IPAC2013 - List of Authors (Doebert, S.)

Paper	Title	Page
MOPFI058	Studies of Cs3Sb Cathodes for the CLIC Drive Beam Photoinjector Option	413
	I. Martini, E. Chevallay, S. Döbert, V. Fedosseev, C. Heßler, M. Martyanov CERN, Geneva, Switzerland
	Within the CLIC (Compact Linear Collider) project, feasibility studies of a photoinjector option for the drive beam as an alternative to its baseline design using a thermionic electron gun are on-going. This R&D program covers both the laser and the photocathode side. Whereas the available laser pulse energy in ultra-violet (UV) is currently limited by the optical defects in the 4th harmonics frequency conversion crystal induced by the 0.14 ms long pulse trains, recent measurements of Cs3Sb photocathodes sensitive to green light showed their potential to overcome this limitation. Moreover, using visible laser beams leads to better stability of produced electron bunches and one can take advantages of the availability of higher quality optics. The studied Cs3Sb photocathodes have been produced in the CERN photoemission laboratory using the co-deposition technique and tested in a DC gun set-up. The analysis of data acquired during the cathode production process will be presented in this paper, as well as the results of life-time measurements in the DC gun.

TUPFI040	Experimental Verification of the CLIC Two-Beam Acceleration Technology in CTF3	1436
	P. Skowroński, A. Andersson, J. Barranco, B. Constance, R. Corsini, S. Döbert, A. Dubrovskiy, W. Farabolini, E. Ikarios, R.L. Lillestøl, T. Persson, F. Tecker CERN, Geneva, Switzerland W. Farabolini CEA/DSM/IRFU, France E. Ikarios National Technical University of Athens, Athens, Greece M. Jacewicz, A. Palaia, R.J.M.Y. Ruber Uppsala University, Uppsala, Sweden R.L. Lillestøl University of Oslo, Oslo, Norway T. Persson Chalmers University of Technology, Chalmers Tekniska Högskola, Gothenburg, Sweden
	The Compact Linear Collider (CLIC) International Collaboration is pursuing an extensive R&D program towards a multi-TeV electron-positron collider. In particular, the development of two beam acceleration technology is the focus of the CLIC test facility CTF3. In this paper we summarize the most recent results obtained at CTF3: the results of the studies on the drive beam generation are presented, the achieved two beam acceleration performance is reported and the measured break-down rates and related observations are summarized. The stability of deceleration process performed over 13 subsequent modules and the comparison of the obtained results with the theoretical expectations are discussed. We also outline and discuss the future experimental program.

TUPME047	Sub-Harmonic Bunching System of CLIC Drive Beam Injector	1670
	S. Sanaye Hajari, S. Döbert, S. Döbert, H. Shaker CERN, Geneva, Switzerland S. Sanaye Hajari, H. Shaker IPM, Tehran, Iran
	In the Compact Linear Collider (CLIC) the RF power for the acceleration of the Main Beam is extracted from a high-current Drive Beam that runs parallel with the main linac. The sub-harmonic bunching system of the drive beam injector has been studied in detail and optimized. The model consists of a thermionic gun, three travelling wave sub-harmonic bunchers followed by a tapered travelling wave buncher. The simulation of the beam dynamics has been carried out with PARMELA with the goal of optimizing the overall bunching process and in particular capturing particles as much as possible in the buncher acceptance and decreasing the satellite population.

TUPME047	Sub-Harmonic Bunching System of CLIC Drive Beam Injector	1670
	S. Sanaye Hajari, S. Döbert, S. Döbert, H. Shaker CERN, Geneva, Switzerland S. Sanaye Hajari, H. Shaker IPM, Tehran, Iran
	In the Compact Linear Collider (CLIC) the RF power for the acceleration of the Main Beam is extracted from a high-current Drive Beam that runs parallel with the main linac. The sub-harmonic bunching system of the drive beam injector has been studied in detail and optimized. The model consists of a thermionic gun, three travelling wave sub-harmonic bunchers followed by a tapered travelling wave buncher. The simulation of the beam dynamics has been carried out with PARMELA with the goal of optimizing the overall bunching process and in particular capturing particles as much as possible in the buncher acceptance and decreasing the satellite population.

TUPME052	Sub-harmonic Buncher Design for the CLIC Drive Beam Injector	1685
	H. Shaker, S. Döbert, R. Leuxe, S. Sanaye Hajari CERN, Geneva, Switzerland L. Dassa Università di Brescia, Brescia, Italy S. Sanaye Hajari, H. Shaker IPM, Tehran, Iran
	The CLIC (Compact LInear Collider) is based on two beam concept where a high current drive beam provides the energy needed for acceleration of the main beam. The CLIC drive beam accelerator starts with a high current injector using a sophisticated sub-harmonic bunching system. This paper will focus on the design of the Sub Harmonic Bunchers (SHBs) the first RF components of the injector. A backward traveling wave structure has been optimized for this task. It will be shown also how to avoid asymmetrical fields inside the coupler cells and how to compensate beam loading by changing the phase velocity in comparison to the beam velocity.

