%81&+,1*6<67(02)7+(.(.%/,1$&-DH<RXQJ&KRL6DWRVKL2KVDZD7DNX\D.DPLWDQL<XMLUR2JDZD$WVXVKL(QRPRWRDQG,VDPX6DWR
1DWLRQDO/DERUDWRU\IRU+LJK(QHUJ\3K\VLFV .(. 2KR7VXNXED,EDUDNL-DSDQ$EVWUDFW'HVLJQRI%XQFKLQJ6\VWHP$WSUHVHQWWKH.(.*H9/LQDFLVEHLQJXSJUDGHGDV
WKH LQMHFWRU RI WKH .(. %IDFWRU\ .(.%   2QH RI WKH PRVWLPSRUWDQW FKDQJHV LV WR LQFUHDVH WKH LQWHQVLWLHV RI SRVLWURQEHDPV LQMHFWHG LQWR D .(.% ULQJ LW LV WKHUHIRUH UHTXLUHG WR
DFFHOHUDWH KLJKLQWHQVLW\ VLQJOHEXQFK HOHFWURQ EHDPV WR KLJKHQHUJ\*H9ZKHUHWKH\DUHFRQYHUWHGWRSRVLWURQEHDPV)RUWKHSXUSRVHWKHSULPDU\HOHFWURQEXQFKVKRXOGKDYHPRUH
WKDQQ&)XUWKHUPRUHWKHEXQFKOHQJWKVPXVWEHOLPLWHGDVVKRUW DV  SV LQ RUGHU WR DFKLHYH QDUURZ HQHUJ\ VSUHDGV RISULPDU\ HOHFWURQ EHDPV DQG SURGXFH SRVLWURQ EHDPV RI VKRUWEXQFK OHQJWKV DV ZHOO  7KH EXQFKLQJ V\VWHP KDV EHHQ
GHVLJQHGWRPHHWWKHVHUHTXLUHPHQWVLQWURGXFLQJVXEKDUPRQLF
EXQFKHUV 6+% 7KLVSDSHUGHVFULEHVWKHXSJUDGHRIWKHEXQFKLQJV\VWHPDQG
WKH UHVXOWV RI VLPXODWLRQV RI EXQFKLQJ XVLQJ 3$50(/$ 7KH
GHVLJQVDQG5)WHVWRI6+%FDYLWLHVDUHGHVFULEHG

