FIRST SIMULTANEOUS TOP-UP OPERATION OF THREE DIFFERENTRINGS IN KEK INJECTOR LINAC
M. Satoh#, for the IUC*
Accelerator Laboratory, High Energy Accelerator Research Organization (KEK)
1-1 Oho, Tsukuba, Ibaraki 305-0801, Japan
Abstract
The KEK injector linac provides beams with four
different rings: a KEKB high-energy ring (HER; 8
GeV/electron), a KEKB low-energy ring (LER; 3.5
GeV/positron), a Photon Factory ring (PF; 2.5
GeV/electron), and an Advanced Ring for Pulse X-rays(PF-AR; 3 GeV**/electron). In original operation, thebeam injection of the PF ring and PF-AR had been carriedout twice daily. The injection of the KEKB rings had
been operated in every 90 minutes. In such operation
scheme, the stored beam current decreases until next
beam injection, and it results in the heavy drop of
integrated luminosity and brilliance. In 2004, we has
started the KEK injector linac upgrade project aiming at
the simultaneous top-up operation for three different rings(KEKB HER, LER, and PF).
In the simultaneous top-up operation, the common DC
magnet settings are utilized for the beams with different
energies and amount of charges, whereas the different
optimized settings of RF timing and phase are applied toeach beam acceleration by using a fast low-level RF(LLRF) phase and trigger delay control up to 50 Hz.
With this noble operation scheme, a simultaneous top-up
operation for different three rings was successfully
achieved for the first time over the world, and has beenstably in operation since April 2009. We report theoperation scheme and status of simultaneous top-up
operation in detail.

Figures 2 and 3 show the typical one day stored beam
current at KEKB and PF, respectively. Here, about 16
times beam injection of the KEKB was carried out dailyin every 90 minutes. The PF and PF-AR injections wereoperated twice daily on scheduled time. For increasing

Figure 1: Accelerator complex in KEK Tsukuba
campus.

INTRODUCTION
The lepton accelerator complex in KEK Tsukuba
campus consists of four storage rings and one injector
linac as shown in Fig.1. The maximum beam repetitionof the linac is 50 Hz. In the original operation, the beam
injection for each ring was sequentially carried out since
the four rings share only one injector linac with. The
beam properties required for each ring injection are muchdifferent. The required beam energy is from 2.5 GeV for
PF to 8 GeV for KEKB HER, and the required amount ofbeam charge is from 0.1 nC for PF to 10 nC for positron
production of KEKB LER. For each ring injection, we
should use the different optimized linac parameters which
are the settings of trigger delay, RF phase, magnet power
supply, and other subsystems. The linac parameterswitching took a several minutes in original operation.

Figure 2: Stored beam current of HER (top), LER(middle), and luminosity (bottom) of KEKB in theoriginal injection operation (24 hours).

___________________________________________#

masanori.satoh@kek.jp* Injector Upgrade Committee: Cross-functional team for the injector
upgrade from PF/ KEKB and Linac members.
** The injected beam is accelerated up to 6.5 GeV for user experiment.

Figure 3: Stored beam current of PF in the original
injection operation (24 hours).

Figure 4: Stored beam current of HER (top), LER(middle), and luminosity (bottom) of KEKB in
continuous injection operation (24 hours).
the integrated luminosity, we started the continuous
injection operation for KEKB in 2005 [1]. It is a quasitop-up operation, where the linac parameters should befrequently switched for KEKB HER and LER injection.
The much more stability of stored current was demanded,
whereas the continuous injection improved the integrated
luminosity of KEKB very much in comparison with theoriginal operation scheme. In addition, the demand for
PF top-up operation was glowing up from theexperimental user community. For these reasons, westarted the injector upgrade aiming at the simultaneous
top-up operation of three different rings [2, 3, 4, and 5].

up, we change only the minimum linac parameters related
to timing signals and LLRF phases. Almost all theremaining parameters including the DC magnet settings
are never changed even for the different ring injection.
Figures 5 and 6 show the schematic drawing of the beamenergy variation along linac in the original operation andsimultaneous top-up operation schemes, respectively. In
original operation, the different electron guns (GUN #1
and #2) were used for the KEKB and PF injections, andthe energy differences between KEKB HER and PF werevery large at each position along linac.
In the simultaneous top-up operation, GUN #1 isutilized also for the PF injection instead of GUN #2. The
PF beam is accelerated up to about 5 GeV which is muchhigher energy required for the PF injection. In the middleof linac, it is transported without any acceleration. Finally,
the PF injection beam is decelerated down to 2.5 GeV in
the end of linac. By using such scheme, the common
magnet settings can be utilized for all of three different
beams (KEKB HER, LER, and PF) since they aretransported with almost same energy in first half of thelinac. In downstream of the linac, the happy-medium
settings of magnets are utilized for transporting the beams
with different energies [6].

