Vacuum

Progress and TroublesofUpgrade WorksThe 20th KEKB Accelerator Review Committee
February 23, 2015
Kyo Shibata(on behalf of KEKB Vacuum Group)
Inter‐University Research Institute Corporation High Energy Accelerator Research Organization (KEK)
大学共同利用機関法人 高エネルギー加速器研究機構 (KEK)Contents
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Introduction
Pre‐installation works
Installation
Collimator
ControlDamping Ring
Remained works
Summary– Original slides of Installation and trouble reports in Pre‐installation works were
provided by Suetsugu‐san.
– Original slides of Collimator and Control were provided by Ishibashi‐san.
– Vacuum system around IP was presented by Kanazawa‐san (IR Overview).
2015/2/23

The 20th KEKB Accelerator Review Committee2Introduction•

Outline of upgrade of MR (except IR and
Damping Ring)

LER– LER : Most of beam pipes and components are
replaced with new ones.
• Replacement rate : 93 % (2610 m / 2800 m)• New 2 horizontal collimators (for Phase‐I operation)• Countermeasures against electron cloud (clearing
electrode, groove surface, TiN coating and solenoid field.)– HER : Most of beam pipes and components arereused.
• Only local chromaticity correction, wiggler sections andetc. are replaced with new ones.
• Replacement rate : 18 % (500 m/2800 m)

HER– Design of control and monitoring system follows
that of the KEKB.
• Most of control devices are reused.

•

Pre‐installation and installation works,
fabrication of collimators, test of control systemwere done in this past year.

•

DR : Fabrication and TiN coating of beam pipes
are now in progress.
2015/2/23

The 20th KEKB Accelerator Review Committee3Pre‐installation works 1•

Pre‐installation works

Progress in this past year
– Coating :••Main Ring : 179 beam pipes
Damping Ring : 38 beam pipes

Bringing beam pipes to KEKB
Oho Lab. from storage area

– Baking :•••Main Ring : 354 beam pipes
Damping ring : 0 (as originally planned)

Pre‐installation works for all beam pipes
required for Phase‐I except IP pipe havebeen finished successfully.
– IP pipe was damaged with crack on welding linein the process of installation into verticalcoating equipment.

•

SEY during the production and after long
air venting was not measured. (pointed out

Visual check on the beam pipe
LER beam pipe
without electrodeTiN Coating

2015/2/23

HER beam pipe
LER beam pipewith electrode

Assembling(NEG pump & BPM electrode)in last KEKB Review)– Still unclear if the low SEY is conserved for along time.
– No air leak during the coating process.
– Planning long‐term SEY measurement .

DR beam pipe

KEKB Oho Lab.

BakingReturning the beam pipes to storage area

The 20th KEKB Accelerator Review Committee

4Pre‐installation works 2
Hot‐air heating method was
adopted. (150, 26 h)

Bent pipes were coated byhorizontal coating equipment.

KEKB Oho Lab.

Coating was done by DC magnetron
sputtering of Ti in Ar and N2.

Baking equipment

Visual check and assembling weredone in Oho clean room.

2015/2/23

Straight pipes were coated byvirtical coating equipment.

The 20th KEKB Accelerator Review Committee

5Pre‐installation works 3• Coating of bent pipes without antechambers by horizontal facility– To coat bent pipe by horizontal facility, Ti cathode position is fixed by ceramics supports.
– Conventional ceramics support is available only for beam pipes with antechambers.
– About 10 bent pipes without antechambers were coated with new ceramics support.

Ceramics support set in antechamber(Conventional type)

Ceramics support on sidewall of beam pipe(new type)Ti cathode

Ceramics cover for
insulation protection

Ceramics
support

WheelsMagnetron discharge sputtering

2015/2/23

The 20th KEKB Accelerator Review Committee

6Pre‐installation works 4•

Coating of Damping Ring beam pipes by horizontal facility– Flat cathode shown in last review did not work.
• Discharge didn’t occur in the center of beam pipe.

