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Experimental research on photon-stimulated desorption from CuCrZr
Vacuum 171 (2020) 108981
Contents lists available at ScienceDirect
Vacuum journal homepage: http://www.elsevier.com/locate/vacuum
Experimental research on photon-stimulated desorption from CuCrZr Ming Chen a, b, c, d, Song Xue b, d, *, Zhongliang Li b, d, Bo Li b, d, Junnan Liu b, d, Jiahua Chen b, d a
Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai, 201800, China Shanghai Advanced Research Institute, Chinese Academy of Sciences, Shanghai, 201210, China c University of Chinese Academy of Sciences, Beijing, 100049, China d Shanghai Synchrotron Radiation Facility, Zhangjiang Laboratory, Shanghai, 201204, China b
A R T I C L E I N F O
A B S T R A C T
Keywords: CuCrZr Glidcop Photon-stimulated desorption yield Incident angle
In this study, photon-stimulated gas desorption yields from CuCrZr, which are used for manufacturing high-heatload elements, were measured using a synchrotron light with a critical energy of 10.4 keV at the Shanghai Synchrotron Radiation Facility. CuCrZr samples were exposed to synchrotron radiation (SR) under both normal and grazing incidences. For comparison, a Glidcop sample was also exposed to SR under normal incidence. The experimental apparatus and measurement principles for photon desorption yield are described in this paper and the results of measurements are discussed.
1. Introduction
2. Experimental setup and methods
The Shanghai synchrotron radiation facility (SSRF) contains a thirdgeneration light source with a 3.5 GeV electron beam in its storage ring. High-heat-load components for a beamline, including masks, absorbers, slits, and photon shutters, are typically manufactured from Glidcop based on its good thermal conductivity and high strength at high tem peratures [1,2]. However, a novel design that replaces Glidcop with the less expensive and readily available copper alloy CuCrZr was used in the NSLS-II, ESRF, and TPS facilities. CuCrZr has good thermal conductivity, a high softening temperature, and high mechanical strength [3–6]. The desorption of gases from CuCrZr during baking and the stability of CuCrZr flanges fabricated for use as vacuum seals following baking were reported in Ref. [6]. The measurement of desorption yield under a light source is very important and is an essential experimental research topic, particularly when a vacuum system is composed of new materials and subjected to new surface treatments. In this study, two types of high-heat-load materials, namely CuCrZr and Glidcop, were placed in a test vacuum chamber to evaluate the dependence of the desorption yield of CuCrZr on photon dose and incident angle. Inclining the surfaces of the high-heat-load components with respect to the photon beam reduces power density, but increases the probability of photon reflection and photoelectron production, both of which cause gas desorption [7]. Therefore, a slit was used to determine the number of the introduced photons and scrape the low-photon-energy portion of synchrotron ra diation (SR) to reduce the gas desorption caused by reflected photons.
Experiments were performed at the BL09B beamline of the SSRF, as shown in Fig. 1 [8]. SR was extracted from a bending magnet in the storage ring. The beamline was operated in white beam mode with the monochromator and toroidal mirror moved out of the photon beam path. The synchrotron light with a critical energy of 10.4 keV was used to generate photons. The SR was scraped by a slit with vertical and horizontal opening sizes of 1.5 mm and 6 mm, respectively. The slit was located 18 m from the source point. The photons entered the test chamber, which is constructed from SUS316L stainless steel with the vacuum fired at 950 � C for 2 h, through an orifice (φ20 � 20 mm). The area of the normal incident photons on the sample, which was located at a distance of 31 m from the source point, was approximately 2.6 mm high and 10.3 mm wide. The samples were set on a stainless-steel stage with a cooling channel and deionised (DI) water was used to reduce the thermal desorption contribution. The temperature was measured using a thermocouple. The experimental apparatus was connected to the beamline through a gate valve. A combination of an ion pump (100 l s 1 for N2) and a nonevaporable getter pump (400 l s 1 for H2) installed on the pumping chamber offered a total pumping speed of 200 l s 1 for N2, which is much greater than the conductance of the orifice (19.1 l s 1 for N2). The total pressure and partial pressure (nitrogen-equivalent) were measured using calibrated extractor gauges (Leybold IE514) [9] and calibrated quadrupole mass spectrometers (Inficon MPS100 M) [10].
* Corresponding author. Shanghai Synchrotron Radiation Facility, Zhangjiang Laboratory, Shanghai, 201204, China. E-mail address: [email protected] (S. Xue). https://doi.org/10.1016/j.vacuum.2019.108981 Received 1 May 2019; Received in revised form 28 September 2019; Accepted 29 September 2019 Available online 30 September 2019 0042-207X/© 2019 Elsevier Ltd. All rights reserved.