DEVELOPMENT OF SUBSYSTEMSFast Event Based Timing Control System
In the old timing system, about 150 timing delay
modules based on VME-bus (TD4V) and CAMAC (TD4)OPERATION SCHEME FORSIMULTANEOUS TOP-UP

Beam energy (GeV)

In the new operation scheme toward simultaneous top-

Figure 7: Photograph of the new event based timing
system.

Beam energy (GeV)

Figure 5: Beam energy variation along linac in theordinary operation scheme.

Figure 6: Beam energy variation along linac in thesimultaneous top-up operation scheme.

Figure 8: Schematic drawing of the connection
between the event generator and receivers.

were used for controlling the timing signals distributed tothe many different types of local controllers. The timing
system upgrade was indispensable since it was not
feasible for the old system to realize a fast timing control
up to 50 Hz.
The event generator and receiver (EVG/EVR) system
based on VME64x-bus has been adopted as a new timing
system. Its photograph is shown in Fig. 7 [7, 8]. In the
new system, one EVG and twenty one EVRs areconnected via optical fibre on star topology as shown in
Fig. 8. The event information, RF clock (114 MHz),
timestamp and data buffer can be quickly transferred from
EVG to EVR. Twelve DAC modules based on VME-bus
are utilized for a fast LLRF phase control. The control
software was developed by using EPICS system on
VxWorks.
EVR can output the timing signal corresponding to theevent id set on EVG. Associating each event id withspecific trigger delay settings, the beam energy and rf
phase can be immediately changed to the optimized
setting in every 20 ms by switching event id on EVG. In
addition, the total number of used module for the timing
system can be drastically reduced by using the EVG/EVR
system. This can gratefully increase the reliability oftiming system and beam operation.

Construction of the New PF-BT LineIn the original PF-BT line, the standardization of theenergy compensation system (ECS) bends were required
for switching the beam injection between PF and otherrings since PF-BT was branched off at downstream of
ECS. Such procedure took several minutes because it
needed to change a current of large bends slowly forkeeping its hysteresis cycle.
In order to avoid standardizing ECS, a new PF-BT linewith 60 m has been constructed as shown Fig. 9 [9]. The
new PF-BT is branched off at upstream of the first ECS
bend. Only the PF injection beam can be selectively
kicked toward the new PF-BT since the new pulsed bend
and its power supply have been developed and installed
as mentioned in next subsection. After the constructionof new PF-BT, the constant settings of ECS are available
during the simultaneous top-up injection.
Beam switchyard

pulsed power supply, and the ceramic chamber. Table 1
shows the main parameters of the pulsed bend system [10,11]. The photograph of pulsed bend and power supply
are shown in Figs. 10 and 11, respectively.
Though the electron beam with 2.5 GeV is required for
the PF injection, the pulsed bend system has been
designed for the beam operation up to 3 GeV for the
future demand. The maximum repetition rates are 25 Hz
and 18 Hz for the beams with 2.5 GeV and 3 GeV,
respectively. Its output current has the half-sinusoidal
shape with 200 µs duration. The both at long and shortterm stability of power supply output current is satisfied
less than 0.1%.
Table 1: Main parameters of pulsed bend system.
Pulsed bend:
Beam bending angle:
7 deg. (up to 3 GeV)
Max. magnetic field:
1.36 TGap:
157 x 30 mm (W x H)
Coil:
1 turnPower supply:
Max. current:
32 kA (12.5 Hz)
27 kA (25 Hz)
Pulse width:
200 µs (half-sinusoidal)
Stability:
0.1%
Ceramic chamber:
Length:1200 mm
Coating:
Ti (1 µm)

Figure 10: Photograph of the pulsed bending magnet for
the new PF-BT.

PF

New PF-BT
Bends
for ECS
Pulsed Bend

Original PF-BTKEKB e+(3.5 GeV)KEKB e(8 GeV)

Figure 9: Schematic drawing of the new PF-BT atbeam switchyard of linac end.

Pulsed Bend System
For the new PF-BT line, we have developed the newpulsed bend system comprising of the pulsed bend, theFigure 11: Photograph of the pulsed power supply.

The 1200-mm-long ceramic chamber has been also
developed and installed. Its cross-section is a race trackshaped. To avoid the heating, the inner wall of ceramicchamber is coated with 1-µm-thick Ti.

