The 13th Symposium on Accelerator Science and Technology, Suita, Osaka, Japan, October 2001

Successful beam injection to the smallest synchrotron
and brilliant x-rays production
H. Yamada, T. Ozaki, Y. Sakai, K Minami, D. Hasegawa, Y. Kitazawa, and 1 Tohyama
Ritsumeikan University, 1-1 Nojihigashi, Kusatsu-City, 525
A.L Kleev and G.D. Bogomolov
P.L.Kapitza Institute for Physical problems, Moscow, Russia
Abstract
We have made a successful beam injection to theworld smallest electron storage ring by the 2/3-resonanceinjection method. Usefulness of the resonance injection
to the extremely small ring was demonstrated. The
brilliance of the produced x-ray is not high but the total
flux exceeds the synchrotron. The advantage is in thehigh coherence, and in the wider angular distrubution.

1.

INTRODUCTION

Downsizing of accelerator must be an important
subject for the 21 Century accelerator communities.
There are many cutting edges such as novel accelerator
scheme using higher microwave frequency or a laser, ormicro fabrication of the accelerator column, and so on.
Our approach is the down sizing of synchrotron. Ourbeam injection scheme, we hope, will open up new
application fields.
We have made a successful beam injection to theworld smallest electron storage ring by the 2/3-resonanceinjection method [1]. The 20 MeV tabletop electron
storage ring named "MIRRORCLE-20" is composed of asingle peace of normal conducting magnet of 1.2 m out
diameter and 0.15m orbit radius. The usefulness of theresonance injection to the small ring of 1m-orbit
circumference was demonstrated. No fast response kicker
magnets are available so that the standard beam injection
scheme is not useful. This method has been successfully
adapted firstly by AURORA with a 112-resonance method[2].
Since this ring is exactly circular we are not able tomeasure the stored beam current, but the ionization
counter measures the generated x-ray beam intensity fromtarget placed in the orbit as bright as synchrotron light.
The x-ray beam is generated by the bremsstrahlung with athin AI or Ph-target placed in the orbit. The brilliance is
not high but the total flux exceeds that of the synchrotron.
The advantage is in the high coherence, and in the ratherwide divergence. This source is suitable for the phase
contrast x-ray imaging oflarge specimens.

2.

2/3 RESONANCE INJECTION METHOD

The beam injection is an established technology for alarge synchrotron. But when the synchrotron orbit
circumference is extremely small, we have to adapt a newtechnology. The circumference of our ring is only 1 mor 3 nsec. There are no such fast kicker magnet is madein the past. A use of horizontal betatron resonancemoderates the conditions on the necessary kicker force
and the pulse width. On the other hand, however, thebeam instability appears. The successful beam injection ismade when the pulse width invoking the resonance andthe heating speed is valanced.
Fig. 1. Pair of perturbators, a microwave cavity, and aquadrupole doublet (QD) is placed inside the vacuum
chamber under the strong magnetic field.

'X-ray beam.

•· ' Target andscreen

CavityScreenMIRRORCLE is an exact circular machine similar
to AURORA. Purterbator (PB), the pair of one- tumcoils to excite the betatron resonance, is placed under themain magnetic field, so the coil is made of air core andgenerates as much as 300 gaus.
The pulse width of thehalf sinusoidal shape of the Perturbator (PB) was the-46-The 13th Symposium on Accelerator Science and Technology, Suita, Osaka, Japan, October 2001

subject to be studied. The configuration of PB and thebeam trajectory is shown in Fig. I. Each purterbator
kicks beam toward inside at the outer and inner edge ofthe orbits, respectively. The n-value of the main
magnetic field is set close to 0.54, while the n-value 0.556
corresponds to the 2/3-betatron tune. In principle theadditional perturebator field makes the betatron tune as
close as 2/3. If the n-value apart further from 0.556,
more pertuerbator force is required.
·.

'~'·.

'.

Fig. l. Cbange it) the phase diagram at tiie iJUCc:lion point· · · · ·· · ·as the pettUibatoi fe)J'()e cbattge$. ·• ....-.....-.-.,......,...;..,.o...,.._,'I·~·. ,,~,.

10I
01¥-'-+--.H~ ,t4·lI&.-i ....:~ ~,~ ;:•! '.

3.

.

•"·--······:li .~'-l._.....;.;.o...,.._...L-.l(a)PIIIIIIdllllirlilR:f: 100%

•I .:!!I...
no(J))J'•iW«toM:tiO.,.

I-t--

.._..
.,
~ I =~..

I- I--.............
•,I•eo -40 _., o 11 40 eo eoRadial pollilion lf(lml)(c)~lilR:f:60%-·· ......jDiiliooix.··.
(~--=-Fig. 3. We have studied the pel'tUrbatorcoil cuirent;thepulse width, the timing. and the cavity voltage.

..............

~--··········........,_.

------·--.

Fig. 4 Screen monitor made of AI foil(5JJ.m) painted withZnS is used to view the circulating beam in the ring.
The left and light columns show beam positions as thescreen is moved in radial direction with and without
perturbator, respectively. The light column shows
captured beams.

• • • • • •• _......

