Frequency dependence of surface resistance and nonequilibrium superconductivity

Frequency dependence of surface resistance and non-equilibrium superconductivity Martina Martinello TESLA Technology Collaboration Meeting 8 Feb 2018

Outline • Introduction • Data analysis • RT field-dependence at different frequencies • Non-equilibrium superconductivity • Trapped flux sensitivity frequency-dependence • Conclusions 2 Martina Martinello | TTC Meeting 2018, Milan

RBCS(Eacc) at 1. 3 GHz A. Romanenko and A. Grassellino, Appl. Phys. Lett. 102, (2013) A. Grassellino et al. , Supercond. Sci. Technol. 26, 102001 (2013) From 1. 3 GHz data we know that: • RBCS(Eacc) increases in regular niobium cavities (EP, BCP, 120 C baking) • RBCS(Eacc) decreases in N-doped niobium cavities 3 Martina Martinello | TTC Meeting 2018, Milan

RBCS(Eacc) at 1. 3 GHz A. Romanenko and A. Grassellino, Appl. Phys. Lett. 102, (2013) A. Grassellino et al. , Supercond. Sci. Technol. 26, 102001 (2013) From 1. 3 GHz data we know that: • RBCS(Eacc) increases in regular niobium cavities (EP, BCP, 120 C baking) • RBCS(Eacc) decreases in N-doped niobium cavities How do these field dependences change with the frequency? 4 Martina Martinello | TTC Meeting 2018, Milan

Outline • Introduction • Data analysis • RT field-dependence at different frequencies • Non-equilibrium superconductivity • Trapped flux sensitivity frequency-dependence • Conclusions 5 Martina Martinello | TTC Meeting 2018, Milan

Analyzed Cavities N-doping 120 C baking EP/BCP 1. 3 GHz, 2 K 650 MHz EP BCP 120 C baking 2/6 N-doping 6 Martina Martinello | TTC Meeting 2018, Milan 1. 3 GHz 2. 6 GHz 3. 9 GHz

Data Analysis For each cavity: • Surface resistance decomposition: 7 Martina Martinello | TTC Meeting 2018, Milan

1 a. T-dependent Surface Resistance (650 MHz and 1. 3 GHz) 1. 3 GHz Because of the exponential decreasing with T, RT at 1. 5 K is negligible at low frequencies : RT (2 K) can be calculated as: Rres 8 Martina Martinello | TTC Meeting 2018, Milan

1 b. T-dependent Surface Resistance (2. 6 and 3. 9 GHz) 2. 6 GHz Fit of Rs (T) acquired at different Eacc values: 2. 6 GHz Accurate determination of Rres (Eacc) At this point RT(2 K) can be easily calculated: 9 Martina Martinello | TTC Meeting 2018, Milan

2. Trapped Flux Surface Resistance RFl defines the dissipation due to flux trapped during the SC transition: 10 Martina Martinello | TTC Meeting 2018, Milan

Outline • Introduction • Data analysis • RT field-dependence at different frequencies • Non-equilibrium superconductivity • Trapped flux sensitivity frequency-dependence • Conclusions 11 Martina Martinello | TTC Meeting 2018, Milan

Field Dependence at Different Frequencies Different thermal treatments were studied at different frequencies: 1. 120 o. C baking 2. BCP and EP 3. Nitrogen doping (2/6 recipe) 12 Martina Martinello | TTC Meeting 2018, Milan

*Some measurements were admin limited between 15 -20 MV/m to avoid quench so, in order to compare the 13 Martina Martinello | TTC Meeting 2018, Milan different curves, only data till ~20 MV/m are shown

*Some measurements were admin limited between 15 -20 MV/m to avoid quench so, in order to compare the 14 Martina Martinello | TTC Meeting 2018, Milan different curves, only data till ~20 MV/m are shown

*Some measurements were admin limited between 15 -20 MV/m to avoid quench so, in order to compare the 15 Martina Martinello | TTC Meeting 2018, Milan different curves, only data till ~20 MV/m are shown

*Some measurements were admin limited between 15 -20 MV/m to avoid quench so, in order to compare the 16 Martina Martinello | TTC Meeting 2018, Milan different curves, only data till ~20 MV/m are shown

*Some measurements were admin limited between 15 -20 MV/m to avoid quench so, in order to compare the 17 Martina Martinello | TTC Meeting 2018, Milan different curves, only data till ~20 MV/m are shown

*Some measurements were admin limited between 15 -20 MV/m to avoid quench so, in order to compare the 18 Martina Martinello | TTC Meeting 2018, Milan different curves, only data till ~20 MV/m are shown

At low field RT follows the w 2 trend suggested by the Mattis-Bardeen theory 19 Martina Martinello | TTC Meeting 2018, Milan RT (n. W)

