Construction Status of SuperKEKB Vacuum System

Transcription

1 Construction Status of SuperKEKB Vacuum System Mt. Tsukuba SuperKEKB ( 3000 m) Damping Ring Linac KEK Tsukuba site Fourth Workshop on the Operation of Large Vacuum systems (OLAV IV) April 2, 2014 Kyo Shibata (on behalf of KEKB Vacuum Group)

2 KEKB was shut down on Jun 30 th 2010, and upgrade of KEKB has started. KEKB B factory Electron positron collider with asymmetric energies of 8 GeV (e ) and 3.5 GeV (e+) Operating period : 1998 to 2010 Total integrated luminosity : 1040 /fb Made a great contribution to confirm CP violation in the neutral B meson system. But we need much more luminosity to pursue research on flavor physics Shut down ceremony (Jun 30 th 2010, KEKB control room) Prof. Suzuki (Director General of KEK) pressed the beam abort switch of KEKB. 2014/4/2 OLAV IV, April 1 4, 2014, NSRRC, Hsinchu, TAIWAN 2

3 Mission of SuperKEKB Next generation B factories Design Luminosity of SuperKEKB is /cm 2 /s, which is about 40 times than the KEKB s record. The total integrated luminosity will reach 50 /ab just over ten years after inauguration. 2014/4/2 OLAV IV, April 1 4, 2014, NSRRC, Hsinchu, TAIWAN 3

4 Design Concept of SuperKEKB How to increase luminosity by 40 times y * at IP : 5.9 > 0.27/0.30 mm (e+/e ) Nano beam scheme (first proposed for SuperB by P. Raimondi) Luminosity gain : 20 Beam current : 1.7/1.4 A > 3.6/2.6 A (e+/e ) Luminosity gain : 2 Beam beam parameter : 0.09 > 0.09 Luminosity gain : 1 Total Luminosity Gain : = 40 Lorentz factor L 2er e Beam aspect ratio at IP Beam current 1 * y * I y * x y Beam Beam parameter R L R y Vertical beta function at IP Geometrical reduction factors (crossing angle, hourglass effect) 2014/4/2 OLAV IV, April 1 4, 2014, NSRRC, Hsinchu, TAIWAN 4

5 Comparison of parameters between KEKB and SuperKEKB KEKB Design KEKB Achieved : with crab SuperKEKB Nano Beam Energy (GeV) (LER/HER) 3.5/ / /7.0 y* (mm) 10/10 5.9/ /0.30 x* (mm) 330/ / /25 x (nm) 18/18 18/24 3.2/5.3 y x (%) / /0.24 y ( m) /0.062 y / /0.081 z (mm) /5 I beam (A) 2.6/ / /2.6 N bunches Luminosity (10 34 cm 2 s 1 ) /4/2 OLAV IV, April 1 4, 2014, NSRRC, Hsinchu, TAIWAN 5

6 Outline of Upgrade to SuperKEKB e+ 4 GeV 3.6 A Belle II Colliding bunches e 7 GeV 2.6 A New IR Replace short dipoles with longer ones (LER) New beam pipe & bellows SuperKEKB Add / modify RF systems for higher beam current New superconducting /permanent final focusing quads near the IP Redesign the lattices of both rings to reduce the emittance TiN coated beam pipe with antechambers Low emittance positrons to inject Damping ring Positron source New positron target / capture section Low emittance gun Low emittance electrons to inject 2014/4/2 OLAV IV, April 1 4, 2014, NSRRC, Hsinchu, TAIWAN 6

7 Upgrade of vacuum system Outline of SuperKEKB vacuum system Ultra high vacuum to keep small beam emittance, reduce background noise to detector, avoid ion instability (HER). Target pressure : 10 7 Pa with beam Distributed pumping system utilizing NEG strips (0.14 m 3 /s/m for CO after activation) and ion pumps (0.4 m 3 /s) placed every 10 m. Low beam impedance to keep small beam emittance and short bunch length, avoid beam instabilities. Beam pipe with antechamber, low impedance components, step less connection flange, new bellows chambers, new gate valves, new collimators. Suppression of electron cloud effect (LER) to avoid emittance growth and beam size blow up. Beam pipe with antechamber, solenoid field, TiN coating, clearing electrode, grooved surface. Reusing KEKB vacuum components Only 18 % beam pipes are replaced to new one in HER, though 93 % beam pipes are replaced in LER. Construction schedule Jun/2010 : KEKB shut down : Dismantling beam pipes : Fabrication of beam pipes and vacuum components : Pre installation, Installation, evacuation works Jan./2015 : SuperKEKB Commissioning (?) It depend on budget 2014/4/2 OLAV IV, April 1 4, 2014, NSRRC, Hsinchu, TAIWAN 7