– New cathode pipe worked well, and 38 beam pipes were coated so far.
– More 36 beam pipes will be coated by the end of this fiscal year (3/31).
New ceramics supports

Magnetron discharge sputtering

New cathode pipeand ceramics support

Didn’t work

Ti cathode (pipe)

Ceramics
supportFlat cathode2015/2/23

The 20th KEKB Accelerator Review Committee

7Pre‐installation works 5
Total output of pre‐installation works– Large‐scale works by 10 workers was continued until the end of 2014. (by 3‐4 workers this year.)– All planned works for MR finished this month.
– Work pace decreased compared to the past fiscal years because of a variety and delay in deliveryof beam pipes.
TiN coating (not counting Damping ring)

BakingFinish!!

Finish!!

numbernumber•354 beam pipes(this fiscal year)

date
2015/2/23

179 beam pipes(this fiscal year)

date
The 20th KEKB Accelerator Review Committee8Pre‐installation works 6•

Ultimate pressure after baking– “Less than 110‐7 Pa” is set as our criterion for check. (If not, beam pipe is re‐baked.)– Almost all beam pipes meet our criterion for check.
• Ultimate pressures higher than 510‐8 Pa have been measured for many beam pipes. (pointed out in last KEKB
Review.)• No measurement of residual gas• A variety of beam pipes: long (6 m) and short (150 mm), w/wo NEG, Cu and Al
Distribution of ultimate pressures

Criterion for check
Including data derived
from all beam pipes.

<1

12

23

34

45

56

67

78

89

910

10 <

[x10‐8 Pa]
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9Pre‐installation works 7• Trouble 1 : High ultimate pressure (> 110‐7 Pa)
In some beam pipes, the ultimate pressure after baking were higher than 110‐7 Pa,
which is our criterion of check.
– Case 1 : Air leak from connection flange 1 (simple case)• Cause : Decrease in fastening power due to baking• Cure : Refastening flanges. Replacement of gasket and re‐baking.

– Case 2 : Air leak from connection flange 2• Cause : Wrong choice of gasket (Cu gasket on Al flange(CF203))– A few special Al beam pipes have Al CF203 flanges, though most of them have SUS
CF203 flanges.
– At worst knife‐edges were damaged, and we gave up re‐baking them to avoid further
damage to flanges. (two beam pipes)– Case 3 : Leak at ceramic brazing of sheath heaters for NEG activation.
• Next slide– Case 4 : Large gas desorption from beam pipe or NEG?
• Cure : Re‐baking. (If it fails again, replacement of NEG strips and heaters.)• In most cases the ultimate pressure reduced on the order of 10‐8 Pa.
2015/2/23

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10Pre‐installation works 8•

Trouble 2 : Leak at ceramic brazing of sheath heaters for NEG activation.
– Cracks at the brazing between ceramics and stainless steel sleeve was found.
– Gas desorption from the cracks leaded to high ultimate pressure even after NEG activation.
– Low insulation resistance was also observed.

•

Cause :– Fastening of ceramic block for insulation was too strong, and the excess stress (moment) wasapplied to the brazing part, if the ceramic was brazed with a slight angle.

•

Cures :– Insert a thin spacer between ceramic blocks to avoid the excess stress on the brazing part.
– Cracked heaters were re‐fabricated.

Air leak

Excess stress
NEG with heater installed into
beam pipe
2015/2/23

Feedthrough of heater withinsulation ceramic blockThe 20th KEKB Accelerator Review Committee

Leaked feedthrough of heater11Pre‐installation works 9•

Trouble 3 : Crack at the welding line of X‐shaped IP pipe.

•– In order to install the beam pipe into the vertical coating equipment, one endof the beam pipe was lifted up by crane while other was fixed to hinge
assembly.
– Crack occurred during crane operation.
Note:
This is not
Stress
Cause :IP pipe. This
– Concentration of stress (moment) at the center ofbeam pipe where the cross‐section is smallest.
– Cracked part has relatively weak structure.

•

picture isshown asreference.

Crack

Lifting

Cures :
– Re‐welding in the
manufacturer.
– Improvement of structural
strength– It will be repaired next fiscal
year.

Fixed to hinge assembly
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12Pre‐installation works 10•

Other Troubles:

Leak– Air leaks of welding line of beam pipe occurred during thebaking and coating. (2 beam pipes)••

Cause : Bad welding ?
Cure : Re‐welding at the manufacturers.

