, H- AND H+
In the FODO structure, the beam envelope at the downstream of F quadrupole, tilts down-stream so that theinjection beam line for horizontal painting must be tilted
accordingly. The separation angle of the H0 beams andcirculating H+ beam envelope become tighter than a caseof a parallel envelope of the two pairs of quadrupole
doublets where α = 0.
The separation of the H0, H- beams and circulating H+
beam envelope is one of the challenging issues to design
the hardware of the injection system. To solve thisproblem the split-type bump magnet has been investigated.
The H0 beams, which are estimated to be 0.3% of theincoming beams, must be converted to H+ by a second
foil to divert to the beam dump. As shown in Fig.1, thesecond foil “A” is inserted in the middle of the fourthbump magnet, “SB-IV“, by a split at the center of the core.
The up-stream part of the split core is used to obtain thesufficient clearance of the H0 and H+ beam separation andthe down-stream part kicks the H+ ions converted from H0.
H- beams, which are estimated to be 3x10-4 % of theincoming beams, are also converted to H+ by anothersecond foil,”B”, set at the entrance of the D quadrupole
magnet,”ODL”.

468730

Fig.4 A cross-sectional view of the paint bumpmagnet

A cross-sectional view of the bump magnet is shown inFig.4. The dipoles are out of the vacuum and a ceramicvacuum chamber is included in the magnet gap. As shownin Fig.1, at the PB-II and PB-III, the separation of the H0,
H- beams and circulating H+ beam envelope is insufficient
to insert the type of window frame magnet. The structureof the magnet is composed of two-turn coils and C-typecore. The envelopes of the circulating beam are close to
the edge of the pole, where it is difficult to form a
uniform magnetic field in such a wide aperture / shortlength magnet. The optimum structure of the core and theconductors are under investigation using 3D calculation.

SUMMARY
The injection system is designed to be constructed in
the FODO structure, which has rather short drift space.
The bump orbit for painting injection has a full
acceptance for the circulating beams.
The H- injection line and the H0,H- disposal lines canbe designed so as to have a sufficient acceptance for lowloss injection
The painting area is optimized for both 3-GeV users
and 50-GeV users in a pulse-to-pulse mode operation

THE PAINTING BUMP MAGNETS
Two sets of bump magnet pairs in the upstream of the Fquadrupole magnet and the downstream of the Dquadrupole magnet. These four dipole bump magnets
named (PB-I~PB-IV), are identical in construction andwill be excited individually to form a local closed
orbitinclude the F and D quadrupole magnets.

REFERENCES[1] I. Sakai et al, EPAC2002, Paris, June 2002
[2] I. Sakai et al, PAC2003, Portland, June 2003
[3] G. Rees, EPAC94, London, June 1994
[4] M. Shrakata et al, EPAC2002, Paris, June 2002
[5] K. Kuramochi et al, This proceedings