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Laser plasma-based ion accelerators are very promising candidates for many applications. In order to ensure the reliability of such accelerators a comprehensive set of diagnostics is required. X-ray emission spectroscopy allows us to directly measure the plasma conditions of the laser-plasma interaction and also provides information about the hot electron population through the cold K-α emission production. Here, we present preliminary results from two new x-ray spectrometers used to study interaction regimes relevant for laser-driven ion acceleration at ultra-short pulse PW-class laser facility. We acquired the emission spectra from flat Ti targets for a range of target thicknesses and laser energies. Additionally, artificial laser pre-pulses were added to alter the laser absorption efficiency.

Recent oncological studies identified beneficial properties of radiation applied at ultra-high dose rates several orders of magnitude higher than the clinical standard of the order of Gy/min. Sources capable of providing these ultra-high dose rates are under investigation. Here, we show that a stable, compact laser-driven proton source with energies greater than 60 MeV enables radiobiological in vivo studies. We performed a pilot irradiation study on human tumors in a mouse model, showing the concerted preparation of mice and laser accelerator, the dose-controlled, tumor-conform irradiation using a laser-driven as well as a clinical reference proton source, and the radiobiological evaluation of irradiated and unirradiated mice for radiation-induced tumor growth delay. The prescribed homogeneous dose of 4 Gy was precisely delivered at the laser-driven source. The results demonstrate a complete laser-driven proton research platform for diverse user-specific small animal models, able to deliver tunable single-shot doses up to around 20 Gy to millimeter-scale volumes on nanosecond time scales, equivalent to around 1E9 Gy/s, spatially homogenized and tailored to the sample. The platform provides a unique infrastructure for translational research with protons at ultra-high dose rate.

Laser plasma based particle accelerators have attracted great interest in fields where conventional accelerators reach limits based on size, cost or beam parameters. Designing future laser ion accelerators requires a high degree of control of the advanced acceleration schemes involved and predictive modelling capabilities. Here, we investigate the interaction of petawatt class laser pulses with a micrometer sized cryogenic hydrogen jet target. Controlled pre-expansion of the target by low intensity pre-pulses allowed for tailored density scans over more than two orders of magnitude. On-shot target characterization using two-color optical probing provided precise starting conditions for numerical simulations. For the optimal target density profile in the near critical regime proton energies of up to 80 MeV were observed which represents a two-fold increase with respect to the initial solid target case. Three-dimensional particle in cell simulations confirmed the transition between different acceleration mechanisms involved and suggested the magnetic-vortex regime to be responsible for the highest proton energies achieved.

Data for the publication: Calorimeter with Bayesian unfolding of spectra of high-flux broadband X-rays Containing: - Raw datasets - Source code for extracting calibrated energy information from datasets - Source code for simulations - Source code for unfolding of spectra

Laser-plasma based proton accelerators as a novel accelerator technology have matured to a level at which laboratory-scale setups for the emerging topic of image-guided precision small animal irradiation studies come into reach [Bra2019]. Providing a high proton energy bandwidth [Sch2016] which is filtered in a tunable pulsed magnet beam transport, these accelerators enable flexibility in terms of scattering-free irradiation field formation [Mas2014, Mas2015]. Regarding temporal dose delivery, with single pulse doses reaching the Gy level at unprecedented peak dose rates of up to 1012 Gy/s [Sch2016], laser-plasma based proton accelerator setups can give access to the dose rate regime of FLASH [Fav2014, Voz2019]. The realization of a full-scale setup for image-guided precision radiobiological studies for small animals focusing on dose rate dependent effects is currently prepared at the PENELOPE laser-plasma based proton accelerator at HZDR and will be presented with a focus on the technological requirements and solutions for dose delivery at laser-plasma based sources. This development relies on our experience in performing dose-controlled radiobiological in vitro studies [Kra2010, Zei2013] and first in vivo irradiation experiments at the DRACO laser-plasma based proton accelerator at HZDR, where we have established a pulsed solenoid beamline for 3D irradiation field formation, yielding a (5 mm)³ homogeneous volumetric dose distribution at a Gy single pulse dose level [8]. [Bra2019] F.-E. Brack, F. Kroll, L. Gaus, C. Bernert, E. Beyreuther, T. E. Cowan, L. Karsch, S. D. Kraft, L. A. Kunz-Schughart, E. Lessmann, J. Metzkes-Ng, L. Obst-Hübl, J. Pawelke, M. Rehwald, H.-P. Schlenvoigt, U. Schramm, M. Sobiella, E. R. Szabó, T. Ziegler, K. Zeil, Spectral and spatial shaping of laser-driven proton beams using a pulsed high-field magnet beamline. arXiv:1910.08430 (2019) [Sch2016] J. Schreiber, P. Bolton, K. Parodi, “Hands-on” laser-driven ion acceleration: A primer for laser-driven source development and potential applications, Rev. Sci. Instr. 87, 071101 (2016)

