# Impurity Content Optimization to Maximize Q-Factors of Superconducting Resonators

## Abstract

Quality factor of superconducting radio-frequency (SRF) cavities is degraded whenever magnetic flux is trapped in the cavity walls during the cooldown. In this contribution we study how the trapped flux sensitivity, defined as the trapped flux surface resistance normalized for the amount of trapped flux, depends on the mean free path. A systematic study of a variety of 1.3 GHz cavities with different surface treatments (EP, 120 C bake and different N-doping) is carried out. A bell shaped trend appears for the range of mean free path studied. Over-doped cavities fall at the maximum of this curve defining the largest values of sensitivity. In addition, we have studied the trend of the BCS surface resistance contribution as a function of mean free path, showing that N-doped cavities follow close to the theoretical minimum. Adding these results together we show that the 2/6 N-doping treatment gives the highest Q-factor values at 2 K and 16 MV/m, as long as the magnetic field fully trapped during the cavity cooldown is lower than 10 mG.

- Authors:

- Fermilab
- IIT, Chicago
- IIT, Chicago (main)

- Publication Date:

- Research Org.:
- Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States)

- Sponsoring Org.:
- USDOE Office of Science (SC), High Energy Physics (HEP) (SC-25)

- OSTI Identifier:
- 1420925

- Report Number(s):
- FERMILAB-CONF-16-740-TD

1633201

- DOE Contract Number:
- AC02-07CH11359

- Resource Type:
- Conference

- Resource Relation:
- Conference: 28th International Linear Accelerator Conference, East Lansing, Michigan, 09/25-09/30/2016

- Country of Publication:
- United States

- Language:
- English

- Subject:
- 43 PARTICLE ACCELERATORS

### Citation Formats

```
Martinello, Martina, Checchin, Mattia, Grassellino, Anna, Melnychuk, Oleksandr, Posen, Sam, Romanenko, Alexander, Sergatskov, Dmitri, and Zasadzinski, John.
```*Impurity Content Optimization to Maximize Q-Factors of Superconducting Resonators*. United States: N. p., 2017.
Web. doi:10.18429/JACoW-LINAC2016-TUPLR023.

```
Martinello, Martina, Checchin, Mattia, Grassellino, Anna, Melnychuk, Oleksandr, Posen, Sam, Romanenko, Alexander, Sergatskov, Dmitri, & Zasadzinski, John.
```*Impurity Content Optimization to Maximize Q-Factors of Superconducting Resonators*. United States. doi:10.18429/JACoW-LINAC2016-TUPLR023.

```
Martinello, Martina, Checchin, Mattia, Grassellino, Anna, Melnychuk, Oleksandr, Posen, Sam, Romanenko, Alexander, Sergatskov, Dmitri, and Zasadzinski, John. Mon .
"Impurity Content Optimization to Maximize Q-Factors of Superconducting Resonators". United States.
doi:10.18429/JACoW-LINAC2016-TUPLR023. https://www.osti.gov/servlets/purl/1420925.
```

```
@article{osti_1420925,
```

title = {Impurity Content Optimization to Maximize Q-Factors of Superconducting Resonators},

author = {Martinello, Martina and Checchin, Mattia and Grassellino, Anna and Melnychuk, Oleksandr and Posen, Sam and Romanenko, Alexander and Sergatskov, Dmitri and Zasadzinski, John},

abstractNote = {Quality factor of superconducting radio-frequency (SRF) cavities is degraded whenever magnetic flux is trapped in the cavity walls during the cooldown. In this contribution we study how the trapped flux sensitivity, defined as the trapped flux surface resistance normalized for the amount of trapped flux, depends on the mean free path. A systematic study of a variety of 1.3 GHz cavities with different surface treatments (EP, 120 C bake and different N-doping) is carried out. A bell shaped trend appears for the range of mean free path studied. Over-doped cavities fall at the maximum of this curve defining the largest values of sensitivity. In addition, we have studied the trend of the BCS surface resistance contribution as a function of mean free path, showing that N-doped cavities follow close to the theoretical minimum. Adding these results together we show that the 2/6 N-doping treatment gives the highest Q-factor values at 2 K and 16 MV/m, as long as the magnetic field fully trapped during the cavity cooldown is lower than 10 mG.},

doi = {10.18429/JACoW-LINAC2016-TUPLR023},

journal = {},

number = ,

volume = ,

place = {United States},

year = {Mon May 01 00:00:00 EDT 2017},

month = {Mon May 01 00:00:00 EDT 2017}

}