– Lots of Burrs in the holes for BPM feedthrough. (risk ofdischarge)••

Cause : Insufficient quality control in the manufacturer
Cure : Check all holes by KEK staff of beam monitor group
Deburring in KEK site by the manufacturer or KEK staff (in most case)Burr– Bad insertion of helicoil for the tapped hole to fix the BPM
electrode.
••

Cause : Bad quality control at the manufacturer
Cure : Re‐installation of helicoil. (if failed, M4 tap was changed to M5 tap)

Hole for BPM electrode(inside view)– Defects or scratches on the standard surface of BPM block••

Cause : Bad quality control at the manufacturer
Cure : Check all holes by KEK staff of beam monitor group
Polishing the defects to remove “projection”
Deburring– Shortage of BPM electrode and Helicoflex gasket••

Cause : Miscalculation? Excess consuming?
Cure : Reorder. (Already delivered in last December and January)
Rescheduling pre‐installation works– And so on.
2015/2/23

Scratches and defects
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Installation 1• Installation of components into the tunnel– 97% of beam pipes required for Phase‐1 has been installed already.
– Most of remained are those for HER around Tsukuba straight section andthe beam injection section at Fuji straight section.
Main Ring [2015.02.19]

2015/2/23

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Installation 2• Installation into arc and wiggler sections were finished.
Beam pipe for wiggler

Beam pipe for quad

2015/2/23

Gate valve at arc

Beam pipe for bend

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Installation 3• Installation of special beam pipes is almost finished.

Ti window

LER beam abort section
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Installation 4• Installation of beam pipes for Tsukuba section is on going.

Straight section
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Installation 5• Installation of beam pipes for Tsukuba section is on going.

IR section
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Installation 6• Installation of bellows chambers follows that of beam pipes.
Al bellows chamber

Cu bellows chamber

2015/2/23

Cu-Al bellows chamber for GV

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Installation 7• Evacuation and NEG activation– NEG activation has started from wiggler section and arc section in eachregion between gate valves.
• In approximately 21% of both of the rings, NEG activations have been finished.
• The average pressures less than 110‐7 Pa were obtained after the NEG activation
without beam pipe baking in‐situ. (Ion pumps are baked.)Main Ring [2015.02.19]

2015/2/23

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Installation 8•

Trouble 1 : High rate of air leak at connection flanges (reported in last KEKB Review)– In the initial stage of bellows connection in the tunnel, the rate of air leak at the connection was
higher (10%) than that experienced in the pre‐installation work (<5%)•

Possible causes:– Scratches or traces of machining (small steps and rolling) on
the seal surface of bellows chambers– Difficulty in alignment of flanges (bellows chamber and beampipe)

scratch on seal surface• Bellows chamber is heavy.
• Some beam pipes are already fixed to magnets– Oxide layer of aluminum gaskets?

•

Cures:– Polish of the sealing surfaces with abrasive cleaning pads
(Scotch‐Brite)– Polishing of gaskets (also effective sometimes)– The rate of leak decreased to less than 5% finally.
– Tool to make the alignment easy (in preparation)
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The 20th KEKB Accelerator Review Committee

Trace of machining
transcribed on used gasket
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Installation 8• Trouble 2 : Cracks on the welding line (Case 1)– Welding line of BPM block of aluminum beam pipe cracked just after starting theevacuation in the tunnel. (3 beam pipes)– BPM block was rigidly fixed to Q‐mag. via support.
– Crack occurred on upper welding lines at Q‐mag. side, where
the longer beam pipe is welded.
– No problem was reported in the pre‐installation work.
Crack

BPM blockCrack

BPM block

Shorter pipe
2015/2/23

Q-mag.

Longer pipe
Top view
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Installation 9• Possible cause 1 : High moment due to theweight of bellows chamber at end.

Connection of bellows– It is suspected that the bellows chambers at ends was
not rigidly fixed to the support.
– There is also a possibility that the flange was alignedwith some vertical excess‐force to connect thebellows.

• Simulation results:

210 N
Atmosphericpressure

BPM block (fixed)– The stress at top and bottom side further
increase by the atmospheric pressure dueto the antechamber cross section.
– The stress at upper welding line is doubled
with atmospheric pressure.
– If the welding thickness is insufficient, suchas less than 2 mm, the welding is likely tobe cracked.

