Present Status of R&D on
Beam Duct with Ante-chamber,
Movable Mask Ver.6, andClearing Electrode for ECIKEKB Vacuum Group
Y. Suetsugu

12/04/2007

2007 KEKB Review

1Beam duct with antechamber
R&D so far
y We have been developing a copper beam ductwith antechambers to reduce;◦ SR power density at side wall.
◦ Electrons in a beam channel (for positron ring).
◦ Beam Impedance.

y Two ducts for arc section and three ducts for

wiggler section have been successfully
manufactured by pressing or cold drawing method.
y They were installed into KEKB LER, and testedwith beam.
y No serious problem up to 1.7 A (1389 bunches)
has been observed for years.
12/04/2007

2007 KEKB Review2

Beam duct with antechamber2007 summer
y New copper beam ducts were installed into Nikko

wiggler section at the most downstream side of
wiggler magnets (about 30 m long including tapers.)
y Seven ducts including two ducts with BPM for
quadrupole magnets (Q-duct).
y Six bellows with comb-type RF-shield.
y Diameter of beam channel is 90 mm.
y Inside was coated with TiN (except for tapers).
y No electron monitor, and the effect of TiN will bechecked by another duct.

QW4NP.2

QW3NP.2

QW2NP.2
12/04/2007

2007 KEKB Review

QDWNP.63

Beam duct with antechamber
Manufacturingy Cold drawn copper pipe, and welded by EB.
y MO-type flange (stain-less steel).
y BPM electrode was connected by ICF flange.
BPM
y No mapping before installation;

Gain mapping will be done by BBA
Straight duct

Q-duct~3.6 m

φ 90 mm12/04/2007

2007 KEKB Review

4Beam duct with antechamber
TiN coatingy TiN was coated in KEK (K. Shibata et al.)y Coating system available for ~4 m pipe was set up.
y Thickness is ~200 nm, which is determined fromadhesiveness of film and δmax (~0.84).
Gas inlet

Coated at only
beam channel
part~4 m

SolenoidDuct

φ 90 mm

Pumpingsystem
12/04/2007

2007 KEKB Review

5Beam duct with antechamber
Installationy Installation was successful (~1 week).
y With a help of other groups, such as RF, Magnet,

Monitor and Cryogenics groups.
BeforeAfter

Circularduct

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2007 KEKB Review

6

Beam duct with antechamber
BPM and magnet
y New wide vertical steering magnets were preparedto fit wide ducts (~280 mm gap).
y BPM system is the same as that of KEKB.
y Solenoids were wound at drift space.
Wide vertical steering magnet

Solenoid at drift space
BPM system

12/04/2007

2007 KEKB Review7

Beam duct with antechamber
Beam test
y Beam test started in October.
y Vacuum pressure is still a little higher thanneighborhood, but the vacuum scrubbing isVacuum scrubbing
smoothly proceeding.

y No excess heating ofbellows chambers.
y A big problem was avacuum leak atflange.

P/I [Pa/mA]◦ High SR density◦ Relatively low pumping
speed

Beam Dose [mA H]
12/04/2007

2007 KEKB Review8Beam duct with antechamber
Problemy Just after starting the beam test, a vacuum leakhad occurred at a flange connection (~1x10-3 Pam3/s).
y Pressure increased just after a beam abort.
y That flange was extremely heated up.
y Color of copper gasket was found to be changed
at the antechamber section due to overheating.
Gasketin trouble
y Local heating of gasket→ plastic strain by heating→ contraction after beam abort→ vacuum leak
Beam
QW4NP.2QW2NP.2

QW3NP.2
12/04/2007

2007 KEKB Review

QDWNP.6
9

Beam duct with antechamber
Causey It was found that the height of bellows was lower

by 3 - 4 mm from a nominal one.
→The SR hit the upper part of flange.
◦ About 50 W Æ over 250°C

y Careless mistake, but the trouble taught that;◦ A careful alignment is important, especially for astraight section, where SR from far upstream magnet
passes through the antechamber.
◦ Any cures will be required considering unexpected
steering of beam, even for arc sections.
x Water cooling, Copper alloy flange, SR masks, etc.