TUPME053	General Beam Loading Compensation in a Traveling Wave Structure	1688
	H. Shaker, S. Döbert CERN, Geneva, Switzerland H. Shaker IPM, Tehran, Iran
	The well-known beam loading in a traveling wave structure is in fact a resistive beam loading which bunches travel on the crest. This type of beam loading could be compensated by increasing RF feed power. But generally, bunches could travel on each phase. General beam loading compensation is well-known for a single cell cavity and it is done by changing the RF feed power and detuning the structure together. In this paper, the concept of detuning for a TW structure will be shown and the evolution of fundamental mode beam-induced field will be derived and finally, it will be shown how to compensate beam loading by changing the phase velocity in comparison to the beam velocity.

TUPME054	Experimental Study of the Effect of Beam Loading on RF Breakdown Rate in CLIC High-gradient Accelerating Structures	1691
	F. Tecker, R. Corsini, M. Dayyani Kelisani, S. Döbert, A. Grudiev, O. Kononenko, S. Lebet, J.L. Navarro Quirante, G. Riddone, I. Syratchev, W. Wuensch CERN, Geneva, Switzerland A. Solodko JINR, Dubna, Moscow Region, Russia
	RF breakdown is a key issue for the multi-TeV high-luminosity e⁺e⁻ Compact Linear Collider (CLIC). Breakdowns in the high-gradient accelerator structures can deflect the beam and decrease the desired luminosity. The limitations of the accelerating structures due to breakdowns have been studied so far without a beam present in the structure. The presence of the beam modifies the distribution of the electrical and magnetic field distributions, which determine the breakdown rate. Therefore an experiment has been designed for high power testing a CLIC prototype accelerating structure with a beam present in the CLIC Test Facility (CTF3). A special beam line allows extracting a beam with nominal CLIC beam current and duration from the CTF3 linac. The paper describes the beam optics design for this experimental beam line and the commissioning of the experiment with beam.

TUPWA045	Longitudinal Space Charge Effects in the CLIC Drive Beam	1811
	R.L. Lillestøl, S. Döbert, A. Latina, D. Schulte CERN, Geneva, Switzerland E. Adli, K.N. Sjobak University of Oslo, Oslo, Norway
	The CLIC main beam is accelerated by rf power generated from a high-intensity, low-energy electron drive beam. The accelerating fields are produced in Power Extraction and Transfer Structures, and are strongly dependent on the drive beam bunch distribution, as well as other parameters. We investigate how longitudinal space charge affects the bunch distribution and the corresponding power production, and discuss how the bunch length evolution can affect the main beam. We also describe the development of a Particle-in-Cell space charge solver which was used for the study.

TUPWA046	Experimental Results from the Test Beam Line in the CLIC Test Facility 3	1814
	R.L. Lillestøl, S. Döbert, M. Olvegård CERN, Geneva, Switzerland E. Adli University of Oslo, Oslo, Norway
	In the CLIC two-beam scheme, the main beam is accelerated by rf power provided by energy extraction from a secondary drive beam. This energy is extracted in decelerators, and the first prototype decelerator is the Test Beam Line in the CLIC Test Facility 3. The line is currently equipped with 12 Power Extraction and Transfer Structures (PETS), which allows for extracting up to 40% of the beam energy. We correlate the measured deceleration with predictions from the beam current and the rf power produced in the PETS. We also discuss recent bunch length measurements and how it influences the deceleration. Finally we look at the evolution of the transverse emittance.

WEPWO044	RF Characterization of Niobium Films for Superconducting Cavities	2399
	S. Aull, S. Calatroni, S. Döbert, T. Junginger, G. Terenziani CERN, Geneva, Switzerland S. Aull University of Siegen, Siegen, Germany A.P. Ehiasarian, G. Terenziani Sheffield University, Sheffield, United Kingdom J. Knobloch HZB, Berlin, Germany
	Funding: Work supported by the Wolfgang-Gentner-Programme of the Bundesministerium für Bildung und Forschung (BMBF) The surface resistance RS of superconductors shows a complex dependence on the external parameters such as temperature, frequency or radio-frequency (RF) field. The excited modes of 400, 800 and 1200 MHz allow measurements at actual operating frequencies of superconducting cavities. Niobium films on copper substrates have several advantages over bulk niobium cavities. HiPIMS (High-power impulse magnetron sputtering) is a promising technique to increase the quality and therefore the performance of niobium films. This contribution will introduce CERNs recently developed HiPIMS coating apparatus. Moreover, first results of niobium coated copper samples will be presented, revealing the dominant loss mechanisms.

