UPGRADE OF SAFETY INTERLOCK SYSTEM OF e+/eí LINACFOR SuperKEKB PROJECT
A. Shirakawa#, H. Honma, Y. Ogawa, KEK, Tsukuba, Ibaraki, JapanOUTLINE OF INTERLOCK SYSTEMKEK e+/eí Linac is the injector for PF-Ring, PF-ARand KEKB (SuperKEKB) accelerators (see Fig. 1). After
KEKB experiment stopped in June 2010, the Linac has
been upgraded gradually for SuperKEKB. Damping Ring(DR) for beam emittance reduction is under constructionin the middle of the Linac [1, 2].
In our system personal and machine protection arecombined. It covers whole the 600m-long accelerator.
Interlock system for DR will be separated and handled byother system.
PF෥RING
Damping Ring

(under construction)

PFíAR
KEKB
SuperKEKB(on the upgrade)

0400m

Figure 1: KEK e+/eí Linac and related accelerators.

System Layout
Figure 2 shows a rough image of the interlock system
structure. We have Yokogawa PLC as a main CPU forinterlock logic program. All the signals from Linac
equipment are electrically connected to PLC via metal
cables. There is another PLC as a gateway. It is connectedwith main PLC via specified link and transfers
information to Linac control network. Status of thesystem is shown on a Windows PC at operator’s console.
Even in case of LAN trouble, the interlock system will___________________________________________#akihiro.shirakawa@kek.jp

Linac control network (LAN)one way

The upgrade of e+/eí Injector Linac is going on for
SuperKEKB project. The Linac interlock system forpersonal and machine protection has been upgraded
several times according to the project phase. One of thebiggest changes has been made when the Linac wasdivided into two areas: upstream and downstream linacs,
which allows us to work out the upgrade even during
injection to Photon Factories at lower energies using thedownstream linac. Most of the interlock system devices
were duplicated to start the 'half' accelerator operation.
Another remarkable update is to adopt an RF-Gun as a
new electron source. We programmed a specific strong
logic for the RF-Gun operation. These upgrades will bereported with the introduction of the whole interlock
system.

keep normal operation.
The system communicates with Ring accelerators andreceives a kind of ‘permission for operation’ from them.
Table 1 shows destinations and number of Linac interlock
signals. Numbers in the table are those handled at PLC
and some of signals spread out at intermediate controllers.

PLC Link

Abstract(SuperKEKB)
PFíAR
PFíRing“Gateway” PLC
PLCOperator’s
consoleMainController

DigitalI/O

Linac
Equipment

Figure 2: A rough view of Linac interlock system layout.
Table 1: Destination and Number of Linac Interlock
Signals at the Central CPU
Destination of Signal
Doors
Emergency switches
Beam trigger system
High power RF PS
eí Guns
Operation console
Charge monitors
Vacuum gate valves
Vacuum gauges
PF-ARPF-Ring
SuperKEKB + DR

#In/Out50 / 010 / 00 / 1070 / 21
7/ 520 / 32
9/ 035 / 0
13 / 05/ 6
4/ 5TBD

PersonalMachineProtection Protection
999999999999999

Conditions for Linac Operation
Since radiation level is high in the accelerator area
during its operation, basic concept for personal safety isto keep out from the area. In our system we have to carrywhat we call a “personal key” (see image in Fig. 3) when
we enter the area for machine maintenance. All thepersonal keys must be returned to resume the operation.
Figure 3 shows all the conditions for Linac operation.
Personal keys returned“READY” from PF-Ring & PF-AR
Doors closed
Emergency SWs OffA personal key

LINAC READYSW “READY” @ Console
Beam Not Over Charge

Operation Permitted

Area Monitor Safe

Figure 3: Conditions for Linac operation and an image of“Personal key” for room access control.

SectoríB

SectoríA

eRF Gune- Thermal Gun
Beam Switchyard

Sectorí1

SectoríC(e+ Target)

Sectorí2e- RF Gun

0100m

Sectorí3

Sectorí4

Beam Switchyard
Sectorí5
Sectorí6

Wall & Shield block

To PF-Ring, PF-AR,
KEKB (SuperKEKB)

Figure 4: An image of the division of e+/eí Linac. It is separated at the beginning of Sector-3 and ‘down half operation’is available.

DIVISION OF LINAC AND NEW
OPERATION MODE
For around 30 years since its foundation, the Linac had
one long straight room for accelerator. After KEKB datataking was stopped, we divided the room into two areas
so that we could proceed with upgrade and inject beam todownstream rings simultaneously. In advance of thedivision, the temporary eí gun was moved downward tothe place where eí beam energy of 3GeV at maximum
can be obtained at the end of Linac. In parallel, RF guns
were installed at the beginnings of ‘upstream’ (Sector-A)and ‘downstream’ (Sector-3) respectively and their tests
have been started [3]. Figure 4 shows an image of thedivision. The partition is built between Sectorí2 and í3.
The division is one of the steps toward SuperKEKB. It
will be entirely cleared before SuperKEKB is started.