7KH DFFHOHUDWLRQ VWXGLHV RQ KLJK LQWHQVLW\ VLQJOHEXQFK
HOHFWURQ EHDPV IRU WKH .(.% /LQDF KDYH EHHQ FDUULHG RXW DW.(.3)*H9/LQDFIRUDFRXSOHRI\HDUV>@XVLQJRQH
VXEKDUPRQLF EXQFKHU 0+]  $QG LW KDV EHHQ FOHDU IURPWKRVH VWXGLHV WKDW RQH PRUH VXEKDUPRQLF EXQFKHUV ZDV
QHFHVVDU\WRSURGXFHVLQJOHEXQFKHVZLWKQRVDWHOOLWHEXQFKHVLIWKHFKDUJHDERXWQ&RUPRUH>@$VPHQWLRQHGDERYHWKHHOHFWURQFKDUJHVUHTXLUHGIRUWKH
SURGXFWLRQRISRVLWURQEHDPV.(.%DUHQ&:HKRZHYHU
KDYHGHVLJQHGWKHEXQFKLQJV\VWHPZLWK3$50(/$VRWKDWLW
FRXOG SURGXFH VLQJOH EXQFKHV XS WR Q& 7KH OD\RXW RI WKH
QHZO\ GHVLJQHG EXQFKLQJ VHFWLRQ LV VKRZQ LQ )LJ   7KH
EXQFKLQJV\VWHPZLWKRQHVXEKDUPRQLFEXQFKHUZDVGHVFULEHG
HOVHZKHUH>@ :H ZLOO EULHIO\ GHVFULEH WKH QHZ EXQFKLQJV\VWHP DQG EXQFKLQJ EHKDYRXU EHORZ PDLQO\ IRU WKH FDVH RI
 Q& 7R JHW  Q& VLQJOH EXQFKHV DW WKH HQG RI WKH SUHLQMHFWRUZHDVVXPHGQ&IURPWKHHOHFWURQJXQFRQVLGHULQJ
FKDUJHORVVHVLQWKHEXQFKLQJSURFHVVHV,QWKLVFDVHWKHVSDFHFKDUJH IRUFH LV VR ODUJH WKDW LW ZDV QHFHVVDU\ WR  VKRUWHQ WKH
GULIW VSDFH DIWHU WKH EHDP ZDV WLJKWO\ EXQFKHG WR PLQLPL]H
GHEXQFKLQJ6LQFHWKHFRQWHUDFWLQJIRUFHVRIWKHVSDFHFKDUJHVPDNHWKHEHDPHQHUJLHVFRQYHUJHQWZLWKEXQFKLQJWKHUHH[LVWVWKH PLQLPXP SRVVLEOH EHDP SXOVH OHQJWK  ,Q WKH GULIW VSDFHGRZQVWUHDP 6+% WKLV LV DERXW  GHJUHHV LQ 6EDQG RU
OLWWOHORQJHUZKLFKFRUUHVSRQGVWRDOPRVWKDOIWKHZDYHOHQJWK
RI WKH UI RI 6+% )XUWKHUPRUH WKH 6+%©V IUHTXHQF\ LV VR
ORZ WKDW WKH WUHPHQGRXV SRZHU LV UHTXLUHG WR SURYLGH ODUJHPRGXODWLRQ:HWKHUHIRUHVHWORZWKHEXQFKLQJILHOGDW6+%
DERXW  N9 7R FRPSUHVV WKH DERYH EHDP SXOVH OHQJWK WR
VKRUWHUWKDQRQHZDYHOHQJWKRIWKH6EDQGSUHEXQFKHUIXUWKHUEXQFKLQJ LV UHTXLUHG DW 6+% ZLWK WKH SHDN HOHFWULF ILHOG RI
N9,QWKLVGHVLJQWKHILUVWSUHEXQFKHUZDVUHPRYHGVLQFHGHEXQFKLQJ RFFXUHG LQ GULIW VSDFH EHWZHHQ WKH SUHEXQFKHUV
DQVWKXVWKHPDLQEXQFKLQJFRPSRQHQWVRIILQDOV\VWHPLQFOXGH
WZR VXEKDUPRQLF EXQFKHUV RI VWDQGLQJ ZDYH W\SHV DQG
SUHEXQFKHU WKH ROG 3%  DQG EXQFKHU 7KH SUHEXQFKHU DQG
EXQFKHU DUH PHFKDQLFDOO\ MRLQHG WRJKHWKHU WR PLQLPL]H GULIWVSDFH ZKHUHDV WKH\ DUH VHSDUDWHG HOHFWURPDJQHWLFDOO\ 2QH
PRUHLPSRUWDQWFKDQJHLQ WKH SUHLQMHFWRU LV WR VWUHQJWKHQ WKH
HOHFWULFILHOGRIWKHEXQFKHUWKHSRZHURIWKHNO\VWURQIRUWKH
SUHLQMHFWRUZLOOEHLQFUHDVHGWZLFHWRSURYLGHWKHHOHFWULFILHOG,QWURGXFWLRQ
7KH .(. 3) *H9 /LQDF LV QRZ EHLQJ XSJUDGHG IRU
WKH .(.% SURMHFW>@  7KH SUHLQMHFWRU RI WKH .(.% /LQDF
PXVW SURYLGH EHDPV ZLWK YDULRXV FKDUJH FRQWHQWV IRU WKH.(.% ULQJV DQG 3) ULQJ>@ VLQJOHEXQFK HOHFWURQ EHDPV RI
 Q& IRU WKH SRVLWURQ EHDP SURGXFWLRQ DQG  Q& IRU GLUHFW
LQMHFWLRQ WR WKH .(.% HOHFWURQ ULQJ 7KH GHPDQGV WR WKH
EXQFKLQJ VHFWLRQ OLHV LQ WKH SULPDU\ HOHFWURQ EHDPV IRU WKH
SRVLWURQ SURGXFWLRQ WKH SUHLQMHFWRU PXVW SURGXFH VLQJOH
EXQFKHOHFWURQEHDPVRI PRUH WKDQ  Q& IXUWKHUPRUH WKHUH
H[LVW WKH RSWLPXP EXQFK OHQJWKV DFFRUGLQJ WR WKH FKDUJHV RI
WKH EXQFKHV  WR PLQLPL]H WKH HQHUJ\ VSUHDGV LQ VXEVHTXHQWDFFHOHUDWLRQ GHWHUPLQHG E\ WKH FRQWULEXWLRQV RI EXQFK OHQJWK
DQG ORQJLWXGLQDO ZDNH ILHOGV WR HQHUJ\ VSUHDG $FFRUGLQJ WR
FDOFXODWLRQ UHVXOWV>@  EXQFK OHQJWKV DERXW  SV DW ):+0
DUHGHVLUDEOHLQWKHFDVHRIVLQJOHEXQFKHVRIQ&
7R PHHW WKHVH UHTXLUHPHQWV WKH SUHLQMHFWRU V\VWHP KDV
EHHQGHVLJQHGWRLQWURGXFHWZRVXEKDUPRQLFEXQFKHUV 6+% 7KH IUHTXHQFLHV RI WKH  WZR 6+%©V ZDV FKRVHQ WR EH 0+]DQG0+]>@:HZLOOGHVFULEHWKHGHVLJQRIWKHZKROHEXQFKLQJV\VWHP
DQG WKH EXQFKLQJ FKDUDFWHULVWLFV WRJHWKHU ZLWK WKH GHVLJQIDEULFDWLRQDQG5)WHVWUHVXOWVRIVXEKDUPRQLFEXQFKHUV
1300

