Vertical EP at Marui & KEK November 2016 TTC High-Gradient WG - - PowerPoint PPT Presentation

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Vertical EP at Marui & KEK November 2016 TTC High-Gradient WG - - PowerPoint PPT Presentation

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Vertical EP at Marui & KEK November 2016 TTC High-Gradient WG Meeting T Saeki KEK V Chouhan, Y Ida, K Ishimi, K Nii & T Yamaguchi (Marui Galvanizing Co., Ltd., Japan) H Hayano, S Kato, H Monjushiro & M Sawabe (KEK, Japan) V

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SLIDE 1

Vertical EP at Marui & KEK

November 2016 TTC High-Gradient WG Meeting T Saeki KEK

V Chouhan, Y Ida, K Ishimi, K Nii & T Yamaguchi (Marui Galvanizing Co., Ltd., Japan) H Hayano, S Kato, H Monjushiro & M Sawabe (KEK, Japan)

1 V Chouhan, MGI (Nov 2016)

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SLIDE 2

Outline

  • VEP setups
  • Coupon cavity & Ninja cathode
  • Optimization of cathode design and VEP parameters
  • Vertical test results
  • Fabrication of 9-cell coupon cavity
  • Summary

2 V Chouhan, MGI (23 Sep 2016)

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SLIDE 3

VEP Setups at Marui

3

For 1-cell Cavity For 9-cell/1-cell Cavity

 Both setups were prepared with PVC materials in order to reduce cost of surface treatment of cavities in mass production.

V Chouhan, MGI (Nov 2016)

Air Cooling Ducts

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SLIDE 4

Single Cell Coupon Cavity

4

Coupon Nb Coupons View Ports

Coupon

Ø 8 mm

  • Cavity contains 6 coupons at beam pipes, irises and equator.
  • An EP current can be measured for individual coupon.
  • Coupon surfaces are analyzed with several surface analytical tools.
  • The cavity is having 4 view ports on the top iris, bottom iris and equator for

light introduction and in-situ observation.

V Chouhan, MGI (Nov 2016)

View Port

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SLIDE 5

Ninja Cathode

V Chouhan, MGI (Nov 2016) 5

EP時 挿入時 空洞へセット した状態 EP時 挿入時 空洞へセット した状態 Side View Top View Ninja in Cavity Cell

Ninja cathode was developed in order to agitate EP acid. The wings are either insulating or metallic/partially metallic which act as a cathode.

Four re-tractable wings (Al or insulating)

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SLIDE 6

V Chouhan, MGI (Nov 2016) 6

VEP with Rod and Ninja Cathode (Al Wings)

Ninja Cathode- Al Wings Rod Cathode

Parameter Value H2SO4:HF 9:1 Electrolyte Flow Direction Bottom to Top Flow Rate 5 L/min Cathode Rotation Speed 1 rpm Applied Voltage ~9 V EP Current Density 25-30 mA/cm2 Target Removal Thickness 50 µm Cavity Surface Temperature ~25 °C

Upper Iris Coupon

Rod Cathode Ninja Cathode

  • Ninja Cathode (Al wings) results in:
  • Smooth surface
  • Asymmetric removal similar as rod cathode
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SLIDE 7

Ninja Improvement

  • Al wings were replaced with insulating and partial

metallic wings.

V Chouhan, MGI (Nov 2016) 7

P時 P時

Cathode

P時 P時

Side View Top View

Insulating Wings Partial Metal Wings

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SLIDE 8

Effect of Stirring in VEP

8

  • The top iris coupon current was the highest at 1 rpm because of accumulation of

H2 bubbles on the top iris.

  • Ninja cathode rotating at 50 rpm displaced the bubbles and might make uniform

acid flow in the cavity cell.

At 1 rpm At 50 rpm Coupon

Ø 8 mm P時 P時

V Chouhan, MGI (Nov 2016)

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SLIDE 9

V Chouhan, MGI (Nov 2016) 9

  • S. Jin et al. Phys. Rev. ST Accel Beams 13, 061001 (2010)

Typical I-V Curve

I-V Characteristic

  • An I-V curve gives an information about phenomenon occurs on Nb

surface based on applied voltage.