8 New Beam Pipes for SuperKEKB 18 % beam pipes (HER) and 93 % beam pipes (LER) are replaced to new one. To cope with the electron cloud issues (LER) and heating problems, antechamber type beam pipes are adopted. LER arc section: Beam pipes are replaced with new aluminum alloy pipes with antechambers. ( 2000 m) HER arc section: Present copper beam pipes are reused. Since the HER energy is reduced from 8.0 to 7.0 GeV, SR power at normal arc section is more or less the same as KEKB. Wiggler section (both ring): New copper beam pipes with antechambers are used. Wiggler section (copper) NEG pumps Beam SR Concept by courtesy of Y. Suetsugu Arc section (aluminum) 2014/4/2 OLAV IV, April 1 4, 2014, NSRRC, Hsinchu, TAIWAN 8

9 Beam pipe with antechamber Features of new beam pipes with antechamber Small effect of photoelectrons, low beam impedance, low SR power density The cross section should fit to the existing magnets. Aluminum alloy is available for LER arc section due to low SR power. Copper is required for wiggler section and HER. NEG strips are installed in one antechamber isolated by the screen for RF shield. (arc section) NEG strip t6 mm Screen (Φ4mm 6mm pitch) Q magnet Feed through 2014/4/2 by courtesy of Y. Suetsugu OLAV IV, April 1 4, 2014, NSRRC, Hsinchu, TAIWAN 9

10 New Flange, Bellows and Gate Valve Flange, bellows and gate valve applicable to antechamber scheme were also developed. Beam impedances of these new components are smaller than those of old ones. Cu-alloy flange (CrZrCu) Al-alloy flange (A2219, A2024) Bellows chamber RF-shield (bellows) RF-shield (gate valve) Gate valve by courtesy of Y. Suetsugu 2014/4/2 OLAV IV, April 1 4, 2014, NSRRC, Hsinchu, TAIWAN 10

11 Countermeasures against Electron cloud instability can be a serious problem for LER (e+) The threshold of electron density to excite the head tail instability is e /m 3. By using these countermeasures, the average electron density on the order of e /m 3 will be obtained. Various mitigation techniques were evaluated at KEKB LER. Sections L [m] L [ %] Countermeasure Material Total electron cloud effect by courtesy of Y. Suetsugu Drift space (arc) 1629 m 54 Antechamber + TiN coating + Solenoid Al (arc) Steering mag. 316 m 10 Antechamber + TiN coating + Solenoid Al Bending mag. 519 m 17 Antechamber +TiN coating + Grooved surface Al Wiggler mag. 154 m 5 Antechamber + Clearing Electrode Cu Q & SX mag. 254 m 9 Antechamber + TiN coating Al (arc) RF section 124 m 4 (TiN coating +) Solenoid Cu IR section 20 m 0.7 (TiN coating +) Solenoid Cu, Al 2014/4/2 OLAV IV, April 1 4, 2014, NSRRC, Hsinchu, TAIWAN 11

12 Electron cloud mitigation 1 Antechamber is effective to mitigation of photoelectrons which can be source of the electron 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) 6~8 ns spacing R = 47 mm (Circular) V r = 30 V Ph = Ph/s/m/ms Antechamber Test result in KEKB LER Circular chamber ~1/5 ~1/100 With antechamber Rough surface at the side wall (Ra 20) reduces the photon reflection. by courtesy of Y. Suetsugu 2014/4/2 OLAV IV, April 1 4, 2014, NSRRC, Hsinchu, TAIWAN 12

