I'm a physicist at the Forschungszentrum Dresden-Rossendorf. My research topics are laser-driven radiation sources, laser cooling of ion beams, plasma physics and computational physics.
Abstract: Recent experiments in the Trident laser facility (Los Alamos National Laboratory) have shown that hollow conical targets with a flat top at the tip can enhance the maximum energy of proton beams created during the interaction of an ultra-intense short laser pulse with the target (Gaillard S A et al 2011 Phys. Plasmas 18 056710). The proton energies that have been seen in these experiments are the highest energies observed so far in laser-driven proton acceleration. This is attributed to a new acceleration mechanism, direct light pressure acceleration of electrons (DLLPA), which increases the number and energy of hot electrons that drive the proton acceleration. This acceleration process of protons due to a two-temperature sheath formed at the flat-top rear side is very robust and produces a large number of protons per shot, similar to what is regularly observed in target normal sheath acceleration (Hatchett S P et al 2000 Phys. Plasmas 7 2076, Maksimchuk A et al 2000 Phys. Rev. Lett. 84 4108, Snavely R A et al 2000 Phys. Rev. Lett. 85 2945) with flat foils. In this paper, we investigate the electron kinetics during DLLPA, showing that they are governed by two mechanisms, both of which lead to continuous electron acceleration along the inner cone wall. Based on our model, we predict the scaling of the hot electron temperature and ion maximum energy with both laser and target geometrical parameters. The scaling of ##IMG## [http://ej.iop.org/images/1367-2630/14/2/023038/nj402517ieqn1.gif] $T^\mathrm hot_\mathrm DLLPA=m_ec_0^2 \frac a_0^24$ with the laser strength parameter a 0 leads to an ion energy scaling that surpasses that of some recently proposed acceleration mechanisms such as radiation pressure acceleration (RPA), while in addition the maximum electron energy is found to scale linearly with the length of the cone neck. We find that when optimizing parameters, high proton energies suitable for applications can be reached using compact short-pulse laser systems with pulse durations of only a few tens to hundreds of laser periods.
Abstract: High intensity laser driven proton beams are at present receiving much attention. The reasons for this are many but high on the list is the potential to produce compact accelerators. However two of the limitations of this technology is that unlike conventional nuclear RF accelerators lasers produce diverging beams with an exponential energy distribution. A number of different approaches have been attempted to monochromise these beams but it has become obvious that magnetic spectrometer technology developed over many years by nuclear physicists to transport and focus proton beams could play an important role for this purpose. This paper deals with the design and characterisation of a magnetic quadrupole system which will attempt to focus and transport laser-accelerated proton beams.
Abstract: A precise knowledge of the temperature and number of hot electrons generated in the interaction of short-pulse high-intensity lasers with solids is crucial for harnessing the energy of a laser pulse in applications such as laser-driven ion acceleration or fast ignition. Nevertheless, present scaling laws tend to overestimate the hot electron temperature when compared to experiment and simulations. We present a novel approach that is based on a weighted average of the kinetic energy of an ensemble of electrons. We find that the scaling of electron energy with laser intensity can be derived from a general Lorentz invariant electron distribution ansatz that does not rely on a specific model of energy absorption. The scaling derived is in perfect agreement with simulation results and clearly follows the trend seen in recent experiments, especially at high laser intensities where other scalings fail to describe the simulations accurately.
Abstract: We present experimental results showing a laser-accelerated proton beam maximum energy cutoff of 67.5 MeV, with more than 5106 protons per MeV at that energy, using flat-top hollow microcone targets. This result was obtained with a modest laser energy of 80 J, on the high-contrast Trident laser at Los Alamos National Laboratory. From 2D particle-in-cell simulations, we attribute the source of these enhanced proton energies to direct laser-light-pressure acceleration of electrons along the inner cone wall surface, where the laser light wave accelerates electrons just outside the surface critical density, in a potential well created by a shift of the electrostatic field maximum with respect to that of the magnetic field maximum. Simulations show that for an increasing acceleration length, the continuous loading of electrons into the accelerating phase of the laser field yields an increase in high-energy electrons.
