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Silica-coated iron oxide nanoparticles are of enormous importance in biotechnology, nanomedicine, and catalysis. The study demonstrates the significant influence of the coating thickness on the particle properties. Though slow magnetophoresis, a thinner shell leads to higher surface areas, lower isoelectric points, and higher magnetizations. However, thick layers prevent oxidation and lead to stabilization. The coating thickness influenced the binding of the cationic peptide lasioglossin, with a maximal loading of 0.23 g g−1 for the smallest particles. This knowledge can be used to specifically design particles for usage with a cationic tag system in biotechnology or drug delivery with antimicrobial peptides. Graphical abstract

At the Photo Injector Test facility at DESY in Zeuthen (PITZ), an RD platform for electron FLASH and very high energy electron radiation therapy and radiation biology is being prepared (FLASHlab@PITZ). The beam parameters available at PITZ are worldwide unique. They are based on experiences from 20 + years of developing high brightness beam sources and an ultra-intensive THz light source demonstrator for ps scale electron bunches with up to 5 nC bunch charge at MHz repetition rate in bunch trains of up to 1 ms length, currently 22 MeV (upgrade to 250 MeV planned). Individual bunches can provide peak dose rates up to 10

Physical review accelerators and beams 25(8), 083401 (2022). doi:10.1103/PhysRevAccelBeams.25.083401, Slice energy spread is one of the key parameters in free electron laser optimizations, but its accurate measurement is not straightforward. Two recent studies from high energy (≥100 MeV) photoinjectors at SwissFEL and European XFEL have reported much higher slice energy spread than expected at their XFEL working points (200 - 250 pC). In this paper, a new method formeasuring slice energy spread at a lower beam energy (∼20 MeV) is proposed and demonstrated at the PhotoInjector Test facility at DESY Zeuthen (PITZ), and the results for 250 pC are much lower than those measured at high energy injectors, Published by American Physical Society, College Park, MD

Synthesis gas fermentation is a microbial process, which uses anaerobic bacteria to convert CO-rich gases to organic acids and alcohols and thus presents a promising technology for the sustainable production of fuels and platform chemicals from renewable sources. Clostridium carboxidivorans and Clostridium autoethanogenum are two acetogenic bacteria, which have shown their high potential for these processes by their high tolerance toward CO and in the production of industrially relevant products such as ethanol, 1-butanol, 1-hexanol, and 2,3-butanediol. A promising approach is the coupling of gasification of biogenic residues with a syngas fermentation process. This study investigated batch processes with C. carboxidivorans and C. autoethanogenum in fully controlled stirred-tank bioreactors and continuous gassing with biogenic syngas produced by an autothermal entrained flow gasifier on a pilot scale >1200 °C. They were then compared to the results of artificial gas mixtures of pure gases. Because the biogenic syngas contained 2459 ppm O2 from the bottling process after gasification of torrefied wood and subsequent syngas cleaning for reducing CH4, NH3, H2S, NOX, and HCN concentrations, the oxygen in the syngas was reduced to 259 ppm O2 with a Pd catalyst before entering the bioreactor. The batch process performance of C. carboxidivorans in a stirred-tank bioreactor with continuous gassing of purified biogenic syngas was identical to an artificial syngas mixture of the pure gases CO, CO2, H2, and N2 within the estimation error. The alcohol production by C. autoethanogenum was even improved with the purified biogenic syngas compared to reference batch processes with the corresponding artificial syngas mixture. Both acetogens have proven their potential for successful fermentation processes with biogenic syngas, but full carbon conversion to ethanol is challenging with the investigated biogenic syngas.

This work discusses the behavior of electron bunch charge produced in an L-band normal conducting radio frequency gun from Cs 2 Te photocathodes illuminated with ps-long UV laser pulses and presumed homogeneous flattop laser transverse distribution. The measured charge shows the expected linear dependence in the quantum efficiency limited emission regime at low laser pulse energies. At higher laser pulse energy, the measured charge in the space charge limited emission regime should saturate, assuming an ideal homogeneous flattop laser transverse distribution. However, this behavior is not observed experimentally. Instead of saturating, the measured charge continues to increase with laser pulse energy, albeit with much weaker dependence than in the quantum efficiency limited emission regime. Simulations with the space charge particle tracking code ASTRA show that the charge saturates as expected using a homogeneous flattop laser transverse distribution. The discrepancy between simulations and measured excess charge may be attributed to the presence of unintentional Gaussian-like decaying radial halo beyond the core of the otherwise presumed homogeneous flattop core. The rate of increase of the measured charge at high laser pulse energies seems to be proportional to the amount of halo despite charge saturation in the core of the transverse laser radial profile. By utilizing core + halo particle distributions based on measured radial laser profiles, ASTRA simulations and semi-analytical emission models reproduce the behavior of the measured charge for a wide range of RF gun and laser operational parameters within the measurement uncertainties.