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Four samples were tested. One was made of Glidcop and subjected to normal incidence. The others were made of CuCrZr (ASTM C18150) and subjected to different incidence angles. The samples were fabricated via low-speed wire electrical discharge machining. The samples were cleaned in an ultrasonic bath using Citranox detergent (2% by volume) at 60 � C for 10 min, followed by rinsing with DI water for 10 min, and drying in a hot oven at 150 � C. The experimental chamber containing the samples was baked at 250 � C for 24 h, after which the average base pressure was approximately 4.9 � 10 7 Pa inside the test chamber. The pressure level during radiation was approximately 50 times greater than that prior to radiation. Desorption experiments were performed using the throughput method [11]. The gas desorption yield η, which is defined as the ratio of desorbed gas molecules Nmol per incident photon Nph, is written as � �� � Pb1 Pb2 K � C � Pa1 Pa2 N η ¼ mol ¼ ; (1) Nph Nph where K, which is the conversion coefficient, is equal to 2.44 � 1017 (molecules Pa 1 l 1); C (l s 1) is the conductance of the orifice for each gas species; P1 and P2 (Pa) are the pressures in the test chamber and pumping chamber, respectively; and the superscripts a and b above P1 and P2 indicate dynamic pressure and base pressure, respectively. A photon flux curve was obtained using the SPECTRA software, as shown in Fig. 2. The number of incident photons per second was determined by integrating the photon flux with respect to the photon energy. The calculated number of incident photons per second was 5.146 � 1015 photons s 1. During the experiments, the SSRF storage ring operated in top-up mode.
Fig. 2. Photon flux curve of BL09B with SR scraped by a 6 (H) � 1.5 mm (V) slit located at a distance of 18 m from the source point.
exhibits a similar trend at doses above 2 � 102 mA h. At a dose of 2.2 � 104 mA h, which corresponds to 6.3 � 1019 photons mm 2, the ηtotal values of CuCrZr and Glidcop are 1.9 � 10 3 molecules photon 1 and 2.5 � 10 3 molecules photon 1, respectively. Data for higher doses can be described by the power function of the doses. The exponential coefficients of the power law were found to be 0.6 for CuCrZr and 0.7 for Glidcop, as shown in Fig. 3. This indicates that the ηtotal value of CuCrZr decreases more slowly than that of Glidcop. The slopes for CuCrZr and Glidcop are lower than that for oxygen-free high-thermalconductivity (OFHC) copper, which was presented in Ref. [12]. Ac cording to the fitting formula, when the cumulative dose reaches 1 � 105 mA h, the ηtotal value will be 7.8 � 10 4 molecules photon 1 for CuCrZr and 9.1 � 10 4 molecules photon 1 for Glidcop. Fig. 4(a) and (b) present the photon-stimulated specific gas desorp tion yields ηi for CuCrZr and Glidcop respectively, as a function of the integrated photon beam dose. In Fig. 4(a), ηi varies from 6.0 � 10 3 molecules photon 1 for CO2 to 3.1 � 10 4 molecules photon 1 for CH4 with an initial dose of 10 mA h, which corresponds to 2.9 � 1016 photons mm 2. With continued photon exposure, the ηi values of CO2, CO, H2, and CH4 largely follow the same trend as the total desorption yield
3. Results and discussion 3.1. Desorption yield as a function of photon dose Fig. 3 presents the dependence of the total desorption yield ηtotal on the photon dose for CuCrZr and Glidcop. The results indicate that the ηtotal value for CuCrZr is lower than that for Glidcop. As shown in the figure, the ηtotal value of CuCrZr is initially 1.4 � 10 2 molecules pho ton 1, which is almost an order of magnitude lower than that of Glidcop. With an increase in the cumulative dose, the desorption yields gradually decrease. After the cumulative dose increases beyond 6 � 103 mA h, the ηtotal value of CuCrZr exhibits a fixed declining trend, whereas Glidcop
Fig. 1. Schematic of the experimental setup: (SR) synchrotron radiation, (SIP) sputtering ion pump, (NEG) non-evaporable getter pump, (TC) thermocouple, (CW) cooling water, (QMS) quadrupole mass spectrometer, (EG) extractor gauge, and (θ) incident angle. 2
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Vacuum 171 (2020) 108981
molecules photon 1, while CH4 decreases by a factor of approximately 10, as shown in Table 1. Compared to the ηi values for Glidcop, the yields of H2 and CH4 for CuCrZr are slightly lower, whereas the yields of H2O, CO, and CO2 are slightly higher. These results are similar to the desorption yields for OFHC copper, which were published in Refs. [12, 15]. 3.2. Photon desorption yields under normal and grazing incidence High-heat-load components typically have inclined surfaces to reduce the power density of synchrotron light. To understand the in fluence of the incident angle on desorption yield, three CuCrZr samples with different incident angles were exposed to SR. From Fig. 5, one can see that at the beginning of photon irradiation, the influence of the incident angle on the total desorption yield is significant. The photon desorption yield at an incident angle of 30� is four times that at normal incidence and the total desorption yield at an incident angle of 5� is 12 times that at normal incidence. With an increasing radiation dose, this effect is diminished. At a dose of 1.5 � 104 mA h, the total desorption yield at an incident angle of 30� is 1.4 times greater than that at normal incidence and the total desorption yield at an incident angle of 5� is two times greater than that at normal incidence. These results indicate that the smaller the incident angle, the higher the total desorption yield. This trend is in agreement with the trend presented in Ref. [16], where the total desorption yield at an incident angle of 10� was approximately four times greater than that at normal incidence for an aluminium alloy. Fig. 6(a) and (b) present the main specific desorption yield ηi for CuCrZr and as a function of the integrated photon beam dose at incident angle of 5� and 30� , respectively. Initially, the yield of CO2 is the highest, but it decreases significantly as the radiation dose increases. The yield of H2 is the highest at the end of the experiments. The trends of the main specific desorption yields at incident angle of 5� and 30� are similar to
Fig. 3. Variation in the total desorption yield ηtotal under normal incidence as a function of the integrated photon dose for CuCrZr and Glidcop.