Abstract: Using a pulse power solenoid, we demonstrate efficient capture of laser accelerated proton beams and the ability to control their large divergence angles and broad energy range. Simulations using measured data for the input parameters give inference into the phase-space and transport efficiencies of the captured proton beams. We conclude with results from a feasibility study of a pulse power compact achromatic gantry concept. Using a scaled target normal sheath acceleration spectrum, we present simulation results of the available spectrum after transport through the gantry.
Abstract: We report on the ¯rst irradiation of in vitro tumour cells with laser-accelerated proton pulses showing dose dependent biological damage. This experiment, paving the way for future radiobiological studies with laser-accelerated protons, demonstrates the simultaneous availability of all components indispensable for systematic radiobiological studies: A laser-plasma accelerator providing proton spectra with maximum energy exceeding 15MeV and applicable doses of a few Gy within few minutes, a beam transport and ¯ltering system, an in-air irradiation site, a dosimetry system providing both online dose monitoring and absolute dose information applied to the cell sample, and the full infrastructure for analysing radiation induced damage in cells.
Abstract: This paper presents a systematic investigation of an ultrashort pulse laser acceleration of protons that yields unprecedented maximum proton energies of 17 MeV at a table-top Ti:sapphire laser power level of 100 TW. For plain few-micron-thick foil targets, a linear scaling of the maximum proton energy with laser power is observed and this is attributed to the short acceleration period close to the target rear surface. Although excellent laser pulse contrast was available, slight deformations of the target rear were found to lead to a predictable shift of the direction of the energetic proton emission away from the target normal that could be used for better discrimination of the low-energy part of the spectrum.
Abstract: Laser-plasma wakefield-based electron accelerators are expected to deliver ultrashort electron bunches with unprecedented peak currents. However, their actual pulse duration has never been directly measured in a single-shot experiment. We present measurements of the ultrashort duration of such electron bunches by means of THz time-domain interferometry. With data obtained using a 0.5 J, 45 fs, 800 nm laser and a ZnTe-based electro-optical setup, we demonstrate the duration of laser-accelerated, quasimonoenergetic electron bunches [best fit of 32 fs (FWHM) with a 90% upper confidence level of 38 fs] to be shorter than the drive laser pulse, but similar to the plasma period.
Abstract: A new scheme to efficiently accelerate protons by a single linear polarized high-intensity ultrashort laser pulse using multiple ultrathin foils is proposed. The foils are stacked at a spacing comparable to their thickness and subsequently irradiated by the same laser pulse. The foil thicknesses are chosen such that the laser light pressure can displace all electrons out of the foil. The authors present a simple, yet precise dynamical model of the acceleration process from which both optimum foil thickness and spacing can be derived. Extensive two-dimensional (2D) particle-in-cell simulations verify the model predictions and suggest an enhancement of the maximum proton kinetic energy by 30% for the two-foil case compared to a single foil.
Abstract: The particle-in-cell (PIC) algorithm is one of the most widely used algorithms in computational plasma physics. With the advent of graphical processing units (GPUs), large-scale plasma simulations on inexpensive GPU clusters are in reach. We present an implementation of a fully relativistic plasma PIC algorithm for GPUs based on the NVIDIA CUDA library. It supports a hybrid architecture consisting of single computation nodes interconnected in a standard cluster topology, with each node carrying one or more GPUs. The internode communication is realized using the message-passing interface. The simulation code PIConGPU presented in this paper is, to our knowledge, the first scalable GPU cluster implementation of the PIC algorithm in plasma physics.
Abstract: This paper reports on simulations of solid mass-limited targets (MLT) via electrodynamic two-dimensional, three velocity component particle-in-cell simulations. The interaction with long (300 fs) high intensity (1020 W/cm2) laser pulses with targets of diameter down to 1 μm is described in detail with respect to electron dynamics and proton and ion acceleration. Depending on the foil diameter, different effects consecutively arise. Electrons laterally recirculate within the target, smoothening the target rear accelerating sheath and increasing the hot electron density and temperature. Our results suggest that the most significant ion energy enhancement should be expected for MLT with diameter below the laser focal spot size. The spread of energetic protons is decreased for medium sized foils while it is greatly increased for foils of size near the focal spot size.