Plasma physics and controlled fusion 61(4), 045012 (2019). doi:10.1088/1361-6587/ab04b9, We present a new method to determine the electron density of a plasma by measuring the periodicity of modulations introduced to the longitudinal phase space of a relativistic particle bunch by the interaction with the plasma via the self-modulation instability. As the modulation is solely depending on the plasma density and the beam parameters, this method allows to determine the time-resolved density of a plasma at the position of beam passage, which is confirmed in particle-in-cell simulations. Densities in the range of 3.6 × 10$^{12}$ cm$^{−3}$ – 7.2 × 10$^{15}$ cm$^{−3}$ have been measured and the measurement accuracy is confirmed by comparison to spectroscopic plasma density measurements., Published by IOP Publ., Bristol

In the frame of conceptual studies for a compact (less than 6 GeV) X-ray FEL at PSI, we report here on the design and beam dynamics simulations of a two-cell two-frequency RF gun-like cavity. The goal of this study is to demonstrate the feasibility and the RF flexibility of such a cavity for manipulating the longitudinal phase space while preserving the initial low transverse emittance. Shaping the longitudinal phase space is mandatory for efficient velocity bunching at an early stage of the accelerator. The cavity, located after the gap of a 500-kV to 1-MV diode, is dimensioned to operate at 1.5 and 4.5 GHz. The RF design of the two-cell cavity and the coupling schemes for both frequencies are presented. Mode separation, which ensures adequate operation, is achieved by profiling the cavity walls. The flexibility of such a design to shape the longitudinal phase space is illustrated with beam dynamics simulations. The transverse emittance is shown to be nearly unchanged by combining emittance compensation and a beam matching scheme. The deleterious effects of the transverse RF fields are consequently reduced to a minimum.

The Photo Injector Test Facility at DESY Zeuthen (PITZ) was built to test and optimize electron sources for Free Electron Lasers and future linear colliders. The focus is on the production of intense electron beams with minimum transverse emittance and short bunch length as required for FEL operation. The experimental setup includes a 1.5 cell L-band gun cavity with coaxial RF coupler, a solenoid for space charge compensation, a laser capable to generate long pulse trains with variable temporal and spatial pulse shape, an UHV photo cathode exchange system, and an extensive diagnostics section. This contribution will give an overview on the facility and will mainly discuss the measurements of the electron beam transverse phase space. This will include measurements of the transverse and longitudinal laser profile, beam charge as a function of RF phase, and transverse emittance as a function of different parameters. The corresponding measurements of momentum and momentum spread as well as the RF commissioning results will be summarized. As a first application of the PITZ electron source it will be installed at the TESLA Test Facility Free Electron Laser at DESY Hamburg in autumn 2003.

The Photo Injector Test facility at DESY Zeuthen (PITZ) was built to develop electron sources for the TESLA Test Facility Free Electron Laser and future linear colliders. The main goal is to study the production of minimum transverse emittance beams with short bunch length at medium charge (∼1 nC). The facility includes a 1.5 cell L-band cavity with coaxial RF coupler, a solenoid for space charge compensation, a laser capable to generate long pulse trains, an UHV photo cathode exchange system, and different diagnostics tools. Besides an overview of the facility, its main components and their commissioning, this contribution will concentrate on the first measurements at PITZ with photoelectrons. This will include measurements of the transverse and longitudinal laser profile, charge and quantum efficiency, momentum and momentum spread, transverse electron beam profiles at different locations and first results on transverse emittance.

The Photo Injector Test facility at DESY, Zeuthen site (PITZ), offers the unique possibility to study and demonstrate the self-modulation of long electron bunches in plasma. A set of numerical simulations with the particle-in-cell code OSIRIS has been carried out for a better understanding of the process. Of particular interest is the measurement of the energy modulation induced to the beam itself by means of the generated wakefields in plasma. It will reflect the key properties of the accelerating electric fields such as their magnitude and their phase velocity, both of significant importance in the design of experiments relying on this technique.

For photocathode rf guns, the amount of dark current depends on the cavity surface as well as on the photocathodes. Smooth conditioning reduces the amount of dark current. Multipacting in the gun cavity changes the surface status of the cathodes and sometimes obstructs the gun operation because of vacuum interlocks. In this paper, dark current and multipacting features of an rf gun are presented including experimental and simulation studies.

