SRF2011 - List of Authors (Reschke, D.)

Paper

Title

Page

Challenges in SRF Module Production for the European XFEL

2

D. Reschke
DESY, Hamburg, Germany

The internationally organized European XFEL free-electron laser is under construction at the Deutsches Elektronen-Synchrotron (DESY). With an electron beam energy of 14 GeV the possible wavelength will be down to 0.05 nm. The project is the first large scale application of the TESLA technology developed over the last 15 years. The main linac will consist of 80 accelerator modules, i.e. 640 superconducting accelerator cavities, operated at a gradient of 24.3 MV/m. The talk describes the activities with respect to the module production within the international collaboration. The challenges and the status of final prototyping, industrialization and commissioning of new infrastructure will be presented.

Slides MOIOA01 [6.688 MB]

TUPO046

Results on Large Grain Nine-Cell Cavities at DESY: Gradients up to 45 MV/m after Electropolishing

490

D. Reschke, S. Aderhold, A. Gössel, J. Iversen, S. Karstensen, D. Kostin, G. Kreps, A. Matheisen, W.-D. Möller, F. Schlander, W. Singer, X. Singer, N. Steinhau Kühl, A.A. Sulimov, K. Twarowski
DESY, Hamburg, Germany

Since 2009 a series of eight nine-cell cavities (AC151 – AC158) of TESLA shape fabricated of large grain (LG) niobium material is under preparation and test at DESY. In a first step all cavities were tested after a BCP treatment. In a second step additional electro polishing is applied to all cavities. In this paper the treatment will be discussed and present results will be reported

TUPO066

Analysis of Recent Results from Second Sound, Temperature Mapping and Optical Inspection of 1.3 GHz Cavities at DESY

558

F. Schlander, S. Aderhold, D. Reschke, K. Twarowski
DESY, Hamburg, Germany

DESY is preparing for the delivery of some 600 superconducting 9-cell cavities for the European XFEL. Analysing the history and recorded data of recently tested cavities gives important evidence for proper treatment, preparation and handling of cavities. The experience given by temperature mapping, the Second Sound technique and optical inspection will be compared and an overview of the results obtained so far will be given in this report.

Poster TUPO066 [1.160 MB]

THPO031

Second Sound as an automated Quench Localisation Tool at DESY

785

F. Schlander, E. Elsen, D. Reschke
DESY, Hamburg, Germany

Funding: This work is supported by the Commission of the European Communities under the 7th Framework Programme “Construction of New Infrastructures – Preparatory Phase”, contract number 206711.
The understanding of local thermal breakdown (“quench“) in superconducting RF cavities is still a challenge. An easy way to find these heat spots is to measure the Second Sound in superfluid helium. This detection technique has been examined in several institutes. At DESY there are currently two vertical bath cryostats where cold RF tests with a cavity mounted in a cryostat insert can be done. At all of the four inserts the Second Sound setup consisting of eight Oscillating Superleak Transducers (OSTs) is mounted. These are connected to amplifier electronics and the measured signals are fed into an ADC to be read out with MATLAB. Within MATLAB the location is derived from the measured propagation times. The present system is already in use on a regular basis. An automated setup which will be implemented into the usual RF measurements is under development and the current status will be described.

Poster THPO031 [0.550 MB]

THPO035

Comparison of Field Emission at Different SRF Cavity Assembly States and Test Stands

795

D. Kostin, A. Gössel, V. Gubarev, W.-D. Möller, D. Reschke, K. Twarowski
DESY, Hamburg, Germany

SRF cavity Field Emission (FE) presents a major diagnostics instrument on the cavity performance, save the FE levels differ significantly from one cavity test setup to another, making the analysis difficult. A comparison study complimented with a direct calibration of FE in the cavities tested with different auxillaries and test stands (vertical / horizontal / module) is presented and discussed.