decreases. The desorption of H2O increases significantly with photon exposure until reaching saturation, which is two to three times greater than the original value. Some authors [13,14] have postulated that the surface desorption process may result in an instant increase in H2O at the beginning of synchrotron light irradiation. As the beam dose increases, surface desorption disappears. Diffusion then controls the photon-induced desorption rate [13,14]. After reaching a dose of 2.2 � 104 mA h, the ηi values of H2, CO, CO2, and H2O decrease to 10 4
Fig. 4. Variation in the main specific desorption yield ηi under normal incidence as a function of integrated photon dose for (a) CuCrZr and (b) Glidcop. Table 1 Total yields and main specific yields at different doses for CuCrZr and Glidcop. Sample CuCrZr Glidcop
Dose (mA⋅h) 10 2.2 � 104 10 2.2 � 104
Dose (photons mm 2.9 � 1016 6.3 � 1019 2.9 � 1016 6.3 � 1019
2
)
Total yield (molecules photon 1.4 � 10 1.9 � 10 1.0 � 10 2.5 � 10
2
1
)
Specific yield (molecules photon
1
H2
H2O
2.8 � 10 5.2 � 10 5.9 � 10 6.7 � 10
3 1 3
3
CH4 3 4 3 4
3.1 � 10 5.2 � 10 7.2 � 10 5.9 � 10
4 5 4 5
)
4.6 � 10 3.5 � 10 7.9 � 10 1.8 � 10
CO 4 4 4 4
2.6 � 10 3.1 � 10 4.1 � 10 2.5 � 10
CO2 3 4 3 4
6.0 � 10 3.7 � 10 1.5 � 10 2.9 � 10
3 4 2 4
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Vacuum 171 (2020) 108981
incident Angle. 4. Conclusions Exposure-dose-dependent photon-stimulated desorption (PSD) phe nomena, including measurements of the total and main desorption yields of CuCrZr and Glidcop, as well as the desorption yields at different incident angles, were described in this paper. The results indicate that the ηtotal value for CuCrZr is lower than that for Glidcop, which has been widely used in high-heat-load components. This can be attributed to the difference in the impurities and the ab sorption on the surface layers. Based on the experimental results, it was determined that CO2 contributes the majority of PSD yield at lower beam doses, whereas H2 is dominant at higher beam doses. This may be because desorption gases in the initial stages of radiation stem from surface oxidation layers. With an increase in radiation dose, a large amount of the hydrogen dissolved in metals is diffused to the surface and begins to desorb. Pumping speeds are typically designed to realise a target dynamic pressure of approximately 10 7 Pa when the PSD yield is 10 6 molecules photon 1 [17]. During machine operation, beam cleaning of a vacuum system effectively reduces desorption yields by several orders of magnitude. According to the slope of CuCrZr, when the dose reaches 1024 photons mm 2, the PSD yield will reach 10 6 molecules photon 1, indicating that CuCrZr is suitable for use in high-heat-load components. From the perspective of the optimised design, an incident angle of 5� for SR irradiation on the surface of CuCrZr is better than an incident angle of 30� and normal incidence. Because power density decreases by an order of magnitude on average, the PSD yield only increases by two times. For the purposes of reducing PSD yield, CuCrZr following glow
Fig. 5. Variation in total desorption yield ηtotal under different incident angles as a function of the integrated photon dose for CuCrZr.