SHB1300

SHB
21438

PB

BUNCHER

(10)
(1)

(2)

(3) (4) (5) (6)

(7)

(8)

(9)

(1)Electron Gun, (2) Magnetic Lens, (3) Profile Monitor, (4) Wall Current Monitor, (5) Core Monitor, (6) Steering Coil, (7) Gate Valve, (8) Ion Pump, (9) Focusing Coil, (10) Q-Magnet)LJ3UHLQMHFWRURIWKH.(.%/LQDF
BBBBBBBBBBBBBBBBBBBBBBBBBBBBB
3UHVHQWDGGUHVV$WRPLF(QHUJ\5HVHDUFK,QVWLWXWH1LKRQ8QLYHUVLW\.DQGD6XUXJDGDL&KL\RGDNX7RN\R-$3$1

of 20 MV/m for the buncher (present : 15 MV/m). Moreefficient bunching was confirmed from the results of thesimulations in the case of high intensity beams.
Figure 2 shows the parameters of a bunched beam of 15 nC
at the exit of the buncher. About 70 % of the initial charges arecontained in 15 degrees around the peak. It is shown thatsingle bunches of about 10 ps at FWHM could be obtained.
The energy spread is rather broad, but a short bunch length ismore important than this energy spread in the bunching
section, since the energy dispersion due to the bunch length
during subsequent acceleration dominates the total energy
spread. In this case, two tiny satellite bunches on each side of
the main bunch was formed containing charges of 6 percent of
total initial charges. For other charges, shorter bunch lengthes
and narrow energy spread was obtained in simulations; 5degrees and 1.2 MeV for 1 nC bunch, and 10 degrees and 2.0
MeV for 10 nC, all at FWHM.
Simulation on charge 15 nC showed that the optimizationof focusing magnetic fields of maximum 1400 G, full capacityof the present focusing coils, could hold the normalized RMS
emittance below 150 π.mm.mrad[6].
120No. of Particles

(a)

100
80
60
40
10mentioned in the previous section, a peak modulation of 50
kV will be necessary for a beam of a pulse width 2 ns and 20
nC in this design. In this case, the peak voltage will be as
high as 77 kV. The shunt impedance value shows that the thecavity should be supplied a peak power as high as 11.2 kW
to sustain the peak voltage. The shunt impedance of thiscavity is made low by large nose tip radii and beam duct
diameter near the gap. We designed a new SHB1 cavity andas its shunt impedance is above 1 MΩ, we can fabricate acavity with the shunt impedance value larger than 0.7 MΩ,
and if this is the case, the required peak power become s
8.6 kW.
Subharmonic Buncher 2 (SHB2)
Design and low power RF test. The structure of theSHB2 cavity newly fabricated is shown in Fig. 3. Thestructure of the cavity is similar to that of 476 MHz SHBcavity[2] . In the case of 476 MHz cavity, a ceramic covering
was used over the input coupling loop to isolate vacuum fromthe atmosphere. By doing so, the coupling of the cavity can bechanged keeping vacuum. In this case, we did not use aceramic covering to prevent electric discharges which may
occur in high field operations. The power input connector isjoined to the cavity by a rotatable ICF flange, and therefore thecoupling can be changed if needed, though it damage cavity
vacuum during change.

o2 05(b)(c)

2015
101 MeV

Kinetic Energy (MeV)20

50-100 -80-60-40Phase (deg.)

-2000

20

40

60

80

100

No. of Particles

Fig. 2. Characteristics of the bunch of 15 nC at the exit of thebuncher. (a)bunch shape; the horizontal axis denotes thephase of a particle with respcet to the fundamental wavein the buncher. (b) the distribution of particles inlongitudinal phase space, (c) energy spread

Subharmonic Buncher 1 (SHB1)
The 119 MHz subharmonic buncher cavity [7] is available
with the removal of the positron beam line according to theend of the TRISTAN experiments. To examine its usability
as the SHB for the KEKB Linac, we measured the main
parameters of the cavity and calculated the parameters for thesame geometry with SUPERFISH. The results ofSUPERFISH showed that minor changes of the acceleration
gap structure make the cavity usable as SHB1 of the KEKB
Linac as far as the frequency is concerned. But the measured
shunt impedance (0.54 MΩ, compared to the calculated value
0.79 MΩ) is so low that it requires a very large peak power
for bunching high intensity beams . For example, as

Fig. 3. Structure of SHB2 cavity.