Poster THPO035 [0.312 MB]

THPO055

Investigation of Samples Separated From Prototype Cavities of the European XFEL

855

X. Singer, S. Aderhold, A. Ermakov, D. Reschke, W. Singer, K. Twarowski
DESY, Hamburg, Germany
M. Hoss
W.C. Heraeus GmbH, Materials Technology Dept., Hanau, Germany

XFEL prototype cavities fabricated in industry and treated at DESY mainly meet the specification. Few cavities demonstrated low performance (13-20 MV/m) limited by thermal breakdown. The T-map analysis detected quench areas mainly close to the equator. Optical inspection by high resolution camera allowed tracking the several stages of preparation (as received, after the main electropolishing EP, after RF test) and in some cases makes possible monitoring the evolution of defects. In order to understand the nature of reduced performance and get more detailed information on the origin of defects, some samples have been extracted from four cavities and investigated by light microscope, 3D-microscope, SEM, EDX and Auger spectroscopy. Several surface flaws with sizes from a few μm to hundreds of μm have been detected. The defects can be grouped in four categories. The first category of defects indicates foreign elements (often with increased content of carbon). Deviation from smooth surface profile characterizes the second type of defects (holes, bumps). Damaged surface areas at high pressure water rinsing and etching pits belong to the third and fourth category of defects.

Poster THPO055 [3.802 MB]

THPO061

Activation of Field Emitters on Clean Nb Surfaces

869

A. Navitski, S. Lagotzky, G. Müller
Bergische Universität Wuppertal, Wuppertal, Germany
D. Reschke, X. Singer
DESY, Hamburg, Germany

Funding: Funded by Helmholtz-Allianz ’Physics at the Terascale’ and das BMBF-Verbundprojekt 05H09PX5.
Systematic investigations of the enhanced field emission (EFE) from surface irregularities of typical EP and HPR treated Nb samples revealed an exponential increase of the emitter site density N with the initial onset surface field (Eon = 80-160 MV/m) and a strong activation effect, i.e. the final occurrence of EFE at 2-4 times lower Eon relevant for superconducting XFEL and ILC cavities. Possible explanations for this activation are breakdown across the surface oxide, surface erosion by a local microplasma or de/adsorption effects. Such emitter activation might also be caused by the usual baking or rf power processing of cavities. Therefore, we have started a systematic test series with large-grain Nb samples based on correlated field emission microscopy (FESM) and high-resolution SEM investigations before and after heating at temperatures between 122 and 800°C. As expected, we have obtained slightly (x 2) increased N after baking and strongly (x 10) after heating at 800°C. Moreover, the Eon of the activated emitters is reduced down to 40 MV/m. Most emitters could be identified by SEM as micro-scratches. We will discuss the impact of these results on the EFE of SRF cavities.

Paper	Title	Page
MOIOA01	Challenges in SRF Module Production for the European XFEL	2
	D. Reschke DESY, Hamburg, Germany
	The internationally organized European XFEL free-electron laser is under construction at the Deutsches Elektronen-Synchrotron (DESY). With an electron beam energy of 14 GeV the possible wavelength will be down to 0.05 nm. The project is the first large scale application of the TESLA technology developed over the last 15 years. The main linac will consist of 80 accelerator modules, i.e. 640 superconducting accelerator cavities, operated at a gradient of 24.3 MV/m. The talk describes the activities with respect to the module production within the international collaboration. The challenges and the status of final prototyping, industrialization and commissioning of new infrastructure will be presented.
	Slides MOIOA01 [6.688 MB]

TUPO046	Results on Large Grain Nine-Cell Cavities at DESY: Gradients up to 45 MV/m after Electropolishing	490
	D. Reschke, S. Aderhold, A. Gössel, J. Iversen, S. Karstensen, D. Kostin, G. Kreps, A. Matheisen, W.-D. Möller, F. Schlander, W. Singer, X. Singer, N. Steinhau Kühl, A.A. Sulimov, K. Twarowski DESY, Hamburg, Germany
	Since 2009 a series of eight nine-cell cavities (AC151 – AC158) of TESLA shape fabricated of large grain (LG) niobium material is under preparation and test at DESY. In a first step all cavities were tested after a BCP treatment. In a second step additional electro polishing is applied to all cavities. In this paper the treatment will be discussed and present results will be reported

TUPO066	Analysis of Recent Results from Second Sound, Temperature Mapping and Optical Inspection of 1.3 GHz Cavities at DESY	558
	F. Schlander, S. Aderhold, D. Reschke, K. Twarowski DESY, Hamburg, Germany
	DESY is preparing for the delivery of some 600 superconducting 9-cell cavities for the European XFEL. Analysing the history and recorded data of recently tested cavities gives important evidence for proper treatment, preparation and handling of cavities. The experience given by temperature mapping, the Second Sound technique and optical inspection will be compared and an overview of the results obtained so far will be given in this report.
	Poster TUPO066 [1.160 MB]