No atmospheric pressure
Crack point

210 N

Atmospheric pressure

210 N
2015/2/23

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Installation 10• Possible cause 2 : Thin welding thickness

Penetration depth

Weight of bellows +No atmospheric pressure

safe

Welding thickness

Weight of bellows +Atmospheric pressure

danger– With decreasing the welding thickness, the degree ofcracking risk increases as shown in the simulation– The investigation using X‐ray and cut samples
revealed that the penetration depth is 1.52 mm,
whereas the design value is 2.53 mm.
– We checked the height of excess metal of most of
beam pipes with BPM blocks (1254 welding lines intotal).
Excess metal

Simulation of stress

Welding thickness t [mm]• Measurement results:– The height of excess metal are mostly in the rangeof 0.52 mm.
– If the height is less than 0.5 mm, the welding
thickness can be less than 2mm.
– It should be safe to re‐weld these beam pipes.
2015/2/23

The 20th KEKB Accelerator Review Committee(Average of 3 points
near center)

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Installation 11• Cures– Surely fix the bellows chambers to the supports before evacuation.
– Avoid forced alignment of flanges.
– Re‐welding of the welding lines with a height of excess metal less than 0.5mm.
– Re‐welding of the welding line with some defects, that were found in theinvestigation of excess metal.

• No crack at this position has been observed since then.
– However, great cares should be paid during the final alignment of magnets,
where the beam pipes can move with magnets.

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Installation 12• Trouble 3 : Cracks on the welding line (Case 2)– Crack was found on the welding line of flange in thespecial beam pipes for the rotating sextupole magnet,
with a taper section from antechamber to circular crosssection. (2 beam pipes)– No moment by the bellows. Not top or bottom. Not in
the evacuation timing. (i.e., different case from Case‐1)– In 2013 the similar crack at the same positon (butdifferent beam pipe) was found in Oho Lab. Some ofthem were re‐welded. (But this trouble occurred.)– There are 8 beam pipes with the same structure.

Beam pipe for rotating
sextupole magnet• Cause:– Unclear (wrong welding condition? Structural stress?)

Crack• Cure:– Re‐welding with other new flange.
– We have to keep watching.
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Crack

26

Installation 13•

Trouble 4 : Interference with other components– Interferences between
•
•
•
•

•

Cause :––––•

Beam pipes and magnet coil, shims and various monitor sensor
Cooling pipes and magnet coils
Beam pipe support and magnet, power cables or support
And so on.

Sometimes cut the beam pipe or cooling pipe
Sometimes move components.
Sometimes, re‐disassembling of Q‐mag. were required.
Thank a lot for the cooperation of other group.

Other troubles :–Air leak at welding line of gate valve (2 gate valves)••–

Air leak in bellows chamber (2 bellows chambers)••–

Cause :chemical cleaning solvent was remained at the welding
line during the assembling process.
Cure :Re‐welding at the manufacturer
Change of structure
Cause : unclear. Bad HIP condition?
Cure : Replaced by a reserved one. Asking the investigation andre‐manufacturing to the manufacture

And so on.
2015/2/23

The 20th KEKB Accelerator Review Committee27Collimator 1• Plan and Location– Phase‐I : 2 new models (horizontal type) for LER. (Conventional collimators arereused in HER.)– Phase‐II : More 11 new models for LER, and 6 for HER. (not fixed yet for HER)
Phase‐I

HER (not fixed yet for HER)
D01: H1, H2, H3, H4, H5
V1
D01

D03

D12
HER
D12: H1, H2, H3, H4
V1, V2, V3, V4
D11

D10

D09
HER
D09: H1, H2, H3, H4
V1, V2, V3, V4
2015/2/23

D08

D01

D02

D07

Phase‐II

LER
D02: H1, H2, H3, H4
V1
LER
D02
D03: H1, H2
V1, V2
D03

New

D12

D04

HER
D12: H1, H2, H3, H4
D11 V1, V2, V3, V4

D04

D05

D10

D05

D09

D06

New
LER
D06: H3, H4

HER
D09: H1, H2, H3, H4
V1, V2, V3, V4

The 20th KEKB Accelerator Review Committee

D06
D08

D07 New
LER
D06: H1, H2, H3, H428

Collimator 2•

New collimators for Phase‐I– Production of two horizontal collimators (D06H3, H4) was finished.
•

They will be installed on early next fiscal year.