that under normal incidence. From Table 2, one can see that the specific desorption yields of H2, CO, and CO2 also follow the trend that the smaller the incident angle, the higher the desorption yield. However, at a dose of 10 mA h, the desorption yields of H2O at incident angle of 5� and 30� are almost equal. This phenomenon also occurs for CH4 and H2O at a dose of 1.5 � 104 mA h. The results indicate that the desorption yields of H2, CO and CO2 are strongly correlated with the incident Angle, while the desorption yields of H2O and CH4 are weakly correlated with the
Fig. 6. Variation in main specific desorption yield ηi as a function of the integrated photon dose for CuCrZr at incident angles of (a) 5� and (b) 30� . Table 2 Total yield and main specific yield at different doses and incident angles for CuCrZr. Dose (mA⋅h)
incident angle
Total yield (molecules photon 1)
10
normal incidence 30� incidence 5� incidence normal incidence 30� incidence 5� incidence
1.4 � 10 5.9 � 10 1.7 � 10 2.5 � 10 3.4 � 10 5.0 � 10
Specific yield (molecules photon 1) CH4
H2
1.5 � 104
2 2 1 3 3 3
2.8 � 10 6.3 � 10 1.5 � 10 6.2 � 10 9.6 � 10 1.3 � 10
4
3 3 2 4 4 3
3.1 � 10 1.3 � 10 2.3 � 10 7.2 � 10 1.1 � 10 1.2 � 10
H2O 4 3 3 5 4 4
4.6 � 10 2.4 � 10 2.5 � 10 4.2 � 10 4.3 � 10 4.8 � 10
CO 4 3 3 4 4 4
2.6 � 10 6.4 � 10 1.1 � 10 3.8 � 10 5.0 � 10 7.2 � 10
CO2 3 3 2 4 4 4
6.0 � 10 1.9 � 10 2.9 � 10 4.7 � 10 6.3 � 10 8.7 � 10
3 2 2 4 4 4
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Vacuum 171 (2020) 108981
discharge pre-treatment and TiZrV-coated CuCrZr will be studied in the future.
[5] P. Raimondi, ESRF EBS accelerator upgrade, in: Proceedings of IPAC 2016, May. 2016. Busan, Korea. [6] C. Shueh, C.K. Chan, C.C. Chang, I.C. Sheng, Investigation of vacuum properties of CuCrZr alloy for high-heat-load absorber, Nucl. Instrum. Methods Phys. Res. 841 (2017) 1–4. [7] B.A. Trickett, C. Burnside, G. Le Flem, D. Schmied, Effects of high energy synchrotron radiation at copper surfaces, Vacuum 41 (1990) 2086–2088. [8] Zhongliang Li, Yichen Fan, Lian Xue, Zengyan Zhang, Jie Wang, The design of the test beamline at SSRF, in: AIP Conference Proceedings, vol. 2054, 2019, 060040. [9] Detian Li, Meiru Guo, Yongjun Cheng, Feng Yan, Dixin Zhang, Vacuum-calibration apparatus with pressure down to 10 -10 Pa, J. Vac. Sci. Technol. A 28 (2010) 1099–1104. [10] Meng Dong, Yongjun Cheng, Detian Li, Wenjun Sun, Lan Zhao, Meriru Guo, Yongjun Wang, Huzhong Zhang, Yanwu Li, Gang Li, Newly developed apparatus for calibration of quadrupole mass spectrometer, Meas. Sci. Technol. 28 (2017), 015002. [11] N. Ota, K. Kanazawa, M. Kobayashi, H. Ishimaru, Outgassing from aluminum surface layer induced by synchrotron radiation, J. Vac. Sci. Technol. A 14 (1996) 2641–2644. [12] O. Gr€ obner, A.G. Mathewson, P.C. Marin, Gas desorption from an oxygen free high conductivity copper vacuum chamber by synchrotron radiation photons, J. Vac. Sci. Technol. A 12 (1994) 846–853. [13] J.R. Chen, G.Y. Hsiung, J.R. Huang, C.M. Chang, Y.C. Liu, Synchrotron radiation induced H2O desorption from aluminum surfaces, J. Vac. Sci. Technol. A 15 (1994) 736. [14] J. G� omez-Go~ ni, Photon stimulated desorption from copper and aluminum chambers, J. Vac. Sci. Technol. A 25 (4) (2007) 1251–1255. [15] C.L. Foerster, C. Lanni, C. Perkins, M. Calderon, W. Barletta, Photon stimulated desorption measurements of extruded copper and of welded copper beam chambers for the PEPII asymmetric B factory, J. Vac. Sci. Technol. A 13 (1995) 581. [16] Y. Hori, M. Kobayashi, Photodesorption and photoelectron yields at normal and grazing incidence, Vacuum 44 (1993) 531–533. [17] K. Kanazawa, S. Kato, Y. Suetsugu, H. Hisamatsu, M. Shimamoto, M. Shirai, The vacuum system of KEKB, Nucl. Instrum. Methods Phys. Res. 499 (2003) 66–74.
