SRF2013 - List of Authors (Palmieri, V.)

Paper

Title

Page

Heat Transfer at the Interface Between Niobium and Liquid Helium for 6 GHz SRF Cavities

57

V. Palmieri
INFN/LNL, Legnaro (PD), Italy

Cavity Thermal Boundary Resistance is something extremely complex and not completely understood by the theory. Often identified with the Kapitza resistance or with the Khalatnikov acoustic phonon mismatch at the interface metal-liquid Helium, it depends on so many different and uncontrolled parameters, that its interpretation is not covered by a complete treatise of the phenomenon. Therefore, 99% of the literature on superconducting cavities worries about the cavity interior surface state,while almost nothing is reported on treatments applied to the exterior. In the authors opinion, there is a lack in experimental data analysis due to the fact that the cavity is often considered as a whole adiabatic entity interacting only with RF fields. On the contrary, the cavity is immersed in liquid Helium and the cavity behavior cannot prescind from its thermal properties. Indeed in the normal state He-I has poor thermal conductivity and high specific heat. Moreover the heat exchange at HeII obeys to further mechanisms besides the phonon mismatch. Driven by the hypothesis that thermal losses are dominant for ultraclean cavities, we have collected a plethora of surprising experimental results.

Slides MOIOC01 [15.558 MB]

TUIOC03

Fluorine Free Ionic Liquid Electropolishing of Niobium Cavities

410

V.B. Pastushenko, O.V. Malkova, V. Palmieri, A.A. Rossi, F. Stivanello, G. Yu
INFN/LNL, Legnaro (PD), Italy
G. Yu
CIAE, Beijing, People's Republic of China

Ionic liquids are an emerging breakthrough in green chemistry since the years 2000. In 2006, INFN-LNL was the first to apply a mixture of Choline Chloride and Urea to Niobium electropolishing. It was found that mirror like surfaces could be obtained at temperature higher than 120°C, with high throwing power. Subsequently the process was successfully applied to the electropolishing of a 6 GHz monocell cavity with the addition of sulphamic acid. In this work, we will report an intense investigation of the possible variants of the original recipe. We studied the influence on Niobium surface roughness of several parameters such as: other sulphamic, ammonium and carboxylic containing additives different than sulfamic acid, the possible substitution of Urea with ethylene glycol and malic acid, the current regime; the electrolyte temperature and the cathode shape, rotating horizontal electropolishing versus vertical electropolishing. Due to the cavity hollow cylindrical shape, the electrolyte temperature appeared to be the most crucial parameters among those above mentioned for a uniform dissolution of niobium.

Slides TUIOC03 [14.464 MB]

TUIOC05

Purification of 6 GHz Cavities by Induction Heating

419

A.A. Rossi, A. Battistello, M. Checchin, V. Palmieri, S. Stark, F. Stivanello, R.K. Thakur, G. Yu
INFN/LNL, Legnaro (PD), Italy

We have developed an innovative technique for purification of bulk-Nb 6GHz RF cavities under ultra-high vacuum (UHV) system. The main advantages of 6 GHz bulk-Nb cavities are saving cost, materials and time to collect statistics of surface treatments and RF test. Cavities are RF tested before and after high temperature treatment under UHV conditions. Induction heating method is used to anneal the cavity at temperatures higher than 2000°C and close to the melting point of Nb for less than a minute while few seconds at maximum temperature. Before RF test and UHV annealing, the surface treatment processes like tumbling, chemical, electro-chemical (such as BCP and EP), ultrasonic cleaning and high pressure rinsing (HPR) have been employed. This kind of Nb 6 GHz cavity purification allow to reduce hydrogen, oxygen and other elemental impurities content, which effects on cavity Q-factor degradation, by a rapid annealing over 2000°C and a subsequent rapid reduction at room temperature.