– Sliver plated INCONEL for the RF fingers and rhodium
plated stainless steel for the contact surface were Tungsten
adopted. (pointed out in last KEKB Review)on tip– Position of jaws is measured directly by displacement
Taperedsensor. (pointed out in last KEKB Review)
beam pipe– Longitudinal length of the tip is 10 mm (>2 RL).
– HOM absorber in the cavity is not considered yet.

Ramp
12
CoolingchannelBellows(pointed out in last KEKB Review)••

R&D of HOM absorber chamber is now in progress.
Same technique may be applied to the collimator.

2015/2/23

The 20th KEKB Accelerator Review Committee29Collimator 3• Loss and kick factor vs d (distance between beam axis and head)– Impedances were estimated with GdfidL (bunch length z= 6 mm)– Loss and kick factors of SuperKEKB type are smaller than those of KEKB type.
– These results were used to estimate the threshold of the Transverse Mode
Coupling Instability (TMCI)

2015/2/23

The 20th KEKB Accelerator Review Committee30Collimator 4• TMCI in LER (pointed out in last KEKB Review)– We estimated the threshold of the Transverse Mode Coupling Instability using
actual β value at location of each collimator with σz = 6 mm.
– D02V1 is the main impedance source because it would be used with the narrow
aperture (d = ±2 mm).
– The threshold is about 1.71 mA/bunch (Design value: 1.44 mA/bunch) in thelatest collimator design.

TMC threshold (mA/bunch)
All Closed

Actual apertures

Horizontal

1.41

13.15

Vertical

1.32

1.71

Bunch current (design)>

1.44 mA/bunch

Collimator Aperture List (mm)C1 : constant 8
fs : synchrotron frequency
E : beam energy : beta functionk : kick factor

2015/2/23

D06H1‐16.0/+17.0

D03H1‐21.0/+20.0

D02H1‐10.6/+12.0

D06H2‐16.0/+16.0

D03H2‐18.0/+20.0

D02H2‐16.0/+20.0

D06H3‐16.0/+15.0

D03V1‐9.0/+9.0

D02H3‐18.0/+21.0

D06H4‐13.0/+13.0

D03V2‐9.0/+9.0

D02H4‐13.0/+9.0

D02V1‐2.0/+2.0

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Control 1•

Design of control and monitoring system follows that of KEKB.
– Most of control devices that has been used since TRISTAN or KEKB are reused.
• Priority was given to renewal of antiquated devices. (Budgetary restrictions)• CMAC to cRIO, VME to F3RP61, Renewal of Ion pump controller (gradually), and so on.

– A set of a CCG and an ion pump is installed at intervals of 10 m.
– At least one vacuum switch is installed in a section divided by two gate valves.

•Interlocking operations are performed by PLC (pointed out in last KEKB Review)– CCG, Ion pump, NEG activation• HV to CCGs can be applied when the vacuum switch closes in the section.
• Each CCG within intervals of 30 m is turned on, and this refers to the steady state for the vacuum in thesection.
• Steady state allows supplying power to ion pumps and NEG activation. (Cancelable)• Magnet current status is also checked for NEG activation to avoid the strip type NEG in the magnet
oscillating with AC for the activation.

– Gate valve• The sequence CPU in PLC checks the steady statuses of two vacuum sections divided with gate valves.
• Gate valves can be opened when the statuses are steady .

– Beam abort• Temperature sensors, flow meters, gate valves and beam stoppers can activate the beam abort trigger
directly.
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Control 2• Integrative tests for the control system was done successfully. (NEG
activation)– NEG activation was performed by following procedure:
1. TMPs are started up, which areinstalled on angle valves.
2. High voltage is applied to CCGs andIon pumps in the section
3. Ion pumps are baked using heaters
for 1‐2 days
4. NEG pumps are activated with apattern operation for 0.5‐2 days
5. Baking heaters of the ion pumps areturned off after 1‐2 hours of thestart of NEG activation.
6. Angle valves are closed just after theactivation.

2015/2/23

History of CCG pressures during and after NEG activation

The 20th KEKB Accelerator Review Committee

33Damping Ring 1•

Fabrication of beam pipes has almost finished.
– Remained pipes : Injection and extraction sections, beam pipe for SR monitor.
– They will be fabricated next fiscal year.

•

Pre‐installation works of beam pipes for arc sections are now in progress.
– 38 beam pipes for arc sections were coated so far.
– More 36 beam pipes will be coated by the end of this fiscal year (3/31).
– Baking of beam pipes will be done next fiscal year.