Declaration of competing interest The authors declared that they have no conflicts of interest to this work. We declare that we do not have any commercial or associative interest that represents a conflict of interest in connection with the work submitted. Acknowledgements The authors wish to thank Zhouxia Zhu, WenBin Zhao, Yuzhu Wang, and Chaofan Xue for their excellent support. The assistance provided by the SSRF operations team for their expertise in running the storage ring in top-up mode is also gratefully acknowledged. This work was sup ported by the National Natural Science Foundation of China under Contract NO. U1832172. References [1] Abderrazak Daoud, Jean-Bernard Vogt, Eric Charkaluk, Lin Zhang, JeanClaude Biasci, Effect of temperature on the low cycle fatigue behavior of Glidcop Al-15, Procedia Eng. 2 (2010) 1487–1495. [2] Sunao Takahashi, Mutsumi Sano, Tetsuro Mochizuki, Atsuo Watanabe, Hideo Kitamura, Fatigue life prediction for high-heat-load components made of GlidCop by elastic-plastic analysis, J. Synchrotron Radiat. 15 (2008) 144–150. [3] S. Sharma, A novel design of high power masks and slits, in: Proceedings of MEDSI 2014, Sep. 2014. Melbourne, Australia. [4] F. DePaola, C. Amundsen, S. Sharma, Manufacturing of photon beam-intercepting components from CuCrZr, in: Proceedings of MEDSI 2016, Sep. 2016. Barcelona, Spain.
5
Contents lists available at ScienceDirect
Vacuum journal homepage: http://www.elsevier.com/locate/vacuum
Experimental research on photon-stimulated desorption from CuCrZr Ming Chen a, b, c, d, Song Xue b, d, *, Zhongliang Li b, d, Bo Li b, d, Junnan Liu b, d, Jiahua Chen b, d a
Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai, 201800, China Shanghai Advanced Research Institute, Chinese Academy of Sciences, Shanghai, 201210, China c University of Chinese Academy of Sciences, Beijing, 100049, China d Shanghai Synchrotron Radiation Facility, Zhangjiang Laboratory, Shanghai, 201204, China b
A R T I C L E I N F O
A B S T R A C T
Keywords: CuCrZr Glidcop Photon-stimulated desorption yield Incident angle
In this study, photon-stimulated gas desorption yields from CuCrZr, which are used for manufacturing high-heatload elements, were measured using a synchrotron light with a critical energy of 10.4 keV at the Shanghai Synchrotron Radiation Facility. CuCrZr samples were exposed to synchrotron radiation (SR) under both normal and grazing incidences. For comparison, a Glidcop sample was also exposed to SR under normal incidence. The experimental apparatus and measurement principles for photon desorption yield are described in this paper and the results of measurements are discussed.
1. Introduction
2. Experimental setup and methods
The Shanghai synchrotron radiation facility (SSRF) contains a thirdgeneration light source with a 3.5 GeV electron beam in its storage ring. High-heat-load components for a beamline, including masks, absorbers, slits, and photon shutters, are typically manufactured from Glidcop based on its good thermal conductivity and high strength at high tem peratures [1,2]. However, a novel design that replaces Glidcop with the less expensive and readily available copper alloy CuCrZr was used in the NSLS-II, ESRF, and TPS facilities. CuCrZr has good thermal conductivity, a high softening temperature, and high mechanical strength [3–6]. The desorption of gases from CuCrZr during baking and the stability of CuCrZr flanges fabricated for use as vacuum seals following baking were reported in Ref. [6]. The measurement of desorption yield under a light source is very important and is an essential experimental research topic, particularly when a vacuum system is composed of new materials and subjected to new surface treatments. In this study, two types of high-heat-load materials, namely CuCrZr and Glidcop, were placed in a test vacuum chamber to evaluate the dependence of the desorption yield of CuCrZr on photon dose and incident angle. Inclining the surfaces of the high-heat-load components with respect to the photon beam reduces power density, but increases the probability of photon reflection and photoelectron production, both of which cause gas desorption [7]. Therefore, a slit was used to determine the number of the introduced photons and scrape the low-photon-energy portion of synchrotron ra diation (SR) to reduce the gas desorption caused by reflected photons.