•!II ••Of •~EXPERIMENTAL RESULTS

3.1 BEAM INJECTION
The beam diagnostics of the exact circular andextremely low energy synchrotron is another problem.
A current troid cannot be used as same as AURORA,
since it disturbs the main magnetic field. In addition
there are no fast response photon detectors at this critical
wavelength region of synchrotron light. The solid sate
FIR detector is also sensitive to X-rays. Until now wedo not have a means to measure the stored current.
To monitor the stored beam current we useradiations from a 5 mm wide and 5JJ.m thick AI foil. The
ZnS fluorescent martial painted on the AI foil is used forviewing the beam position.

bcliai~X(-}•I$

dynamical change of the tune, as the perturbator force ischanged as time, which is shown in Fig. 2. The meaningof the 2/3 resonance is clear from Fig. (a) and (b).
When the PB force is lower than 40%, the resonancedisappear and the beam is captured in the central orbit as
seen in Fig. (c) and (d).
The effect of the PB was studied by searching theparameters such as the PB coil current, the pulse width,
the timing to excite it, as well as the ring cavity voltage.
The results are shown in Fig. 3. We found the optimized
parameters to be 0.3 ~ec pulse width, 6000A coil current,
and 60 kV'cavity voltage. We learned that the too large
cavity voltage decreases the acceptance. The obtainedacceptance is about 30 mm·mrad.

•The phase diagram at the injection point shows the-47-

The 13th Symposium on Accelerator Science and Technology, Suita, Osaka, Japan, October 2001

The injection trajectory must be specified exactly toexcite the resonance. At the first step we ensure thebeam radial position with the screen monitor at the target
position (see Fig. 1) by moving the screen monitor.
When the first and second turns are identified, we excite
the PB. The results are seen in Fig. 4. If the PB is not
excited we see only the first and second turn beams, butwith excited PB the beam spot turns to extremely bright at
the center, and can be seen at any points around thecentral orbit within ±50mm. So the beam is circulating.
If the injection conditions are setup properly, theresonance appears at 75% PB current while the maximum
is 6600A. We have obtained the maximum injection
efficiency at 90% PB. These results are quite consistent
with our simulation shown in Fig. 3.

3.2

corresponds to 1000 times revolution. This means thatthe coherence of MIRROCLE should be counted so as
106 times more of the average photon number. This is
one of the reasons why we see the enhanced edge in thex-ray image due to interference shown in Fig. 5. Fine
stracture of the soft tissue is imaged with hard x-rays.
Fig. S X-ray image of a butterfly taken by MIRROCLE.
The edge of the soft tissue is enhanced due to the highbeam.
:.-:-~.,;.:,: . :.•:,,.. ,;,.~,·:··:·::ciliii

FUTURE OF THE NEW X-RAY SOURCE

Measurement of the beam current is difficult. Only
we can show the x-ray intensity from the target. Since
photon coutings are also impossible, we show in Table
1 the radiation dose measured by the calibrated ionizationchamber.
The DOSE of MIRRORCLE; I 00
Rls/JOmA/I5cm 2, indicates 100 Rontogenls integrated overI5cm2 area at 1OmA injected beam pulse current and at
30Hz operatin. In this case the 5 mm wide and 0.5mm
thick AI target was used, but 5J.1m thick AI foil gives
nearly equal results. The dose is independent of the target
thickness. If that is thin, the beam just circulates longertime. The radiation power is namely determeind by theinjector power, since the ring power is only one KW.
This is not enough to recover the beam energy, but
contribute only to the radiation damping. On the other
hand the unit of SR power is of standard. We see here
the brilliance of MIRROCOE which is yet the order ofthe rotating anode source, but the total photon iscomparable to the SR undulator radiation.
TheMIRRORCLE radiation is characterized by the large
angular spread. This beam is useful for the x-ray
imaging of large specimes like a human body comparedwith SR.
Another feature is the high coherence. Most ofradiations are generated within a fewlOO ns time window.
This is due to the short lifetime, an order of f.1S, which

4.
CONCLUSION
We have discussed the successful beam injection tothe smallest ring, and novel feature of the produced x-ray
beam such as the high coherence and large angular spread.
According to this success, the construction of the second
machine has beean appproved by the Ministry ofEducation and Science. We have started constracting
MIRRORCLE-6X, which is the 6 MeV version. Foot
print of the machine will be 1 x 0.5 m2•

5.

REFERENCES[I] H. Yamada, et ai, Nucl. Instrum. Methods in Phys. Res.,(200 I), accepted for publication, Proc. SRI' 2000, Berlin,
August 20-25, 2000
[2] T.Takayama, Nucl. lnstrum. Methods in Phys. Res. B24/25(1987) 420; H. Yamada, J. Vac. Sci. Tech. B8(6) (1990) 1628.
[3] H. Yamada, J. Synchrotron Radiation, (1998) 1326
(Invited paper for SRI97).

Table 1. X-ray_ beam DOSE measured by an ionization counter is compared with the SR unduiator source(PF-AR).
MIRRORCLE-20X
5GeV SR light source(PF-AR)
Radiation scheme
Target radiation
UndulatorRadiation angle
25mrad<lmradPhoton Spectrum
Broadband from few keV-20 MeV
33 keYTime structure
Pulse; -I JJ. s, Repetition 30Hz
Continuous; 400MHz
Max DOSE
100 Rls/10mNI5cm2
135Ris/25mNI 06cm2
Calculated Brilliance
6.8E+08 Photons/s/mrad2/mm2/0.l %A.
3.0E+l5 Photons/s/mrad2/mm2/0.l%A.

Calculated Total photons

1.3E+8 photons/s/0.1 %A.

- 48-

3E+7j>_hotons/mrad/s/O.I%A.