Slides TUIOC05 [42.171 MB]

WEIOA03

Nb Sputtered Quarter Wave Resonators for the HIE-ISOLDE

767

W. Venturini Delsolaro, S. Calatroni, A. D'Elia, B. Delaup, N.M. Jecklin, Y. Kadi, P. Maesen, I. Mondino, A. Sublet, M. Therasse
CERN, Geneva, Switzerland
A. D'Elia
UMAN, Manchester, United Kingdom
D.A. Franco Lespinasse, G. Keppel, V. Palmieri, S. Stark
INFN/LNL, Legnaro (PD), Italy

The HIE-ISOLDE superconducting linac will be based on quarter wave resonators (QWRs), made by Niobium sputtering on Copper. The operating frequency at 4.5 K is 101.28 MHz and the required performance for the high beta cavity is 6 MV/m accelerating field for 10 W maximum power dissipation. These challenging specifications were recently met at CERN at the end of a vigorous development program. The paper reports on the progress of the cavity RF performance with the evolution of the sputtering process; it equally illustrates the parallel R&D which is ongoing at CERN and at INFN in the quest for even higher performances.

Slides WEIOA03 [14.564 MB]

THP096

Recent Upgrade of Ultra-Broadband RF System for Cavity Characterization

1151

S. Stark, V. Palmieri, A.M. Porcellato, A.A. Rossi
INFN/LNL, Legnaro (PD), Italy
V. Palmieri
Univ. degli Studi di Padova, Padova, Italy

The first computer controlled RF system for SC cavity characterization entered into operation at INFN-LNL in 1994. Since then it has been successfully used for testing SC cavities of different shapes and frequencies. Recently we performed an important upgrade on it in order to cover a wider frequency range and to take advantage of the better performance of nowadays electronic devices. The paper describes the present system layout, dedicated software, sequences of calibration and testing procedures and moreover discusses further upgrading possibilities.

THP096

Recent Upgrade of Ultra-Broadband RF System for Cavity Characterization

1151

S. Stark, V. Palmieri, A.M. Porcellato, A.A. Rossi
INFN/LNL, Legnaro (PD), Italy
V. Palmieri
Univ. degli Studi di Padova, Padova, Italy

The first computer controlled RF system for SC cavity characterization entered into operation at INFN-LNL in 1994. Since then it has been successfully used for testing SC cavities of different shapes and frequencies. Recently we performed an important upgrade on it in order to cover a wider frequency range and to take advantage of the better performance of nowadays electronic devices. The paper describes the present system layout, dedicated software, sequences of calibration and testing procedures and moreover discusses further upgrading possibilities.

Paper	Title	Page
MOIOC01	Heat Transfer at the Interface Between Niobium and Liquid Helium for 6 GHz SRF Cavities	57
	V. Palmieri INFN/LNL, Legnaro (PD), Italy
	Cavity Thermal Boundary Resistance is something extremely complex and not completely understood by the theory. Often identified with the Kapitza resistance or with the Khalatnikov acoustic phonon mismatch at the interface metal-liquid Helium, it depends on so many different and uncontrolled parameters, that its interpretation is not covered by a complete treatise of the phenomenon. Therefore, 99% of the literature on superconducting cavities worries about the cavity interior surface state,while almost nothing is reported on treatments applied to the exterior. In the authors opinion, there is a lack in experimental data analysis due to the fact that the cavity is often considered as a whole adiabatic entity interacting only with RF fields. On the contrary, the cavity is immersed in liquid Helium and the cavity behavior cannot prescind from its thermal properties. Indeed in the normal state He-I has poor thermal conductivity and high specific heat. Moreover the heat exchange at HeII obeys to further mechanisms besides the phonon mismatch. Driven by the hypothesis that thermal losses are dominant for ultraclean cavities, we have collected a plethora of surprising experimental results.
	Slides MOIOC01 [15.558 MB]

TUIOC03	Fluorine Free Ionic Liquid Electropolishing of Niobium Cavities	410
	V.B. Pastushenko, O.V. Malkova, V. Palmieri, A.A. Rossi, F. Stivanello, G. Yu INFN/LNL, Legnaro (PD), Italy G. Yu CIAE, Beijing, People's Republic of China
	Ionic liquids are an emerging breakthrough in green chemistry since the years 2000. In 2006, INFN-LNL was the first to apply a mixture of Choline Chloride and Urea to Niobium electropolishing. It was found that mirror like surfaces could be obtained at temperature higher than 120°C, with high throwing power. Subsequently the process was successfully applied to the electropolishing of a 6 GHz monocell cavity with the addition of sulphamic acid. In this work, we will report an intense investigation of the possible variants of the original recipe. We studied the influence on Niobium surface roughness of several parameters such as: other sulphamic, ammonium and carboxylic containing additives different than sulfamic acid, the possible substitution of Urea with ethylene glycol and malic acid, the current regime; the electrolyte temperature and the cathode shape, rotating horizontal electropolishing versus vertical electropolishing. Due to the cavity hollow cylindrical shape, the electrolyte temperature appeared to be the most crucial parameters among those above mentioned for a uniform dissolution of niobium.
	Slides TUIOC03 [14.464 MB]