Ion acceleration by compact laser-plasma sources promises a variety of applications ranging from medical relevance to fusion experiments.Reaching the required beam quality parameters for those applications demands a very high level of understanding and control over the laserplasma interaction process. Central components in this context are the absorption of the electromagnetic laser field by the plasma and the quality of the resulting acceleration field structure. Measuring and analyzing unabsorbed light - as transmitted and/or specularly reflected parts - thus allows insight into properties of the underlying laser-plasma interaction. We experimentally investigate these interactions for high and low-contrast laser pulses with thin solid density foil targets at the Draco PW laser system (HZDR). The results of spectral, spatial, and energy analysis of transmitted and reflected light indicate changes in the plasma interaction and will be presented.

Source data for all figures of publication: "Tumor irradiation in mice with a laser-accelerated proton beam". The folder structure is adapted to match thefigures in the publication.

This dataset contains the raw and evaluated data of the paper plus the script for plotting the results.

Background and Aims Laser-plasma accelerators (LPA) are a viable addition to the ultra-high dose rate accelerator portfolio, as they generate extremely intense proton bunches of several 10 MeV kinetic energy. Efficiently transported and spectrally shaped, a single LPA proton bunch enables homogeneous dose delivery above 20 Gy to mm-scale volumes with a dose rate well above 108 Gy/s. At Draco PW we have recently shown the successful establishment of a proton LPA research platform for small animal studies employing a multi-shot accumulated dose delivery for a mouse model pilot study. [Kroll et al, Nature Physics 2022]. Methods Reaching the range of FLASH-associated parameters at an LPA proton source requires single-shot irradiation. We performed such irradiations with zebrafish embryos and dosimeters using the pulsed beamline at Draco PW. Since LPA based accelerators are prone to inherent fluctuations of the source, to measure the applied dose, a minimally invasive, online spectral characterization of the delivered proton bunches is necessary. Clinically used ionization chambers saturate under LPA beam conditions. Therefore, we present a scintillator-based time-of-flight (ToF) beam monitoring system for the recording of kinetic energy spectra of single LPA proton bunches. The deduced spectra are used as an input for Monte-Carlo simulations to predict the delivered dose to the irradiated sample. Results The ToF ansatz enabled the reconstruction of the kinetic energy spectrum of the transported protons with a relative energy uncertainty down to ca. 11% (2σ). Subsequent Monte-Carlo simulations predict the applied depth dose distribution with an uncertainty of ca. 6% (2σ). Conclusions We present a laser-based proton irradiation platform at the Draco PW facility that enables systematic radiobiological studies within an unprecedented range of beam parameters and demonstrate a solution for minimally invasive volumetric dosimetry at ultra-high dose rates.

Due to the non-linear nature of relativistic laser induced plasma processes, the development of laser-plasma accelerators requires precise numerical modeling. Especially high intensity laser-solid interactions are sensitive to the temporal laser rising edge and the predictive capability of simulations suffers from incomplete information on the plasma state at the onset of the relativistic interaction. Experimental diagnostics utilizing ultra-fast optical backlighters can help to ease this challenge by providing temporally resolved inside into the plasma density evolution. We present the successful implementation of an off-harmonic optical probe laser setup to investigate the interaction of a high-intensity laser at 5.4E21 W / cm^2 peak intensity with a solid-density cylindrical cryogenic hydrogen jet target of 5 um diameter as a target test bed. The temporal synchronization of pump and probe laser, spectral filtering and spectrally resolved data of the parasitic plasma self-emission are discussed. The probing technique mitigates detector saturation by self-emission and allowed to record a temporal scan of shadowgraphy data revealing details of the target ionization and expansion dynamics that were so far not accessible for the given laser intensity. Plasma expansion speeds of up to (2.3+-0.4)E7 m / s followed by full target transparency at 1.4 ps after the high intensity laser peak are observed. A three dimensional particle-in-cell simulation initiated with the diagnosed target pre-expansion at -0.2 ps and post processed by ray tracing simulations supports the experimental observations and demonstrates the capability of time resolved optical diagnostics to provide quantitative input and feedback to the numerical treatment within the time frame of the relativistic laser-plasma interaction.