Paper

Title

Page

Studies of Cs3Sb Cathodes for the CLIC Drive Beam Photoinjector Option

413

I. Martini, E. Chevallay, S. Döbert, V. Fedosseev, C. Heßler, M. Martyanov
CERN, Geneva, Switzerland

Within the CLIC (Compact Linear Collider) project, feasibility studies of a photoinjector option for the drive beam as an alternative to its baseline design using a thermionic electron gun are on-going. This R&D program covers both the laser and the photocathode side. Whereas the available laser pulse energy in ultra-violet (UV) is currently limited by the optical defects in the 4th harmonics frequency conversion crystal induced by the 0.14 ms long pulse trains, recent measurements of Cs3Sb photocathodes sensitive to green light showed their potential to overcome this limitation. Moreover, using visible laser beams leads to better stability of produced electron bunches and one can take advantages of the availability of higher quality optics. The studied Cs3Sb photocathodes have been produced in the CERN photoemission laboratory using the co-deposition technique and tested in a DC gun set-up. The analysis of data acquired during the cathode production process will be presented in this paper, as well as the results of life-time measurements in the DC gun.

TUPFI040

Experimental Verification of the CLIC Two-Beam Acceleration Technology in CTF3

1436

P. Skowroński, A. Andersson, J. Barranco, B. Constance, R. Corsini, S. Döbert, A. Dubrovskiy, W. Farabolini, E. Ikarios, R.L. Lillestøl, T. Persson, F. Tecker
CERN, Geneva, Switzerland
W. Farabolini
CEA/DSM/IRFU, France
E. Ikarios
National Technical University of Athens, Athens, Greece
M. Jacewicz, A. Palaia, R.J.M.Y. Ruber
Uppsala University, Uppsala, Sweden
R.L. Lillestøl
University of Oslo, Oslo, Norway
T. Persson
Chalmers University of Technology, Chalmers Tekniska Högskola, Gothenburg, Sweden

The Compact Linear Collider (CLIC) International Collaboration is pursuing an extensive R&D program towards a multi-TeV electron-positron collider. In particular, the development of two beam acceleration technology is the focus of the CLIC test facility CTF3. In this paper we summarize the most recent results obtained at CTF3: the results of the studies on the drive beam generation are presented, the achieved two beam acceleration performance is reported and the measured break-down rates and related observations are summarized. The stability of deceleration process performed over 13 subsequent modules and the comparison of the obtained results with the theoretical expectations are discussed. We also outline and discuss the future experimental program.

TUPME047

Sub-Harmonic Bunching System of CLIC Drive Beam Injector

1670

S. Sanaye Hajari, S. Döbert, S. Döbert, H. Shaker
CERN, Geneva, Switzerland
S. Sanaye Hajari, H. Shaker
IPM, Tehran, Iran

In the Compact Linear Collider (CLIC) the RF power for the acceleration of the Main Beam is extracted from a high-current Drive Beam that runs parallel with the main linac. The sub-harmonic bunching system of the drive beam injector has been studied in detail and optimized. The model consists of a thermionic gun, three travelling wave sub-harmonic bunchers followed by a tapered travelling wave buncher. The simulation of the beam dynamics has been carried out with PARMELA with the goal of optimizing the overall bunching process and in particular capturing particles as much as possible in the buncher acceptance and decreasing the satellite population.

TUPME047

Sub-Harmonic Bunching System of CLIC Drive Beam Injector

1670

S. Sanaye Hajari, S. Döbert, S. Döbert, H. Shaker
CERN, Geneva, Switzerland
S. Sanaye Hajari, H. Shaker
IPM, Tehran, Iran

In the Compact Linear Collider (CLIC) the RF power for the acceleration of the Main Beam is extracted from a high-current Drive Beam that runs parallel with the main linac. The sub-harmonic bunching system of the drive beam injector has been studied in detail and optimized. The model consists of a thermionic gun, three travelling wave sub-harmonic bunchers followed by a tapered travelling wave buncher. The simulation of the beam dynamics has been carried out with PARMELA with the goal of optimizing the overall bunching process and in particular capturing particles as much as possible in the buncher acceptance and decreasing the satellite population.

TUPME052

Sub-harmonic Buncher Design for the CLIC Drive Beam Injector

1685

H. Shaker, S. Döbert, R. Leuxe, S. Sanaye Hajari
CERN, Geneva, Switzerland
L. Dassa
Università di Brescia, Brescia, Italy
S. Sanaye Hajari, H. Shaker
IPM, Tehran, Iran

The CLIC (Compact LInear Collider) is based on two beam concept where a high current drive beam provides the energy needed for acceleration of the main beam. The CLIC drive beam accelerator starts with a high current injector using a sophisticated sub-harmonic bunching system. This paper will focus on the design of the Sub Harmonic Bunchers (SHBs) the first RF components of the injector. A backward traveling wave structure has been optimized for this task. It will be shown also how to avoid asymmetrical fields inside the coupler cells and how to compensate beam loading by changing the phase velocity in comparison to the beam velocity.

