April 12 ~ 16, 2010

Electron Accelerator Complex
at Tohoku University,
42 - Year - Operation and Future
H. Hama, M. Kawai, F. Hinode*), Y. Shibasaki,
S. Takahashi, K. Nanbu, I. Nagasawa,T. Muto, M. Hiraga

Research Center of Electron Photon Science,Tohoku University
1-2-1 Mikamine, Taihaku, Sendai 982-0826, Japan*)e-mail : hinode@lns.tohoku.ac.jp

outline• introduction about the facility
History (How We Did Business)• present status• operation status• machine status ( feature and difficulties )• machine improvements• future prospects• summary2facility introduction(since1966)
Laboratory of Nuclear Science (LNS),
Faculty of Scienceestablished in 1966
first pulse-neutron generation
pulsed neutron source (1971 ~ 1994)
M. Kimura , NIM 71, 102 (1969)

1.2 GeV Booster Synchrotron
STB ring (since 1997)
hadron phys. by GeV - gpresent

300 MeV Electron Linac(since 1967)

nuclear phys. by c.w. e-beam
150 MeV pulse stretcher (1981 ~ 1994)
T. Tamae , NIM-A 264, 173 (1988)

42-year-old

Research Center ofElectron Photon Science
first observation of coherent SR
T. Nakazato Phys. Rev. Lett. 63 1245, (1989)

target : user facility opened
for worldwide

reorganized in 20093

Experimental Halls andAcceleratorspresent activities
Nuclear Physics(such as hyper nucleus)by neutral-K spectrometer

RI production for
Nuclear Chemistry(since 2002)

Hadron Physics, detector R&D4

1.2 GeV Booster Synchrotron (STB ring)
Stretcher mode (slow extraction with 3rd-resonance)
Convert pulsed beam to c.w.-beam (Eb = 140 ~ 200 MeV)

Booster (storage) mode
• Injected beam with the Eb = 150 or 200 MeV is ramped up to 1.2 GeV(max.) in about 1 second.
• After the consumption of circulating beam due to high energy gamma-ray
generation via bremsstrahlung, beam injection is repeated.
( radiator : 10 mm carbon fiber)
γ- generation

beam current
１．２ ＧｅＶ （max.）

beam energy

０．２ ＧｅＶ5operation status in FY20096

record of beam operating
times

7

machine status (features &difficulties)

300 MeV Linac

20 acc. structures driven by 5 klystrons.
typical energy = < 50 MeV (for low-energy mode)
150 ~ 200 MeV (for high-energy mode)
300 Hz repetition (max)  High average current (~150 mA)

1. Very very old (since 1967) with essentially no-update vacuum leak, much trip rates in modulators,
old modulators make a wide energy spread
2. Poor design of the injector part and no well-considered beam optics
 give a lot of beam loss, large beam emittance (200 mmmrad)
low BBU threshold (<100 mA), poor beam monitors

1.2 GeV Synchrotron
One linac burst gives 20~30 mA.
Ramp-up time ~ 1 sec. @1.2 GeV
1. Poor vacuum
2. High ring impedance ( may be |z/n|=100 W)
3. Many HOMs in a used cavity
4. No chromatic sextupole !!

 lifetime ~10 min.@1.2GeV
 microwave instability
 Serious coupled-bunch inst.
 a lot of problems
8

machine improvements• replacement of LINAC beam line (still underprogress)
installed more IPs and beam monitors improved vac. performance, beam tuningwork• replacement of a component in DC-gun power
supplyIVR  inverter power supply• replacement of some components in a LINAC
modulator (still under progress)
IVR  inverter power supply
old thylatron (F-175) and driver  CX2411• replacement of controller for synchrotron
magnet power supplies
9replacement of linac beamline
slit

Q-magnets

steering
magnets

slit

CM

gate
valve

BEFORE
slitscreen
monitorQ-magnets

IPAFTERCT

gate
valve

steering
magnetsIP
10machine improvements• replacement of LINAC beam line (still underprogress)
installed more IPs and beam monitors improved vac. performance, beam tuningwork• replacement of a component in DC-gun power
supplyIVR  inverter power supply (improvedreliability)• replacement of some components in a LINAC
modulator (still under progress)
IVR  inverter power supply
old thylatron (F-175) and driver  CX2411
suppressed the down time
• replacement of controller for synchrotron
magnet power supplies (almost completed)11

progress in machine operation• establishment of operation parameters
There are many operation modes depending on user.
shorten the beam tuning time
• introducing lattice modification for the 2nd GeV-g beam line
huge spread of g-profile and poor tagging efficiency
beforeafter

improvement of g-ray beam quality
and tagging efficiency (e = 20  80 %)( PAC’05 by F. Hinode et.al. )g-profile• transverse phase space manipulation by a mono-frequency RFKO
in stretcher-mode operation
quasi-CW beam for nuclear physics (e- scattering exp.)
emittance reduction for extracted beam ( PAC’05 by A. Miyamoto et.al.)12

upgrade plan of injector
present

13

upgrade plan of injector
divide the high- and low-energy part of linac& separate the function and operation
 improve the flexibility of scheduling the user time much easier operation with better beam quality
 more available time for user shift ?
(depends on the budget for the electricity rates)

injector linac

thermionic RF-gun

high-intensity linac

low-emittance DC-gun

14

Low Emittance DC-gun
50 kV power supply

beam slits

DC-gunCT15

Design parameters of DC-gun
DesignMeasured

50 keV (Max.)← OK

Electron beam current> 300 mA

← OK

Pulse width (FWHM)

1-5 msec← OK

Repetition rate

300 pps (Max.)← OK

Normalized emittance<5 mm mrad.