•

Installation will start next fiscal year
at the earliest.

Injection section(Not yet)– Delivery of NEG pumps, gate valves andbeam stopper were completed.
– Ion pumps and power supplies to themwill be purchased next fiscal year.

•

Vacuum control system will bealmost same as that of MR.
– The number of control data item ismuch smaller than that of MR.
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RF section

Fabrication
finished.

SR monitor(Not yet)extraction section(Not yet)34

Damping Ring 2• Aluminum Beam pipes for arc sections– Antechambers on both sides of beam channel– Grooved structures at top and bottom of the beam
channel (countermeasure against electron cloud)– Grooved structures at side walls of antechambers for
antireflection of SR– Water cooling channel on both sides– Designed to fit narrow space– Having RF shielded bellows, BPM block and Pumping port

Type ITwo beam pipes in one cell

Type II

Type II

2015/2/23

Type IThe 20th KEKB Accelerator Review Committee

35Damping Ring 3• Rough estimation of average pressure in arc sections– Required averaged pressure is lower than 110‐5 Pa to obtain enough beam life time.
– Beam pipes have three pumping ports in one cell with a length of about 2 m. (d  0.7 m)– Two of them are for the NEG pumps and one is for ion pump.
• Average effective pumping speed will be 0.037 (just after activation)  0.025 m3s‐1– Photon stimulated desorption by SR is major dynamic gas load during beam operation.
• After the sufficient scrubbing,  will drop to below less than 110‐4 molec./photon.

– 110‐5 Pa is achievable goal with sufficient scrubbing.

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Remained works• Main Ring (for Phase‐I operation)– Installation of components for Tsukuba local chromaticity region (HER) andFuji beam injection/abort region (HER). Installation of collimators.
• Installation will be finished by September.

– Cabling (power supply, monitoring), piping of cooling water line at straightsections and piping of compressed air line.
– Adjustment of flow rate of cooling water in whole ring.
– Final alignment of beam pipes and bellows chambers.
– NEG activation (Final check).
– Final check of operation software.
– All will be finished by December.

• For Phase‐II operation– Fabrication of remained collimators.
– Fabrication of remained beam pipes for Damping Ring.
– Purchase order of ion pumps, power supply, etc. for Damping Ring.
– Pre‐installation and installation works of Damping Ring.
– And so on

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Summary•

Preparation for Phase‐I operation is steadily in progress though some troubles
occurred.
– Pre‐installation works : 100% except for IP pipe
– Installation : 97%
– Evacuation and NEG activations : 21%
– Collimator : already completed and waiting for installation••

All remained works for Phase‐I will be finished by December.
We have begun works for Phase‐II– Damping ring, Collimators, etc.

•

We welcome any comments or suggestions especially on– Aluminum welding.
•

Crack trouble seems to be a frequent occurrence.

– What we should pay attentions to.
••

At the start of evacuation.
During Phase‐I operation (vacuum scrubbing).

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Fin.
Thank you for your attentions.

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Back‐up

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New beam pipesNew beam pipes have antechambers.
Realize low beam impedance by putting SR masks andpump ports in antechambers
 Effective to reduce photo electron effect LER arcs: Aluminum alloy (A6063)
 Formed by extrusion method
 HER and Wigglers: OFC (C1011)
 Formed by cold-drawing methodBeam pipes for wigglers

Beam pipes forbending magnets

Beam pipes forquad magnets
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Connection flangeStep-less flange: MO-type flanges
 Little step inside and low beam impedance Adaptable to various types of cross sections
 Various types of copper (C18200) and aluminum-alloy(A2219) flanges were developed.
Various types of MO flange

Cu Gasket for Cu flange

2015/2/23

Test flange (SUS316)

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Connection flange

Result up to now.
Type

Material

Cross section

Numbersf90220f90220f90220H24
f80220
f5019012250
f90
f90
f80

Al
Cu
Al
Cu
Cu
Al
Al
Cu, SUSCu

Antechamber
Antechamber
Antechamber
Antechamber
Antechamber
Racetrack
Circular
Circular
Circular

3288
762
24
20
12
8
24
52
8

Approximately 4140 flanges out of 4890
have been used (connections are ~2070).
 The rate of air leakage at the first
fastening is less than 5 % even in thering.


