| Paper | Title | Page |
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| MOPC038 | Ultra-high Brightness Electron Beams by All-optical Plasma-based Injectors | 157 |
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| We study the generation of low emittance high current mono-energetic beams from plasma waves driven by ultra-short laser pulses, in view of achieving beam brightness of interest for FEL applications. The aim is to show the feasibility of generating nC charged beams carrying peak currents much higher than those attainable with photoinjectors, together with comparable emittances and energy spread, compatibly with typical FEL requirements. We identified a particularly suitable regime which is based on a LWFA plasma driving scheme on a gas jet modulated in areas of different densities with sharp density gradients. Simulations show that in the first regime, using a properly density modulated gas jet, it is possible to generate beams at energies of about 30 MeV with peak currents of 20 kA, slice transverse emittances as low as 0.3 mm.mrad and energy spread around 0.4%. This beams break the barrier of 1018 A/(mm.mrad)2 in brightness, a value definitely above the ultimate performances of photo-injectors, therefore opening a new range of opportunities for FEL applications. A few examples of FELs driven by such kind of beams injected into laser undulators are finally shown. | ||
| MOPC040 | COBALD - an Inverse Compton Back-scattering Source at Daresbury | 160 |
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| An inverse Compton Back-scattering (CBS) ultra-short pulsed x-ray source driven by the multi-terawatt laser installed at Daresbury’s Energy Recovery Linac Prototype (ERLP) is being developed. Hard x-rays, ranging from 15 keV to 30 keV, depending on the backscattering geometry, will be generated through the interaction of the laser pulse and an electron bunch delivered by ERLP. The X-rays created contain 15 ·106 photons per pulse from head-on collisions, with a pulse duration comparable to that of the incoming electron bunch, and 5 ·106 photons per pulse from side-on collisions, where the laser pulse defines the pulse width. The peak spectral brightness of ≈1020 photons/s/mm2/mrad2/0.1% ΔE/E is close to that of 4th-generation synchrotron light sources. Called COBALD, it will initially be used as a short pulse diagnostic for the ERLP electron beam and will explore the extreme challenges of photon/electron beam synchronization, which is a fundamental requirement for all accelerator-based (whether FEL or spontaneous SR) dynamics programmes. Furthermore, a fast-melting experiment will be used as a diagnostic tool to provide further information on the stability of the source. | ||
| MOPC041 | Microfabrication of Relativistic Electron Beam by Laser and its Application to THz Coherent Synchrotron Radiation | 163 |
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| It is well known that broadband coherent synchrotron radiation (CSR) is emitted by an electron bunch whose length is shorter than radiation wavelength. However, even a long electron bunch can emit CSR when it has micro-density structure whose characteristic length is equal to the radiation wavelength. Recently, we have demonstrated that, by injecting amplitude modulated laser pulses into an electron storage ring, quasi-monochromatic and tunable terahertz (THz) CSR could be produced. In this method, periodic micro-density structure of THz scale was created on the electron bunch, as the result of the laser-electron interaction. The bunch emitted quasi-monochromatic THz radiation in a uniform dipole filed, not in an undulator. This new technology provides a way to imprint periodic wave patterns inside the electron bunch phase space. In adding to the light source applications, this would be a new tool to investigate electron beam dynamics. | ||
| MOPC043 | Design of LINAC Based Compact X-ray Source via Inverse Compton Scattering at Waseda University | 166 |
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| A table-top size soft X-ray source based on inverse Compton scattering has been developed at Waseda University. We have already succeeded in generating X-rays via inverse Compton scattering between 4.6 MeV electron beam generated from a photocathode RF-gun and 1047nm Nd:YLF laser. The energy of the X-ray is within the 'water window' region which can be applied for the soft X-ray microscope for biological observation. In 2007, new RF-gun cavity with Cs-Te photocathode in place of copper has been installed. The energy of electron beam became up to 5.5MeV due to the increase of Q-value of the gun cavity. According to this achievement, generated X-ray energies will cover overall the 'water window' region. We are planning a multi-pulse inverse Compton scattering X-ray generation system in order to enhance a luminous intensity of the X-rays. For this purpose, we are considering a multi-pulse UV laser system for generating a multi-bunch electron beam, the method for beam loading compensation, and the multi-pulse IR laser system for the Compton collisions. Experimental results of X-ray generation and multi-pulse X-ray plans will be presented at the conference. | ||