Abstract: Abstract We present a novel high-yield Thomson scattering geometry that takes advantage of compact electron bunches, as available in advanced, low-emittance linear accelerators or laser wakefield accelerators. In order to avoid the restrictions on the X-ray photon yield imposed by the Rayleigh limit, we use ultrashort, pulse-front tilted laser pulses in a side-scattering geometry. Such a traveling-wave setup allows an overlap of electron and laser beams, even after propagating over distances much longer than the Rayleigh length. Experimental designs are discussed and optimized for different scattering angles. Specifically, to minimize group delay dispersion at large scattering angles >10°, we propose the use of varied-line spacing (VLS) gratings for spatio-temporal laser pulse shaping. Compared to head-on (180°) Thomson scattering, interaction lengths are in the centimeter to meter range and photon numbers for ultrashort X-ray pulses can increase by several orders of magnitudes.
Abstract: The application of quadrupole devices with high field gradients and small apertures requires precise control over higher order multipole field components. We present a new scheme for performance control and tuning; which allows the illumination of most of the quadrupole device aperture because of the reduction of higher order field components. Consequently, the size of the aperture can be minimized to match the beam size achieving field gradients of up to 500 T m -1 at good imaging quality. The characterization method based on a Hall probe measurement and a Fourier analysis was confirmed using the high quality electron beam at the Mainz Microtron MAMI.
Abstract: The MLLTRAP at the Maier-Leibnitz-Laboratory (Garching) is a new Penning trap facility designed to combine several novel technologies to decelerate, charge breed, cool, bunch and purify the reaction products and perform high-accuracy nuclear and atomic mass measurements. It is now in the commissioning phase, achieving a mass-resolving power of about 105 in the purification trap for stable ions.
Notes: penning trap, hci, highly charged ions, mass spectrometry, precision mass measurement, purification, cooling
Abstract: A cylindrical double Penning trap system has been installed and commissioned at the Maier-Leibnitz-Laboratory (MLL) in Garching. This trap system has been designed to isobarically purify low-energy ion beams and perform highly accurate mass measurements. Technical details of the device and the first results of the commissioning measurements will be presented. The mass resolving power achieved in the first trap for 119Rb ions is R=139(2)×10^3, while a relative mass uncertainty of δm/m=2.9×10^−8 was reached with the second trap (no analysis of systematic uncertainties included) when using 87Rb as a reference ion for 85Rb.
Notes: The MLLTRAP, presently under construction at the Maier-Leibnitz-Laboratory (Garching), is a Penning trap facility designed to combine several novel techniques to decelerate, purify, charge breed and cool the reaction products and perform high-accuracy nuclear mass measurements of highly charged, laser-cooled ions.
Abstract: The MLLTRAP, presently under construction at the Maier---Leibnitz Laboratory (Garching), is a Penning trap system designed to decelerate, purify, charge-breed and cool the radioactive ions with the aim to perform the high-accuracy nuclear mass measurements. It involves novel techniques, like sympathetic cooling of highly-charged ions of interest with laser-cooled Mg+ ions. The goal is to reach an accuracy of 10-10, which is required for high precision fundamental physics studies like the determination of fundamental constants and measurement of electron binding energies for QED at strong fields.
Abstract: We introduce a method for stopping highly charged ions (HCIs) in a laser-cooled one-component plasma (OCP) of 24Mg+ ions and present results on stopping times derived from realistic molecular dynamics simulations of the complete stopping process. This stopping scheme can provide ultra-cold highly charged ions for future in-trap precision mass measurements. The choice of an ultra-cold ion plasma as a stopping medium is governed by the almost negligible charge exchange of the HCI with the laser-cooled ions and the very low temperatures which can be reached. In our analysis we focus on the stability and fast recooling of the plasma – two features essential for the experimental realization of this stopping scheme.
Abstract: We present a new cooling scheme for the preparation of highly charged ions for future in-trap precision experiments. A plasma of laser cooled 24Mg+ ions trapped in a 3D harmonic confinement potential is used as a stopping medium for the highly charged ions. We focus on the dynamic evolution of the plasma, determining suitable cooling conditions for fast recooling of the 24Mg+ ions. The results of a realistic parallel simulation of the complete stopping process presented here indicate that a small, constant detuning of the laser frequency is sufficient for subsequent recooling of the plasma, thus maintaining the stability of the plasma.
