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Radio-frequency accelerators are engines of discovery, powering high-energy physics and photon science, but are also large and expensive due to their limited accelerating fields. Plasma-wakefield accelerators (PWFAs) provide orders-of-magnitude stronger fields in the charge-density wave behind a particle bunch travelling in a plasma, promising particle accelerators of greatly reduced size and cost. However, PWFAs easily degrade the beam quality of the bunches they accelerate. Emittance, which determines how tightly beams can be focused, is a critical beam quality in for instance colliders and free-electron lasers, but is particularly prone to degradation. We demonstrate, for the first time, emittance preservation in a high-gradient and high-efficiency PWFA while simultaneously preserving charge and energy spread. This establishes that PWFAs can accelerate without degradation—essential for energy boosters in photon science and multistage facilities for compact high-energy particle colliders.

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

After the spherical theta pinch had been developed at the Institute of Applied Physics in Frankfurt, considerable progress in creating high efficiency and long lifetime plasma sources had been made. Several devices have been built to study the characteristics of the spherically confined plasma. Scaling rules and investigated setups are presented, showing devices with electron densities of up to some $10^{23}~{\rm m}^{-3}$ , electron temperatures of several eV and confinement times of ${\sim}{\rm 10}~\mu{\rm s}$ . Typical dimensions are: discharge vessel radius $R=10~{\rm cm}$ , radius of the pinched plasma $r=2~{\rm cm}$ , initial gas pressures of 1–200 Pa at currents of up to 35 kA and resonance frequencies of 10–40 kHz. During the harmonic discharge of the stored energy, the plasma periodically pinches and expands again as long as the current rise rate creates sufficient electrical field strengths for ionization, which allows for pinching sequences in the millisecond range. The principles, improvements, theoretical approaches, and applications including pulsed ion source, plasma ion stripping, and vacuum ultraviolet flash lighting are discussed.

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

Summary form only given. The Spherical Theta Pinch was developed at the Institute for Applied Physics at the Goethe University Frankfurt. It consists of a spherical coil with less than 10 windings which are arranged around a glass vessel with a volume of several liters. A capacitor bank is discharged trough a self-developed thyristor stack. The rising current in the coil ionizes the gas inside the glas vessel and the magnetic fields compress the plasma on the symmetry axis. Due to the spherical assembly the pinch is more stable than in common linear theta pinch machines.1 The capacitors and the coil form a LCR-circuit with a resonance frequency of around 10kHz, the stored energy in the capacitors reaches 5kJ at a voltage of 15kV and the maximum currents are 8kA.After the development of several prototypes and intense e,amination, the first theta pinch device was now tested as a plasma stripper at the GSI facility, Darmstadt. For reaching higher charge states of ions, which minimize the acceleration distance, stripping foils are used at the moment. As these foils bear several mechanical and technical problems and furthermore only allow a small increment of the charge state, stripping plasmas have been proposed as an alternative. Compared to formerly used Z-pinches the theta pinch has the advantage of almost unlimited lifetime, as no electrodes are in contact with the plasma discharge and could thus erode. Other applications which are investigated are the generation of intense VUV-pulses and the use as a pulsed high current H+ ion source.

Summary form only given. For handling high currents and voltages reliable and durable switching devices are needed. When it comes to maximum power applications the use of gas-discharge-switches is still inevitable.

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.