Exploiting the strong electromagnetic fields that can be supported by a plasma, high-power laser driven compact plasma accelerators can generate short, high-intensity pulses of high energy ions with special beam properties interesting for many application areas. The transition of laser driven ion accelerators from physics experiments to turn-key sources for these applications relies on improvement of generated beam parameters (kinetic energy, flux), as well as increased reproducibility, robustness and scalability to high repetition rate. Recent developments at the high-power laser facility DRACO-PW enabled the production of polychromatic proton beams with unprecedented stability [1] which enabled the first in vivo radiobiological study to be conducted using a laser-driven proton source [2]. Yet, the ability to achieve highest energies around or even beyond the 100 MeV frontier is matter of ongoing research, mainly addressed by exploring advanced acceleration schemes. In parallel to the testing of these schemes an important challenge is to provide convincing evidence that these very high energies could be reached at all for a significant number of particles. Occurring complications are due to the nature of the multi-species beams with typically exponentially decaying spectra and low shot statistics of laser-plasma experiments at the necessary laser pulse energy levels. The latter is in particular complicated for highly non-linear acceleration regimes with intrinsically low reproducibility. In this talk we summarize our approaches for the spatial and spectral characterization of our proton beam parameters with cut-off energies larger than 80 MeV. Key is the combination of a multitude of different methods based on different detection principles established for single shot measurements. Time-of-flight methods are discussed for energy cross-calibration of our Thomson parabola spectrometers and the use of different screen types for on-shot particle number calibration is presented.

Laser-driven plasma accelerators (LPA) are compact sources of ultra-short, intense proton pulses in the multi-10-MeV energy range. These unique parameters predestine LPAs as powerful tools for ultra-high dose rate radiobiology research. The sources’ capabilities were recently demonstrated in the first successful small animal pilot study on radiation-induced tumor growth delay in mice using an LPA proton source [1]. To promote further sophisticated radiobiological studies at LPAs, adapted approaches for primary LPA source characterization, beam monitoring and dosimeters are required. Here, most prominent challenges are LPA-inherent pulse-to-pulse fluctuation in terms of intensity as well as proton energy distribution, the ultra-high pulse dose rate and the harsh plasma environment, featuring a strong electromagnetic pulse (EMP) and an intense mixed radiation background. These conditions call for robust online monitoring solutions. We present the solutions for source-to-sample characterization implemented at the ALBUS-2S beamline [2] at the Draco Petawatt laser system [3] at Helmholtz-Zentrum Dresden-Rossendorf. These include firstly an online beam monitoring system based on a time-of-flight spectrometer (ToF BMS). A core feature of the ToF BMS method is a precise spectrum-based forward-calculation of the corresponding volumetric dose distribution via Monte-Carlo simulation. Secondly, a dosimetric system for volumetric mm-scale sample irradiations was conceptualized and tested during an in vivo irradiation study, showing a solution for precise dosimetric characterization of ultra-high dose rate pulses at the ~500 mGy pulse dose range. Lastly, with the OCTOPOD and MiniSCIDOM, two devices for online, single pulse characterization of volumetric dose distributions are presented, applicable for the primary LPA source and mm-scale dose distributions at the sample site, respectively. Both devices are based on volumetric scintillators as active detector material and rely on tomographic reconstruction for signal retrieval. [1] F. Kroll, et al., Tumour irradiation in mice with a laser-accelerated proton beam, Nat Phys, 18, (2022), 316. [2] F.-E. Brack, et al., Spectral and spatial shaping of laser-driven proton beams using a pulsed high-field magnet beamline, Sci Rep, 10, (2020), 9118. [3] U. Schramm, et al., First results with the novel petawatt laser acceleration facility in Dresden, J. Physics: Conf. Ser, 874, (2017), 012028.

Background and Aims The Flash effect, i.e. the radiobiological observation of normal tissue sparing but efficient tumor killing by ultra-high dose rate (UHDR) irradiation, promise great benefits for cancer patient treatment. The translation process of the Flash effect should be accompanied by systematic studies on the necessary beam parameters for each clinical applied radiation. Using the zebrafish embryo model, the influence of partial oxygen level (https://doi.org/10.1016/j.radonc.2021.02.003), electron pulse structure and dose were studied thoroughly. To investigate a similar range of proton beam parameters UHDR experiments at different accelerators, but under comparable conditions, are required. Methods To cover a broad range of proton dose rates, experiments have been prepared at the University Proton Therapy Dresden (UPTD) and at the Draco laser accelerator (Helmholtz-Zentrum Dresden-Rossendorf) providing quasi-continuous and single-shot proton beam delivery in the range of 0.12 to 10^9 Gy/s. To fulfil the requirements of the model, i.e., irradiating a sufficiently high number of embryos at low oxygen level, dedicated setups were established that also allow for the online measurement of oxygen partial pressure and cope with the geometric restrictions of the respective accelerator. Results A comparison experiment at UPTD reveal a significant protecting Flash effect in both setups for zebrafish embryo treated with 300 Gy/s relative to conventional proton dose rate. Moreover, a higher protection of the embryos was indicated comparing the embryo length after irradiation with 10^9 Gy/s and conventional proton dose rate, respectively. Conclusions Experimental setups have been established that allow for systematic proton dose rate studies using the zebrafish embryo model at the clinical cyclotron of UPTD and at the Draco laser accelerator. Therewith, the experimental possibilities at the Dresden platform for UHDR radiobiology are extended providing electron and proton dose rates up to 10^9 Gy/s.