Abstract: We discuss the axial dynamics of laser-cooled relativistic C3+ ion beams at moderate bunching voltages. Schottky noise spectra measured at a beam energy of 122 MeV/u are compared to simulations of the axial beam dynamics. Ions confined in the bucket are addressed by the narrow-band force of a laser beam counter-propagating to the ion beam, while the laser frequency is detuned relatively to the cooling transition frequency in the rest frame of the bucket.
At large detuning comparable to the momentum acceptance of the bucket, the axial dynamics can be well explained by the secular motion of individual non-interacting ions. At small detuning, corresponding to a small axial momentum spread Δp_axial/p_axial < 10^(-6) of the ions, the measured Schottky noise spectra can no longer be explained using an approach which neglects the ion-ion interaction. Instead, the model fails when the ion bunch enters the space-charge dominatedregime, at which the mutual Coulomb-energy of the ions becomes comparable to the kinetic energy of the ions.
Abstract: In-trap preparation of highly charged ions (HCIs) for precision mass measurements by cooling in a strongly coupled plasma of laser-cooled 24Mg+ ions is investigated by molecular dynamics simulations. For HCIs electrostatically decelerated below 1 eV the simulation suggests stopping times of a few 10 µs for high charge states (Q_HCI=40, A_HCI=100). The deposited energy is found to be distributed almost over the entire crystalline plasma of N=10^5 24Mg+ ions due to collective target response. Almost all 24Mg+ ions stay within the acceptance range of the laser cooling force, thus allowing for the maintenance of the plasma conditions and efficient continuous cooling. Energy loss due to collective effects and hard binary collisions can be clearly distinguished, and can be of the same magnitude for the highest projectile charge states. While the former one can be described by the action of an effective stopping power, the latter is governed by large statistical fluctuations.
Abstract: We report on the first laser cooling of a bunched beam of multiply charged C3+ ions performed at the ESR (GSI) at a beam energy of E=1.47 GeV. Moderate bunching provided a force counteracting the decelerating laser force of one counterpropagating laser beam. This versatile type of laser cooling lead to longitudinally space-charge dominated beams with an unprecedented momentum spread of Δp/p ≈ 10^(−7). Concerning the beam energy and charge state of the ion, the experiment depicts an important intermediate step from the established field of laser cooling of ion beams at low energies toward the unique laser cooling scheme proposed for relativistic beams of highly charged heavy ions at SIS 300 (FAIR).
Abstract: Laser cooling of stored 24Mg+ ion beams recently led to the long anticipated experimental realization of Coulomb-ordered ‘crystalline’ ion beams in the low-energy RF-quadrupole storage ring PAul Laser CooLing Acceleration System (Munich). Moreover, systematic studies revealed severe constraints on the cooling scheme and the storage ring lattice for the attainment and maintenance of the crystalline state of the beam, which will be summarized. With the envisaged advent of high-energy heavy ion storage rings like SIS 300 at GSI (Darmstadt), which offer favourable lattice conditions for space-charge-dominated beams, we here discuss the general scaling of laser cooling of highly relativistic beams of highly charged ions and present a novel idea for direct three-dimensional beam cooling by forcing the ions onto a helical path.
Abstract: The crystallization of ion beams has recently been established in the rf quadrupole storage ring PALLAS (PAul Laser CooLing Acceleration System) for laser-cooled 24Mg+ ion beams at an energy of about 1 eV. Yet, unexpectedly sharp constraints had to be met concerning the confinement strength and the longitudinal laser cooling rate. In this paper, related and up to now unseen heating mechanisms are pinpointed for crystalline beams. The weak but inevitable diffusive transverse heating associated with the laser cooling process itself is investigated, possibly allowing the future measurement of the latent heat of the ion crystal. As a function of the beam velocity, the influence of bending shear on the attainability of larger crystalline structures is presented. Finally, rf heating of crystalline beams of different structure is studied for discontinuous cooling.