Comparison in terms of Q-factor at 2. 0 K *Some measurements were admin limited between 15 -20 MV/m to avoid quench so, in order to compare the 20 Martina Martinello | TTC Meeting 2018, Milan different curves, only data till ~20 MV/m are shown

Q-factor of 2. 6 GHz at high field tends to the one at 1. 3 GHz Q-factor of 2. 6 GHz cavity converge to the one at 1. 3 GHz at high gradients 120 C baked cavities 21 Martina Martinello | TTC Meeting 2018, Milan T=2 K

Field Dependence at Different Frequencies Different thermal treatments were studied at different frequencies: 1. 120 o. C baking 2. BCP and EP 3. Nitrogen doping (2/6 recipe) 22 Martina Martinello | TTC Meeting 2018, Milan

*Some measurements were admin limited between 15 -20 MV/m to avoid quench so, in order to compare the 23 Martina Martinello | TTC Meeting 2018, Milan different curves, only data till ~16 MV/m are shown

*Some measurements were admin limited between 15 -20 MV/m to avoid quench so, in order to compare the 24 Martina Martinello | TTC Meeting 2018, Milan different curves, only data till ~16 MV/m are shown

*Some measurements were admin limited between 15 -20 MV/m to avoid quench so, in order to compare the 25 Martina Martinello | TTC Meeting 2018, Milan different curves, only data till ~16 MV/m are shown

*Some measurements were admin limited between 15 -20 MV/m to avoid quench so, in order to compare the 26 Martina Martinello | TTC Meeting 2018, Milan different curves, only data till ~16 MV/m are shown

Anti Q-slope in BCP’d 3. 9 GHz Cavities T=2 K 27 pe o l s Q anti Martina Martinello | TTC Meeting 2018, Milan

Field Dependence at Different Frequencies Different thermal treatments were studied at different frequencies: 1. 120 o. C baking 2. BCP and EP 3. Nitrogen doping (2/6 recipe) 28 Martina Martinello | TTC Meeting 2018, Milan

*Some measurements were admin limited between 15 -20 MV/m to avoid quench so, in order to compare the 29 Martina Martinello | TTC Meeting 2018, Milan different curves, only data till ~17 MV/m are shown

*Some measurements were admin limited between 15 -20 MV/m to avoid quench so, in order to compare the 30 Martina Martinello | TTC Meeting 2018, Milan different curves, only data till ~17 MV/m are shown

*Some measurements were admin limited between 15 -20 MV/m to avoid quench so, in order to compare the 31 Martina Martinello | TTC Meeting 2018, Milan different curves, only data till ~17 MV/m are shown

*Some measurements were admin limited between 15 -20 MV/m to avoid quench so, in order to compare the 32 Martina Martinello | TTC Meeting 2018, Milan different curves, only data till ~17 MV/m are shown

*Some measurements were admin limited between 15 -20 MV/m to avoid quench so, in order to compare the 33 Martina Martinello | TTC Meeting 2018, Milan different curves, only data till ~17 MV/m are shown

Comparison in terms of Q-factor at 2. 0 K T=2 K *Some measurements were admin limited between 15 -20 MV/m to avoid quench so, in order to compare the 34 Martina Martinello | TTC Meeting 2018, Milan different curves, only data till ~17 MV/m are shown

Comparison in terms of Q-factor at 2. 0 K 1. 3 GHz wins over 650 MHz at ~10 MV/m T=2 K *Some measurements were admin limited between 15 -20 MV/m to avoid quench so, in order to compare the 35 Martina Martinello | TTC Meeting 2018, Milan different curves, only data till ~17 MV/m are shown

Comparison in terms of Q-factor at 2. 0 K 3. 9 GHz wins over 2. 6 GHz at ~13 MV/m T=2 K *Some measurements were admin limited between 15 -20 MV/m to avoid quench so, in order to compare the 36 Martina Martinello | TTC Meeting 2018, Milan different curves, only data till ~17 MV/m are shown

Unprecedented Medium Field Q 0 at 3. 9 GHz T=2 K 37 Martina Martinello | TTC Meeting 2018, Milan

Further Improvement in Q 0 at 3. 9 GHz w 900 C baking T=2 K 38 Martina Martinello | TTC Meeting 2018, Milan

RT Comparison: 800 C vs 900 C Doping at 3. 9 GHz 39 Martina Martinello | TTC Meeting 2018, Milan

RT Comparison: 800 C vs 900 C Doping at 3. 9 GHz 35 n. W 25 n. W 40 Martina Martinello | TTC Meeting 2018, Milan

Unprecedented Medium Field Q 0 at 3. 9 GHz 41 Martina Martinello | TTC Meeting 2018, Milan