| MOPC045 | First Measurement Results of the PSI 500kV Low Emittance Electron Source | 169 |
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| The Paul Scherrer Insitute (PSI) is presently developing a low emittance electron source for the PSI-XFEL project. The target beam parameters at the source are I=5.5 A, Q=0.2 nC and a slice emittance below 0.2 mm.mrad. The gun concept consists of a high gradient "diode“ stage followed by a two-frequency two-cell cavity to allow fine tuning of the longitudinal phase space. This paper reports on the first experimental results obtained with the PSI 500 kV test stand. The facility consists of a 500 kV diode stage followed by a diagnostic beam line including an emittance monitor. An air-core transformer based high voltage pulser is capable of delivering a pulse of 250 ns FWHM with amplitude up to 500 kV. The diode gap between two mirror polished electrodes is adjustable to allow systematic gradient studies. The electrons are produced by a 266nm UV laser delivering 4μJoules on the Cu-cathode. | ||
| MOPC046 | Femtoslicing at BESSY - Detecting More Photons | 172 |
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The BESSY femtoslicing facility is now well established* and has proven its succesful operation for femtosecond laser-pump and x-ray-probe experiments**. However, many interesting physical phenomena cannot be addressed with the presently available comparably low number of photons detected at the sample. The most direct way to increase the photon flux is to increase the laser repetition rate. In order to preserve the excellent fs-signal to ps-background ratio special storage ring fill patterns and corresponding laser synchronisation schemes have been studied. We present calculations showing the influence of a dedicated new radiator promising better flux and polarisation properties. Recent results from a new beamline based on high transmission reflection zone plates will be presented. A new avalanche photo diode-array-based detection system has been successfully tested. This allows a parallel detection in the dispersion plane behind the monochomator. The status of these improvements will be presented.
*S. Khan et al. Phys. Rev. Lett, (97), 074801 (2006). |
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| MOPC047 | Status of Kharkov X-ray Generator NESTOR Based on Compton Back Scattering | 175 |
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| The purpose of the NESTOR (New Electron STOrage Ring) project is to create intense X-ray generator based on compact storage ring and Compton back scattering in the National Science Centre “Kharkov Institute of Physics and Technology”. It allows to carry out investigations in the wide range of fundamental and applied sciences such as physics, biology, medicine and so on. The facility consists of the compact 40-225 MeV storage ring, linear 35-90 MeV electron accelerator as an injector, transportation system and Nd:Yag laser and optical cavity. In addition to hard Compton radiation it is supposed to use 4 soft vacuum ultraviolet radiation channels of natural synchrotron radiation of dipole. The facility is going to be in operation in the middle of 2009 and the expected X-rays flux will be of about 1013 phot/s. In the paper the main facility parameters are presented. | ||
| MOPC048 | Coherent Synchrotron Radiation Burst from Electron Storage Ring under External RF Modulation | 178 |
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| It is known that a high-peak-current beam in an electron storage ring emits a burst of coherent synchrotron radiation (CSR) in the THz region. This CSR is powerful and easily obtained with no special expense, but is not used by synchrotron radiation users. This is because the burst arises from a fine time structure in the bunch due to longitudinal beam instabilities, and is unstable. We quantitatively investigated its time structure to find out how unstable it is. The measurements of CSR from one bunch showed that with an average period of 10ms (comparable with the damping time, 12 ms) the fluctuation of averaged power was about 10%. This would be reduced to 1% with 100 bunches. The fluctuation ratio had small dependence on beam charge, rf acceleration voltage and momentum compaction factor. The successive bursts had a correlation because the beam had a memory of former bursts. This worked to reduce the fluctuation in long period. When the rf phase was modulated with 2fs (twice of the synchrotron oscillation frequency), the burst structure was modulated with 2fs and the long term fluctuation was reduced. This modulation can be used to eliminate background noise in user experiments. | ||
