Workshop Program and Proceedings

Abstracts, Presentations and Video of the talks

Monday 6th October, 2014

INTERNATIONAL PANORAMA FOR THIN FILM TECHNOLOGY APPLIED TO SRF CAVITIES
(Chairman: Larry Phillips)
The Sixth Workshop on (Enzo Palmieri - 20')
Speaker: Enzo Palmieri - INFN-LNL   |   Duration: 20 min.

Abstract
Born in 2004 as a Satellite meeting of the main SRF Conference, the workshops on "Thin films and New Ideas for SRF" are held every two years in two alternate locations: Jefferson Lab and the Legnaro National Laboratories of the INFN.
The mission of the Thin Film and New Idea Workshop is to coagulate a part of the scientific Community believing that Innovation, Research, constant development and continuous improvement are the keys for a better comprehension of SRF.
Therefore, besides thin film technology, the matter of study of the workshop is in general every innovation in cavity fabrication technology.

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Future CERN projects and their technological challenges (José Miguel Jimenez - 40')
Speaker: José Miguel Jimenez - CERN   |   Duration: 40 min.

Abstract
The CERN Medium Term Plan approved by June’14 Council, implements the European Strategy for Particle Physics including a long-term outlook. This scientific programme is concentrated around four priorities: Full LHC exploitation – the highest priority - including the construction of the High Luminosity Upgrade until 2025; High Energy Frontier – CERN’s role and preparation for the next large scale facility; Neutrino Platform – allow for to contribute to a future long baseline facility in the US and for detector R&D for neutrino experiments; Fixed-target programme – maintain the diversity of the field and honour ongoing obligations by exploiting the unique facilities at CERN. The R&D part of this MTP aims at staying at the technology forefront and to recover its key role player in SC RF technology.

FCC SC-RF systems and opportunities (Erk Jensen - 30')
Speaker: Erk Jensen - CERN   |   Duration: 30 min.

Abstract
Europe needs to be in a position to propose an ambitious post-LHC accelerator project at CERN by the time of the next Strategy update, when physics results from the LHC running at nominal energy will be available. CERN has started design studies for accelerator projects in a global context, with emphasis on proton-proton and electron-positron high-energy frontier machines. Complementary to Linear Colliders, the FCC (Future Circular Collider) study looks at ring-based colliders, both for hadrons and leptons. With a circumference of 80 to 100 km and dipole fields of about 15 T, this would allow an c.m. energy reach of 100 TeV for the proton machine. A lepton machine, dedicated to precision measurements, could be an intermediate step, another option is a hadron-electron machine. The FCC design study concentrates on related R&D challenges, both for high field magnets and for superconducting RF. The lepton collider is dominated by SR losses, so its SRF system cope with 100 MW cw; R&D will concentrate on a system scalable to this size. The study should conclude in time for the next update of the European Strategy for Particle Physics foreseen to take place in 2018

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Multilayers and Gurevich Model
(Chairman: Larry Phillips)
Maximum screening fields and the optimum parameters of superconducting multilayers for resonator cavities (Alex Gurevich - 30')
Speaker: Alex Gurevich - Old Dominion University   |   Duration: 30 min.

Abstract
Alex Gurevich, It is shown that multilayer coating can screen the applied field above the superheating fields of both the superconducting layers and the Nb substrate. There is an optimum multilayer thickness for which the breakdown field at which the multilayer remains in the vortex-free Meissner reaches maximum. It is shown that a dirty layer about the London penetration depth thick at the non-structured Nb surface can increase the superheating field of up to 290 mT. Growing optimized multilayer structures of Nb3Sn or iron pnictides or forming a dirty layer at the surface of the Nb resonator cavities for particle accelerators offer opportunities to increase the peak accelerating electric fields above 100 MV/m.

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Multilayer Approach to Increase the Performance of SRF Accelerating Structures beyond Bulk Nb (Anne-Marie Valente-Feliciano - 30')
Speaker: Anne-Marie Valente-Feliciano - Jlab   |   Duration: 30 min.