Assembly of a Partition
One of the most difficult steps for upgrade wasassembling a partition to separate areas. Concrete shieldblocks with a thickness of 60cm were piled up alternately
in two rows, with intervals of 113cm for a passageway.
An iron wall with an interlocked door is attached to thefirst row (Figs. 5, 6a). The radiation level in front of theblocks during operation is low enough against KEK rulefor admitted area (< 20PSv/h) [4].
The assembly was done in 2010 and later the wall andblocks have been moved by 10m downward (Fig. 6b) in2012. The reasons for the first place were:• there occupied rather wide area as a beam switchyard• could have enough distance between shields andbeam bunching section (i.e., lower radiation level infront of the wall)
Inlet Duct

60 cm

Iron Wall

3T_GUN113 cmBuncher

9.2m
BeamRoom for Ventilation

Concrete Shields for Partition

Figure 5: A layout of the partition.

And after two years of operation, we had to move thewall to vacate the switchyard to start construction of beamlines to Damping Ring. As space is more restricted at newplace, a part of ventilation room had to be removed forabout 10m long. The specification of shields and relative
position of block rows are same as before.

a)b)

Figure 6: Partition at original position (a) and aftermovement (b).

Operation Modes after the Division of Linac
Now we have a thermal eí gun at Sector-3, and RF
guns at Sector-A and -3. After the division of Linac, we
can carry on development or maintenance work in
upstream side regardless of operation status of Sector-3
guns. Beam injection to PF-Ring and PF-AR is from thethermal gun. The condition of ‘Ready’ shown in Fig. 3
has been newly set for ‘Sector 3í6’ in addition toconventional ‘All Linac Ready’. To run RF gun in SectorA, ‘ALL Linac’ must be ready because there is no beam
dump at the end of Sector-2 and beam will go through tothe end.

Duplication of Personal Key Management
SystemA new set of personal key management system isassembled to form ‘Sector 3-6 Ready’ as described above.
Figure 7 shows an image of the system layout. As someof the components are from other system and adjusted tothis system, we could save cost and time.
A specified PLC is in the key box controller. It receives
information on Linac operation status from main PLC andmanages key I/O. We use magnetic ID card to pull out thekeys. A PC as an indicator is connected via anindependent LAN.
There are an electric lock on the partition door and adoor controller next to it. The “personal key” is used tounlock the door. Those specifications are identical withthe conventional system.

Digital I/O
PLC

PLC

Key Box (reused)

Safety Main Controller(software revised)

Key BoxController(new)Operation
Status Indicator(reused)LAN(1 : 1 )Digital I/OElectricLock(new)

ID CardReader(new)

Operator’s Console(remade)

DoorPC as a Key
Status Indicator(new)

Keybox & controller at main entrance of Linac

DoorController(reused)A wall and a door for division of Linac

Figure 7: Layout of the personal key management system newly set for down half part of Linac. Some of the parts
are secondhand articles.

INTERLOCK FOR RF GUN OPERATIONSUMMARY

Figure 8 shows a rough view of composition around RFgun. Since it is new to our system, we referred toconventional safety interlock for thermal gun when we
programmed the logic. In the thermal gun, we regard“High voltage on to gun electrodes” as “Beam on”. In
comparison to it, “RF source power on” should be thesame for RF guns. Therefore, the condition “Linac Ready”(shown in Fig. 3) is required to permit “High Power RF”(Fig. 9).
In addition to terms above, we placed “Laser shutter”
on laser beam path and gate valve on the beamline (Fig.8).
The gate valve is to guarantee safety during machine
maintenance. In order to supply laser to the gun, both
“Linac Ready” and “gate valve open” should hold. The
logic performs a kind of fail-safe.

KEK e+/eí Linac presently operates as the injector toPF-Ring, PF-AR and on the upgrade toward SuperKEKB.
One of the biggest changes in the safety interlock system
upgrade was the division of Linac into two areas. Apartition with iron wall and shield blocks has beenassembled and an access control system for down halfpart of Linac is newly composed.
After the division, development at upstream side andbeam injection to PF-Ring from downstream Linac areavailable simultaneously.
RF guns have been installed as a new electron source attwo sections. We programmed a specific strong logic for
the RF gun operation.

Laser BeamHigh Power RF Source

Laser Shuttere Beam

BeamGate Valve

RF GunFigure 8: A rough view of composition around RF gun.
Underlined components are related to safety interlock.
LINAC READY

Permit High Power RF

Beam Gate Valve Open

Open Laser Shutter

Laser Shutter Open Request

Figure 9: Conditions for beam operation from RF gun.

ACKNOWLEDGMENTAuthors would like to acknowledge M. Yoshida andT. Natsui for their collaboration to establish safety
interlock architecture for RF gun operation.

REFERENCES[1] T. Kamitani et al., “Injector Linac Upgrade forSuperKEKB,” LINAC2010, Tsukuba, September 2010,MOP011, p. 70 (2010).
[2] K. Furukawa et al., “High-intensity and Low-emittance
Upgrade of 7-GeV Injector Linac towards SuperKEKB”,
IPAC2013, Shanghai,2013,
TUPME010,
theseproceedings.
[3] M. Yoshida et al., “SuperKEKB Injector Upgrade for High
Charge and Low Emittance Electron Beam,” IPAC2012,
New Orleans, May 2012, TUPPD035, p. 1482 (2012).
[4] H. Honma, “Present Status of the KEK Electron/Positron Injector Linac (in Japanese),” 8th Annual
Meeting of Particle Accelerator Society of Japan, Tsukuba,
August 2011, TUPS033, p. 926 (2011).