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Pumps

Main pump: Three layers of NEG strips ST707 (arc)Installed into an antechamber: provide effective distributed
pumping system
 Activation by micro-heaters (sheath heaters) inserted
between strips
 Screens between pump and beam
 Average pumping speed of 0.14 m3s-1m-1
for CO

3 layer NEG strips

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Pumps

Auxiliary pump: Ion pumps
 Noble pump with a pumping speed of ~ 0.4 m3s-1. Every ~10 m.



Roughing pump: Turbo-molecular pump+Scroll pump
Photon line density at arc

Effective pumping
speed and pressure(=110-6 mole. pho.-1)
Eff. pumping speed

0.11 m3s-1m-1

Pressure
2.310-7 Pa
in average
Bending magnets
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Countermeasures againstelectron cloud effect• Electron cloud instability can be a serious problem for LER (e+)
 The threshold of electron density to excite the head‐tail instability is1.6×1011 e‐/m3.
 By using these countermeasures, the average electron density on the order of1010 e‐/m3 will be obtained.
 Various mitigation techniques were evaluated at KEKB LER.
by courtesy of Y. Suetsugu
Sections

L [m]

L [ %]Countermeasure

Material

Total

3016

100

Drift space (arc)1629 m54

Antechamber + TiN coating + Solenoid

Al (arc)

Steering mag.

316 m

10

Antechamber + TiN coating + SolenoidAl

Bending mag.

519 m

17

Antechamber +TiN coating + Grooved surface

Al

Wiggler mag.

154 m

5

Antechamber + Clearing ElectrodeCu

Q & SX mag.

254 m

9

Antechamber + TiN coating

Al (arc)

RF section

124 m

4

(TiN coating +) SolenoidCu

IR section

20 m

0.7

(TiN coating +) Solenoid

Cu, Al2015/2/23

The 20th KEKB Accelerator Review Committee46

Electron cloud mitigation 1
Antechamber•

Antechamber is effective to mitigation of photoelectrons which can be source of theelectron cloud.
 Expected reduction efficiency of electron cloud in SuperKEKB LER is 1/5.

•

Almost all new beam pipes of LER has antechambers.
1/1284/3.07 (1284) Test result in KEKB LER
6~8 ns spacing
R = 4７ mm (Circular)
Vr = 30 V
Ph = 81015 Ph/s/m/ms

Circular chamber~1/100~1/5

Withantechamber

Rough surface at the side wall (Ra 20) reduces thephoton reflection.
by courtesy of Y. Suetsugu

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Electron cloud mitigation 2
Solenoid field•

It was confirmed that the solenoid field at drift section (50 G) is effective to bothphotoelectrons and secondary electrons in KEKB LER.
 Expected reduction efficiency of electron could in SuperKEKB LER is 1/50.

Solenoid filed will be used as widely as possible in SuperKEKB LER.
 It can not be available in magnets other than steering magnets because of no room for coil winding.
1013
Near Beam Electron Cloud Density [m -3]•

Test result in KEKB LER

by courtesy of
K. Kanazawa

1012

Solenoid coil

B=0G

1011

<1/1000

1010
109
108

B = 50 G

107
106

0

0.2

0.4

0.6

0.8

8/100/2 (800)
4 ns spacing
R = 47 mm (Circular)
1

1.2

LER Bunch Current [mA]

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The 20th KEKB Accelerator Review Committee48Electron cloud mitigation 3
TiN coating•

TiN coating is effective to reduction of the secondary electrons.
 Expected reduction efficiency of electron cloud in SuperKEKB LER is 3/5.

•

Almost all new beam pipes without clearing electrode are coated with TiN.
Test result in KEKB LER

1010

D(D7)[4,200,3]Cu
D(D7)[4,200,3]Cu+TiN(BNL)
D(D7)[4,200,3]Al
D(D7)[4,200,3]Al+TiN(KEK)

Al

-3

Near
Beam
ElectronCloud
CloudDensity
Density [m[m-3]]Near
Beam
Electron1313

Electron microscopic
image of TiN coatingby courtesy of
K. Kanazawa

101212

10

Cu101111

10

Al + TiN
Cu + TiN
1010

1010

0

0.2

0.4

0.6

0.8

1

1.2

LER Bunch Current [mA]
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Electron cloud mitigation 4
Grooved Surface (in Bending Magnets)• Grooved surface can reduce effective SEY of beam pipe in bending
magnet.
 Secondary electrons hardly get away from the grooved structure in the dipole field.
 Grooved structure is formed by extrusion method.
 Beam pipe with groove structure can be bent.
 Expected reduction efficiency of electron cloud in SuperKEKB LER is ½.
Beam pipe(SuperKEKB LER)

Valley ：R0.1~0.12
Top ：R0.15
Angle：18~18.3°

Rt (Roundness)

Bd(Depth)by L. Wang et al.