13 Electron cloud mitigation 2 Solenoid field It was confirmed that the solenoid field at drift section (50 G) is effective to both photoelectrons 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. Near Beam Electron Cloud Density [m -3 ] Test result in KEKB LER B = 0 G B = 50 G <1/ LER Bunch Current [ma] by courtesy of K. Kanazawa 8/100/2 (800) 4 ns spacing R = 47 mm (Circular) Solenoid coil 2014/4/2 OLAV IV, April 1 4, 2014, NSRRC, Hsinchu, TAIWAN 13

14 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. Near Near Beam Beam Electron Cloud Density [m -3-3 ] Electron cloud mitigation 3 Test result in KEKB LER LER Bunch Current [ma] TiN coating Al Cu Al + TiN Cu + TiN 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) by courtesy of K. Kanazawa Electron microscopic image of TiN coating 2014/4/2 OLAV IV, April 1 4, 2014, NSRRC, Hsinchu, TAIWAN 14

15 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) Electron cloud mitigation 4 Grooved Surface (in Bending Magnets) Valley :R0.1~0.12 Top :R0.15 Angle:18~18.3 R t (Roundness) B d (Depth) by L. Wang et al. 2014/4/2 OLAV IV, April 1 4, 2014, NSRRC, Hsinchu, TAIWAN 15

16 Electron cloud mitigation 5 Clearing Electrode (in Wiggler Magnets) Clearing electrode attracts the electrons by electrostatic field. Very thin electrode was developed. (0.1 mm tungsten on 0.2 mm Al 2 O 3 ) It was tested in KEKB and CserTA. It is expected to reduce the electron density around beam up to 1/100. Beam pipe (SuperKEKB LER) Electron density 0 V Beam pipe (Damping ring) +75 V ~3kV/m by courtesy of Y. Suetsugu Valley :R0.1~0.12 Top :R0.15 Angle:18~18.3 Beam channel ( 90mm) Antechamber Electrode (+) L. Wang et al, EPAC2006, p V 2014/4/2 OLAV IV, April 1 4, 2014, NSRRC, Hsinchu, TAIWAN 16

17 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) and 1/100 (electrode). TiN TiN-coated flat surface Grooved surface ( ~20 ) 1/6~1/10 ~1/10 Clearing electrode Groove Clearing electrode by courtesy of Y. Suetsugu 2014/4/2 OLAV IV, April 1 4, 2014, NSRRC, Hsinchu, TAIWAN 17

18 Fabrication status of new beam pipes All beam pips were ordered. Approximately 87 % of LER and 30 % of HER have been delivered. HER LER 2014/4/2 OLAV IV, April 1 4, 2014, NSRRC, Hsinchu, TAIWAN 18

19 Pre installation works What should we do before the installation of new beam pipes? For HER (e ) : Baking at the laboratory(not in situ) For LER (e+) : Baking & TiN coating at the laboratory For Damping Ring : TiN coating at the laboratory For all beam pipes : assembling work (NEG pump, BPM electrode) How many beam pipes should be processed? For HER (e ) : 180 For LER (e+) : 1000 (of which 25 have electron clearing electrodes and TiN coating is unnecessary. ) Damping Ring : 100 New facilities for baking and TiN coating were constructed in KEK. Pre installation work started on April Pre installation work means: Bringing beam pipes to KEKB Oho Lab. from storage area > Coating (3days) > Baking (3days) > returning the beam pipes to storage area Large scale works by 10 workers started on September /4/2 OLAV IV, April 1 4, 2014, NSRRC, Hsinchu, TAIWAN 19

20 Flow chart of pre installation works Bringing beam pipes to KEKB Oho Lab. from storage area LER beam pipe without electrode Visual check on the beam pipe DR beam pipe TiN Coating HER beam pipe LER beam pipe with electrode Assembling (NEG pump & BPM electrode) Pre installation work facility Baking DR beam pipe Returning the beam pipes to storage area 2014/4/2 OLAV IV, April 1 4, 2014, NSRRC, Hsinchu, TAIWAN 20

21 Facility for pre installation work Baking equipment : 2 long type ( 5 m) and 2 short type ( 3 m) Vertical TiN coating facility with 4 equipment systems for straight beam pipes Horizontal coating facility with 2 equipment systems for bent beam pipes Coating facility (horizontal) 16m 16m Baking equipment (long type) Baking equipment (long type) stairway Baking equipment (short type) Baking equipment (short type) stairway 4.5mm coating facility (vertical) 6.5 m Oho experimental deck (top view) Clean room 2014/4/2 OLAV IV, April 1 4, 2014, NSRRC, Hsinchu, TAIWAN 21