  • A particular range of voltage (in polishing region) needs to be applied

for EP.

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SLIDE 10

Effect of Partial Cathode Wings

10

  • H2 bubbles can screen the

cathode and reduce ion migration to the cathode.

  • A distance between anode and

cathode might be important for a small area of cathode.

  • Electric field on equator was
  • bviously lower due to a large

distance from cathode.

  • Wing cathode enhanced ion

transportation and electric field on equator surface. Insulating Wings

V Chouhan, MGI (Nov 2016)

Partial Cathode Wings Cathode

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SLIDE 11

Removal Thickness W/O and W/ Wings

11

Partial Metal Wings

Ninja wings were found to be effective as a stirrer in order to minimize longitudinal asymmetry of Nb removal.

Cathode Rotation: 50 rpm

P時 P時 V Chouhan, MGI (Nov 2016)

Partial Metal Wings Rod Cathode

 Removal thickness was measured with ultrasonic thickness gauge.

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SLIDE 12

V Chouhan, MGI (Nov 2016) 12

Surfaces of Coupons

Top Iris

Rod Cathode

Equator Bottom Iris

500 µm

  • Rough equator surface of equator with rod cathode and insulating wings might be

due to Nb removal in etching region. (Since equator remains in etching region at the applied voltages.)

  • Ninja with partial metal wings resulted in smooth surface of the equator.

Insulating Wings at 50 rpm

Top Iris Equator Bottom Iris

500 µm

P時 P時

Partial Metal Wings at 50 rpm 500 µm

P時 P時

Typical roughness of coupons before VEPs: Rz=~4 µm

Top BP Top Iris Equator Bottom Iris Bottom BP

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SLIDE 13
  • Ninja cathode with Insulating Wings:

– Cannot be used since it resulted in rough equator surface due to cathode screening by H2 bubbles.

  • Ninja cathode with Partial Metal Wings:

– May not be appropriate for VEP of a 9-cell cavity because bubbles generating on the wings will finally accumulate in the upper cells of a cavity.

V Chouhan, MGI (Nov 2016) 13

The problem of cathode screening by H2 bubbles should be solved.

What We Learned

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SLIDE 14

V Chouhan, MGI (Nov 2016) 14

P時 P時

Ninja with Enhanced Cathode Area

  • Cathode surface area was enhanced to reduce the screening

effect.

  • The cathode was covered well with a meshed shield to trap

H2 bubbles and guide them along the cathode.

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SLIDE 15

15

Insulating Wings

Insulating Wings with Enhanced Cathode area

  • EP plateau for equator

was obtained with Ninja cathode having larger cathode area.

Effect of Enhanced Cathode Area

V Chouhan, MGI (Nov 2016)

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SLIDE 16

Surfaces of Coupons

V Chouhan, MGI (Nov 2016) 16

Insulating Wings at 50 rpm Partial Metal Wings at 50 rpm Enhanced Cathode area with Insulating Wings at 50 rpm

P時 P時

Top Iris Equator Bottom Iris Top Iris Equator Bottom Iris Top Iris Equator Bottom Iris

P時 P時 P時 P時

200 µm 200 µm 200 µm

 The enhanced cathode area resulted in smooth surface of the equator surface.

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SLIDE 17
  • Since the Ninja cathode was prepared with bubble guide, the rotation

speed of the cathode was reduced.

  • VEP was carried out at 20 rpm.

17

VEP at Lower Rotation Speed

At 50 rpm At 20 rpm At 50 rpm

200 µm Partial Metal Wings

Enhanced Cathode area

  • Surface roughness
  • f equator was

reduced in case of 20 rpm.

P時 P時 P時 P時 P時 P時

Top Iris Equator Bottom Iris Top Iris Equator Bottom Iris Top Iris Equator Bottom Iris

V Chouhan, MGI (Nov 2016)

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SLIDE 18

V Chouhan, MGI (Nov 2016) 18

Removal Trend at Lower Rotation Speed

Almost symmetric removal was obtained with the Ninja cathode due to bubble guide and uniform acid flow in cavity cell.