A wide range of rf photo injector parameters has to be optimized in order to achieve an electron source performance as required for linac based high gain FELs. Some of the machine parameters can not be precisely controlled by direct measurements, whereas the tolerances on them are extremely tight. Therefore, this should be met with beam-based techniques. Procedures for beam-based alignment (BBA) of the laser on the photocathode as well as solenoid alignment have been developed. They were applied at the Photo Injector Test facility at DESY at Zeuthen (PITZ) and at the photo injector of the VUV-FEL at DESY at Hamburg. The field balance of the accelerating mode in the 1 1/2 cell gun cavity is one of the key beam dynamics issues of the rf gun. Since no direct field measurement in the half and full cell of the cavity is available for the PITZ gun, a beam-based technique to determine the field balance has been proposed. A beam-based rf phase monitoring proce dure has been developed as well.

The ability to produce high brightness electron beams as required for modern Free Electron Lasers (FELs) has been demonstrated during the first stage of the Photo Injector Test Facility at DESY Zeuthen (PITZ1). The electron source optimization at PITZ1 was successfully completed, resulting in the installation of the PITZ rf gun at the VUV-FEL (DESY, Hamburg). One of the main goals of the second stage of PITZ (PITZ2) is to apply higher gradients in the rf gun cavity in order to obtain smaller beam emittance by faster acceleration of the space charge dominated beams. In order to reach the required gradients a 10 MW klystron has to be installed and the gun cavity has to be conditioned for higher peak power. Another important goal of PITZ2 is a detailed study of the emittance conservation principle by using proper electron beam acceleration with a booster. Further photo injector optimization, including update of the photocathode laser and diagnostic tools, is foreseen as well. Recent progress on the PITZ developments will be reported.

The Photo Injector Test facility PITZ will be upgraded in 2004. Its main research goals are studies on the production and the conservation of low transverse emittance electron beams. The installation of an additional accelerating cavity is planned, which increases the beam energy from − 5 MeV after the gun to about 30 MeV after the booster. The goal is to produce and conserve a normalized transverse emittance of about 1 π mm mrad at 1 nC charge. For the characterization of the low emittance beam at higher beam energy, new diagnostics tools need to be installed. In this article, an overview about the layout of the upgraded facility and the planned physics activities is given.

A setup for the measurement of the longitudinal phase space at the photo injector test facility at DESY Zeuthen is described. The measurements of the momentum distribution, the length of an electron bunch and of their correlation are discussed. The results of the momentum distribution measurement are shown, a maximum mean momentum of 4.7 MeV/c and a RMS momentum spread of 14 keV/c is observed. The setup for the measurement of the bunch length includes a Cherenkov radiator which is used to convert the electron beam into a photon beam with a wavelength in the visible range. The Cherenkov radiation mechanism is chosen in order to measure the bunch length with good time resolution. A silica aerogel radiator with low refractive index will be used. Geant 4 simulations show that a resolution of 0.12 ps can be reached. The time dependent behaviour and the position of the photon bunch will be measured by a streak camera system. A simultaneous measurement of the bunch length and the momentum spread will provide the full information about the longitudinal phase space. The design considerations of the radiators and their properties are discussed.

The photo injector test facility at DESY Zeuthen (PITZ) was built to develop, operate and optimize photo injectors for future free electron lasers and linear colliders. First photo electrons were produced in January 2002. An extensive conditioning work on the rf gun has been done in order to achieve high gradients for different pulse lengths and repetition rates. To increase the efficiency and safety aspects of the rf commissioning an Automatic Conditioning Program (ACP) was developed. In addition, a Data Aquisition system (DAQ) which enables a deeper analysis of the commissioning work was realized. The conditioning procedures, the specific diagnostic elements and the achieved results are described. Furthermore, dark current measurements under different conditions are presented.

Physical review letters 121(6), 064801 (2018). doi:10.1103/PhysRevLett.121.064801, Particle-beam-driven plasma wakefield acceleration (PWFA) enables various novel high-gradient techniques for powering future compact light-source and high-energy physics applications. Here, a driving particle bunch excites a wakefield response in a plasma medium, which may rapidly accelerate a trailing witness beam. In this Letter, we present the measurement of ratios of acceleration of the witness bunch to deceleration of the driver bunch, the so-called transformer ratio, significantly exceeding the fundamental theoretical and thus far experimental limit of 2 in a PWFA. An electron bunch with ramped current profile was utilized to accelerate a witness bunch with a transformer ratio of $4.6^{+2.2}_{−0.7}$ in a plasma with length $∼10 cm$, also demonstrating stable transport of driver bunches with lengths on the order of the plasma wavelength., Published by APS, College Park, Md.