We report technological developments at DRACO-PW to monitor and improve laser-plasma conditions resulting in a stable particle-source >60MeV, which in combination with our transport-beamline and high-quality dosimetry enabled first dose-controlled “in-vivo” studies with laser-driven protons.

All source data and scripts for publication: "Tumor irradiation in mice with a laser-accelerated proton beam"

Extreme states of matter exist throughout the universe e.g. inside planetary cores, stars or astrophysical jets. Such conditions can be generated in the laboratory in the interaction of powerful lasers with solids. Yet, the measurement of the subsequent plasma dynamics with regard to density, temperature and ionization is a major experimental challenge. However, ultra-short X-ray pulses provided by X-ray free electron lasers (XFELs) allow for dedicated studies, which are highly relevant to study laboratory astrophysics, laser-fusion research or laser-plasma-based particle acceleration. Here, we report on experiments that employ a novel ultrafast method, which allows to simultaneously access temperature, ionization state and nanometer scale expansion dynamics in high-intensity laser-driven solid-density plasmas with a single X-ray detector. Using this method, we gain access to the expansion dynamics of a buried layer in compound samples, and we measure opacity changes arising from bound-bound resonance transitions in highly ionized copper. The presence of highly ionized copper leads to a temperature estimate of at least 2 million Kelvin already after the first 100 femtoseconds following the high-intensity laser irradiation. More specifically, we make use of asymmetries in small-angle X-ray scattering (SAXS) patterns, which arise from different spatial distributions of absorption and scattering cross sections in nanostructured grating samples when we tune an XFEL to atomic resonant energies of copper. Thereby, changes in asymmetry can be connected with the evolution of the plasma expansion and ionization dynamics. The potential of XFEL-based resonant SAXS to obtain three-dimensional ultrafast, nanoscopic information on density and opacity may offer a unique path for the characterization of dynamic processes in High Energy Density plasmas.

This repository contains the experimental raw data, the analyzed data and corresponding scripts as well as figures for the "Proton beam quality enhancement by spectral phase control of a PW-class laser system" publication. https://doi.org/10.1038/s41598-021-86547-x

Background and aims In FLASH radiotherapy (RT), a protective effect of healthy tissue was observed, while tumor control remains comparable to conventional RT[1]. One possible explanation is the oxygen depletion hypothesis, in which radiolysis of water/cytoplasma causes the production of radicals that then react with O2 dissolved in water. This would cause a reduction in O2, which results in a hypoxic target and thus a radio-protective effect. In a previous study[2], we measured O2 depletion in sealed water phantoms during irradiation at high dose rates (

The recent rediscovery of the “Flash-effect” revived the interest in high dose-rate radiation effects throughout the radiobiology community, promising protection of normal tissue, while simultaneously not altering tumour control. Several preclinical and clinical studies are presently dedicated to electron FLASH with Linacs. However, the mechanisms of Flash is still unresolved albeit its clear impact in tissue sparing to radiation toxicity. For protons, the Flash effect was confirmed in a few animal experiments using the beam parameters available at clinical cyclotrons. Laser-driven proton accelerators offer the possibility to extend the range of proton beam parameters to higher dose rates enabling the investigation in vivo of high dose-rate effects for up to 10^9 Gy/s. The general applicability of these beams for radiobiological studies was proven with simple cellular models and zebrafish embryos. One-step further, systematic in vivo experiments were prepared with a proof-of-principle mouse irradiation campaign at the Draco laser accelerator and, for comparison, at the University Proton Therapy Dresden (UPTD). Moreover, to investigate the interplay of oxygen tension, oxygen consumption and proton dose rate in more detail, an experiment with zebrafish embryos was performed at both proton sources. At the conference, we will give an overview of our radiobiological experiments performed at both DRACO and Oncoray/UPTD, for different dose rates and varying oxygen pressures.