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50Electron cloud mitigation 5
Clearing Electrode (in Wiggler Magnets)• Clearing electrode attracts the electrons
by electrostatic field.

by courtesy of Y. Suetsugu

 Very thin electrode was developed. (0.1 mm
tungsten on 0.2 mm Al2O3)
 It was tested in KEKB and CserTA.
pipe
It is expected to reduce the electron density
Beam(SuperKEKB
LER) beam up to 1/100.
aroundElectron density

Valley ：R0.1~0.12
Top ：R0.15
Angle：18~18.3°

0V

Beam pipe (Damping ring)

Beam channel( 90mm)+75 V~3kV/mB
Antechamber

Rt (Roundness)d(Depth)Electrode (+)

2015/2/23

L. Wang et al, EPAC2006, p.1489+500 VThe 20th KEKB Accelerator Review Committee

by L. Wang et al.

51

Electron Cloud Mitigation 6
Evaluation on Groove and Electrode• Effectiveness of the grooved surface and the clearing electrode was
evaluated at KEKB LER.
 Expected reduction efficiencies of electron cloud in SuperKEKB LER are ½ (groove) and1/100 (electrode).
TiN-coatedflat surface

TiN

Groovedsurface(~20)1/6~1/10

Clearing
electrode~1/10

GrooveClearing electrodeby courtesy of Y. Suetsugu

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TiN coating 1 : Coating method•

For SuperKEKB LER, it is an important issue to mitigate
the electron cloud instability.
– In order to reduce the electron cloud, inner surfaces ofalmost all LER beam pipes are coated with TiN (except
beam pipes with clearing electrodes).
– TiN coating tests had been performed and the coating
method was established.

•

TiN coating is done by a DC magnetron sputtering of Ti
in Ar and N2 atmospheres.
– A Ti cathode rod (‐400 V) is set on the center axis of beampipe.
– Gases are supplied into the beam pipes uniformly though
the Ti rod.
– Magnetic field (16 mT) is supplied by solenoid coils.
– Preliminary experiments were performed at a test stand to
decide the coating parameters.
– Thickness of TiN coating : 200 nm (at least)– Straight beam pipes are coated by vertical type and bent
pipes are coated by horizontal type.
2015/2/23

The 20th KEKB Accelerator Review Committee

Mass Flow Controller
Ar gas (2.0 Pa)
N2 gas (0.5 Pa)
Discharge
Power
SourceSolenoid CoilBeam pipe

Solenoid Coil’s
Power Source
Ti Cathode Rod(-400 V)

16 mT
Gauge

Pumping System

stand
MassTest
Spectrometer

53

TiN coating 2 : Magnetron sputtering
Introduced gases : Ar (2.2 Pa), N2 (1.8 Pa)
Discharged current : 6.3 A
Required time : 5 min (Ti coating for base of TiN) + 75 min (TiN coating)
Vertical typePartial pressure during discharge (just upstream of pumping unit)
1x100

Ar

1x10‐1N2

1x10‐2

Partial Pressure [Pa]•••Ti cathode rod

1x10‐3
1x10‐4

H2
Ti coating

Horizontal type

TiN coating

1x10‐5
1x10‐6
1x10‐7
1x10‐8Time
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TiN coating 3 : Magnetron sputtering• SEY of Al samples coated with TiN at this facility were measured.
 It was confirmed that SEY of TiN coating drops to below 0.8 after sufficientelectron bombardment (i.e. scrubbing). (incident electron energy : 250 eV)
By S. Terui

Al samples before coating

By S. Terui

2.2

1.3
1.1

TiN coated samples

0.9

0.72
0.5

Al flat

Al groove

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2015/2/23

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Committee

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