Abstract: The crystallisation of laser-cooled Mg+ ion beams circulating in the table-top rf quadrupole storage ring PALLAS at a velocity of the order of 2800 m/s (beam energy 1 eV) is reviewed. Emphasis is given to the description of the experimental techniques that were required for this first realisation of crystalline beams. The equivalence of the equations of motion for rf electric and magnetic confinement and thus for PALLAS and high-energy storage rings is pointed out. The phase transition is indicated by the detection of a sudden collapse of the transverse beam size, by the low velocity spread, and by the exceptional stability of the crystalline state, persisting for more than 3000 revolutions or 10^6 focusing periods without any cooling.
Abstract: Measurements of the spatial distribution of bunched crystalline ion beams in the radio frequency quadrupole storage ring PALLAS are presented for different ratios of the longitudinal and the transverse confinement strengths.
The length of highly elongated crystalline ion bunches and its dependence on the bunching voltage is compared to predictions for a one-dimensional ion string and three-dimensional space-charge-dominated beams. The length is found to be considerably shorter than that predicted by the models. Furthermore, the scaling of the length with the bunching voltage is shown to differ from the expected inverse cube root scaling. These differences can partially be attributed to the formation of a mixed crystalline structure.
Additionally, a concise mapping of the structural transition from a string to a zig-zag configuration as a function of the ratio of the confinement strengths is presented, which in a similar way deviates from the predictions.
Abstract: Recently, bunched crystalline ion beams have been realized in the table-top rf quadrupole storage ring PALLAS by means of laser cooling. Here, a novel method for the measurement of the spatial distribution of the ion bunch is presented which is based on the time-resolved analysis of the fluorescence emitted by the ions during cooling. Thus, the phase transition from a gaseous to a crystalline beam can be followed monitoring the whole phase space, and structural transitions can be studied as a function of the variable longitudinal confinement. Surprisingly, the length of crystalline bunches was found to be considerably shortened by a factor of three with respect to the length expected for space charge dominated bunches.
Abstract: The phase transition of an ion beam into its crystalline state has long been expected to dramatically influence beam dynamics beyond the limitations of standard accelerator physics. Yet, although considerable improvement in beam cooling techniques has been made, strong heating mechanisms inherent to existing high-energy storage rings have prohibited the formation of the crystalline state in these machines up to now. Only recently, laser cooling of low-energy beams in the table-top rf quadrupole storage ring PAaul Laser cooLing Acceleration System (PALLAS) has lead to the experimental realization of crystalline beams. In this article, the quest for crystalline beams as well as their unique properties as experienced in PALLAS will be reviewed.
Abstract: Recent experiments at the Experimental Storage Ring (ESR) at GSI have shown that relativistic Li-like carbon (C3+) ion beams can be laser-cooled to an unprecedented momentum spread of Dp/p ~ 10-7. Here, a single-frequency laser was tuned to the Doppler-shifted 1s22s to 1s22p (2P1/2 and 2P3/2) transitions. These results encourage the application of laser cooling to beams of other Li- and Na-like ions at even higher energies, as will e.g. be available at FAIR.
Abstract: In 2004 and 2006 the feasibility of laser cooling of bunched C3+ ion beams with a relativistic energy of 122 MeV/u was successfully demonstrated at the ESR, GSI, see [1] and references therein. While the longitudinal momentum spread was measured to a record value of Dp/p < 4×10−7 using optical diagnostics, standard beam diagnostics such as the Schottky pickup diagnostics were limited in resolution and could only resolvemomentumspreads down to Dp/p ~ 10−6.
Abstract: Simulating strongly coupled plasmas is a demanding computational task. When a plasma is strongly coupled, the mutual Coulomb energy between the plasma particles is much stronger than their kinetic energy. Such a system can undergo a phase transition into a state in which long-range ordering of the plasma constituents can be observed. In a realistic simulation of the plasma dynamics one has to compute the total mutual interaction of each particle with each other particle for particle numbers up to hundred thousand particles. To study the microscopic and macroscopic dynamics of the plasma on a long time scale one thus has to rely on the computational power which is only available at supercomputing centers such as the Leibniz Rechenzentrum.