Archiving of raw and results data and scripts as describef in the associated paper

A large amount of complex processes within laser-produced plasmas put a huge demand for precise diagnostics methods. For example, x-ray emission spectroscopy can be used to study atomic physics and plasma conditions. Here, we introduce two new x-ray spectrometers installed in the Ion acceleration lab at the Draco PW laser facility. Availability of such diagnostics at the Draco PW Ti:sapphire 30 fs laser system (i.e. ultra-short pulse system) allows not only for studying unique plasma conditions driving the ion acceleration, but also exploring new possibilities for x-ray backlighters suitable for high energy density experiments. Both spectrometers are utilized for acquisition of Ti spectral lines, but offer different spectral resolution and range. Quartz crystal spectrometer has wider spectral range, including Ti K-α and He-α emission lines in the spectrum, whereas Ge crystal spectrometer focuses on K-α emission lines and offers 1D spatial imaging. We present first results demonstrating the capabilities of both spectrometers. The first spectroscopic measurements include the emission spectra measurements from flat Ti targets used for proton acceleration calibration and optimization with and without laser pre-pulse and the use of structured targets for enhanced x-ray emission as well as tailoring of the electron spectra for optimization of the proton acceleration process.

Background and Aims After the rediscovery of the normal tissue sparing FLASH effect of high dose rate radiation, research activities on this topic have been revived. But especially for protons, the portfolio of accelerators capable of performing studies at ultra-high dose rates is limited. Laser-plasma accelerators (LPA) can generate extremely intense proton bunches of many 10 MeV kinetic energy. In combination with dedicated dose delivery systems, LPA proton sources facilitate peak dose rates well above 10^8 Gy/s in a pulse structure regime complementary to conventional accelerators. Methods The reliable generation of proton spectra beyond 60 MeV at DRACO-PW [Ziegler et al, SciRep2021], combined with a dedicated energy selective pulsed magnet beam transport system [Brack et al, SciRep2020], allows tailored sample-specific dose distributions. Adapted on-shot dosimetry enables the required spectral monitoring of every proton bunch. Two irradiation series on volumetric biological samples were performed at DRACO-PW, accompanied by reference irradiations at the University Proton Therapy Dresden. Results The first small animal pilot study at a laser-driven proton source was conducted successfully. The mouse-ear tumor model’s requirements [Beyreuther et al, PLoS One2018] were fulfilled and verified at high precision (+/- 5%) concerning predefined dose value and conformity. Complementary, a study investigating dose-rate effects such as FLASH was performed irradiating zebrafish embryos with above 10^9 Gy/s. Conclusions We present a laser-based irradiation platform at the DRACO-PW facility that enables systematic radiobiological studies, laying the foundations for further studies at LPA sources exploring ultra-high dose-rate effects, such as FLASH, over previously unreachable parameter space.

Ultra-intense short-pulse lasers in the Petawatt regime and intensity range of 1021W/cm2 offer the possibility to study new compact accelerator schemes by utilizing solid density targets for the generation of energetic ion beams. The optimization of the acceleration process demands comprehensive exploration of the involved plasma dynamics. This applies not only on the femtosecond but also on the pico- to nanosecond timescale, where the laser rising edge modifies the target prior to the 30 fs laser peak. Cryogenic hydrogen jet targets with µm-scale transverse size and solid density (5.2x1022 cm-3) offer the superb opportunity for renewable and debris-free acceleration sources and at the same time allow for comprehensive experimental investigation and realistic simulation of the rich physics involved in the laser target interaction. Here, we present the results of an experiment for laser proton acceleration from a cryogenic hydrogen jet target at the DRACO-PW laser. Optimized acceleration performance is achieved by tailoring the targets plasma density via hydrodynamic expansion induced by a short low-intensity pre-pulse. Optical shadowgraphy probing is utilized to give a realistic input of the targets plasma density for 3 dimensional particle-in-cell simulations of the particle acceleration process.

Resonant Small-angle x-ray scattering raw data obtained in measurements at MEC at LCLS and evalutation of the asymmetry in the scattering patterns. The data set is structured in case 1/Si-Cu-compound targets and case 2/Cu-only-targets as presented in the publication for on- and off-resonant XFEL probe energies.

High-intensity short-pulse lasers enable novel compact accelerator schemes for the generation of energetic ion beams. The experimental investigation of the process remains challenging due to the femtosecond timescale and micrometer size of the acceleration. Commonly, diagnostic results are explained by a comparison of the experimental findings with computationally expensive particle-in-cell simulations. Cryogenic hydrogen jet targets (~30 critical densities) with µm-scale transverse size are particularly well suited for this approach. Time-resolved diagnostics like optical probing can infer the state of the target at the initialization time of the simulation and benchmark the simulation results. Here we present the implementation of an off-harmonic optical probing setup at an experiment for laser proton acceleration with a cylindrical hydrogen jet target at the DRACO PW laser with plasma-mirror cleaned laser contrast. We show under which conditions the technique overcomes the problem of parasitic plasma self-emission, present technical aspects of the off-harmonic probing technique together with experimental results of the observed plasma dynamics.