| MOPC049 | Comparative Study of Vibration Stability at Operating Light Source Facilities and Lessons Learned in Achieving NSLS II Stability Goals | 181 |
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Understanding the correlation between storage ring vibration and electron beam oscillation is key in achieving the design beam parameters of a 3rd generation light source. Spectral properties of the vibration at the storage ring floor, in addition to amplitude, and its relation to the dynamic properties of the lattice govern the complex relation between lattice movement and beam jitter. Spectral characteristics are, in general, site-specific and motions exhibit spatial variability. To best describe the relationship between the ground motion field at the NSLS II site and the accelerator while quantifying the storage ring oscillations resulting from its interaction with the undisturbed site, field studies have been conducted at various light source facilities. By using the same metric data characterizing the achieved stability levels in operating light sources are generated and used in the assessment of the NSLS II stability which in turn linked to the specific site, subsurface and design characteristics. The paper summarizes the results of these comprehensive findings and presents an overall assessment of stability levels that can be achieved.
Work performed under the auspices of the US DOE. |
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| MOPC050 | Ground Motion Studies at NSLS II | 184 |
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In 3rd generation light sources such as the 3 GeV NSLS II under design at BNL, strict requirements associated with vibration on the storage ring floor are imposed in order to minimize the jitter in the electron beam. Spectral characteristics storage ring vibration and dynamic properties of the ring lattice are controlling parameters. Ground motion at the NSLS-II site is characterized by a complex spectrum consisting of fast and slow motions stemming from natural and cultural sources. Cultural noise with frequencies higher than a few Hz has the potential of dramatically affecting the accelerator performance. In this study, an array of vibration measurements at the undisturbed NSLS II site has been made in order to establish the “green-field” vibration environment and its spectral characteristics. Its interaction with the NSLS II accelerator structure and the quantification of the storage ring vibration, both in terms of amplitude and spectral content have been assessed through a state-of-the-art wave propagation and scattering analysis. This paper focuses primarily on the wave propagation and scattering aspect as well as on the filtering effects of accelerator structural parameters.
Work performed under the auspices of the US DOE. |
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| MOPC053 | BEAM DYNAMICS IN THE LASER-ELECTRON STORAGE RING FOR A COMPTON X-RAY SOURCE | 187 |
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| We present the lattice analysis and simulation study of the beam dynamics in the pulse mode of the laser-electron storage ring. Compton Scattering (CS), Intra-beam Scattering (IBS) with non-Gaussian beam and Synchro-tron Radiation (SR) are taken into consideration. Emittance growth, energy spread and phase space of the electron beam, as well as spatial and temporal distribution of the scattered photon are studied in this paper. | ||
| MOPP155 | Superconducting RF Deflecting Cavity Design and Prototype for Short X-ray Pulse Generation | 913 |
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Deflecting RF cavities are proposed to be used in generating short x-ray pulses (on ~1-picosecond order) at the Advanced Photon Source (APS) at Argonne National Laboratory (ANL)* using a novel scheme by Zholents**. To meet the required deflecting voltage, impedance budget from higher order, lower order and the same order modes (HOM, LOM and SOM) of the APS storage ring, extensive deflecting cavity design studies have been conducted with numerical simulations and cavity prototypes. In this paper, we report recent progress on a single cell S-band (2.8-GHz) superconducting deflecting cavity design with waveguide damping. A copper and a niobium prototype cavity were fabricated and tested, respectively to benchmark the cavity and damping designs. A new damping scheme has been proposed which provides stronger damping to both HOM and LOM by directly coupling to a damping waveguide on the cavity equator.
* A. Nassiri, private communication, 2007 |