◦ Careful control of beam orbit is also important.
12/04/2007

2007 KEKB Review

10Beam duct with antechamber
R&D in progressy Ducts for a bending magnet (B-duct)◦ Now manufacturing with a curvature of 16 m (for LER)
using a cold drawn pipe.
Bending testy Development of pump systeminstalled in ante-chamber.

◦ Ex., three layers of ST707 strips.

y Copper alloy flange.

◦ Ex., Zr-Cr-Cu or Cr-Cuy Check TiN effect using ante-chamber.

Copper alloy flange test

12/04/2007

2007 KEKB Review

11Beam duct with antechamber
Summaryy R&D for key components for the vacuum systemwith ante-chamber scheme has almost completed.
y Remained important issues for the concrete
design of Super KEKB;◦ Optimization of beam duct shape.

x CSR effect, Resistive wall effect, Conductance, Impedance, ….

◦ Deformation of beam duct by heating.

x Displacement gauge for BPM, Rigid duct support?, ….

◦ ECI cure in magnet

x Drift space :TiN coating + Solenoid will be OK.
x In magnet ? TiN coating + ??? [See the last topic]◦ Design of special components
x septum, abort window, …

◦ Design of vacuum system at IR.
x How to deal intens SR power,…
12/04/2007

2007 KEKB Review

12Movable Mask Ver.6
Concepty Proposal :Metal head supported by dielectricmaterial◦ Little interference withbeam◦

Small impedance

Loss factor [V/pC]

Loss factor

Trapped mode

Ver.4

Ver.6

Bunch length [mm]12/04/2007

2007 KEKB Review

13Movable Mask Ver.6
The first test model (Ver. 6.0)
y In 2006, Ver.6.0 was manufactured.
y Head： Al2O3 Coated with coppery Support： Al2O3 (Ti coating at one side)◦ Head and support was shaped as a unit.

y HOM absorber: SiC (Inside of chamber)y Installed into LER for proof of concept.
Inside view of mask chamber

Mask head and support of Ver.6.0
Head (Al2O3)
Cu Coating: 10µm

HeadSiC

Support (Al2O3)
One block

90 mm

SupportInside view

Ti coating
1 µm,~2 kΩ
12/04/2007

2007 KEKB Review

14Movable Mask Ver.6
Problemy Excess heating was observed from the beginning.
y At 700 mA (1389 bunches), copper coating had

evaporated, and Al2O3 had melted! (spring, 2007).
y Cause：◦ The head with Cu coating shaped a cavity.
◦ Underestimate of tanδ ; temperature dependence of tanδwas not considered.
◦ Over reliance on heat radiation.
Side view
No Cu coating

Melted Al2O3

Original shape
12/04/2007

2007 KEKB Review

15Movable Mask Ver.6
Next model (Ver. 6.1)
y Ver. 6.1 was designed based on the trouble of Ver.

6.0.
◦ Return to original structure.
◦ Improvement of thermal strength.

Head (Graphite)y Head: Graphite◦ σc = 2 x105 1/Ω/m (electric conductivity)◦ k = 0.1 W/mm/K (thermal conductivity)◦ Available temperature > 3000°C

Support (Diamond)y Support： Artificial diamond (mechanical grade)◦ εr = 6.0 (relative dielectric constant)◦ k > 1 W/mm/K (cf. copper: k ~ 0.4 W/mm/K)→Heat transfer via support can be expected.
◦ Available temperature ~ 1500 °C (before carbonization)
12/04/2007

2007 KEKB Review

16Movable Mask Ver.6
Estimation of temperaturey Analysis by ANSYS
Chamber
HeadSupporttanδ

Temperaturedependence of tanδ

◦ Input powerx Head: Joule loss andtrapped modes.
x Support: Dielectric loss
◦ Including exponential
dependence of tanδ ontemperature.
◦ Radiation

Temperature [K]12/04/2007

2007 KEKB Review

17Movable Mask Ver.6
Temperature for some materials
y Max. temperature of support
Headmaterial

Supportmaterial

Preset KEKB
Max. T(K)(I2/N=2000)