22 Baking 1 : Equipment Hot air heating method was adopted. Two beam pipes are mounted up and down in one hot air oven. Hot air oven consists of movable insulated walls and insulated frame. Hot air is circulated in the hot air oven. Each pipe is evacuated by a turbo molecular pump (0.3 m 3 /sec) during the baking. Movable walls Now baking Beam pipe (double decker) Pumping unit Short type Hot air circulator (7.5 kw) Long type 2014/4/2 OLAV IV, April 1 4, 2014, NSRRC, Hsinchu, TAIWAN 22

23 Baking 2 : Baking conditions Baking conditions Temperature : 150 C ( 120 C for beam pipes with electrodes) Baking period : 26 hours Temperature of the beam pipes in the oven became 150 C within a several hours. Targeted pressure after baking : < 10 7 Pa NEG pump is activated at the same time. Before baking TiN coating (if necessary) Installation of NEG pumps and BPM electrodes at Oho clean room. After baking Filling with dry nitrogen up to atmospheric pressure. Isolating the beam pipe and putting a blank flange on the beam pipe. Keeping the beam pipe in the storage area until the installation. Clean room Storage area (Oho lab.) 2014/4/2 OLAV IV, April 1 4, 2014, NSRRC, Hsinchu, TAIWAN 23

24 Baking 3 : Achieved pressure after baking For almost all beam pipes, achieved pressures after baking are below Pa. If achieved pressure is higher than Pa, the beam pipe is baked again. Mass pattern after baking is not monitored. (Though 2 of 4 baking equipment systems have RGAs, we don t use them.) < < [x10 8 Pa] 2014/4/2 OLAV IV, April 1 4, 2014, NSRRC, Hsinchu, TAIWAN 24

25 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 of almost 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 N 2 atmospheres. A Ti cathode rod ( 400 V) is set on the center axis of beam pipe. 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. Discharge Power Source Solenoid Coil s Power Source 16 mt Pumping System Solenoid Coil Mass Flow Controller Ar gas (2.0 Pa) N 2 gas (0.5 Pa) Gauge Test stand Mass Spectrometer Beam pipe Ti Cathode Rod (-400 V) 2014/4/2 OLAV IV, April 1 4, 2014, NSRRC, Hsinchu, TAIWAN 25

26 TiN coating 2 : Facility Straight beam pipes are coated by vertical facility with 4 equipment systems Bent pipes are coated by horizontal one with 2 equipment systems. Beam pipe with a length up to 5.5 m can be coated. Two lines of the beam pipes can be mounted side by side in one equipment. Combination of hot air oven and circulators are adopted for pre baking. Now Installing beam pipes (vertical type) Vertical coating facility Horizontal coating facility 2014/4/2 OLAV IV, April 1 4, 2014, NSRRC, Hsinchu, TAIWAN 26

27 TiN coating 3: Magnetron sputtering Introduced gases : Ar ( 2.2 Pa), N2 ( 1.8 Pa) Discharged current : 6.3 A Required time : 5min (Ti coating for base of TiN) + 75 min (TiN coating) Vertical type Partial Pressure [Pa] 1x10 0 1x10 1 1x10 2 1x10 3 1x10 4 1x10 5 1x10 6 1x10 7 1x10 8 Partial pressure during discharge (just upstream of pumping unit) Ar N 2 H 2 Ti coating TiN coating Time Ti cathode rod Horizontal type 2014/4/2 OLAV IV, April 1 4, 2014, NSRRC, Hsinchu, TAIWAN 27

28 TiN coating 4: Performance evaluation 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 sufficient electron bombardment (i.e. scrubbing). (incident electron energy : 250 ev) Al samples before coating 2.2 By S. Terui By S. Terui TiN coated samples Al flat Al groove 2014/4/2 OLAV IV, April 1 4, 2014, NSRRC, Hsinchu, TAIWAN 28