The main parameters of the SHB2 cavity are shown Table
1. The Q value was measured by both the reflection method
and the impedance method[8]. The temperature of the cavity
was kept constant at 31± 0.2 ° C by circulating the coolingwater used in actual beam line, and vacuum was kept by aturbomolecular pump, lower than 10-2 mbar. The cavity has a
Q value of 83 % of the calculated one. The shunt impedanceof Table 1 was obtained from R/Q values measured by Slater’s
bead perturbation method[8]. The measurements were doneusing aluminum spheres of diameter 2,3,4 mm as perturbaters.
It is the value obtained when these values are extrapolated tothe limit of zero volume. This R/Q value is nearly the same as
the one by SUPERFISH. Figure 4 shows the electric field
distribution on the beam axis near the acceleration gap. Theagreement between measured curve and the calculated one isgood. From this shunt impedance value, it can be seen that apeak power 6.7 kW is necessary to get the peak electric field,

100 keV, required to be provided by the SHB2 cavity tobunch 20 nC beams. A SHB2 power source capable of peak
power 10 kW is now being fabricated. It will be a sloid state
amplifier and completed in this fiscal year.
Table 1.

discharge up to this level except for initial stage discharges.
Figure 3 shows the power pulses observed by anoscilloscope.
When a 571.2 MHz power source becomes available, wewill perform again high power test through the full range at theresonant frequency.

Main parameters of the SHB2 cavity

Cavity Length
Gap Length
Resonant Frequency
Tuning Range

Electric Field, Ez (Normalized)

Qo value
Coupling Parameter
Shunt Impedance

Calculated
Measured
117 mm12.2 mm
12.48 mm
571.2 MHz
570.44 - 572.32 MHz( total stroke of tuner : 30mm)
10,8709010
1.4
1.83 MΩ
1.50 MΩ

Outputof Amp.
(5.5 kW)

CavityMonitor(4.2 kW)

1.2Ez (SUPERFISH)

1Ez (measured)

0.8

Fig. 3. Power pulse forms in high power test observed at powersource (above) and cavity monitor(below)

0.6Conclusion

0.4
0.2
0-0.2

-40

-2002040z (mm)Fig. 4 Electric field distribution on axis near the acceleration gapof SHB2.

High Power Test. Since a high power source of 571.2
MHz is not available to us at present, as a preliminary test, weperformed a high power test of the newly fabricated cavity
using the 476 MHz power source which is installed in thepresent beam line. To adjust the resonant frequency of thecavity to 476 MHz, we inserted a copper spacer of thickness
26.7 mm in the cavity and lengthened the cavity.
The test was done at 31± 0.2°C, and 3×10 -7 mbar. The
electric discharges by multipactoring has been observed duringinitial rf aging, and we perfomed the high power tests at
various levels through two days. We finally put peak power
4.2 kW into the cavity , though this is not a sufficient level.
We confirmed a stable operation with no continuous electrical

We designed the bunching system for the KEKB Linac bysimulation code PARMELA. The result showed that thenewly designed bunching system can produce bunched beams
required for the KEKB pre-injector. We fabricated a new SHB
cavity and confirmed that it has required properties. Another
SHB cavity will be fabricated in the near future.
References[1] A. Enomoto, “Upgrade to the 8-GeV Electron Linac for
KEKB”, this proceeding.
[2] Y. Ogawa, et al., “ Wake-field issues concerning the KEK BFactory Injector Linac”, Proc. 1994 Int. Linac Conf., 535[3] S. Ohsawa et al., “High-Intensity Single-Bunch Beam of thePF 2.5-GeV Linac”, Proc. 1994 Int. Linac Conf., 193[4] Photon Factory Activity Report 1994, KEK, 1996
[5] S. Ohsawa, et al., “Pre-Injector of the KEK 2.5-GeV Linac andHigh-Current Single- Bunch Acceleration”, these proceedings.
[6] Design Report on PF Injector Linac Upgrade for KEKB (inJapanese), KEK Report 95-18 March 1996
[7] A. Asami, et al., “Injector of the Positron Generator”, Proc.
1986 Int. Linac Conf., 496[8] E. L. Ginzton, Microwave measurements, McGraw-Hill, 435(1957)