IPAC2011 - List of Authors (Ziemann, V.G.)

Paper

Title

Page

Two Beam Test Stand Experiments in the CTF3 Facility

29

W. Farabolini, F. Peauger
CEA/DSM/IRFU, France
J. Barranco, S. Bettoni, B. Constance, R. Corsini, M. Csatari, S. Döbert, A. Dubrovskiy, C. Heßler, T. Persson, G. Riddone, P.K. Skowroński, F. Tecker
CERN, Geneva, Switzerland
D. Gudkov, A. Solodko
JINR, Dubna, Moscow Region, Russia
M. Jacewicz, T. Muranaka, A. Palaia, R.J.M.Y. Ruber, V.G. Ziemann
Uppsala University, Uppsala, Sweden

The CLEX building in the CTF3 facility is the place where essential experiments are performed to validate the Two-Beam Acceleration scheme upon which the CLIC project relies. The Drive Beam enters the CLEX after being recombined in the Delay loop and the Combiner Ring in intense beam trains of 24 A – 150 MeV lasting 140 ns and bunched at 12 GHz, although other beam parameters are also accessible. This beam is then decelerated in dedicated structures installed in the Test Beam Line (TBL) and in the Two-Beam Test Stand (TBTS) aimed at delivering bursts of 12 GHz RF power. In the TBTS this power is used to generate a high accelerating gradient of 100 MV/m in specially designed accelerating structures. To assess the performances of these structures a probe beam is used, produced by a small Linac. We reported here the various experiences conducted in the TBTS making use of the versatility the probe beam and of dedicated diagnostics.

Slides MOOCA02 [3.003 MB]

TUPC133

Instrumentation for the 12 GHz Stand-alone Test-stand to Test CLIC Acceleration Structures

1335

M. Jacewicz, R.J.M.Y. Ruber, V.G. Ziemann
Uppsala University, Uppsala, Sweden
J.W. Kovermann
CERN, Geneva, Switzerland

Vacuum breakdown is one of the primary limitations in the design and construction of high energy accelerators operating with warm accelerating structures (ACS) such as CLIC linear collider because the mechanisms that cause the breakdown are still a mystery. The ongoing experimental work is trying to benchmark the theoretical models focusing on the physics of vacuum breakdown which is responsible for the observed discharges. The CLIC collaboration is preparing a dedicated 12 GHz test-stand to observe the characteristics of the RF discharges and their eroding effects on the ACS. The instrumentation for the test-stand must be versatile and allow for the conditioning of the ACS with measurements of the breakdown rates at different power levels as well as detection of the dark current and light emission directly relevant to breakdown physics. For that purpose we are developing 2 novel instruments. A pepper-pot chamber with an external magnetic spectrometer for measurement of the spatial and energy distributions of the electrons emitted from the ACS and an optical laser system for probing the ACS to observe the effect of a discharge on the transmitted light.

TUPS097

In-situ Experiments of Vacuum Discharge using Scanning Electron Microscopes

1765

T. Muranaka, V.G. Ziemann
Uppsala University, Uppsala, Sweden
T. Blom, K. Leifer
Uppsala University, Department of Engineering Sciences, Uppsala, Sweden

Funding: This work is supported by the 7th European Framework Program EuCARD under grant number 227579
Fundamental understandings of vacuum discharge mechanisms and involving surface damage is an indispensable for CLIC feasibility study. We have been conducting dc experiments inside a Scanning Electron Microscope (SEM) at Uppsala university in order to investigate localised breakdown phenomena. By using a SEM, we achieve the resolution of the electron probe in the few-nm range, which is of great advantage as the surface roughness of the polished accelerating structures is in the same scale. The high accelerating field of 1 GV/m is realised by biasing an electrode with 1 kV set above the sample with a gap of sub μm. Furthermore, a second SEM equipped with a Focused Ion Beam (FIB) is used to modify the topography of sample surfaces thus the geometrical dependence of field emissions and vacuum discharges could be studied. The FIB can be used for the surface damage analysis as well. We have demonstrated subsurface damage observations by using FIB to sputter a rectangular recess into the sample in the breakdown region. Those powerful surface analysis techniques can be productively applied to the study of fatigue in prototype accelerating structures.

THPC097

Transverse Alignment Tolerances for the European XFEL Laser Heater

3116

V.A. Goryashko
NASU/IRE, Kharkov, Ukraine
M. Dohlus
DESY, Hamburg, Germany
M. Hamberg, V.G. Ziemann
Uppsala University, Uppsala, Sweden

Funding: Supported by the KTH-SU-UU FEL Center.
We study the impact of misalignments between a laser beam and an electron bunch on the energy distribution function of the electron bunch in the laser heater. Transverse position and angular misalignment as well as different spot size of the laser and electron beam are considered. We find that the transverse misalignment makes the energy distribution function narrower compared to the case of ideal adjustment and a distinct peak in the distribution around the initial mean value of the energy appears. We demonstrate that despite these misalignments a uniform heating in terms of the energy spread can be achieved by appropriately adapting the transverse size and power of the laser beam such that the energy distribution function of the electron bunch at the end of the laser heater can be made similar to a Gaussian, thus providing more effective Landau damping against the micro-bunching instability. The laser power mainly determines the local energy spread while the laser spot size governs the shape of the energy distribution function. The transverse oscillations of electrons induced by the magnetic field in the laser heater are found to be non-essential for typical operation parameters.