Experiments were performed at the BL09B beamline of the SSRF, as shown in Fig. 1 [8]. SR was extracted from a bending magnet in the storage ring. The beamline was operated in white beam mode with the monochromator and toroidal mirror moved out of the photon beam path. The synchrotron light with a critical energy of 10.4 keV was used to generate photons. The SR was scraped by a slit with vertical and horizontal opening sizes of 1.5 mm and 6 mm, respectively. The slit was located 18 m from the source point. The photons entered the test chamber, which is constructed from SUS316L stainless steel with the vacuum fired at 950 � C for 2 h, through an orifice (φ20 � 20 mm). The area of the normal incident photons on the sample, which was located at a distance of 31 m from the source point, was approximately 2.6 mm high and 10.3 mm wide. The samples were set on a stainless-steel stage with a cooling channel and deionised (DI) water was used to reduce the thermal desorption contribution. The temperature was measured using a thermocouple. The experimental apparatus was connected to the beamline through a gate valve. A combination of an ion pump (100 l s 1 for N2) and a nonevaporable getter pump (400 l s 1 for H2) installed on the pumping chamber offered a total pumping speed of 200 l s 1 for N2, which is much greater than the conductance of the orifice (19.1 l s 1 for N2). The total pressure and partial pressure (nitrogen-equivalent) were measured using calibrated extractor gauges (Leybold IE514) [9] and calibrated quadrupole mass spectrometers (Inficon MPS100 M) [10].
* Corresponding author. Shanghai Synchrotron Radiation Facility, Zhangjiang Laboratory, Shanghai, 201204, China. E-mail address: [email protected] (S. Xue). https://doi.org/10.1016/j.vacuum.2019.108981 Received 1 May 2019; Received in revised form 28 September 2019; Accepted 29 September 2019 Available online 30 September 2019 0042-207X/© 2019 Elsevier Ltd. All rights reserved.
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Four samples were tested. One was made of Glidcop and subjected to normal incidence. The others were made of CuCrZr (ASTM C18150) and subjected to different incidence angles. The samples were fabricated via low-speed wire electrical discharge machining. The samples were cleaned in an ultrasonic bath using Citranox detergent (2% by volume) at 60 � C for 10 min, followed by rinsing with DI water for 10 min, and drying in a hot oven at 150 � C. The experimental chamber containing the samples was baked at 250 � C for 24 h, after which the average base pressure was approximately 4.9 � 10 7 Pa inside the test chamber. The pressure level during radiation was approximately 50 times greater than that prior to radiation. Desorption experiments were performed using the throughput method [11]. The gas desorption yield η, which is defined as the ratio of desorbed gas molecules Nmol per incident photon Nph, is written as � �� � Pb1 Pb2 K � C � Pa1 Pa2 N η ¼ mol ¼ ; (1) Nph Nph where K, which is the conversion coefficient, is equal to 2.44 � 1017 (molecules Pa 1 l 1); C (l s 1) is the conductance of the orifice for each gas species; P1 and P2 (Pa) are the pressures in the test chamber and pumping chamber, respectively; and the superscripts a and b above P1 and P2 indicate dynamic pressure and base pressure, respectively. A photon flux curve was obtained using the SPECTRA software, as shown in Fig. 2. The number of incident photons per second was determined by integrating the photon flux with respect to the photon energy. The calculated number of incident photons per second was 5.146 � 1015 photons s 1. During the experiments, the SSRF storage ring operated in top-up mode.
Fig. 2. Photon flux curve of BL09B with SR scraped by a 6 (H) � 1.5 mm (V) slit located at a distance of 18 m from the source point.
exhibits a similar trend at doses above 2 � 102 mA h. At a dose of 2.2 � 104 mA h, which corresponds to 6.3 � 1019 photons mm 2, the ηtotal values of CuCrZr and Glidcop are 1.9 � 10 3 molecules photon 1 and 2.5 � 10 3 molecules photon 1, respectively. Data for higher doses can be described by the power function of the doses. The exponential coefficients of the power law were found to be 0.6 for CuCrZr and 0.7 for Glidcop, as shown in Fig. 3. This indicates that the ηtotal value of CuCrZr decreases more slowly than that of Glidcop. The slopes for CuCrZr and Glidcop are lower than that for oxygen-free high-thermalconductivity (OFHC) copper, which was presented in Ref. [12]. Ac cording to the fitting formula, when the cumulative dose reaches 1 � 105 mA h, the ηtotal value will be 7.8 � 10 4 molecules photon 1 for CuCrZr and 9.1 � 10 4 molecules photon 1 for Glidcop. Fig. 4(a) and (b) present the photon-stimulated specific gas desorp tion yields ηi for CuCrZr and Glidcop respectively, as a function of the integrated photon beam dose. In Fig. 4(a), ηi varies from 6.0 � 10 3 molecules photon 1 for CO2 to 3.1 � 10 4 molecules photon 1 for CH4 with an initial dose of 10 mA h, which corresponds to 2.9 � 1016 photons mm 2. With continued photon exposure, the ηi values of CO2, CO, H2, and CH4 largely follow the same trend as the total desorption yield
3. Results and discussion 3.1. Desorption yield as a function of photon dose Fig. 3 presents the dependence of the total desorption yield ηtotal on the photon dose for CuCrZr and Glidcop. The results indicate that the ηtotal value for CuCrZr is lower than that for Glidcop. As shown in the figure, the ηtotal value of CuCrZr is initially 1.4 � 10 2 molecules pho ton 1, which is almost an order of magnitude lower than that of Glidcop. With an increase in the cumulative dose, the desorption yields gradually decrease. After the cumulative dose increases beyond 6 � 103 mA h, the ηtotal value of CuCrZr exhibits a fixed declining trend, whereas Glidcop