TUPME053

General Beam Loading Compensation in a Traveling Wave Structure

1688

H. Shaker, S. Döbert
CERN, Geneva, Switzerland
H. Shaker
IPM, Tehran, Iran

The well-known beam loading in a traveling wave structure is in fact a resistive beam loading which bunches travel on the crest. This type of beam loading could be compensated by increasing RF feed power. But generally, bunches could travel on each phase. General beam loading compensation is well-known for a single cell cavity and it is done by changing the RF feed power and detuning the structure together. In this paper, the concept of detuning for a TW structure will be shown and the evolution of fundamental mode beam-induced field will be derived and finally, it will be shown how to compensate beam loading by changing the phase velocity in comparison to the beam velocity.

TUPME054

Experimental Study of the Effect of Beam Loading on RF Breakdown Rate in CLIC High-gradient Accelerating Structures

1691

F. Tecker, R. Corsini, M. Dayyani Kelisani, S. Döbert, A. Grudiev, O. Kononenko, S. Lebet, J.L. Navarro Quirante, G. Riddone, I. Syratchev, W. Wuensch
CERN, Geneva, Switzerland
A. Solodko
JINR, Dubna, Moscow Region, Russia

RF breakdown is a key issue for the multi-TeV high-luminosity e⁺e⁻ Compact Linear Collider (CLIC). Breakdowns in the high-gradient accelerator structures can deflect the beam and decrease the desired luminosity. The limitations of the accelerating structures due to breakdowns have been studied so far without a beam present in the structure. The presence of the beam modifies the distribution of the electrical and magnetic field distributions, which determine the breakdown rate. Therefore an experiment has been designed for high power testing a CLIC prototype accelerating structure with a beam present in the CLIC Test Facility (CTF3). A special beam line allows extracting a beam with nominal CLIC beam current and duration from the CTF3 linac. The paper describes the beam optics design for this experimental beam line and the commissioning of the experiment with beam.

TUPWA045

Longitudinal Space Charge Effects in the CLIC Drive Beam

1811

R.L. Lillestøl, S. Döbert, A. Latina, D. Schulte
CERN, Geneva, Switzerland
E. Adli, K.N. Sjobak
University of Oslo, Oslo, Norway

The CLIC main beam is accelerated by rf power generated from a high-intensity, low-energy electron drive beam. The accelerating fields are produced in Power Extraction and Transfer Structures, and are strongly dependent on the drive beam bunch distribution, as well as other parameters. We investigate how longitudinal space charge affects the bunch distribution and the corresponding power production, and discuss how the bunch length evolution can affect the main beam. We also describe the development of a Particle-in-Cell space charge solver which was used for the study.

TUPWA046

Experimental Results from the Test Beam Line in the CLIC Test Facility 3

1814

R.L. Lillestøl, S. Döbert, M. Olvegård
CERN, Geneva, Switzerland
E. Adli
University of Oslo, Oslo, Norway

In the CLIC two-beam scheme, the main beam is accelerated by rf power provided by energy extraction from a secondary drive beam. This energy is extracted in decelerators, and the first prototype decelerator is the Test Beam Line in the CLIC Test Facility 3. The line is currently equipped with 12 Power Extraction and Transfer Structures (PETS), which allows for extracting up to 40% of the beam energy. We correlate the measured deceleration with predictions from the beam current and the rf power produced in the PETS. We also discuss recent bunch length measurements and how it influences the deceleration. Finally we look at the evolution of the transverse emittance.

WEPWO044

RF Characterization of Niobium Films for Superconducting Cavities

2399

S. Aull, S. Calatroni, S. Döbert, T. Junginger, G. Terenziani
CERN, Geneva, Switzerland
S. Aull
University of Siegen, Siegen, Germany
A.P. Ehiasarian, G. Terenziani
Sheffield University, Sheffield, United Kingdom
J. Knobloch
HZB, Berlin, Germany

Funding: Work supported by the Wolfgang-Gentner-Programme of the Bundesministerium für Bildung und Forschung (BMBF)
The surface resistance RS of superconductors shows a complex dependence on the external parameters such as temperature, frequency or radio-frequency (RF) field. The excited modes of 400, 800 and 1200 MHz allow measurements at actual operating frequencies of superconducting cavities. Niobium films on copper substrates have several advantages over bulk niobium cavities. HiPIMS (High-power impulse magnetron sputtering) is a promising technique to increase the quality and therefore the performance of niobium films. This contribution will introduce CERNs recently developed HiPIMS coating apparatus. Moreover, first results of niobium coated copper samples will be presented, revealing the dominant loss mechanisms.