PRESENT STATUS OF THE KEK INJECTOR UPGRADE FOR THE FAST
BEAM-MODE SWITCH
M. Satoh# for the IUC*Accelerator Laboratory, High Energy Accelerator Research Organization (KEK), 1-1 Oho, Tsukuba,
Ibaraki, 305-0801
Abstract
The KEK Linac provides the four different quality
beams for the four independent rings. The KEK Linac
upgrade aiming a fast beam-mode switch operation is
now in progress so that the KEKB continuous injection
and PF top-up injection can be carried out at the sametime. In this paper, we will report the present status of theKEK Linac upgrade in detail.

INTRODUCTION
The KEK Linac provides the beams of the different
modes sequentially with four storage rings (KEKB 3.5
GeV positron/ 8 GeV electron, Photon Factory (PF) 2.5
GeV electron and Advanced Ring for pulse X-rays (PFAR) 3 GeV electron).
For a typical operation, the PF and PF-AR need thebeam injection twice a day on scheduled time. On theother hand, the KEKB rings are operated by thecontinuous injection mode (CIM) for keeping the stored
current almost constant. In the CIM operation, the switch
time between the electron and positron modes takes abouta half minute so that all settings of magnet power supplies,
RF phases and timings should be changed according tothe electron and positron beam properties. In the nearfuture, the PF top-up operation will be started to enhance
the integrated photon flux. For these reasons, the linac
upgrade is strongly required for a fast beam-mode switch[1, 2, 3 and 4].
Figure 1 shows the schematic drawing of ultimate fast
beam-mode switch operation. In this operation scheme,
we will change only the minimum parameters of thetiming signals and Low-Level RF (LLRF) phases, and all
the rest of parameters like DC magnet settings are neverchanged even for the different beam-mode. In the final
stage of the linac upgrade, the beam mode can be changedin every 50 Hz of an arbitrary beam-mode pattern.
KEKB e- KEKB e+ PF

20 ms

PF-AR KEKB e- KEKB e+

Beam mode switch

Fig. 1: Schematic drawing of fast beam mode switch.

UPGRADE PLAN
OutlineThis project is a phased upgrade, and the phase-I has
been already completed in the summer of FY2005. The
detailed upgrade phases are shown in following subsections.

Phase-IIn the phase-I, the new PF-BT line has been constructed
for shortening the beam-mode switch time between theKEKB and PF modes. Here, the initialization proceduresof the energy compensation system (ECS) bends are
required since the original DC switch bend was placeddownstream of the ECS bends. In order to bypass theECS, a new DC switch bend has been installed byremoving four accelerating structures, and a new PF-BT
line of 60-m-long has been constructed [5].
After the phase-I, the beam-mode switch between theKEKB and PF modes does not need to change the ECSparameters. The round trip mode switch time including
PF injection was reduced by half from 5.5 min. to 2.5 min.
In addition, the beam injection efficiency has been
increased.

Phase-IIThe phase-II aims to perform the fast beam-mode
switch between the KEKB electron and PF modes up to50 Hz. For the phase-II and later, we will use the new
operation scheme called “Multi-Energy Linac” [6 and 7].
In this scheme, the common magnet settings are used forthe different beam modes. The adjustment of the beamenergy is performed by a fast control of LLRF phase.
Though PF ring injection requires the 2.5 GeV electron,
the beam is accelerated up to about 5 GeV in the multienergy scheme. After then, the beam energy is adjusted to
2.5 GeV by using the deceleration RF phases. Thismethod is effective for enlarging the common optics
region. The result of a preliminary machine study showsthat this scheme is feasible for a realistic beam operation.
In this autumn, the more detailed machine study will becarried out to develop the daily operation parameters.

Phase-III
In the phase-III, the fast beam-mode switch will include
the KEKB positron mode. In the current operation, the___________________________________________#masanori.satoh@kek.jp* Injector Upgrade Committee: Cross-functional team for the injector upgrade from PF/ KEKB and Linac members

positron production target is controlled by a mechanicalmovement. For the fast beam-mode switch between theelectron and positron modes, the positron target with ahole will be used. In this scheme, the fast beam-mode
switch will be performed by a fast control of the electron
beam orbit at upstream of the positron target.
The tungsten crystalline target with a hole has been
installed as shown in Fig. 2. A centre of a hole is placed
4.5 mm apart from that of a crystalline tungsten target.
The diameter of a hole is about 5 mm. The electron beam
goes through the inside of a hole for the electron mode,
whereas the electron beam hits the centre of target for thepositron mode.
In the machine study, it was measured that almost
100% of the electron beam can traverse the inside a target
hole in comparison with a normal operation (targetremoved). We convinced that this scheme is applicable tothe practical beam operation. For a fast control of thebeam orbit upstream target, the pulsed steering magnets
have been installed in the winter of FY2007.
W crystalline target (Φ4.5 mm)