Abstract
A-M. Valente-Feliciano, D. Beringer, G. Eremeev, R. A. Lukaszew, L. Phillips, C. Reece, J. K. Spradlin

For the past three decades, bulk niobium has been the material of choice for SRF cavities applications. RF cavity performance is now approaching the theoretical limit for bulk niobium. For further improvement of RF cavity performance for future accelerator projects, Superconductor-Insulator-Superconductor (SIS) multilayer structures (as proposed by Alex Gurevich) present the theoretical prospect to reach RF performance beyond bulk Nb, using thinly layered higher-Tc superconductors with enhanced Hc1. Jefferson Lab (JLab) is pursuing this approach with the development of NbTiN and AlN based multilayer SIS structures via magnetron sputtering and High Power Impulse Magnetron Sputtering (HiPIMS). This contribution presents the characterization of NbTiN and insulator films and some RF measurements on NbTiN-based multilayer structures.

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Tests of the Gurevich model toward larger field gradients in SRF cavities (Rosa Alejandra Lukaszew - 40')
Speaker: Rosa Alejandra Lukaszew - College of William and Mary (VA)   |   Duration: 40 min.

Abstract
SRF properties are inherently a surface phenomenon involving a material thickness of a few microns thus opening up the possibility of using thin film coatings to achieve a desired performance. I will describe our experimental attempts to test the superconducting/insulating/superconducting (SIS) multilayer model proposed by A. Gurevich [1] to shield the bulk of the cavity from vortex penetration and hence enable larger accelerating fields than presently possible.

[1] A. Gurevich, “Enhancement of rf breakdown field of superconductors by multilayer coating,” Appl. Phys. Lett., vol. 88, p. 12 511, 2006.

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Open Discussion (Chair: Larry Phillips - 30')
Speaker: Chair: Larry Phillips -   |   Duration: 30 min.

Abstract

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NIOBIUM DEPOSITION: STATUS OF ART
(Chairman: Walter Venturini)
Development of thin films for superconducting RF cavities in ASTeC (Oleg Malishev - 30')
Speaker: Oleg Malishev -   |   Duration: 30 min.

Abstract
Superconducting coatings for superconducting radio frequency (SRF) cavities is an intensively developing field that should ultimately lead to acceleration gradients better than those obtained by bulk Nb RF cavities. ASTeC has built and developed experimental systems for superconducting thin-film deposition, surface analysis and measurement of Residual Resistivity Ratio (RRR). Nb thin-films were deposited by magnetron sputtering in DC or pulsed DC mode (100 to 350 kHz with 50% duty cycle) with powers ranging from 100 to 600 W at various temperatures ranging from room temperature to 800 °C on Si (100) substrates. The first results gave RRR in the range from 2 to 22 with a critical temperature Tc=~9.5 K. Scanning electron microscopy (SEM), x-ray diffraction (XRD), electron back scattering diffraction (EBSD) and DC SQUID magnetometry revealed significant correlations between the film structure, morphology and superconducting properties.

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Porosity of Nb magnetron sputtered thin films and dependence on sputtering parameters (Hanna Skliarova - 30')
Speaker: Hanna Skliarova - INFN-LNL   |   Duration: 30 min.

Abstract
Pinholes (or through film porosity) in Nb thin film deposited on the inner walls of SRF cavities are harmful for cavity performance because they may expose inferior copper that has much higher resistance than niobium at 4.2 K. Aluminated quartz substrates allowed us to make visible the pore sites for inspection and counting by production visible corrosion products. We showed the correlation between the amount of pinholes in niobium thin film prepared by magnetron sputtering and the deposition parameters, such as sputtering gas pressure, substrate temperature, applied bias, placing of the sample in UBM sputtering mode. Thus low temperature of the substrate and high sputtering gas pressure promoted growth of a voided film (that corresponds to SZM approach) with high amount of pinholes. Heating of the substrate during deposition has resulted in moderate decrease of the pinhole amount, while negative bias applied to the substrate showed stronger decrease of the pinhole amount thanks to additional bombardment of the substrate by Ar+ serving to remove weakly bounded particles during deposition.

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Niobium Coated HIE-ISOLDE QWR Superconducting Accelerating Cavities: coating process and film characterization (Alban Sublet - 30')
Speaker: Alban Sublet - CERN   |   Duration: 30 min.