Abstract: Recent success in laser-driven particle acceleration has increased interest in laser-generated ” accelerator-quality” beams. For example, protons and ions have been produced with up to several tens of MeV per nucleon and monoenergetic features could be generated. Compact, high-gradient laser-accelerators are therefore now being discussed as a potentially viable technology for a host of particle-beam applications, including future compact medical accelerators for medical diagnostics and therapy. For this purpose, a new center for radiation therapy in oncology is founded in Dresden. Following the commissioning of a 150 TW laser system at the Forschungszentrum Dresden-Rossendorf the first acceleration of ion beams has been performed. In this test experiment proton beams with energies up to 6 MeV could be reached.
Abstract: Amongst the almost 2800 nuclides presently known to exist, 229Th is outstanding because of its first excited state, which exhibits the lowest excitation energy known in nuclear physics, thus bearing the potential to bridge the gap between nuclear and laser physics. Since the first studies already more than 30 years ago a precise determination of the transition energy to the ground state was attempted, resulting in the value of 3.5(10) eV adopted for the last 15 years together with the assignment of the single-particle quantum numbers for the ground state of 229Th as Jpi = 5/2+ [633] and 3/2+ [631] for the first excited state. In contrast to the ground state of 229Th, exhibiting a halflife of 7340 years, the first excited state happens to be a long-lived isomer with a halflife of 3-5 hours (which has not yet been experimentally observed).
Abstract: We report on the first laser cooling of a bunched beam of multiply charged C3+ ions performed at the ESR (GSI) at a beam energy of E = 1.47 GeV. Moderate bunching provided a force counteracting the decelerating laser force of one counterpropagating laser beam. This versatile type of laser cooling lead to longitudinally space-charge dominated beams with an unprecedented momentum spread of Δp/p ≈ 10^(−7). Concerning the beam energy and charge state of the ion, the experiment depicts an important intermediate step from the established field of laser cooling of ion beams at low energies toward the unique laser cooling scheme proposed for relativistic beams of highly charged heavy ions at SIS 300 (FAIR).
Notes: reprint of Hyperfine Interactions 162(1) 181-188
Abstract: It is widely accepted that proton or light ion beams may have a high potential for improving cancer cure by means of radiation therapy. However, at present the large dimensions of electromagnetic accelerators prevent particle therapy from being clinically introduced on a broad scale. Therefore, several technological approaches among them laser driven particle acceleration are under investigation. Parallel to the development of suitable high intensity lasers, research is necessary to transfer laser accelerated particle beams to radiotherapy, since the relevant parameters of laser driven particle beams dramatically differ from those of beams delivered by conventional accelerators: The duty cycle is low, whereas the number of particles and thus the dose rate per pulse are high. Laser accelerated particle beams show a broad energy spectrum and substantial intensity fluctuations from pulse to pulse. These properties may influence the biological efficiency and they require completely new techniques of beam delivery and quality assurance. For this translational research a new facility is currently constructed on the campus of the university hospital Dresden. It will be connected to the department of radiooncology and host a petawatt laser system delivering an experimental proton beam and a conventional therapeutic proton cyclotron. The cyclotron beam will be delivered on the one hand to an isocentric gantry for patient treatments and on the other hand to an experimental irradiation site. This way the conventional accelerator will deliver a reference beam for all steps of developing the laser based technology towards clinical applicability.
Abstract: We report on the generation of proton pulses with maximum energies exceeding 15 MeV by means of the irradiation of few micron thick metal foils by ultrashort (30 fs) laser pulses at a power level of 100 TW. In contrast to the well known situation for longer laser pulses, here, a near linear scaling of the maximum proton energy with laser power can be found. Aiming for radiobiological applications the long and short term stability of the laser plasma accelerator as well as a compact energy selection and dosimetry system is presented. The first irradiation of in vitro tumour cells showing dose dependent biological damage is demonstrated paving the way for systematic radiobiological studies.
Abstract: In this work we report on a recent experiment where an energetic, well-collimated electron beam has been observed in the laser direction following the short pulse (600 fs) high-intensity laser interaction with ultra-thin solid foils. These results are in contrast to the typical low-energy divergent electrons accompanying ions in the target normal direction usually seen in solid targets. We observe the foils being preheated and expanded by ASE prior to the main pulse which makes them transparent for the laser. The experimental evidence as well as 2D particle-in-cell simulations suggest the excitation of a wakefield that can accelerate electrons to energies of tens of MeV.