THPO031	Second Sound as an automated Quench Localisation Tool at DESY	785
	F. Schlander, E. Elsen, D. Reschke DESY, Hamburg, Germany
	Funding: This work is supported by the Commission of the European Communities under the 7th Framework Programme “Construction of New Infrastructures – Preparatory Phase”, contract number 206711. The understanding of local thermal breakdown (“quench“) in superconducting RF cavities is still a challenge. An easy way to find these heat spots is to measure the Second Sound in superfluid helium. This detection technique has been examined in several institutes. At DESY there are currently two vertical bath cryostats where cold RF tests with a cavity mounted in a cryostat insert can be done. At all of the four inserts the Second Sound setup consisting of eight Oscillating Superleak Transducers (OSTs) is mounted. These are connected to amplifier electronics and the measured signals are fed into an ADC to be read out with MATLAB. Within MATLAB the location is derived from the measured propagation times. The present system is already in use on a regular basis. An automated setup which will be implemented into the usual RF measurements is under development and the current status will be described.
	Poster THPO031 [0.550 MB]

THPO035	Comparison of Field Emission at Different SRF Cavity Assembly States and Test Stands	795
	D. Kostin, A. Gössel, V. Gubarev, W.-D. Möller, D. Reschke, K. Twarowski DESY, Hamburg, Germany
	SRF cavity Field Emission (FE) presents a major diagnostics instrument on the cavity performance, save the FE levels differ significantly from one cavity test setup to another, making the analysis difficult. A comparison study complimented with a direct calibration of FE in the cavities tested with different auxillaries and test stands (vertical / horizontal / module) is presented and discussed.
	Poster THPO035 [0.312 MB]

THPO055	Investigation of Samples Separated From Prototype Cavities of the European XFEL	855
	X. Singer, S. Aderhold, A. Ermakov, D. Reschke, W. Singer, K. Twarowski DESY, Hamburg, Germany M. Hoss W.C. Heraeus GmbH, Materials Technology Dept., Hanau, Germany
	XFEL prototype cavities fabricated in industry and treated at DESY mainly meet the specification. Few cavities demonstrated low performance (13-20 MV/m) limited by thermal breakdown. The T-map analysis detected quench areas mainly close to the equator. Optical inspection by high resolution camera allowed tracking the several stages of preparation (as received, after the main electropolishing EP, after RF test) and in some cases makes possible monitoring the evolution of defects. In order to understand the nature of reduced performance and get more detailed information on the origin of defects, some samples have been extracted from four cavities and investigated by light microscope, 3D-microscope, SEM, EDX and Auger spectroscopy. Several surface flaws with sizes from a few μm to hundreds of μm have been detected. The defects can be grouped in four categories. The first category of defects indicates foreign elements (often with increased content of carbon). Deviation from smooth surface profile characterizes the second type of defects (holes, bumps). Damaged surface areas at high pressure water rinsing and etching pits belong to the third and fourth category of defects.
	Poster THPO055 [3.802 MB]

THPO061	Activation of Field Emitters on Clean Nb Surfaces	869
	A. Navitski, S. Lagotzky, G. Müller Bergische Universität Wuppertal, Wuppertal, Germany D. Reschke, X. Singer DESY, Hamburg, Germany
	Funding: Funded by Helmholtz-Allianz ’Physics at the Terascale’ and das BMBF-Verbundprojekt 05H09PX5. Systematic investigations of the enhanced field emission (EFE) from surface irregularities of typical EP and HPR treated Nb samples revealed an exponential increase of the emitter site density N with the initial onset surface field (Eon = 80-160 MV/m) and a strong activation effect, i.e. the final occurrence of EFE at 2-4 times lower Eon relevant for superconducting XFEL and ILC cavities. Possible explanations for this activation are breakdown across the surface oxide, surface erosion by a local microplasma or de/adsorption effects. Such emitter activation might also be caused by the usual baking or rf power processing of cavities. Therefore, we have started a systematic test series with large-grain Nb samples based on correlated field emission microscopy (FESM) and high-resolution SEM investigations before and after heating at temperatures between 122 and 800°C. As expected, we have obtained slightly (x 2) increased N after baking and strongly (x 10) after heating at 800°C. Moreover, the Eon of the activated emitters is reduced down to 40 MV/m. Most emitters could be identified by SEM as micro-scratches. We will discuss the impact of these results on the EFE of SRF cavities.