Abstract
The new HIE-ISOLDE accelerator at CERN requires the production of 32 superconducting cavities (20 high-beta and 12 low-beta) in order to increase the energy of the rare isotope beam delivered to the experiments. The Quarter Wave Resonators (QWRs) cavities (0.3m diameter and 0.8m height) are made of OFE 3D-forged copper and are coated by DC-bias diode sputtering with a superconducting niobium thin film. The series production of the high-beta cavities has started. In parallel to the production, a systematic characterization of the film has been launched. Thickness measurement, RRR and FIB-SEM cross section and TEM analysis are conducted in collaboration with EPFL (CIME) to investigate the film growth and its morphological properties at different places along the cavity inner and outer conductor. Samples are produced in a test cavity with the baseline production coating recipe and in the same hardware to be as close as possible to the production conditions.
The production coating cycle and setup to match the HIE-ISOLDE specifications (operation at 4.5 K with an accelerating field of 6 MV/m at 10W RF losses and Q0=4.5x108) is described and the resulting niobium film characteristics is presented.

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Status of Magnetron Sputtered QWR (Danel Adrien Franco-Lespinasse - 20')
Speaker: Danel Adrien Franco-Lespinasse - INFN-LNL   |   Duration: 20 min.

Abstract
The objective of this research is the deposition of a superconductive thin film onto copper Quarter Wave Resonator cavities that can be used in the HIE-ISOLDE facility at CERN. To do this, it was developed an innovative magnetron configuration source. Our experience has shown the efficiency of this particular configuration in order to deposit a uniform thin film, and also improve the superconductive properties of the niobium (Residual Resistance Ratio and Critical Temperature). This presentation presents the recent improvement of the niobium thin film properties and the procedure used to deposit and measure the first resonator at LNL of HIE-ISOLDE type.

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Open Discussion (Chair: Walter Venturini - 10')
Speaker: Chair: Walter Venturini -   |   Duration: 10 min.

Abstract

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FILM CHARACTERIZATION
(Chairman: K. Liu 刘克新)
Cryogenic RF Characterization of SC Materials at SLAC with Cu and Nb-Coated Cavities (Paul Welander - 30')
Speaker: Paul Welander - SLAC   |   Duration: 30 min.

Abstract
Paul B. Welander, Matt Franzi, Sami Tantawi SLAC National Accelerator Laboratory, Menlo Park, CA 94025

A second-generation, X-band cryostat has been developed for the characterization of superconducting materials at low temperatures and high powers. The system utilizes two interchangeable hemisperhical cavities that can accommodate 50 mm-diameter samples on the flat surface. Both operate in a TE013-like mode where the magnetic field is strongest on the sample surface, which accounts for about 1/3 of the total cavity loss. The first cavity is a medium-Q copper one, and is utilized for measuring the sample’s critical temperature and magnetic quenching field. The second is a high-Q niobium-coated cavity that is employed for measuring surface resistance in the low-temperature, low-power limit. We will discuss cryostat design, measurement limits, and testing of samples grown both at SLAC and elsewhere.

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Low energy muon spin rotation and point contact tunneling on niobium thin films (Tobias Junginger - 20')
Speaker: Tobias Junginger -   |   Duration: 20 min.

Abstract
Muon spin rotation (muSR) and point contact tunneling (PCT) are used since several years for bulk niobium studies. Here we present studies on niobium thin film samples of different deposition techniques (diode, magnetron and HIPIMS) and compare the results with RF measurements and bulk niobium results. It is consistently found from muSR and RF measurements that HIPIMS can be used to produce thin films of high RRR. Hints for magnetic impurities are found on HIPIMS and dcms samples. The Meissner effect is linear on all tested samples.

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Status of the HZB Quadrupole Resonator (Sebastian Keckert - 20')
Speaker: Sebastian Keckert - HZB   |   Duration: 20 min.

Abstract
Authors: Sebastian Keckert, Raphael Kleindienst, Jens Knobloch, Oliver Kugeler

The systematic research on superconducting thin films requires dedicated testing equipment. The Quadrupole Resonator (QPR) is a specialized tool to characterize the superconducting properties of circular samples. A calorimetric measurement of the RF surface losses allows the surface resistance to be measured with sub nano-ohm resolution. This measurement can be performed over a wide temperature and magnetic field range, at frequencies of 433, 866 and 1300 MHz. The system at Helmholtz-Zentrum Berlin (HZB) is based on a resonator built at CERN and has been optimized to lower peak electric fields and an improved resolution. An alternative calorimetry chamber has been designed in order to provide flat samples for coating and to ease changing of samples. In this talk the current status of the project at HZB will be presented.

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Secondary Electron Yield of SRF Materials (Sarah Aull - 20')
Speaker: Sarah Aull - CERN   |   Duration: 20 min.