Max. T (K)(I2/N=353)

Cu (Coating) Al2O3(980 @42mA,#51)

Ver.6.0 (Initial)

Al2O3

Al2O3

2607

Ver.6.0

Graphite

Al2O3

800

N/A (Thermalrun away)

Graphite

Quarts (SiO2) 706

N/A (Thermalrun away)

Graphite

AlN~4801220

Graphite

BN~5801078

Graphite

DIamond~410~700

12/04/2007

2007 KEKB Review(No Cu coating)

Reproduce
the trouble

Ver.6.118

Movable Mask Ver.6
Estimation of temperaturey Analysis by ANSYS

889 K

Head

692 K
Support◦ At 1.7A (1389 bunches).
◦ Input powerx Head: 67.5 W
x Support: 7.7 W◦ Max. T：616°C @Head
and 430°C @support◦ tanδ = 0.0128 (@~700K)

300 K

12/04/2007

2007 KEKB Review

19Movable Mask Ver. 6
Ver. 6.1
y Now chamber was under manufacturing.

◦ The chamber has the same structure with that of Ver.4.
◦ The chamber will be installed this winter (January).

12/04/2007

2007 KEKB Review

20Movable Mask Ver.6
Test for manufacturing
Diamondy Blazing test

◦ Wetness between diamond andblazing filler metal.
◦ Brazing between copper anddiamond.
◦ Blazing between diamond andgraphite. (+mechanical fix)y Forming of graphite anddiamond

CopperGraphite
DiamondGraphite

Diamondt1.2 x W5 x H37

Coppert10 x W10 x H100

12/04/2007

2007 KEKB Review

21Movable Mask Ver.6
Issue of Ver. 6.1
y Ver.6.1 will be not available for 10A @5000 bunches,

if nothing is done.

• Ver.6.x

Temperature of diamond
Thermal run away

◦ Head： Graphite +Tungsten coatingx Thermal spray： Used forfusion reactor.
x Higher electric conductivity.

Ver.6.1◦ Support： Optical-grade
artificial diamondVer.6.x(W + Optical grade)x Higher thermal conductivity,Still highbut expensive.

◦ Structural change.
◦ Further investigation isrequired.

KEKB at present
12/04/2007

2007 KEKB Review

22Movable Mask Ver.6
Summaryy Ver.6.1 are under manufacturing based on theexperiences of Ver.6.0.
y Ver.6.1 will be tested using LER next February.
◦ Proof of concept (revenge of Ver.6.0)◦ Data taking for the case of further high currenty Ver.6.x should be considered for Super KEKB (10A at 5000 bunches).

12/04/2007

2007 KEKB Review

23

Clearing Electrode
Backgroundy A solution to suppress electron cloud in magnets.
y Experimental study on a clearing electrode using

KEKB positron ring is planed.
y The experiment is also a chain of ILC DR R&Dstudy.
◦ With H. Fukuma (KEK), M. Pivi and L. Wang (SLAC)y Goal◦ Establish the technique of clearing electrode for ECI,
which is available for high current machine and with alow beam impedance.
◦ Demonstrate the effect on electron cloud formation.

12/04/2007

2007 KEKB Review

24

Clearing Electrode
Effect of electrodey Simulation (by L. Wang)
R-pipe=38mm
bunch intensity=9.36e10
3.5 Bunch Spacing
B = 0.75 Tδmax = 1.4

Electrode(+)

Electrondensity
in magnetic
field
Twopeaks
3.5

x 10

13

3-3

ρ (m )

2.5
2
1.5
1
0.5

0-50

-40

-30

-20

-10

0

10203040

L. Wang et al, EPAC2006, p.1489

50X (mm)12/04/2007

2007 KEKB Review

25Clearing Electrode
Test plany Install a test chamber with a electron monitor(bottom) and a clearing electrode (top) into awiggler magnet of LER.
◦ At the most upstream side of wigglers
x Very weak SR

Wiggler magnets◦ Magnetic field: 0.75 T◦ Effective length: 346 mm◦ Aperture (height): 110 mm