Fig. 1. Schematic of the experimental setup: (SR) synchrotron radiation, (SIP) sputtering ion pump, (NEG) non-evaporable getter pump, (TC) thermocouple, (CW) cooling water, (QMS) quadrupole mass spectrometer, (EG) extractor gauge, and (θ) incident angle. 2
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molecules photon 1, while CH4 decreases by a factor of approximately 10, as shown in Table 1. Compared to the ηi values for Glidcop, the yields of H2 and CH4 for CuCrZr are slightly lower, whereas the yields of H2O, CO, and CO2 are slightly higher. These results are similar to the desorption yields for OFHC copper, which were published in Refs. [12, 15]. 3.2. Photon desorption yields under normal and grazing incidence High-heat-load components typically have inclined surfaces to reduce the power density of synchrotron light. To understand the in fluence of the incident angle on desorption yield, three CuCrZr samples with different incident angles were exposed to SR. From Fig. 5, one can see that at the beginning of photon irradiation, the influence of the incident angle on the total desorption yield is significant. The photon desorption yield at an incident angle of 30� is four times that at normal incidence and the total desorption yield at an incident angle of 5� is 12 times that at normal incidence. With an increasing radiation dose, this effect is diminished. At a dose of 1.5 � 104 mA h, the total desorption yield at an incident angle of 30� is 1.4 times greater than that at normal incidence and the total desorption yield at an incident angle of 5� is two times greater than that at normal incidence. These results indicate that the smaller the incident angle, the higher the total desorption yield. This trend is in agreement with the trend presented in Ref. [16], where the total desorption yield at an incident angle of 10� was approximately four times greater than that at normal incidence for an aluminium alloy. Fig. 6(a) and (b) present the main specific desorption yield ηi for CuCrZr and as a function of the integrated photon beam dose at incident angle of 5� and 30� , respectively. Initially, the yield of CO2 is the highest, but it decreases significantly as the radiation dose increases. The yield of H2 is the highest at the end of the experiments. The trends of the main specific desorption yields at incident angle of 5� and 30� are similar to
Fig. 3. Variation in the total desorption yield ηtotal under normal incidence as a function of the integrated photon dose for CuCrZr and Glidcop.
decreases. The desorption of H2O increases significantly with photon exposure until reaching saturation, which is two to three times greater than the original value. Some authors [13,14] have postulated that the surface desorption process may result in an instant increase in H2O at the beginning of synchrotron light irradiation. As the beam dose increases, surface desorption disappears. Diffusion then controls the photon-induced desorption rate [13,14]. After reaching a dose of 2.2 � 104 mA h, the ηi values of H2, CO, CO2, and H2O decrease to 10 4
Fig. 4. Variation in the main specific desorption yield ηi under normal incidence as a function of integrated photon dose for (a) CuCrZr and (b) Glidcop. Table 1 Total yields and main specific yields at different doses for CuCrZr and Glidcop. Sample CuCrZr Glidcop
Dose (mA⋅h) 10 2.2 � 104 10 2.2 � 104
Dose (photons mm 2.9 � 1016 6.3 � 1019 2.9 � 1016 6.3 � 1019
2
)
Total yield (molecules photon 1.4 � 10 1.9 � 10 1.0 � 10 2.5 � 10
2
1
)
Specific yield (molecules photon
1
H2
H2O
2.8 � 10 5.2 � 10 5.9 � 10 6.7 � 10
3 1 3
3
CH4 3 4 3 4
3.1 � 10 5.2 � 10 7.2 � 10 5.9 � 10
4 5 4 5
)
4.6 � 10 3.5 � 10 7.9 � 10 1.8 � 10
CO 4 4 4 4
2.6 � 10 3.1 � 10 4.1 � 10 2.5 � 10
CO2 3 4 3 4
6.0 � 10 3.7 � 10 1.5 � 10 2.9 � 10
3 4 2 4
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incident Angle. 4. Conclusions Exposure-dose-dependent photon-stimulated desorption (PSD) phe nomena, including measurements of the total and main desorption yields of CuCrZr and Glidcop, as well as the desorption yields at different incident angles, were described in this paper. The results indicate that the ηtotal value for CuCrZr is lower than that for Glidcop, which has been widely used in high-heat-load components. This can be attributed to the difference in the impurities and the ab sorption on the surface layers. Based on the experimental results, it was determined that CO2 contributes the majority of PSD yield at lower beam doses, whereas H2 is dominant at higher beam doses. This may be because desorption gases in the initial stages of radiation stem from surface oxidation layers. With an increase in radiation dose, a large amount of the hydrogen dissolved in metals is diffused to the surface and begins to desorb. Pumping speeds are typically designed to realise a target dynamic pressure of approximately 10 7 Pa when the PSD yield is 10 6 molecules photon 1 [17]. During machine operation, beam cleaning of a vacuum system effectively reduces desorption yields by several orders of magnitude. According to the slope of CuCrZr, when the dose reaches 1024 photons mm 2, the PSD yield will reach 10 6 molecules photon 1, indicating that CuCrZr is suitable for use in high-heat-load components. From the perspective of the optimised design, an incident angle of 5� for SR irradiation on the surface of CuCrZr is better than an incident angle of 30� and normal incidence. Because power density decreases by an order of magnitude on average, the PSD yield only increases by two times. For the purposes of reducing PSD yield, CuCrZr following glow
Fig. 5. Variation in total desorption yield ηtotal under different incident angles as a function of the integrated photon dose for CuCrZr.