Abstract
In the quest of new materials for SRF applications, the secondary electron yield (SEY) needs also to be taken into consideration. A high SEY holds the risk that multipacting becomes again a main performance limitation of an SRF cavity. In the worst case, a too high SEY makes a material completely unsuitablefor an RF exposed surface. This talk will discuss general aspects of the role of the surface condition and present SEY measurements on different SRF relevant materials, i.e. MgB2, Nb3Sn and NbTiN.

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Registration     (8:40 - 9:10)
Session Opening     (9:10 - 19:00)
Coffee Break     (10:40 - 11:10)
Lunch     (13:20 - 14:30)
Coffee Break     (16:30 - 17:00)
Bus Transfer     (18:30 - 18:40)

Tuesday 7th October, 2014

Thermal Boundary Resistance between the Superconductor and Liquid Helium
(Chairman: Claire Antoine)
The problem of heat transfer at Liquid helium temperatures (Enzo Palmieri - 30')
Speaker: Enzo Palmieri - INFN-LNL   |   Duration: 30 min.

Abstract
For decades the attention of Scientists working on the performance improvement of superconducting cavities has been focused onto the study of the cavity interior and more precisely to the optimization of the first hundreds nanolayers of the Niobium surface exposed to the electromagnetic fields. In the meantime, little attention has been played to the status of the external surface in contact with liquid Helium. In our analysis we will see that both from the literature analysis and from the experimental results, the status of the cavity external surface has a non-negligible importance.

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Kapitza resistance at Niobium/superfluid He interfaces (Jay Amrit - 40')
Speaker: Jay Amrit - Université Paris-Sud / LIMSI-CNRS   |   Duration: 40 min.

Abstract
Heat removal from SRF cavity walls to superfluid (HeII) plays a decisive on the thermo-magnetic stability and therefore on the performance of these cavities. The two main parameters are the thermal conductivity of Niobium and the thermal boundary resistance (Kapitza resistance) at the Niobium/superfluid He interface. Here we shall focus mainly on the Kapitza resistance .Theoretical models shall be present to demonstrate that the Kapitza resistance is anomalous at the Niobium/HeII interface, justifying the empirical experimental approach. Various sets of data shall be presented for polycrystalline and single crystal Niobium having different surface morphologies and bulk purities. The impact of surface impurities and dislocations on the Kapitza resistance shall be discussed. New analysis shall be present showing an intrinsic limit to the Kapitza resistance due to interactions between phonons (heat carriers) in He-II and the nanoscale surface roughness of Niobium surface. Potential future experiments shall be proposed.

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Experimental results on Thermal boundary resistance for Niobium and for Niobium sputtered Copper (Enzo Palmieri - 30')
Speaker: Enzo Palmieri - INFN-LNL   |   Duration: 30 min.

Abstract
Unless of a few eclectic scientists that have studied the problem of Kapitza resistance, a superconducting cavity is almost always seen as an adiabatic system of the electromagnetic fields interacting with a Niobium sheet cooled at 4,2K or at temperatures between 1,8K and 2 K. In this talk it will be shown that the real system to consider is that of Electromagnetic fields, Niobium and liquid Helium.
And liquid Helium is a component much more complex than an infinite heat exchanger at fixed temperature. Even at superfluid temperatures indeed, at the interface between Helium and the superfluid, it will be always a nanometric thick layer of normal helium and the thickness of this layer depends on the RF power.
Niobium sputtered cavities will be also examined under the point of view of thermal boundary Resistance, arriving to the conclusion that more advanced comprehension of SRF cannot prescind from a deep understanding of Cryogenics

Slides

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Nucleation of Nb Films on Cu Substrates (Anne Marie Valente-Feliciano - 20')
Speaker: Anne Marie Valente-Feliciano - Jlab   |   Duration: 20 min.

Abstract
In the pursuit of niobium (Nb) films with similar performance with the commonly used bulk Nb surfaces for Superconducting RF (SRF) applications, significant progress has been made with the development of energetic condensation deposition techniques. The controlled incoming ion energy enables a number of processes such as desorption of adsorbed species, enhanced mobility of surface atoms and sub-implantation of impinging ions, thus producing improved film structures at lower process temperatures. All these along with the quality of the Cu substrate have an important influence on the nucleation and subsequent growth of the Nb film, creating a favorable template for growing the final surface exposed to SRF fields. This contribution shows how the structure and defect density thus electron mean free path (represented by residual resistance ratio values) of Nb films can be tailored on Cu substrates, by varying the ion energy and thermal energy provided to the substrate, favoring the hetero-epitaxial or the fiber growth mode.

