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

PRESENT STATUS OF NEWSUBARU
A. Ando, S. Hashimoto and Y. Shoji,LASTI, Himeji Institute of Technology, 678-1205, Japan,Abstract

Beam Decay @1.5 GeV

Present status of the NewSUBARU storage ring issummarized. The machine performance is now in thebetter level than those of the designed. The efforts for thisachievement will be described in another activity reports.

300

Stored Current (mA)250

1 INTRODUCTION
NewSUBARU [1] is a 1.5 GeV synchrotron radiation
ring at the SPring-8 site. Laboratory of Advanced Scienceand Technology for Industry (LASTI) at the HimejiInstitute of Technology is in charge of its operation,
collaborating with SPring-8. The main parameters of thestorage ring are listed in Table 1.
The ring has two operation modes for users. In the 1.5
GeV mode, the beam is accelerated to 1.5 GeV and stored.
The user time starts at the stored beam current of 300mA
as shown in Fig.1. In another mode, 1.0 GeV top-up mode,the beam current is kept at 250+0.15 mA by an occasional
injection as shown in Fig.2, with the gaps of undulators
closed.
The design goal of the beam current and the beam
lifetime were successfully achieved as shown in Table 1.
The RMS of the closed orbit distortion (COD) can beadjusted to less than 6 µm in horizontal and 8 µm in
vertical at both 1.0 GeV and 1.5 GeV.

200
150
100Stored Current (mA)

50002235

Lifetime (hrs)30

1.5I*τ (A*hrs)
I*t-fit

2520

115
100.52 EFFORTS FOR IMPROVEMENTThe beam physics and accelerator physic group paid
many efforts day by day to improve the storage ringperformance. Figure 3 shows the achieved maximum
stored current and corresponding typical efforts. The
followings are the main improvements and their results.

Lifetime (hrs)
Lifetime-fit

00050 100 150 200 250 300 350
Stored Current (mA)

τ (hrs) = 1/[ 5.26E-4 * I (mA) + 1.78E-2 ]Figure 1: Stored beam current and and lifetime during the1.5GeV user time.
250.2
250

250.1
200

250

150

249.9

100

249.8
249.7
16:03:00

16:02:00

16:00:00

16:00:00

15:30:00

15:00:00

14:30:00

14:00:00

13:30:00

249.6
0

16:01:00

50

13:00:00

stored beam current (mA)

300timeTuneνx / ν y
Chromaticity ξx / ξyLinear coupling constant
RMS -COD x / y

1040

12:30:00

Lifetime

Successive80+80 bunches
50 mA/bunch
500 mA /ring @ 1 GeV
14 hours@ 100 mA & 1.5 GeV
6.30 / 2.23
3.2 / 5.8
1%
6 / 8 µm

8I*τ (A*hrs)

Filling pattern
Maximum current

6

1.5 GeV with Phase Modulation

5Table 1: Main Parameters
Energy0.5 ~ 1.5 GeV
Circumference
118.731 m
RF frequency
499.956 MHz
Natural emittance38
nm @ 1 GeV

4Time (hrs)

Figure 2: Stored beam current during the top-up operation
at 1.0GeV.

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

Improvement of the maximum stored beam current
under the new permission of radiation safety conditionchange sextupolechange sextupolechange sextupolechange sextupole

300

200

100

07/20 '02

05/23 '02

03/26 '02

11/30 '01

10/04 '01

01/27 '02

02.2 COD optimisation and Correction of Beta
functionchange feed back parameterschange beta of RF coupler

maximum stored current (mA)

400change sextupole

500

most effective way for this purpose and results in the~ 30 % increase of beam lifetime at 1 GeV.
f) Installation of new HOM tuner.
The fixed tuner was just replaced by a SPring-8 typemovable tuner. Its commissioning will start this fall for
more stable operation.

dateFigure 3: Maximum stored beam current and the typicalevents. The maximum current was limited to 500mA by a
new radiation safety condition.