Summary on the frequency dependence of RBCS(Eacc) EP/BCP N-doping 120 C baking • The physical mechanism underneath the RT reversal has a stronger effect at high frequencies • The RT reversal, that has been considered the signature of the Ndoped treatment, is actually visible also in clean Nb but at high frequency • On the other hand, N-doped cavities at low frequencies do not show the RT reversal observed at 1. 3 GHz 42 Martina Martinello | TTC Meeting 2018, Milan

Outline • Introduction • Data analysis • RT field-dependence at different frequencies • Non-equilibrium superconductivity • Trapped flux sensitivity frequency-dependence • Conclusions 43 Martina Martinello | TTC Meeting 2018, Milan

Thermal equilibrium distribution of quasiparticles 44 Martina Martinello | TTC Meeting 2018, Milan

Non-equilibrium distribution of quasiparticles Condition for nonequilibrium SC: 45 Martina Martinello | TTC Meeting 2018, Milan

Non-equilibrium distribution of quasiparticles Condition for nonequilibrium SC: Higher the frequency, higher the probability to match the condition for non-equilibrium 46 Martina Martinello | TTC Meeting 2018, Milan

Non-equilibrium distribution of quasiparticles Condition for nonequilibrium SC: 47 Martina Martinello | TTC Meeting 2018, Milan

Non-equilibrium distribution of quasiparticles How is this related with lower surface resistance? Equilibrium distribution of QPs 48 Martina Martinello | TTC Meeting 2018, Milan Non-equilibrium distribution of QPs

Non-equilibrium distribution of quasiparticles How is this related with lower surface resistance? Equilibrium distribution of QPs 49 Martina Martinello | TTC Meeting 2018, Milan Non-equilibrium distribution of QPs

Non-equilibrium distribution of quasiparticles How is this related with lower surface resistance? Equilibrium distribution of QPs Non-equilibrium distribution of QPs Smaller with non-equilibrium QPs distribution 50 Martina Martinello | TTC Meeting 2018, Milan

Outline • Introduction • Data analysis • RT field-dependence at different frequencies • Non-equilibrium superconductivity • Trapped flux sensitivity frequency-dependence • Conclusions 51 Martina Martinello | TTC Meeting 2018, Milan

Sensitivity for different frequencies 120 C baking BCP/EP N-doping • Trapped flux sensitivity increases with frequency • The increment strongly depends on the surface treatment, i. e. on the mean free path • Higher frequencies seem to have a larger field dependence M. Checchin, M. Martinello et al. , accepted for publication in APL 52 Martina Martinello | TTC Meeting 2018, Milan

The advantage of N-doping at 1. 3 GHz 12 15 N-doping wins over standard treatments as long as the field trapped is <10 m. G M. Martinello et al. , App. Phys. Lett. 109, 062601 (2016) 53 Martina Martinello | TTC Meeting 2018, Milan

The advantage of N-doping at 3. 9 GHz N-doping wins over standard treatments as long as the field trapped is <17 m. G 54 Martina Martinello | TTC Meeting 2018, Milan

Outline • Introduction • Data analysis • RT field-dependence at different frequencies • Non-equilibrium superconductivity • Trapped flux sensitivity frequency-dependence • Conclusions 55 Martina Martinello | TTC Meeting 2018, Milan

Conclusions • RT(Eacc) shows a strong frequency dependence: high frequencies are favorable to lower RT at high field • The decreasing of RT(Eacc) can appear also in highfrequencies non-doped cavities and, vice versa, RT(Eacc) increases in low frequencies N-doped cavities • High-Q in high-frequency cavity is possible, especially at medium field → new possibility for CW machine • Non-equilibrium SC may qualitatively explain the decreasing of the surface resistance as a function of the field and its enhancement at higher frequencies • Trapped flux sensitivity increases with frequency but depending on the treatment magnetic shielding may be more or less stringent 56 Martina Martinello | TTC Meeting 2018, Milan

Thank you for your attention! 57 Martina Martinello | TTC Meeting 2018, Milan

Anti Q-slope in BCP’d 3. 9 GHz Cavities T=2 K pe o l s Q anti Data from E-XFEL database courtesy of V. Gubarev pe -slo Q i t n a 58 Martina Martinello | TTC Meeting 2018, Milan

Non-equilibrium QP distribution enhances superconductivity 59 Martina Martinello | TTC Meeting 2018, Milan P. De Visser, TTC FNAL 2017

Non-equilibrium QP distribution enhances superconductivity P. De Visser, TTC FNAL 2017 60 Martina Martinello | TTC Meeting 2018, Milan

1 a. BCS Surface Resistance (650 MHz and 1. 3 GHz) 61 Martina Martinello | TTC Meeting 2018, Milan