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Open Discussion (Chair Claire Antoine - 20')
Speaker: Chair Claire Antoine -   |   Duration: 20 min.

Abstract

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SUPERCONDUCTING RF LOSSES
(Chairman: Jens Knobloch)
Superconducting Surface Impedance under Radiofrequency Field (Binping Xiao - 20')
Speaker: Binping Xiao - Jlab   |   Duration: 20 min.

Abstract
Based on BCS theory with moving Cooper pairs, the electron states distribution at 0 K and the probability of electron occupation with finite temperature have been derived and applied to anomalous skin effect theory to obtain the surface impedance of a superconductor under radiofrequency (RF) field. We present the numerical results for Nb and compare these with representative RF field-dependent effective surface resistance measurements from a 1.5 GHz resonant structure.

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TEM studies of niobium hydrides participants in superconducting niobium cavitiey cutouts (Yulia Trenikhina - 30')
Speaker: Yulia Trenikhina - Fermilab   |   Duration: 30 min.

Abstract
Nanoscale near-surface investigation of cutouts from niobium cavities is the most direct way to understand the material features affecting the SRF performance. We will present temperature dependent TEM studies on cutouts from Q-disease free cavities prepared by EP, EP+120C baking, and N doping. We have found that several niobium hydride phases form upon cooldown to <100K in the penetration depth for EP and EP/120C cutouts with the difference in the density/size caused by 120C. No hydrides were found in the first few tens of nanometers of the N doped cutouts.These findings support the proposed involved of niobium nanohydrides in the high field Q slope, and the effect of N doping.

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Open Discussion (Chair: Jens Knobloch - 30')
Speaker: Chair: Jens Knobloch -   |   Duration: 30 min.

Abstract

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The influence of cooldown conditions at transition temperature on the quality factor of niobium sputtered quarter-wave resonators (Pei Zhang - 30')
Speaker: Pei Zhang - CERN   |   Duration: 30 min.

Abstract
Quarter-wave resonators (QWR) are to be used in the ongoing linac upgrade of the ISOLDE facility at CERN. The cavities are made of niobium sputtered on copper substrate. They will be operated at 101.28 MHz at 4.5 K providing 6 MV/m accelerating gradient with maximum 10 W power dissipation. In recent measurements, we found the thermal gradient along the cavity during the niobium superconducting transition has an impact on the cavity quality factor. The influence of external magnetic field on the cavity performance has also been observed for the sputtered cavities.

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Surface Resistance of a bulk-like Nb Film (Sarah Aull - 20')
Speaker: Sarah Aull - CERN   |   Duration: 20 min.

Abstract
CERNs quadrupole resonator allows surface resistance measurements throughout a broad parameter range. Besides measuring the surface resistance as function of RF field and temperature for different frequencies, it is also possible to vary the cooling rate and apply additional magnetic fields.  This talk will present RF results on a bulk-like Nb film with special focus on the cooling conditions.

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Session Opening     (9:00 - 16:30)
Coffee Break     (11:20 - 11:50)
Lunch     (13:10 - 14:10)
Lab Tour     (15:20 - 16:30)
Bus Transfer     (16:30 - 16:40)
Gala Dinner (Tie is requested for gentlemen)     (19:30 - 23:00)

Wednesday 8th October, 2014

Energetic condensation Deposition
(Chairman: Larry Philips)
HIPIMS Development for Superconducting Cavities (Giovanni Terenziani - 30')
Speaker: Giovanni Terenziani - CERN   |   Duration: 30 min.

Abstract
HIPIMS is gaining large consensus around the world as a possible solution to overcome the problems faced with standard dcMS for the superconductive thin film coatings on copper RF cavities. Given the wide parameter space available with HIPIMS it is informative to draw out th relationship between plasma parameters microstructure and quality of the film produced. Influence of different discharge settings (pulse width, current density and frequency) has been studied in order to improve film performance. Samples have been produced in order to analyse the film microstructure, correlated to the plasma parameters, as well as superconductive properties. The microstructure showed an interesting behaviour, with the grain size increasing with the peak discharge current; the Residual Resistance Ratio (RRR) is inversely proportional to the current for short pulse widths, while it is directly proportional to the current for longer pulse widths. This seems to be related to an increasing number of grains with (110) crystallographic orientation in the deposited film. The performance of superconductive cavities produced with HIPIMS is comparable with some of the best dcMS coated ones. Interesting results are obtained with OES and MS comparing argon and krypton process gases. In particular more energetic ions are produced when using krypton as process gas due to the longer mean free path for elastic collisions for the same pressure. Experiments on cavities have been conducted at CERN while samples have been prepared both at Sheffield Hallam University and at CERN. This allows us to make a comparison between the two different experimental setups. Results on plasma analysis, superconductive properties and film morphology will be presented as well as the performance of the latest HIPIMS-coated cavities.