Abstract: Recent advances in laser-ion acceleration have motivated research towards laser-driven compact accelerators for medical therapy. Realizing laser-ion acceleration for medical therapy will require adapting the medical requirements to the foreseeable laser constraints, as well as advances in laser-acceleration physics, beam manipulation and delivery, real-time dosimetry, treatment planning and translational research into a clinical setting.
Abstract: For the past ten years, the highest proton energies accelerated with high-intensity lasers was 58 MeV, observed in 2000 at the LLNL NOVA Petawatt laser, using flat foil targets. Recently, 67.5 MeV protons were observed in experiments at the Los Alamos National Laboratory (LANL) Trident laser, using one-fifth of the PW laser pulse energy, incident into novel conical targets. We present a focused study of new theoretical understanding of this measured enhancement from collisional Particle-in-Cell simulations, which shows that the hot electron temperature, number and maximum energy, responsible for the Target Normal Sheath Acceleration (TNSA) at the cone-top, are significantly increased when the laser grazes the cone wall. This is mainly due to the extraction of electrons from the cone wall by the laser electric field, and their boost in the forward direction by the v×B term of the Lorentz force. This result is in contrast to previous predictions of optical collection and wall-guiding of electrons in angled cones. This new wall-grazing mechanism offers the prospect to linearly increase the hot electron temperature, and thereby the TNSA proton energy, by extending the length over which the laser interacts in a grazing fashion in suitably optimized targets. This may allow achieving much higher proton energies for interesting future applications, with smaller, lower energy laser systems that allow for a high repetition rate.
Abstract: Laser-plasma accelerated ion and electron beam sources are an emerging field with vast prospects, and promise many superior applications in a variety of fields such as hadron cancer therapy, compact radioisotope generation, table-top nuclear physics, laboratory astrophysics, nuclear forensics, waste transmutation, Special Nuclear Material (SNM) detection, and inertial fusion energy. LANL is engaged in several projects seeking to develop compact high-current and high-energy ion and electron sources. We are especially interested in two specific applications: ion fast ignition/capsule perturbation and radiation oncology. Laser-to-beam conversion efficiencies of over 10% are needed for practical applications, and we have already shown inherent efficiencies of >5% from flat foils, on Trident using only a 5th of the intensity [1] and energy of the Nova Petawatt laser [2]. With clever target designs, like structured curved cone targets, we have also been able to achieve major ion energy gains, leading to the highest energy laser-accelerated proton beams in the world [3]. These new target designs promise to help usher in the next generation of particle sources realizing the potential of laser-accelerated beams.
Abstract: Recent experiments at the Experimental Storage Ring (ESR) at GSI have shown that relativistic Li-like C3+ ion beams can be cooled to an unprecedented momentum spread of dp=p ~ 10-7 using a single-frequency laser tuned to the Doppler-shifted 2S1/2 -> 2P1/2 and 2S1/2 -> 2P3/2 atomic transitions. Although these results encourage the application of laser cooling to beams of other Li-like and Na-like ions at even higher energies as will be available at future storage rings at FAIR (Facility for Antiproton and Ion Research), two major concepts have to be demonstrated experimentally: First, efficient laser cooling of ion beams with large initial momentum spread, thus avoiding additional electron cooling to match the large momentum spread to the usually small momentum acceptance of the laser force. Second, all-optical measurements of the relevant beam parameters, thus overcoming the limited resolution of standard storage ring detectors such as the Schottky pickup electrode at ultra-low momentum spreads. The aim of this paper is to discuss the technical realization of these concepts as planned for an upcoming beam time at ESR.
Abstract: Compact tuneable sources of ultrashort hard x-ray pulses can be realized by Thomson scattering, taking advantage of the comparatively short wavelength of a scattered laser pulse with respect to the period length of conventional undulators. Here, we present a detailed analysis and optimization of the efficiency of linear and non-linear Thomson scattering when the process is driven with relativistic laser pulses and when the conventional accelerator is replaced by a laser-plasma wakefield accelerator.
