Matching small β\beta functions using centroid jitter and two beam position monitors

Matching to small beta functions is required to preserve emittance in plasma accelerators. The plasma wake provides strong focusing fields, which typically require beta functions on the mm-scale, comparable to those found in the final focusing of a linear collider. Such beams can be time consuming to experimentally produce and diagnose. We present a simple, fast, and noninvasive method to measure Twiss parameters in a linac using two beam position monitors only, relying on the similarity of the beam phase space and the jitter phase space. By benchmarking against conventional quadrupole scans, the viability of this technique was experimentally demonstrated at the FLASHForward plasma-accelerator facility.Comment: 8 pages, 7 figure

Electron beam profile imaging in the presence of coherent optical radiation effects

High-brightness electron beams with low energy spread at existing and future x-ray free-electron lasers are affected by various collective beam self-interactions and microbunching instabilities. The corresponding coherent optical radiation effects, e.g., coherent optical transition radiation, render electron beam profile imaging impossible and become a serious issue for all kinds of electron beam diagnostics using imaging screens. Furthermore, coherent optical radiation effects can also be related to intrinsically ultrashort electron bunches or the existence of ultrashort spikes inside the electron bunches. In this paper, we discuss methods to suppress coherent optical radiation effects both by electron beam profile imaging in dispersive beamlines and by using scintillation imaging screens in combination with separation techniques. The suppression of coherent optical emission in dispersive beamlines is shown by analytical calculations, numerical simulations, and measurements. Transverse and longitudinal electron beam profile measurements in the presence of coherent optical radiation effects in non-dispersive beamlines are demonstrated by applying a temporal separation technique.Comment: 12 pages, 11 figures, submitted to Phys. Rev. ST Accel. Beam

Booster cavity and fundamental power coupler design issues for bERLinPro

HZB has started building the 50 MeV, 100mA demonstrator energy recovery linac ERL facility bERLinPro. The high power injector system needs to deliver this beam at 6.5 MeV by combining the energy gain of a 1.4 cell SRF photo injector and three Cornell style 2 cell booster cavities. One booster cavity will be operated at zero crossing for bunch energy chirping. Thus two booster cavities have to deliver 2MV each requiring a strong coupling with a loaded Q of 105. To house the two envisaged KEK fundamental power couplers FPC with the cavity, the geometry was slightly modified. Further, to increase coupling and reduce transverse kick effects to the beam, a golf tee antenna tip was designed. This paper summarizes the SRF challenges for the booster cavities, the operational conditions and the modification to the KEK couplers, including tracking calculations to estimate the coupler kick effect to higher orde

Machine Protection Considerations for BERLinPro

The Berlin energy recovery linac project BERLinPro at the HZB is a 50 MeV ERL test facility, which addresses physical and technological questions for future superconducting rf based high brightness, high current electron beam sources. The combination of a 100 mA cw beam, electron bunches with normalized emittances lower than 1 mm mrad and the magnet optics of BERLinPro leads to power densities capable to harm the accelerator components within microseconds if total beam loss occurs. Furthermore, continuous beam loss on the level of 10 5 has to be controlled to avoid activation and to protect the SRF, beam diagnostics and other infrastructure components. In this paper, we present the evaluation of the required key parameters of the BERLinPro machine protection system and present its first conceptual desig

The Injector Layout of BERLinPro

BERLinPro is an Energy Recovery Linac Project running since 2011 at the HZB in Berlin. A conceptual design report has been published in 2012 [1]. One of the key components of the project is the 100 mA superconducting RF photocathode gun under development at the HZB since 2010. Starting in 2016 the injector will go into operation, providing 6.6 MeV electrons with an emittance well below 1mm mrad and bunches shorter than 5 ps. In 2017 the 50 MeV linac will be set up and full recirculation is planned for 2018. The injector design has been finalized and is described in detail in this paper. Emphasis is further laid on beam dynamics aspects and performance simulations of two different gun cavitie

Introducing GUNLAB a compact test facility for SRF photoinjectors

Superconducting radio frequency photoelectron injectors SRF photoinjectors are promising electron sources for high brightness accelerators with high average current and short pulse duration like FELs and ERLs. For the upcoming ERL project bERLinPro we want to test and commission different SRF photoinjectors, optimize the beam performance and examine photocathode materials in an independent test facility. Therefore we designed GunLab to characterize beam parameters from the SRF photoinjectors in a compact diagnostics beamline. The main challenge of GunLab is to characterize the full six dimensional phase space as a function of drive laser and RF parameters. Here we present design and estimated performance of GunLa

Structure and Optical Properties of Silicon Layers with GaSb Nanocrystals Created by Ion-Beam Synthesis

We have studied the ion-beam synthesis of GaSb nanocrystals in Si by high-fluence “hot” implantation of Sb and Ga ions followed by thermal annealing. The Rutherford backscattering, transmission electron microscopy/ transmission electron di˙raction, Raman spectroscopy and photoluminescence were used to characterize the implanted layers. It was found that the nanocrystal size increases from 5 to 60 nm in the samples annealed at 900 ±C up to 20–90 nm in those annealed at 1100 ±C. For the samples annealed at 900 ±C a broad band in the region of 0.75–1.05 eV is registered in the photoluminescence spectra. The nature of this photoluminescence band is discussed

Observation of soft X-ray Cherenkov radiation in Al

The soft X-ray radiation generated by 5.7 MeV electrons from both an Al foil and a Mylar film in forward direction was experimentally studied. A narrow specific directivity, an ultra-narrow spectral bandwidth and a good consistency between the experiment and theory prove that the Cherenkov radiation (CR) with photon energy near the L-edge of absorption in Al was observed. The results demonstrate that the CR spectral-angular properties and the absolute photon yield can be described well enough using Pafomov's theoretical model and Henke's refractive index database, which is essential for all practical applications

Tunable and precise two-bunch generation at FLASHForward

Beam-driven plasma-wakefield acceleration based on external injection has the potential to significantly reduce the size of future accelerators. Stability and quality of the acceleration process substantially depends on the incoming bunch parameters. Precise control of the current profile is essential for optimising energy-transfer efficiency and preserving energy spread. At the FLASHForward facility, driver--witness bunch pairs of adjustable bunch length and separation are generated by a set of collimators in a dispersive section, which enables fs-level control of the longitudinal bunch profile. The design of the collimator apparatus and its commissioning is presented.Comment: 7 pages, 5 figures, to be published in the proceedings of the 4th European Advanced Accelerator Concepts Workshop, 15-21 September 2019, La Biodola Bay, Isola d'Elba, Ital

Pitfalls in the characterization of circulating and tissue-resident human γδ T cells

Dissection of the role and function of human γδ T cells and their heterogeneous subsets in cancer, inflammation, and auto-immune diseases is a growing and dynamic research field of increasing interest to the scientific community. Therefore, harmonization and standardization of techniques for the characterization of peripheral and tissue-resident γδ T cells is crucial to facilitate comparability between published and emerging research. The application of commercially available reagents to classify γδ T cells, in particular the combination of multiple Abs, is not always trouble-free, posing major demands on researchers entering this field. Occasionally, even entire γδ T cell subsets may remain undetected when certain Abs are combined in flow cytometric analysis with multicolor Ab panels, or might be lost during cell isolation procedures. Here, based on the recent literature and our own experience, we provide an overview of methods commonly employed for the phenotypic and functional characterization of human γδ T cells including advanced polychromatic flow cytometry, mass cytometry, immunohistochemistry, and magnetic cell isolation. We highlight potential pitfalls and discuss how to circumvent these obstacles