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A review of the thin film techniques potentially applicable to cavities (Rosa Alejandra Lukaszew - 30')
Speaker: Rosa Alejandra Lukaszew - College of William and Mary (VA)   |   Duration: 30 min.

Abstract
SRF is a surface phenomenon where only ~10 penetration depths are needed (l=40 nm for niobium), thus it has been recognized for some time now that it would be economically convenient to use thin film coated cavities. But problems arise with defects within 1 or 2 l of the surface or on the surface, and insufficient attention has been paid to this topic, including trapping of impurities like oxygen in defects as well as surface roughness enabling magnetic field pinning sites. Earlier attempts at CERN applied standard sputter PVD methods, but the grain size for the CERN Nb/Cu films was 100 nm, which is 10,000 times smaller than for conventional SRF cavities with the ensuing problems that appear at grain boundaries. Thus, these prior attempts showed higher surface resistance and worst Q-slope than bulk. I will review more modern approaches using higher energetic PVD methods for thin film deposition which offer promise to achieve thin films with improved superconducting performance.

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Coaxial Energetic Deposition of thin films (Mahadevan Krishnan - 30')
Speaker: Mahadevan Krishnan - Alameda Applied Sciences Corporation   |   Duration: 30 min.

Abstract
Mahadevan Krishnan, Irfan Irfan, Steven Chapman, Katherine Velas and Matt Worstell, Alameda Applied Sciences Corporation, San Leandro, CA 94577, USA

AASC has been studying thin film coating of Nb on coupon substrates as well as on1300MHz RF cells. At the last Thinfilm workshop in Padua, we reported on high RRR measurements and good crystallinity in Nb films coated onto crystal substrates such as a-sapphire, MgO and also on polished Copper coupons. Since then, we have coated several 1300MHz RF cells provided to us and tested by LANL, ANL and JLab. The Qo vs. E measurements suggest that better surface preparation is a must for high quality RF performance. Future work will coat Copper cells with different surface preparation (centrifugal barrel polishing and EP) and try to improve upon our preliminary results. Results from Nb films coated on to Al6061 coupons are encouraging and motivate coating of a barrel polished Aluminum RF cell. Recently AASC has embarked upon two new thinfilm coating projects: Nb on stainless steel bellows for SRF accelerators and Cu films on stainless steel tubes for high power RF Couplers. We are also collaborating with CERN to coat a Cu disk of a quadrupole resonator with Nb, for RF tests at high fields. This talk will provide details of all of these ongoing activities, all of which are supported by the US Department of Energy via SBIR contracts.

This research is supported at AASC by DOE Grants: #DE-SC0011371, DE-SC0011294, DE-SC0007678 and DE-SC0009581.

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Power Spectral Density Analysis of ECR Deposited Niobium Thin Films (Joshua Spradlin - 30')
Speaker: Joshua Spradlin - Jlab   |   Duration: 30 min.

Abstract

Other SC Materials besides Niobium
(Chairman: Anne Marie Valente-Feliciano)
Preparation of Nb3GaAl Superconductors (Andrea Maria Camacho-Romero - 20')
Speaker: Andrea Maria Camacho-Romero - INFN-LNL   |   Duration: 20 min.

Abstract
A15 compounds Nb3Ga, Nb3Al and Nb-Al-Ga have been synthesized on niobium samples by means of induction heating. For the preparation before of treatment, the niobium samples were treated with BCP solution in order to polish the surface. Subsequent, the samples were annealing using an inductor and setup the voltage, time, sample position, temperature, type and pressure of gas used. The inductive measurements indicate that the highest critical temperature was 18 K with DTc 0.35 K, in Nb-Al-Ga#1 sample. Mapping analysis showed the uniform diffusion of aluminium into the niobium. On the contrary, the gallium diffuses creating channels into niobium. The chemical composition was measured by EDS obtaining 82% wt. Niobium, 11.3%wt., Gallium, 4.7% wt., Aluminium and 1.9% wt. Oxygen. Finally, the results indicate that the new technique is feasible for synthesis of A15 superconductor without using a vacuum system.