TUIOC05	Purification of 6 GHz Cavities by Induction Heating	419
	A.A. Rossi, A. Battistello, M. Checchin, V. Palmieri, S. Stark, F. Stivanello, R.K. Thakur, G. Yu INFN/LNL, Legnaro (PD), Italy
	We have developed an innovative technique for purification of bulk-Nb 6GHz RF cavities under ultra-high vacuum (UHV) system. The main advantages of 6 GHz bulk-Nb cavities are saving cost, materials and time to collect statistics of surface treatments and RF test. Cavities are RF tested before and after high temperature treatment under UHV conditions. Induction heating method is used to anneal the cavity at temperatures higher than 2000°C and close to the melting point of Nb for less than a minute while few seconds at maximum temperature. Before RF test and UHV annealing, the surface treatment processes like tumbling, chemical, electro-chemical (such as BCP and EP), ultrasonic cleaning and high pressure rinsing (HPR) have been employed. This kind of Nb 6 GHz cavity purification allow to reduce hydrogen, oxygen and other elemental impurities content, which effects on cavity Q-factor degradation, by a rapid annealing over 2000°C and a subsequent rapid reduction at room temperature.
	Slides TUIOC05 [42.171 MB]

WEIOA03	Nb Sputtered Quarter Wave Resonators for the HIE-ISOLDE	767
	W. Venturini Delsolaro, S. Calatroni, A. D'Elia, B. Delaup, N.M. Jecklin, Y. Kadi, P. Maesen, I. Mondino, A. Sublet, M. Therasse CERN, Geneva, Switzerland A. D'Elia UMAN, Manchester, United Kingdom D.A. Franco Lespinasse, G. Keppel, V. Palmieri, S. Stark INFN/LNL, Legnaro (PD), Italy
	The HIE-ISOLDE superconducting linac will be based on quarter wave resonators (QWRs), made by Niobium sputtering on Copper. The operating frequency at 4.5 K is 101.28 MHz and the required performance for the high beta cavity is 6 MV/m accelerating field for 10 W maximum power dissipation. These challenging specifications were recently met at CERN at the end of a vigorous development program. The paper reports on the progress of the cavity RF performance with the evolution of the sputtering process; it equally illustrates the parallel R&D which is ongoing at CERN and at INFN in the quest for even higher performances.
	Slides WEIOA03 [14.564 MB]

THP096	Recent Upgrade of Ultra-Broadband RF System for Cavity Characterization	1151
	S. Stark, V. Palmieri, A.M. Porcellato, A.A. Rossi INFN/LNL, Legnaro (PD), Italy V. Palmieri Univ. degli Studi di Padova, Padova, Italy
	The first computer controlled RF system for SC cavity characterization entered into operation at INFN-LNL in 1994. Since then it has been successfully used for testing SC cavities of different shapes and frequencies. Recently we performed an important upgrade on it in order to cover a wider frequency range and to take advantage of the better performance of nowadays electronic devices. The paper describes the present system layout, dedicated software, sequences of calibration and testing procedures and moreover discusses further upgrading possibilities.

THP096	Recent Upgrade of Ultra-Broadband RF System for Cavity Characterization	1151
	S. Stark, V. Palmieri, A.M. Porcellato, A.A. Rossi INFN/LNL, Legnaro (PD), Italy V. Palmieri Univ. degli Studi di Padova, Padova, Italy
	The first computer controlled RF system for SC cavity characterization entered into operation at INFN-LNL in 1994. Since then it has been successfully used for testing SC cavities of different shapes and frequencies. Recently we performed an important upgrade on it in order to cover a wider frequency range and to take advantage of the better performance of nowadays electronic devices. The paper describes the present system layout, dedicated software, sequences of calibration and testing procedures and moreover discusses further upgrading possibilities.