2.1 RF systema) HOM (Higher Order Mode of cavity) suppression
by temperature and detuning angle
The transverse HOM near 792 MHz excites thehorizontal coupled bunch instability with the ordinalsetting of sextupole magnets and limits the maximum
stored current at ~ 80 mA. Also ~990 MHz HOM
becomes very strong and causes abrupt beam loss
when the RF voltage is ∼ 300 kV before 1.5 GeV
acceleration. The temperature of cooling water forcavity was carefully adjusted to avoid these HOM's.
Now the operation frequency of the cavity is a little bit
lowered by changing the detuning angle ( -5 degree to- 20 degree) and almost HOM free operation isachieved.
b) Adjustment of the klystron power supply
The analogue signal for interlock of the klystronpower supply was very noisy and fault turn off of thepower supply occurred very often. No fault turn off isachieved after careful adjustments.
c) Double PLL feedback
The feedback circuits of amplitude stabilization
both for the cavity and the klystron work very stably,in particular, at very high beam current (more than ~300 mA).
d) Optimise the input coupling constant to the cavity
The storage ring is now often operated at thestored current of ∼ 300 mA. The initial coupling
constant (β) was ∼ 2.6 supposing the beam current of∼ 100 mA. This constant was changed to ∼ 5.6 torealize more stable operation of the RF system forhigher beam current.
e) Phase modulation in PLL feedback
The Touschek effect becomes not negligible at ∼1
mA / bunch. The reduction of the line density is thekey to enlarge the beam lifetime against this effect.
The phase modulation in the phase lock loop is thea) The aperture survey by steering magnets found akind of the golden orbit and resulted in the ~ 40 %increase of beam lifetime.
b) The βx and βy correction by trim windings ofquadrupole magnets
The careful analysis of the COD generated by asteering magnet and the insertion devices suggest thesignificant distortion of βy caused by the systematicerror in the one family of quadrupole magnet (QB).
The correcting pole windings were added and then thebeam lifetimes was increased by ∼ 5 %.

2.3 Optimisation of correcting sextupoles
magnets
The adjustment of chromaticity was very importantand sensitive to keep higher current than ~ 300 mA.
The harmonic sextupoles were also adjusted to avoid
transverse instabilities. This adjust controls theamplitude dependent tune shifts. Both the optimisationof sextupole magnets and the HOM control are thekey for the stable operation with high beam current.

2.4 Acceleration and Deceleration
A precise parameter search of tracking quadrupole
magnets took place for the acceleration up to 1.5 GeV,
and deceleration down to 0.5GeV. The ring is operated
with 0.5GeV during the R&D of FEL. The upgrading of
the horizontal steering system in the summer of 2002
enabled a COD control at 1.5GeV.

2.5 COD shift
The horizontal COD shift due to the temperaturechange of the cooling water was ∼ 60 µm at the dispersive
BPM ( ∼ 50 mm/°C; Fig.4). The control parameters of thewater cooling are optimised so as to the temperaturechange is less than ±0.1°C, then the horizontal COD shift
is almost negligible in taking account of the accuracy as
seen in Fig.3 The observed vertical COD shows typicalbehaviour due to random kicks as seen in the figure. Thisis understood at present by the reading errors or accuracyof the vertical position.
The high frequency components of the orbit oscillation
were measured by spectrally analysing of the SR monitor(visible light of SR). There is no significant oscillation
due to the ripples of the magnet power supplies (Fig.5).
The inverter system for the water cooling was
installed in summer of 2003 for more stable operation.

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

3 R&D

COD Variation during
Air Temperature Changeµm

3.1 Very Short Bunch

40∆x∆y200-20-40
0369121518

BPM N0.

Toward generating the coherent radiation in mm
wavelength region, the very short bunch operation has
been tested by reducing the momentum compaction
factor. The preliminary result is shown in Fig.6. The
bunch current is very weak and almost 1/10,000 of
those of normal operation. Even the number electrons
in a bunch is only 3×105, The strength of the coherent
radiation is corresponds to those of incoherent one
from 1011 electrons. The obtained rms bunch length is
1.7 psec and this is the world shortest bunch in astorage ring.

Figure 4: COD shift against room temperature.
Spectra of SR Monitor @2002-10-17
10(43mA)-(0mA)

dBcount50-5-100100200300
Frequency (Hz)400500Figure 5: Spectral of SR Monitor.

2.6 Control systema) Automatic COD correction
The COD are easily realize to keep 6~ 8 µm in rms
just by one button operation. This is very useful forthe user time to keep the SR axes stable.
b) Simultaneous observation of air and watertemperature
The systematic analysis of the drifts in COD andSR axes became possible. The sign of the beamenergy drift due to the air temperature change wasobserved even when there was no COD drift. The
more accurate orbit control is going to be implanted.
c) Improvement of the database of the storage ring
The model machine in the database should be thesame as the real storage ring. This is the key to realizea very small and/or negative αp lattice to obtain a very
short bunch. The database has been updated mainly byadjusting the effective lengths of magnets comparing
measured Twiss parameters with calculated ones.

9 104
-5
8 104 α 1=1.36X10
7 104
6 104
5 104
FWHM=3.8ps
4 104
3 104
2 104
1 104
0-1 1041520
25time (ps)3035

Figure 6: Preliminary result of short bunch.

3.2 Negative α p
The operation of αp = -1×10-3 has successfully
performed with the injection efficiency of ~70 %(without beam centre correction in the beam transformline). The appearance of energy widening, bunch
lengthening and head-tail instabilities are completely
different from those at positive αp. The quantitative
research is possible only at NewSUBARU in theworld and our analysis will contribute thedevelopment of beam physics.

4 ACKNOWLEDGEMENT
The authors wish to thank members of the SPring-8
accelerator division for their support on the machine
operation.

5 REFERENCES[1] A. Ando, et al., J. Synchrotron Rad. 5, 342-344 (19