that under normal incidence. From Table 2, one can see that the specific desorption yields of H2, CO, and CO2 also follow the trend that the smaller the incident angle, the higher the desorption yield. However, at a dose of 10 mA h, the desorption yields of H2O at incident angle of 5� and 30� are almost equal. This phenomenon also occurs for CH4 and H2O at a dose of 1.5 � 104 mA h. The results indicate that the desorption yields of H2, CO and CO2 are strongly correlated with the incident Angle, while the desorption yields of H2O and CH4 are weakly correlated with the
Fig. 6. Variation in main specific desorption yield ηi as a function of the integrated photon dose for CuCrZr at incident angles of (a) 5� and (b) 30� . Table 2 Total yield and main specific yield at different doses and incident angles for CuCrZr. Dose (mA⋅h)
incident angle
Total yield (molecules photon 1)
10
normal incidence 30� incidence 5� incidence normal incidence 30� incidence 5� incidence
1.4 � 10 5.9 � 10 1.7 � 10 2.5 � 10 3.4 � 10 5.0 � 10
Specific yield (molecules photon 1) CH4
H2
1.5 � 104
2 2 1 3 3 3
2.8 � 10 6.3 � 10 1.5 � 10 6.2 � 10 9.6 � 10 1.3 � 10
4
3 3 2 4 4 3
3.1 � 10 1.3 � 10 2.3 � 10 7.2 � 10 1.1 � 10 1.2 � 10
H2O 4 3 3 5 4 4
4.6 � 10 2.4 � 10 2.5 � 10 4.2 � 10 4.3 � 10 4.8 � 10
CO 4 3 3 4 4 4
2.6 � 10 6.4 � 10 1.1 � 10 3.8 � 10 5.0 � 10 7.2 � 10
CO2 3 3 2 4 4 4
6.0 � 10 1.9 � 10 2.9 � 10 4.7 � 10 6.3 � 10 8.7 � 10
3 2 2 4 4 4
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discharge pre-treatment and TiZrV-coated CuCrZr will be studied in the future.
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Declaration of competing interest The authors declared that they have no conflicts of interest to this work. We declare that we do not have any commercial or associative interest that represents a conflict of interest in connection with the work submitted. Acknowledgements The authors wish to thank Zhouxia Zhu, WenBin Zhao, Yuzhu Wang, and Chaofan Xue for their excellent support. The assistance provided by the SSRF operations team for their expertise in running the storage ring in top-up mode is also gratefully acknowledged. This work was sup ported by the National Natural Science Foundation of China under Contract NO. U1832172. References [1] Abderrazak Daoud, Jean-Bernard Vogt, Eric Charkaluk, Lin Zhang, JeanClaude Biasci, Effect of temperature on the low cycle fatigue behavior of Glidcop Al-15, Procedia Eng. 2 (2010) 1487–1495. [2] Sunao Takahashi, Mutsumi Sano, Tetsuro Mochizuki, Atsuo Watanabe, Hideo Kitamura, Fatigue life prediction for high-heat-load components made of GlidCop by elastic-plastic analysis, J. Synchrotron Radiat. 15 (2008) 144–150. [3] S. Sharma, A novel design of high power masks and slits, in: Proceedings of MEDSI 2014, Sep. 2014. Melbourne, Australia. [4] F. DePaola, C. Amundsen, S. Sharma, Manufacturing of photon beam-intercepting components from CuCrZr, in: Proceedings of MEDSI 2016, Sep. 2016. Barcelona, Spain.
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