29 Output of pre installation work Pre installation work started on April Total output by last month (2014/2/28) is 925. More 350 beam pipes must be processed by the end of November at the latest. Last year 367 beam pipes were processed in 7 months (from April to October). 170 HER beam pipes are not coated. More 100 beam pipes for Damping Ring must be coated by July Now we are here. (waiting for new beam pipes.) 2014/4/2 OLAV IV, April 1 4, 2014, NSRRC, Hsinchu, TAIWAN 29

30 Installation and Evacuation Status Installation and evacuation works started on 2013 and will finish by the end of HER : 24 % new beam pipe has been installed and 16 % has been evacuated. LER : 82 % new beam pipe has been installed and 32 % has been evacuated. HER LER 2014/4/2 OLAV IV, April 1 4, 2014, NSRRC, Hsinchu, TAIWAN 30

31 Present view in SuperKEKB tunnel LER Arc LER LER wiggler HER wiggler Reused beam pipe HER Arc 2014/4/2 OLAV IV, April 1 4, 2014, NSRRC, Hsinchu, TAIWAN 31

32 Summary Upgrade of vacuum system for SuperKEKB is underway now. 93 % (LER) and 18 % (HER) beam pipes are replaced to new one. All new beam pipes were ordered. Approximately 87 % (LER) and 30 % (HER) have been delivered. As countermeasures against electron cloud effect in LER, various mitigation techniques are adopted. Antechamber, TiN coating, solenoid filed, grooved surface, clearing electrode By using these countermeasures, the average electron density in SuperKEKB LER will be below threshold of electron cloud instability. TiN coating and baking facilities were constructed in KEK Tsukuba site for pre installation work. Pre installation work started on April Pre installation work is almost on schedule and 925 beam pipes were treated in total so far. More 350 beam pipes will be treated in about 8 months. Installation and evacuation work are underway now. 24 % new beam pipe has been installed and 16 % has been evacuated in HER. 82 % new beam pipe has been installed and 32 % has been evacuated in LER. Installation and evacuation work will be finished by the end of this year. 2014/4/2 OLAV IV, April 1 4, 2014, NSRRC, Hsinchu, TAIWAN 32

33 Thank you for your attention.

34 Back up

35 Sections Length [m] ([%]) Countermeasure Drift space 1629 (54) Antechamber + TiN coating + Solenoid Steering magnet 316 (10) Antechamber + TiN coating + Solenoid Bending magnet 519 (17) Antechamber + TiN coating + Groove structure Wiggler magnet 154 (5) Q & SX magnet 254 (8) Acceleration section 124 (4) Interaction region 20 (1) Total 3016 (100) Antechamber + Clearing electrode Antechamber + TiN coating Expected electron density [m 3 ] Material Al, Cu Al, Cu Al Cu Al, Cu TiN coating + Solenoid Cu TiN coating + Solenoid Al, Cu

36 TiN coating : Installation of beam pipes 1 Hinge assembly to get beam pipe upright Beam pipes are transported and installed on the coating equipment by crane.

37 TiN coating : Installation of beam pipes 2 Beam pipes are transported and installed in the coating equipment by crane.

38 TiN coating : Installation of beam pipes 3 Introduced gas line Ti cathode Insulator Bellows for positioning of Ti cathode rod Ti cathode rod ( 6m) is also installed by crane.

39 TiN coating : Facility (horizontal) Bent beam pipes are coated by horizontal facility with 2 equipment systems. Basically, horizontal equipment has the same structure with vertical equipment. Beam pipes lie down in the solenoid coils. Ti cathode is set horizontally on the center axis of beam pipe by the ceramics supports with wheels. Large scale work started on April 2013.

40 TiN coating : Coating 2 Electron microscopic image of TiN coating Beam pipe (bent type) was successfully coated. Though the color of the ceramic support was changed, insulation breakdown did not occurred.

41 TiN coating 10 : Coating output Coating work started on July Total output by last month (2014/2/28) is 805. More 280 beam pipes (LER:180, DR:100) must be coated by the end of this year. Last year 345 beam pipes were coated in 7 months (from April to October). LER : From April to October at the latest. DR : March, November and December. Damping ring (100) LER (180) Now we are here. (modifying the horizontal facility and waiting for new beam pipes.)

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