25 Hz, and its output current has the half-sinusoidal shapeof 200 µs. The both at long and short term stability ofpower supply output current was satisfied less than 0.1%.
The 1200-mm-long ceramic chamber has been also
installed, and its cross-section is a race track-shaped. To
avoid the heating, the inner wall of ceramic chamber wascoated with 1-µm-thick Ti.
In the first week of February 2007, the PF top-up test
operation has been successfully performed during singlebunch user operation. Figurer 4 shows the stored current
stability of the PF ring. In this machine study, we canTable 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 tuenPower 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)

4.5 mmΗole (Φ5 mm) for e- mode

Fig. 2: Photograph of tungsten crystalline positron
production target with a hole.

PF-AR injection
The full energy injection of PF-AR is very difficult
since the current beam energy at AR-BT is limited up to3.1 GeV. One solution is to use the 3.5 GeV positron
beam of KEKB positron mode for the PF-AR injection,
though this scheme involves the installation of a pulsed
bend and the improvement of two power supplies at theAR-BT line. In addition, all quadrupole magnets andvacuum chambers should be remodelled for increasing
magnetic field. The detailed design study is now inprogress, and its result will be reported elsewhere.

Fig. 3: Photograph of pulsed bend.

PULSED BEND SYSTEM
For the fast beam-mode switch, the PF beam should beselectively kicked out toward the PF-BT by using thepulsed bend. The DC switch bend installed in the phase-I
was replaced by the new pulsed bend system in the last
winter maintenance. Table 1 shows the main parametersof the pulsed bend system. The photograph of pulsed
bend is shown in Fig. 3.
Though the 2.5 GeV electron are used for the PFinjection, the pulsed bend was designed for the beam
operation up to 3 GeV. The maximum beam repetition isBeam current [mA]

6040
51.10

5 min.

51.05

20

51.00
50.95

0.1 mA
001/29/2008 23:54:59

50.90
01/30/2008 11:51:5901/30/2008 23:51:19

Date Time [MM/dd/yyyy HH:mm:ss]

Fig. 4: Stability of stored beam current at PF ring forsingle-bunch Top-up injection study.

achieve the stability of 10-3 by using a newly installed slit
at the PF-BT. The pulsed bend has worked well during
the one week continuous operation without any problem.

upgrade will be very effective to increase the beam
operation efficiency of KEK Linac. Eventually, theoperational availability of each ring will be also greatly
enhanced.

OTHER NEW SUBSYSTEMS
Beam-charge interlock system
Toward the fast beam-mode switch operation, a new
PLC-based beam-charge interlock system was developed
for radiation safety [8]. This system restricts a regulated
amount of integrated beam charges traversing through atseveral locations for machine protection, and it also
monitors the amount of integrated beam charges delivered
to the four different storage rings at the linac beamswitchyard.
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. This system has
been already used for a daily operation.

Timing system
In the present timing system, about 150 timing delay
modules based on VME-bus and CAMAC (TD4V/ TD4)
are used for controlling the timing signals distributed tothe many different types of local controllers. The timing
system upgrade is indispensable since it is very difficult
for the current system to realize a fast timing control.
The event generator and receiver (EVG/EVR) system
based on VME64x-bus was adopted as a new timing
system [9, 10, 11 and 12]. In the new system, one EVG
and eleven EVRs are connected via optical fibre. The
event information (beam-mode), RF clock (114 MHz),
timestamp and data buffer can be quickly transferred from
EVG to EVR. In addition, the number of used module forthe timing system can be drastically reduced by using theEVG/EVR system. This can gratefully increase thereliability of timing system and beam operation. The
operation software based on EPICS system has been
already developed. One EVR and nine EVRs are alreadyutilized for the beam operation. In the near future, theoverall system test will be carried out for the practicaloperation after the two rest EVRs will be installed.

SUMMARY AND FUTURE PLAN
The KEK injector upgrade aiming the fast beam-mode
switch is in progress so that the KEKB CIM and PF topup injection can be simultaneously performed. For thisupgrade, the pulsed steering and bend system have been
already installed. The almost part of new timing system
works for a beam commissioning. In addition, many
software development and update are going on. This

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