We report on the ongoing plasma accelerator development at the HZDR, moving from plasma-acceleration studies towards real plasma-accelerators that can be controlled and applied in the lab. We show experimental investigations of proton acceleration from laser-irradiated solid foils with the DRACO PW laser, where highest proton cut-off energies were achieved for temporal pulse shape parameters well different from that of a Fourier transform limited (FTL) pulse. Controlled spectral phase modulation of the driver laser by means of an acousto-optic programmable dispersive filter enabled us to manipulate the temporal laser pulse shape and to study the effect on proton acceleration from thin foil targets. The results show that short and asymmetric pulses generated by positive third order dispersion values are favourable for proton acceleration and can lead to maximum energies of 60 MeV for thin plastic foils. Assuming appropriate control of the spectral phase of the laser and comparable temporal contrast conditions, we believe that the presented method can be universally applied to improve the proton acceleration performance using any other laser system operated in the PW regime.

The availability of high-intensity short-pulse lasers in the Peta-Watt regime drives the development of new and compact accelerator schemes like for example the generation of multiple 10 MeV proton beams from high-density targets. To optimize the acceleration performance and to pave the way towards medical applications of these particle beams both target and diagnostic development are of great importance. Particularly cryogenic hydrogen jet-targets offer the benefit of being debris-free and capable of high-repetition rate applications. Together with spatially and temporally resolved optical probing techniques this target is most suitable for a comparison to numerical particle-in-cell simulations. However, the strong plasma self-emission often masks the laser-target interaction point and thus complicates the data analysis. Recently, the development of a synchronized stand-alone probe-laser-system operating off the harmonics of the driver laser showed promising performance. Here we show the performance of an upgraded probe-laser-system operating at a central wavelength of 1030nm far off the fundamental wavelength of the drive laser at 800nm. It consists of a synchronized fs-oscillator and a novel and robust CPA system based on a chirped volume Bragg grating as a hybrid stretcher and compressor unit, chirped mirrors for GDD compensation and a regenerative amplifier with Yb.CaF2 as laser medium. The system delivers 160fs pulse duration together with 0.9mJ energy at a repetition rate of 200Hz. The application of the upgraded probe-laser-system in an experimental campaign dedicated to laser-proton acceleration together with cryogenic hydrogen jet-targets showed a significant improvement of imaging quality for the laser-target interaction concerning the plasmas self-emission. The recorded probe-images resemble those of z-pinch experiments with metal wires and indicate a sausage-like instability along the hydrogen jet axis.

Laser-driven ion acceleration promises to provide a compact solution for demanding applications like particle therapy, proton radiography or inertial confinement research. Controlling the particle beam parameters to achieve these goals is currently pushing the frontier of laser driven particle accelerators. The performance of the plasma acceleration is strongly dependent on the complex pre-plasma formation process at the target front surface which is determined by the temporal intensity contrast. Particularly low-density targets require an enhanced temporal contrast to remain overcritical until the main pulse arrives. Plasma mirror setups have proven to significantly improve the temporal contrast by reducing pre-pulse intensity and steepening the rising edge of the main laser pulse, enabling the investigation of laser proton acceleration and proton energy scaling using ultra-thin targets. We present new experimental results on the interaction of the DRACO Petawatt ultra-short pulse laser with ultra-thin foil targets. Efficient and on-demand contrast cleaning established through a re-collimating plasma mirror setup facilitated thickness scans from the µm range down to several tens of nm. The combination of a complex set of diagnostics, consisting of proton detectors in target normal, laser forward and laser backward axis, laser pulse transmission and reflection diagnostics as well as detection of front surface electrons, delivered concrete indicators for the acceleration conditions. Furthermore, tremendous progress has been achieved by successfully implementing a novel laser contrast diagnostic by means of self-referenced spectral interferometry with extended time excursion (SRSI-ETE), allowing to characterize the temporal contrast in the experimental area on a single-shot base with unprecedented dynamic and temporal range.

The development of high-intensity short-pulse lasers in the Petawatt regime offers the possibility to design new compact accelerator schemes by utilizing high-density targets for the generation of ion beams with multiple 10 MeV energy per nucleon. The optimization of the acceleration process demands comprehensive exploration of the plasma dynamics involved, for example via spatially and temporally resolved optical probing. Experimental results can then be compared to numerical particle-in-cell simulations, which is particularly sensible in the case of cryogenic hydrogen jet targets. However, strong plasma self-emission and conversion of the plasma’s drive laser wavelength into its harmonics often masks the interaction region and interferes with the data analysis. Recently, the development of a stand-alone and synchronized probe laser system for off-harmonic probing at the DRACO laser operated at the Helmholtz-Zentrum Dresden–Rossendorf showed promising performance. Here, we present an updated stand-alone probe laser system applying a compact CPA system based on a synchronized fs mode-locked oscillator operating at 1030 nm, far off the plasma’s drive laser wavelength of 800 nm. A chirped volume Bragg grating (Optigrate Corp) is used as a hybrid stretcher and compressor unit. The system delivers 160 fs pulses with a maximum energy of 0.9 mJ. By deploying the upgraded probe laser system in the laser-proton acceleration experiment with the renewable cryogenic hydrogen jet target, the plasma self-emission could be significantly suppressed while studying the temporal evolution of the expanding plasma jet. Recorded probe images resemble those of z-pinch experiments with metal wires and indicate a sausage-like instability along the jet axis, which will be discussed.