New Positron Production Target for e-/e+ Fast
Switching
In the original operation scheme, the positron
production target was controlled by extracting or insertinga target holder. For the fast switching between electron
and positron operations, we have developed the newpositron target [12]. In the new operation scheme, the
new target is fixed at the centre of beam line even for theelectron operation.
The new positron production target is a tungsten target
with a hole as shown in Fig. 12. A centre of a hole isplaced 5.2 mm apart from that of the tungsten target. The
diameter of a hole is about 5 mm. The electron beam cango through the inside of a hole for the electron injection,
whereas the primary electron beam with 10 nC collides
the center of target during the positron injection.
The result of machine study by using the new target
shows that the beam loss is less than 5% at the hole incomparison with an original operation as shown in Fig.13.
It was confirmed that this scheme is applicable to thepractical beam operation. For a fast control of the bumporbit, the several pulsed steering magnets have been
installed at both of upstream and downstream of the target.

Figure 12: Photograph of the new positron production
target with a hole.
Xa regulated amount of integrated beam charges traversing
through at several locations for machine protection, and it
also monitors the amount of integrated beam charges
delivered to the four different storage rings at the linac
beam switchyard.
The beam charges delivered from an electron gun aremeasured with the beam-charge interlock system. Thissystem consists of the wall-current monitors, beam-charge
integration circuits, and a PLC-based control system.
This system sends the beam abort signals directly toanother radiation safety system with hard-wire cables
when the amount of the integrated beam charges isbeyond the prescribed threshold level. In addition, thesystem logic of radiation safety at KEKB, linac, and PF
have been replaced by new one from the old exclusive
logic for the simultaneous top-up operation.

PF-AR INJECTION
In this upgrade, the PF-AR injection is still based on
the old scheme which takes a several minutes for the linac
parameter switching. The full energy top-up injection of
PF-AR with 6.5 GeV is very difficult since the transportbeam energy at AR-BT is limited up to 3.1 GeV. In
addition, a large part of BT is shared by both of KEKB
and PF-AR as shown in Fig. 14. The construction of a
new dedicated AR-BT line is not feasible because of atight tunnel space. In the next coming SuperKEKB, thebeam lifetime will be about 10 minutes. For this reason,even PF-AR injection of 15 minutes twice daily willcause a serious problem for the stable SuperKEKB
operation. In the SuperKEKB, the beam energy ofpositron (electron) will be changed from 3.5 GeV (8 GeV)
to 4 GeV (7 GeV). We are planning the simultaneous
injection of four rings including PF-AR. In this plan, thepositron beam for KEKB LER injection will be also used
for the PF-AR injection. The new switching pulsed bend
will be installed at the end of common BT. In the
dedicated BT for PF-AR, all quadrupole magnets andvacuum chambers will be remodelled for increasing
magnetic field. The detailed design will be reported
elsewhere in the near future.

[mm]
Y
[mm]
Charge[nC]
e+ target

Figure 13: Machine study result of the new positrontarget. The horizontal (upper), vertical (middle) beam
orbit and beam charge (bottom) are shown along thelinac. The blue and orange dots mean the results oforiginal and new scheme, respectively.

Beam-Charge Interlock System
Toward the simultaneous top-up operation, a new PLCbased beam-charge interlock system has been also
developed for radiation safety [13]. This system restricts

Figure 14: Schematic drawing of BT for KEKB and
PF-AR.

SIMULTANEOUS TOP-UP OPERATION
Eventually, the simultaneous top-up operation of threedifferent rings was successful for daily operation in April
2009. Figures 14 and 15 show the stored beam current of
KEKB and PF during simultaneous top-up operation,
respectively. The stored beam current variation of KEKB

and PF are about 0.05% and 0.01%, respectively. These
results are far superior to the original operation
performance of around 50% drop in stored beam current,
and significantly improve the experimental performanceat both of KEKB and PF.

Figure 15: Stored beam current of HER (top), LER(middle), and luminosity (bottom) of KEKB in thesimultaneous top-up operation (24 hours).

Figure 16: Stored beam current of PF in thesimultaneous top-up operation (24 hours).

SUMMARY
We have succeeded the KEK injector upgrade aiming at
the simultaneous top-up injection of three different ringsin April 2009. Towards the simultaneous top-up, wedeveloped the many subsystems; new event based timing
system, pulsed bend and power supply, ceramic chamber,construction of the new PF-BT, radiation safety system
upgrade and so on. The achievement of this milestone
has been brought through the grate effort of all membersof linac, KEKB, and PF groups. In the simultaneous topup operation, the stored current variation of KEKB andPF are about 0.05% and 0.01%, respectively. Such highcurrent stability can bring the improvement ofexperimental efficiency to both of KEKB and PF.

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