<2 mm mrad

Normalized thermalemittance

0.25  mm mrad.

LaB6 Cathode diameter

1.75 mmφ

Beam energy( acceleration voltage )(*theoretical)―←
16

Low Emittance DC-gun

Phase space from double slit
measurement
HV : 50 kV
Heater current : 8 A
Beam current : 492 mA

Horizontal X(mm)Solenoid current : 3.2 A

Vertical Y(mm)Norm. emittance ＜ 2πmm mrad
17

Independently Tunable Cells RFGun

ITC RF-Gun
Why thermionic RF Gun ?

Ez [a.u.]• uncoupled two cells with eachother manipulation of phase spacedist.
• small single crystal LaB6cathode improve initial emittance

Simple ! No buncher. No high-voltage stage[cm]

Back-bombardment effect can be acceptable by introducing small size
cathode and short macropulse operation.
18

summary• User group takes over the beam operation from theaccelerator staff after the beam tuning.

to be reliable and stable,
preparation of manuscripts of the trouble-shooting foruser,otherwise down-time …
• continuing the machine maintenanceprogressing in R&D work for upgrade and new fields• towards the further prosperity, aiming at the user
facility authorized by the government
Both efforts would be importantto keep and/or develop the machine performance ashigh as possible,
and the same time to get the more budget.
(Presently, the machine time has been mainly limited
by budget for the electricity rates. )19

test Accelerator as Coherent THz
Sourcet-ACTS

CSR
CSR
CSRa-magnet

isochronous ringC ~ 12 m

3m acc. structurebunch compressor
thermionic RF-gun

R56 ~ 60 mm

undulator
spontaneous THz radiation
pre-bunched FEL (future project)20

end21

22

Present performance of the STB ring
Stretcher Mode
Energy region

140 – 200 MeV

Beam current atinjection~100 mA @0.2 GeV

Repetition rate
Extracted beam current

300 pps (max.)> 1 mADuty factor> 90 %

Extraction efficiency> 50 %

Booster Mode
Beam current @1.2GeV~40 mA

Ramp-up time @1.2GeV

1.1 sec (min.)23

Specification 1.2 GeV Synchrotron (since1997)

1. Nominal injection 150 MeV
2. One linac burst gives 20~30 mA
3. Ramping time from 0.2 to 1.2 GeV is 1sec
4. Poor vacuum> lifetime ~10 min.@1.2GeV
5. High ring impedance ( may be |z/n|=100 W)> microwave instability
6. Many HOMs in a used cavity> Serious coupled-bunch inst.
7. No chromatic sextupole !!
> a lot of problems
24300 MeV Linac (42-year-old)(20 Acc. Structures, 5 Klystrons,300 Hz)
Wave guide
FocuscoilAcc. structure

Buncher

Pre-Buncher
80 kV DC Gun25

1.2 GeV Booster and Storage Ring
(200 MeV Pulse-Stretcher)
SR from Bending Magnet
1.2 GeV Beam

500 MHzKlystron~1.5 mm

RF Cavity

Quadrupoles
Bending Magnets

26

Ion trapping
3 mA

7 mA

10 mA

11 mA

12 mA

16 mA

21 mA

28 mA

27

PXI controller for synchrotron magnet powersupplies
FPGA card
PXI controller

PCI eXtensions for Instrumentation（PXI）FPGA (Field Programmable Gate Array)

レベルアダプタ（DC24Vシンク、RS422等）
28

PCI eXtensions for Instrumentation（PXI）• PCベースのオープンプラットフォーム• コンパクトPCIがベース（バースト転送時の帯域幅は132MB/sec）• 1200種を超えるモジュール• 比較的安価• 同期バス信号• LHCのコリメータコントローラなど（VMEの代替として）
29

Low Emittance DC-gun

e-Beam30

仙台
SendaiLaboratory of Nuclear Science(LNS)
Faculty of ScienceTohoku University31

GeV-energy gamma-ray generation
via Bremsstrahlung from internal target wire

32

33

newold34

Lattice modification
Connect shunt modules
to some QD-magnets.
: before: after
Plot : observed data35

Improvement in gamma profile

beforeafterefficiency

after

beforetagger 36ch.

Pulse stretcher
converts pulse beam generated by RFlinac into quasi-continuous beam.
Schematic Diagram of Beam Extraction
Betatron
amplitude

Larger strength of
sextupole-magnet field

Radiation loss

beam
10/3



37

Emittance reduction for extracted beam by using an RF
shaker driven by a mono-frequency.
(by A. Miyamoto)Mismatched optics
Horizontal tune x
50x10

3.320

-6

3.325

3.330

3.335

3.340

Betatron amplitude J [mrad]

RFKO frequency
40Separatrix

3020

With RFKO

Extract

10

Without RFKO
005000

10000

15000

20000

Turn38東北大学原子核理学研究施設
STBリング
Lattice
Chasman-Green
Superperiodicity 4Circumference
49.751 m
Beam energy
200 MeV (nominal)
Betatron tune
(3.31,~1.20)
Natural Chromaticity(-5.79,-4.98)
Energy loss / turn46 eV @ 200
MeV
Repetition period 3.33 ms @ 200 MeV
Relative energy loss / period
0.46 % @ 200 MeV
Horizontal tune shift / period
0.0267 @ 200 MeV
Twiss at injection pointbx=20.2, ax=-0.06
Number of harmonic sextupole
1

Wire ScannerElectrostatic Septum
Sextupole magnet

Strip-line RF Kicker

39