High-intensity short-pulse lasers in the Petawatt regime offer the possibility to study new compact accelerator schemes by utilizing high-density targets for the generation of energetic ion beams. The optimization of the acceleration process demands comprehensive exploration of the plasma dynamics involved, for example via optical probing. In particular, experiments using low density cryogenic hydrogen jet targets with µm-scale transverse size are well suited to deliver new results which can then be compared to predictive particle-in-cell simulations. However, strong plasma self-emission and conversion of the plasma’s drive laser wavelength into its harmonics often masks the interaction region and complicates data analysis. Here, we present a stand-alone probe laser system operating at 1030 nm, far off the plasma’s drive laser wavelength of 800 nm and its implementation into an experiment dedicated to laser-proton acceleration from the hydrogen jet target irradiated by the DRACO PW laser at Helmholtz-Zentrum Dresden – Rossendorf. We show that the plasma self-emission in the probe images is significantly suppressed and we are able to measure the pre-expansion of the target by the DRACO PW laser for intrinsic and for plasma mirror enhanced laser contrast. The influence of the plasma pre-expansion on the measured proton acceleration performance is presented.

The development of high-intensity short-pulse lasers in the Petawatt regime offers the possibility to design new compact accelerator schemes by utilizing high-density targets for the generation of high energy ion beams. The optimization of the acceleration process demands comprehensive diagnostic of the plasma dynamics involved, for example via spatially and temporally resolved optical probing. Experimental results can then be compared to numerical particle-in-cell simulations, which is particularly sensible in the case of cryogenic hydrogen jet targets [1]. However, strong plasma self-emission and conversion of the plasma’s drive laser wavelength into its harmonics often masks the interaction region and interferes with the data analysis. Recently, the development of a stand-alone and synchronized probe laser system for off-harmonic probing at the DRACO laser operated at the Helmholtz-Zentrum Dresden–Rossendorf showed promising performance [2]. Here, we present an updated stand-alone probe laser system applying a compact CPA system based on a synchronized fs mode-locked oscillator operating at 1030 nm, far off the plasma’s drive laser wavelength of 800 nm. A chirped volume Bragg grating is used as a hybrid stretcher and compressor unit [3]. The system delivers 160 fs pulses with a maximum energy of 0.9 mJ. By deploying the probe laser pulses in laser-proton acceleration experiments with renewable cryogenic hydrogen jet targets, the plasma self-emission could be significantly suppressed while studying the temporal evolution of the expanding plasma jet. Hence, for varied drive laser contrast parameters, by the use of a plasma mirror, the on target contrast was measured and correlated to the temporal drive laser profile. References [1] L. Obst, et al. Efficient laser-driven proton acceleration from cylindrical and planar cryogenic hydrogen jets. Sci. Rep., 7:10248, 2017. [2] T. Ziegler, et al. Optical probing of high intensity laser interaction with micron-sized cryogenic hydrogen jets. Plasma Phys. Control. Fusion, 2018. doi:10.1088/1361-6587/ aabf4f. [3] L. Loeser, et al. A compact and robust millijoule CPA laser system based on Yb:CaF₂ delivering 160fs pulses. under review.

Laser-driven ion acceleration promises to provide a compact solution for demanding applications like radio-biology experiments. For that, controlling particle beam parameters particularly in experiments with high energy Petawatt class ultra-short pulse systems with high repetition rate is a mandatory, yet challenging task. The performance of the plasma acceleration is strongly dependent on the complex laser target interaction which in turn is determined by the temporal laser intensity profile and spatio-temporal couplings on a large dynamic range. Plasma mirror setups have proven to significantly improve the temporal contrast by reducing pre-pulse intensity and steepening the rising edge of the main laser pulse, enabling the investigation of laser proton acceleration using ultra-thin and near critical density targets. Here we present benchmark experiments using the DRACO Petawatt laser at HZDR irradiating ultra-thin foil targets. A combination of particle and plasma diagnostics for ions and electrons as well as reflected and transmitted light revealed clear indications of acceleration in the relativistic transparency regime. The experiments were complemented by a suite of different laser pulse diagnostics, including self-referenced spectral interferometry with extended time excursion for single shot contrast analysis to characterize the laser pulse properties at the high power focus as realistic as possible.

