Development of Hydrogen-free EP
and Hydrogen Absorption Phenomena
Tamao HIGUCHIa and Kenji SAITOb
a) Grad. Univ. Advanced Studies, Japan
b) High Energy Accelerator Research Organization (KEK),
Accelerator Laboratory, Japan
Contents
Introduction
Pursuit the cause for hydrogen Q-disease
No hydrogen Q-disease after ElectroPolishing (EP) only
Hydrogen absorption in Centrifugal Barrel Polishing (CBP)
Hydrogen absorption in Centrifugal Barrel Polishing (CBP)
Surface defects and absorption of hydrogen
Innovation of H-free CBP
Hydrogen Q-disease caused by a combination of H-free CBP and EP
Solution for the hydrogen Q-disease
H-free CBP + Chemical Polishing (CP)
H-free CBP + oxidizer added EP
Conclusion
Introduction
Requirements on Surface Treatment
for Superconducting(SC) RF Cavities
1) High Performance: High Gradient & High Q
2) High Reliability
3) Cost-effective
Purpose of mechanical grinding
Embedded
Cracks
Sputter balls
Mechanical grinding is a powerful method
to remove surface defects
Centrifugal Barrel Polishing (CBP)
Chemical Polishing (CP)
CP solution: Equal mixture of HF(46%), HNO3(60%) and H3PO4(85%)
Horizontal Continuous Electropolishing (EP) TRISTAN
EP solution: mixture of HF(46%) and H2SO4(95%)
Electropolishing (EP) is the preferred technology in KEK
Higher gradient
achievable with EP
10 11
Q0
10 10
10 9
10 80
10
20
30
E acc [MV/m]
40
CBP + pre-EP + EP: Hydrogen Q-disease
10 11
10 10
Q0
10 9
Fast cooling down (1hour)
kept at ~ 100K for 16hours
CBP + pre-EP + EP 50µm
10 8
10 7
0
5
10
E acc [MV/m]
15
20
Discovered: EP-alone does not cause Hydrogen Q-disease.
(KEK 1999)
40
35
Fast cooling down (1 hour)
kept at ~ 100K for 16 hours
30
Rres [ W]
25
20
15
10
5
0
0
50
100
150
200
Removed thickness with EP [µm]
250
Hydrogen-free CBP
Liquid used for CBP Hydrogen concentration comments
in the test sample
Annealing
1.0±0.2
分析前処理
Annealing
1.0±0.2[ppm]
[ppm]
sample conditioning
Soapy water
78.0±2.9 [ppm]
(water + compound)
Demineralized water 79.1±5.0 [ppm]
Standard composition
No compound
(Stones only)
10.9±0.8 [ppm]
無水プロパノール
Propanol
(C33H
H77OH)
OH)
(C
FC-77
FC-77
(C
(C88FF18、
18、C
C88FF1616O)
O)
49.4±2.2 [ppm]
[ppm]
水無し
No water
4.6±2.2
4.6±2.2 [ppm]
[ppm]
水素無し
No hydrogen
(test samples: 2.5mm(H) x 1.0mm(W) x 147mm(L), RRR=200)
H-free CBP + pre-EP + EP: Hydrogen Q-disease
10 11
Fast cooling down (1 hour)
kept at ~ 100 K for 16 hours
10 10
Qo
10 9
H-free CBP (FC-77) + pre-EP + EP 50 µm
10 8
10 7
0
5
10
E acc [MV/m]
15
20
H-free CBP + CP: No Hydrogen Q-disease
10 11
10 10
Q0
10 9
Fast cooling down (1hour)
kept at ~ 100 K for 16 hours
10 8
H-free CBP (FC-77) + CP 50 µm
10 7
0
5
10
15
E acc [MV/m]
20
25
Amount of hydrogen [ppm by weight]
H-free CBP + EP: Hydrogen absorption
H-free CBP + CP: No Hydrogen absorption
20
H-free CBP + EP
H-free CBP + CP
15
10
5
0
0
1
Removed thickness with EP or CP [µm]
H-free CBP + pre-EP (HNO3) + EP: No Hydrogen Q-disease
10 11
10 10
Q0
H-free CBP(FC-77) + pre-EP(HNO 3 ) + EP 50µm
10 9
Fast cooling down (1hour)
kept at ~ 100K for 16hours
10 8
10 7
0
10 11
5
10
15
20
E acc [MV/m]
25
30
35
Dislocation
Grain boundary
Interstitial atoms
tunnel structure
arrangement of atoms at cross section
Other types
Grain boundaries
Dr. Gen KATANO
Tritium SEM autoradiography on high-strength steel
H-free CBP + CP 3 µm
SEM
H-free CBP + EP 1 µm
SEM
Nb
Nb
electric potential
oxide film
Nb
Nb
+
H
Nb
H+
Nb
H+
oxide film
Conclusion
1)
Surface defects due to mechanical grinding is the most likely
cause of hydrogen absorption.
2)
Continuous oxidization process is effective to prevent
hydrogen absorption.
3)
We innovated H-free mechanical grinding method (CBP)
using H-free liquid.
4)
We developed H-free EP by adding a little amount of oxidizer
into the conventional EP solution. This new H-free EP
simplifies the process and reduces the cost dramatically.