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Growth of MgB2 Films on Metallic Substrates by HPCVD (Zhimao Ni - 20')
Speaker: Zhimao Ni - Peking University   |   Duration: 20 min.

Abstract
Authors: Zhimao Ni, Fa He, Kexin Liu and Qingrong Feng

MgB2, due to its high transition temperature of ~40K and absence of weak links between grains, is a candidate material for superconducting radio-frequency (RF) cavities for future particle accelerators. Peking University has developed a HPCVD method for MgB2 fabricating on metallic substrates. We have grown MgB2 films on the substrates of Cu, Nb and Mo[1] successfully. Recently, for better quality of MgB2 film, we tried to fabricate MgB2 film on Cu substrate which was coated a thin film of Mo on the surface. We also tried to obtain the large-area MgB2 film (2-inches in diameter) on metallic substrate with good uniform for RF measurement. The method and results of recent experiments will be presented.

[1] Fa He, et al. MgB2 films fabricated on molybdenum substrate by hybrid physical-chemical vapor deposition for superconducting RF cavity applications. Superconductor Science and Technology, 2012,25(6):065003.

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Progress in the investigation of MgB2 thin films for SRF cavity applications (XiaoXing Xi - 20')
Speaker: XiaoXing Xi - Department of Physics, Temple University   |   Duration: 20 min.

Abstract
MgB2 thin films grown by hybrid physical-chemical vapor deposition (HPCVD) have been investigated for SRF cavity applications. I will present our recent results of research in three directions: enhancement of Hc1 in thin MgB2 films, large area MgB2 films on Cu, and the effort on coating of RF cavities. By reducing the thickness of the MgB2 film from 300 nm to 100 nm, Hc1(0) increases systematically from 38 mT to about 200 mT in both epitaxial and polycrystalline films. The HPCVD process has been successfully applied on 2” diameter Cu substrate. Both the in-situ and two-step processes have been used for the coating of a 6 GHz cavity. Samples from various locations of the cavity show good superconducting properties. Effort is underway to coat 3 GHz RF cavities.

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Open Discussion (Chair: Anne Marie Valente-Feliciano - 30')
Speaker: Chair: Anne Marie Valente-Feliciano -   |   Duration: 30 min.

Abstract

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NEW IDEAS FOR ADVANCED CAVITY CLEANING
(Chairman: Enzo Palmieri)
Progress on Fluorine-free Electropolishing (Vlada Pastushenko - 20')
Speaker: Vlada Pastushenko - INFN-LNL   |   Duration: 20 min.

Abstract
High purity niobium (Nb) is used to make superconducting radio frequency (SRF) cavities. To improve the cavity performance it is necessary to reduce the surface resistance as much as possible. To achieve this goal each Nb cavity undergoes to a series of successive treatments (mechanical polishing, buffered chemical polishing, electropolishing, annealing). Choline Chloride-based ionic liquids are considered as a new class of electrolytes. Comparing to traditional ionic liquids, choline chloride-based ionic liquids are low toxic, biodegradable, and the price is generally low, which make them more and more attractive in green chemistry and industrial chemistry. Since it was found that, the mixture of Choline Chloride and Urea can polish Niobium every year, this solution has been improved. Was investigated the optimal ratio of Choline Chloride and Urea, studied the effect of additives, temperature and current density. When it was found suitable parameters for the polishing of planar samples, we have started to implement it to the polishing of 6 GHz Niobium cavities.

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Plasma Etching for Cleaning and Surface preparation of niobium cavities (Larry Phillips - 30')
Speaker: Larry Phillips - Jlab   |   Duration: 30 min.

Abstract
The current status of plasma etching as a complete cleaning and surface preparation process for niobium will be discussed. A comparison with other methods will be given.

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WORKSHOP CONCLUSIONS (Enzo Palmieri - 10')
Speaker: Enzo Palmieri - INFN-LNL   |   Duration: 10 min.

Abstract
Looking back to the three full days of scientific debate the mainline of the workshop will be outlined and conclusions will be extracted.

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Session Opening     (9:20 - 15:30)
Coffee Break     (11:20 - 11:50)
Lunch     (13:20 - 14:30)
Bus Transfer     (15:30 - 15:40)
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