We performed experiments with the Petawatt beam of the Dresden laser acceleration source Draco to investigate the feasibility of controlled volumetric tumour irradiations with laser-accelerated protons. Therefore, a beamline of two pulsed solenoid magnets was implemented to efficiently capture and shape the beam, which was then analysed by a comprehensive suite of detectors (ionization chamber, scintillator, radiochromic film, ..). We extensively studied how to manipulate and match lateral and depth dose profiles to the desired application and target. These were assisted by benchmark experiments at a conventional accelerator to further characterize the ion-optical properties of the solenoids and to investigate potential distortions of the transported proton beam. With the characterized beamline first proof-of-principle irradiation studies of volumetric normal and tumour tissue samples have been performed successfully. To advance to full scale irradiation experiments, a higher mean dose rate is necessary to deliver high absolute dose values via multiple bunches (dose control) in short times (~min). Current limitations are the low repetition rate of the beamline and its long cooldown times. Therefore, we developed a novel, actively cooled pulsed solenoid, to be implemented in the beamline, enabling complex irradiation studies with high repetition rates and consequently high mean dose rates.

the shape of a wave carries all information about the spatial and temporal structure of its source, given that the medium and its properties are known. Most modern imaging methods seek to utilize this nature of waves originating from Huygens’ principle. We discuss the retrieval of the complete kinetic energy distribution from the acoustic trace that is recorded when a short ion bunch deposits its energy in water. this novel method, which we refer to as Ion-Bunch energy Acoustic tracing (I-BeAt), is a refinement of the ionoacoustic approach. With its capability of completely monitoring a single, focused proton bunch with prompt readout and high repetition rate, I-BeAt is a promising approach to meet future requirements of experiments and applications in the field of laser-based ion acceleration. We demonstrate its functionality at two laser-driven ion sources for quantitative online determination of the kinetic energy distribution in the focus of single proton bunches

Pulsed high-field magnets have become a common, versatile research tool. We present a pulsed magnet technology platform that opens up new areas of application in the field of laser-driven plasma physics. Compact high-field magnets, generating ms-long magnetic field pulses with amplitudes ranging as high as 20 T, have been developed for operation under high vacuum and in close vicinity to the harsh laser-plasma environment. The combination of the presented magnet technology and portable pulsed power systems paves the way for novel experiments in laboratory astrophysics and enables unique studies on beam optics for laser-driven ion sources. We implemented a tunable pulsed beamline at the Dresden laser acceleration source (Draco) for radiobiological irradiation studies. It consists of two pulsed solenoids for shaping laser-accelerated ion beams spatially and spectrally for application. We performed experiments with the PW beam of Draco to investigate the feasibility of worldwide first controlled volumetric in vivo tumour irradiations in a dedicated mouse model with laser-accelerated protons. The study shows the reliable generation of homogeneous dose distributions laterally and in depth. Practical issues, like magnet repetition rate and stability, mean dose rate and future radiobiological challenges will be discussed and an outlook on the already performed volumetric tumour irradiation experiments will be given. Furthermore, a split-pair coil was developed that can be used for the investigation of magnetized plasma in the frame laboratory astrophysical phenomena. The magnet provides optical access to the magnetized laser-driven plasma via two bores perpendicular to the coil axis. These openings enable optical and X-ray probing as well as insertion of obstacles and/or laser targets from solids to gas jets.

The talk summarizes activities of HZDR on the topic of laser-driven particle sources for medical applications. The focus lies on a the development and characterization of a pulsed high-field beamline that allows to transport and spacially as well as spectrally shape a laser-driven ion beam and thereby prepare it for irradiation studies, e.g. on radiobiological studies.

Extreme field gradients intrinsic to relativistic laser plasma interactions enable compact MeV proton accelerators with unique bunch characteristics, yet complicate direct proton beam control. Only complex micro-engineering of the plasma accelerator itself and limited adoption of conventional beam optics, so far provided access to global beam parameters as direction and divergence. Here we present a novel, counter-intuitive, yet readily applicable all-optical approach to imprint detailed spatial information from the driving laser pulse to the proton bunch. In a series of experiments, the spatial profile of the energetic proton bunch was found to exhibit identical features as the fraction of the laser pulse passing around a target of limited size. The formation of quasi-static electric fields in the beam path by ionization of residual gas in the experimental chamber results in asynchronous information transfer between the laser pulse and the naturally delayed proton bunch. Essentially acting as a programmable memory, these fields provide access to a new level of proton beam manipulation.