Paper	Title	Page
MOOCA02	Two Beam Test Stand Experiments in the CTF3 Facility	29
	W. Farabolini, F. Peauger CEA/DSM/IRFU, France J. Barranco, S. Bettoni, B. Constance, R. Corsini, M. Csatari, S. Döbert, A. Dubrovskiy, C. Heßler, T. Persson, G. Riddone, P.K. Skowroński, F. Tecker CERN, Geneva, Switzerland D. Gudkov, A. Solodko JINR, Dubna, Moscow Region, Russia M. Jacewicz, T. Muranaka, A. Palaia, R.J.M.Y. Ruber, V.G. Ziemann Uppsala University, Uppsala, Sweden
	The CLEX building in the CTF3 facility is the place where essential experiments are performed to validate the Two-Beam Acceleration scheme upon which the CLIC project relies. The Drive Beam enters the CLEX after being recombined in the Delay loop and the Combiner Ring in intense beam trains of 24 A – 150 MeV lasting 140 ns and bunched at 12 GHz, although other beam parameters are also accessible. This beam is then decelerated in dedicated structures installed in the Test Beam Line (TBL) and in the Two-Beam Test Stand (TBTS) aimed at delivering bursts of 12 GHz RF power. In the TBTS this power is used to generate a high accelerating gradient of 100 MV/m in specially designed accelerating structures. To assess the performances of these structures a probe beam is used, produced by a small Linac. We reported here the various experiences conducted in the TBTS making use of the versatility the probe beam and of dedicated diagnostics.
	Slides MOOCA02 [3.003 MB]

TUPC133	Instrumentation for the 12 GHz Stand-alone Test-stand to Test CLIC Acceleration Structures	1335
	M. Jacewicz, R.J.M.Y. Ruber, V.G. Ziemann Uppsala University, Uppsala, Sweden J.W. Kovermann CERN, Geneva, Switzerland
	Vacuum breakdown is one of the primary limitations in the design and construction of high energy accelerators operating with warm accelerating structures (ACS) such as CLIC linear collider because the mechanisms that cause the breakdown are still a mystery. The ongoing experimental work is trying to benchmark the theoretical models focusing on the physics of vacuum breakdown which is responsible for the observed discharges. The CLIC collaboration is preparing a dedicated 12 GHz test-stand to observe the characteristics of the RF discharges and their eroding effects on the ACS. The instrumentation for the test-stand must be versatile and allow for the conditioning of the ACS with measurements of the breakdown rates at different power levels as well as detection of the dark current and light emission directly relevant to breakdown physics. For that purpose we are developing 2 novel instruments. A pepper-pot chamber with an external magnetic spectrometer for measurement of the spatial and energy distributions of the electrons emitted from the ACS and an optical laser system for probing the ACS to observe the effect of a discharge on the transmitted light.

TUPS097	In-situ Experiments of Vacuum Discharge using Scanning Electron Microscopes	1765
	T. Muranaka, V.G. Ziemann Uppsala University, Uppsala, Sweden T. Blom, K. Leifer Uppsala University, Department of Engineering Sciences, Uppsala, Sweden
	Funding: This work is supported by the 7th European Framework Program EuCARD under grant number 227579 Fundamental understandings of vacuum discharge mechanisms and involving surface damage is an indispensable for CLIC feasibility study. We have been conducting dc experiments inside a Scanning Electron Microscope (SEM) at Uppsala university in order to investigate localised breakdown phenomena. By using a SEM, we achieve the resolution of the electron probe in the few-nm range, which is of great advantage as the surface roughness of the polished accelerating structures is in the same scale. The high accelerating field of 1 GV/m is realised by biasing an electrode with 1 kV set above the sample with a gap of sub μm. Furthermore, a second SEM equipped with a Focused Ion Beam (FIB) is used to modify the topography of sample surfaces thus the geometrical dependence of field emissions and vacuum discharges could be studied. The FIB can be used for the surface damage analysis as well. We have demonstrated subsurface damage observations by using FIB to sputter a rectangular recess into the sample in the breakdown region. Those powerful surface analysis techniques can be productively applied to the study of fatigue in prototype accelerating structures.

THPC097	Transverse Alignment Tolerances for the European XFEL Laser Heater	3116
	V.A. Goryashko NASU/IRE, Kharkov, Ukraine M. Dohlus DESY, Hamburg, Germany M. Hamberg, V.G. Ziemann Uppsala University, Uppsala, Sweden
	Funding: Supported by the KTH-SU-UU FEL Center. We study the impact of misalignments between a laser beam and an electron bunch on the energy distribution function of the electron bunch in the laser heater. Transverse position and angular misalignment as well as different spot size of the laser and electron beam are considered. We find that the transverse misalignment makes the energy distribution function narrower compared to the case of ideal adjustment and a distinct peak in the distribution around the initial mean value of the energy appears. We demonstrate that despite these misalignments a uniform heating in terms of the energy spread can be achieved by appropriately adapting the transverse size and power of the laser beam such that the energy distribution function of the electron bunch at the end of the laser heater can be made similar to a Gaussian, thus providing more effective Landau damping against the micro-bunching instability. The laser power mainly determines the local energy spread while the laser spot size governs the shape of the energy distribution function. The transverse oscillations of electrons induced by the magnetic field in the laser heater are found to be non-essential for typical operation parameters.