Rod Cathode Partial Metal Wings at 50 rpm Enhanced Area at 20 rpm

Based on the concept of the Ninja cathode (enhanced cathode area), a Ninja cathode for VEP of 9-cell cavities has been fabricated.

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SLIDE 19

Vertical Test Results

NR1-2 Cavity (Cornell Cavity)

  • Pre-treatment: Tumbling, BCP, degassing

at 800 °C

  • Cathode: Ninja cathodes (partial metal

wings and enhance area) with the VEP setup of Cornell University

  • VEP: VEP with each cathode (20+20 µm

removal)

  • Ninja rotation speed: 50 rpm
  • VT: Performed at 2K at Cornell after 120 °C

baking

The both cavities showed good performance in the vertical tests.

35 MV/m at Q0=9×109 21 MV/m at Q0=1.4×1010

Vacuum Leak occurred Quench

  • Two single-cell cavities (NR1-2 and C1-19) were VEPed with the Ninja

cathodes and tested in vertical cryostats. C1-19 Cavity (Saclay Cavity)

  • Pre-treatment: BCP
  • Cathode: Ninja cathode (enhanced area) with Marui VEP setup
  • VEP: Two VEP for 31 and 55 µm removal, degassing at 750°C and final VEP for 11 µm

removal

  • Ninja rotation speed: 30 rpm
  • VT: Performed at 1.6K at Saclay

19

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SLIDE 20

9-Cell VEP Experiment

20

P時 P時 Parameter Value H2SO4:HF 9:1 Electrolyte Flow Direction Bottom to Top Flow Rate 5 L/min Cathode Rotation Speed 50 rpm Applied Voltage ~11 V EP Current Density 30-35 mA/cm2 Cavity Surface Temperature ~ 20 °C

Motor

Cathode

Power Supply

System Controller

Cooler

Pump-1 Pump-2

Chiller

EP Tank

Water Tank Waste Water

V Chouhan, MGI (Nov 2016)

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SLIDE 21

V Chouhan, MGI (Nov 2016) 21

VEP of 9-Cell Cavity with Ninja Cathode of Al Wings (Old Version)

Top View

(a) θ=0º

Top View

(b) θ=180º

 Removal thickness at iris is around 2-3 times larger than that at the equator.

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SLIDE 22
  • The world’s first 9-cell coupon cavity was fabricated to optimize VEP

parameters.

V Chouhan, MGI (Nov 2016) 22

9-Cell Coupon Cavity

1 2 3 4 5 6 7 8 9

Nb Coupon Nb Coupon with view port

Equator Coupon Coupon with View Port near Iris 6 coupons near iris positions 3 coupons at Equator positions

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SLIDE 23

Summary

 VEP setup and unique Ninja cathodes were developed for surface treatment of Nb cavities.  VEP parameters and design of the Ninja cathode were

  • ptimized for single cell cavity.

 Smooth surface and symmetric removal of Nb along cavity length were obtained with the Ninja cathode.  The Ninja cathode and optimized VEP parameters were applied to two single-cell cavities which showed good performance in a vertical tests performed at Cornell University and CEA-Saclay.  The world’s first 9-cell coupon cavity has been fabricated.  Based on the VEP results of 1-cell cavity, 9-cell Ninja has been fabricated.

23 V Chouhan, MGI (Nov 2016)

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SLIDE 24

Conference Presentations

  • V. Chouhan et al., THPP098, LINAC2014.
  • K. Nii et al., MOPP108, LINAC2014.
  • K. Nii et al., TUPP101, LINAC2014.
  • V. Chouhan et al., MOPB105, SRF2015.
  • V. Chouhan et al., THBA02, SRF2015.
  • K. Nii et al., MOPB098, SRF2015.
  • V. Chouhan et al., MOPLR037, LINAC2016.
  • S. Kato et al., MOPLR038, LINAC2016.
  • K. Nii et al., MOPLR039, LINAC2016.

V Chouhan, MGI (Nov 2016) 24

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SLIDE 25

Thank You

25 V Chouhan, MGI (Nov 2016)