Test chamber with antechambers

Gate Valve

Beam
12/04/2007

2007 KEKB Review

Gate Valve26

Clearing Electrode
Test Chambery Over all design

MagnetTop viewDetachable Block

Electron Monitor BlockSide view

Electrode Block
Feed-through27
12/04/2007

2007 KEKB Review

27

Clearing Electrode
Monitor and electrodeCollector (7 strips, w5 mm)

y Cross Section

Grid (~ 1 kV)
ShieldMonitor
Block

φ2 mm holes

7R4

Limited bymagnetaperture

BeamElectrode [W] (~ +1 kV)(w40, l440, t~0.1)
Electrode
Block

Vacuum seal by metal O-ring

Cooling channel
Insulator [Al2O3](t~0.1 mm)

Cooling Water paths
12/04/2007

2007 KEKB Review

28

Clearing ElectrodeFeatures of test chambery Strip type electrode.
y Monitor and electrode are exchangeable.
y Electron collectors are seven strips to measure thespacial distribution.
y Very thin electrode and insulator.
◦ Electrode: ~0.1 mm, Tungsten, by thermal spray.
◦ Insulator: ~0.1 mm, Al2O3, by thermal spray.
→Small beam impedance.
y Water cooling beneaththe electrode.
◦ Absorb dissipated power inelectrode and insulator.
12/04/2007

Cooling Water

2007 KEKB Review

29

Clearing Electrode
Feed throughy Copper bridge to connect feed-through andelectrode was manufactured.

Nonmagnetism feed throughCopper

Metal screw
M4

ElectrodeCeramics
screw
M4

Metalized headN-type connector
12/04/2007

2007 KEKB Review

30

Clearing ElectrodeRF calculationy Loss factor◦ k = 7×109 V/C, and Input power is ~ 150 W (1.7 A @1389 b).
◦ Most of input power into electrode will be dissipated byelectrode and chamber.
y Longitudinal impedanceZ// [Ω]

Loss factor [V/C]◦ Length is 440 mm to avoid resonance with RF frequency.
◦ a few ΩThickness of insulator and electrode12/04/2007

Frequency [Hz]2007 KEKB Review

31Clearing ElectrodeRF calculation (cont’d)y Values are estimated at 1.7 A(1389 bunches)

and assuming no resonance.
y Voltage between electrode and chamber◦ ~ 12 V
y Output voltage of feed-through◦ ~ 600 V (Peak)feed-through◦ ~ 60 W,
if R=50Ω and no loss.

Output voltage [V]y Output power fromOutput voltage

Time [s]12/04/2007

2007 KEKB Review

32

Clearing Electrode
Test scheduley First step (from February, 2008)◦ Install outside of magnet (upstream side)◦ Check the heating of electrode◦ If possible, with electron monitor and Measurement
without magnet.

y Second step

◦ Install into the wiggler magnet with electron monitor

y Third step◦ Groove surface, and other promising surfaces

Second stepFirst stepBeam
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2007 KEKB Review

33

Clearing Electrode
Manufacturingy Machining and assembling are undergoing.
FlangeMachining of chamber

Stain-less steel

GridCollectors

12/04/2007

2007 KEKB Review

34

Clearing Electrode
Summaryy Clearing electrode has been studied for a cure ofEC in magnets.
y Manufacturing of test chamber is undergoing.
y Thin electrode and insulator contribute to decrease
the impedance.
y Beam test will start from next February.

12/04/2007

2007 KEKB Review

3512/04/2007

2007 KEKB Review

36

Clearing ElectrodeRF calculationy Calculation By MAFIA
•••••
••••
•

Model length = 2 m
1/4 model
Electrode position = 195-625mm (430mm)Width = 40 mm
Mesh sizes = 0.5 x 0.1 x 0.4mm
Bunch length = 8 mm
Electrode thickness = 0.2mm
Alumina thickness =0.2 mm
Alumina er =9.9
Port = 14 mm (o), 6 mm (i)(50W)

Pipe (1/4)

Electrode
Feed throughEmbedded + Taper + Feed through12/04/2007

2007 KEKB Review37