# Electron Beam Characterization of REBCO-Coated Conductors at Cryogenic Conditions
## 3 Results and Discussion
### Electron Stimulated Desorption
#### 3.2.2 Dose Dependence  
The conditioning curves, i.e., the ESD yield decreases with the electron doses, were acquired during a 300 eV electron irradiation performed at 12 K and are reported in Figure 5. The initial yields \(\eta_{0}\), although slightly higher for the RCE-deposited sample, are characteristic of UHV-cleaned metal surfaces. The conditioning rates are just as rapid as for bare technical-grade metal surfaces and represent gas desorption from a non-porous surface. The slope of 0.3\(\sim\)0.4 is typical for water electrodeposition from technical-grade metals. It is most likely the reason for a dynamic balance between electron stimulated water desorption and electron irradiation-induced synthesis. This is commonly observed in water electrodesorption because the H\({}_{2}\)O molecule is known to act as a chemical attractor [54] due to its high binding energy.  
The irradiated RCE-deposited surface showed discoloration following the 300 eV electron conditioning at 12 K, as seen in the inset of Figure 2. Going from a dark to a light shade is unusual and the opposite of what happens to metals due to electron-induced surface graphitization. Instead, this bleaching effect could indicate a reduction of surface oxides and hydroxides.  
The ESD conditioning curves measured here for the studied REBCO coatings also reveal no significant departure from the expected behavior when compared to the technical-grade Cu, Al, and steel previously measured using the same methods [36; 37]. The data equally well compare to data from other authors who conditioned metals held at ambient temperatures in terms of the electro-desorbed gas composition, initial ESD yields \(\eta_{0}\), inflection point location \(D_{1}\), and conditioning rates \(\alpha\). This includes work by [PERSON] and [PERSON] [52], [PERSON] et al. [50], [PERSON] [53] from CERN, [PERSON] et al. [51], [PERSON] [48], and [PERSON] [49].  
The fact that both the SEY and ESD decrease during electron irradiation has severe implications for applicability. As outlined in Section 1, the electron conditioning is leveraged in accelerators during beam-scrubbing [17; 23] to bring down the EC activity by decreasing the SEY and mitigating the dynamic vacuum effect by conditioning the desorption yields.  
An empirical fit, initially proposed by [PERSON] [49] for photodesorption, was used here to approximate the ESD yield dose dependence and possibly extrapolate to higher  
Figure 4: ESD energy dependence of as–received REBCO samples. The RCE–deposited sample (**right**) is characterized at 12 K and PLD–deposited at 19 K (**left**). Note the high uncertainty for water on the right plot, partially due to the high background and partially due to the low signal–to–noise ratio. The best–fit parameters for Equation (4) are listed in the legend. More details are in the text.  
electron doses. The fit builds on a classical power law whose exponent \(\alpha\) controls the slope in the log-log plot at high doses \(D\geq 0.1\) mC\(\cdot\)mm\({}^{-2}\). Parameters \(D_{0}\) and \(D_{1}\) are added to the fraction to extend the applicability toward low doses in a way that the curve asymptotically approaches the constant initial ESD yield \(\eta_{0}\) as \(D\to 0\). The parameter \(D_{0}\) represents the dose imparted at the lowest measurable data point (here, it is the first displayed data point). Parameter \(D_{1}\) is solely used to position the end of the initial plateau.  
\[\eta(D)=\eta_{0}\cdot\left(\frac{D+D_{1}}{D_{0}+D_{1}}\right)^{-\alpha} \tag{5}\]  
Values for \(\eta_{0}\), \(D_{1}\), and \(\alpha\) parameters in Equation (5) can be read directly from the legends in Figure 5 and plugged into the presented parametric fits for the ESD yield dose dependence. The same uncertainty analysis leading to \(\sim\)30 % at 1 \(\sigma\) confidence interval applies to the ESD yield values presented here too, although not plotted.