Abstract: We present results on laser-cooling of relativistic bunched C3+ ion beams at the the Experimental Storage Ring at GSI, Darmstadt. With moderate bunching at a few volts, beams of triply charged carbon ions with a beam energy of 122 MeV per nucleon have been lasercooled to relative longitudinal momentum spreads of about 2 × 10^(−6) and below at beam currents of the order of several μA. By detuning the bunching frequency relative to the laser frequency, the acceptance range of the laser force can be increased to match the beam momentum spread. Subsequently decreasing the detuning reduces the momentum spread to values below the resolution of the Schottky noise spectrograph. The reduction of the beam momentum spread is accompanied by a drop in the Schottky noise power by seven to eight orders of magnitude until the signal vanishes completely.
Abstract: We report on first laser cooling studies of bunched beams of triply charged carbon ions stored at an energy of 1.46 GeV at the ESR (GSI). Despite for the high beam energy and charge state laser cooling provided a reduction of the momentum spread of one order of magnitude in space-charge dominated bunches as compared to electron cooling. For ion currents exceeding 10 µA intra-beam-scattering losses could not be compensated by the narrow band laser system presently in use. Yet, no unexpected problems occurred encouraging the envisaged extension of the laser cooling to highly relativistic beams. At ESR, especially the combination with modest electron cooling provided three-dimensionally cold beams in the plasma parameter range of unity, where ordering effects can be expected and a still unexplained signal reduction of the Schottky signal is observed.
Abstract: Realistic molecular dynamics (MD) simulations of the particle dynamics in strongly coupled plasmas require the computation of the mutual Coulomb-force for each pair of charged particles if a correct treatment of long range correlations is required. For plasmas with N > 10^4 particles this requires a tremendous number of computational steps which can only be addressed using efficient parallel algorithms adopted to modern super-computers.We present a new versatile MD simulation code which can simulate the non-relativistic mutual Coulomb-interaction of a large number of charged particles in arbitrary external field configurations. A demanding application is the simulation of the complete dynamics of in-trap stopping of highly charged ions in a laser cooled plasma of N = 10^5 24Mg+ ions. We demonstrate that the simulation is capable of delivering results on stopping times and plasma dynamics under realistic conditions. The results suggest that this stopping scheme can compete with in-trap electron cooling and might be an alternative approach for delivering ultra cold highly charged ions for future trap-based experiments aiming for precision mass measurements of stable and radioactive nuclei.
Abstract: The electronic structure of heavy few-electron systems, i.e., highly charged ions of high nuclear charge Z, provides unique insight into QED terms in the high field of the nucleus and properties of the nucleus itself. Though for atoms and light ions laser spectroscopy represents the method of choice for precision spectroscopy, the increase of the binding energies with nuclear charge prohibits the direct use of visible laser light. This drawback can be overcome with heavy ion storage rings like ESR where the ions are stored at an energy providing the Doppler-tuning to the resonance of interest and cooled providing low Doppler-broadening of the resonance. Here, we present the first laser spectroscopic investigation of the ground state transitions and the 2 2P fine-structure splitting of Li-like carbon ions (C IV), performed oin parallel to a study on laser cooling of relativistic C3+ ion beams at the ESR (GSI). The study represents a test experiment for laser cooling and spectroscopy of Li-like ions at the future facility FAIR.
Abstract: We report on the experimental demonstration of laser cooling of a C3+ ion beam performed at the ESR (GSI) at an energy E=1.47 GeV. The decelerating laser force of one Doppler-tuned UV laser beam was counteracted by moderately bunching the beam. This versatile scheme lead to longitudinally ‘space-charge dominated’ beams with an unprecedented momentum spread Δp/p ≈ 10^(−7) Concerning beam energy and charge state of the ion, the experiment depicts an important step from the field of laser cooling of ion beams at low energies toward the laser cooling scheme proposed for relativistic beams of highly charged heavy ions at the future GSI facility FAIR.
Abstract: Recently, crystalline ion beams have been realized and systematically studied in the table-top rf quadrupole storage ring PALLAS by means of laser cooling. Here, the phase transition of a longitudinally modulated, bunched ion beam in the regime of a linear string of ions is followed monitoring the full spatial distribution of the ion bunch. Structural transitions are investigated as a function of the ratio of the transverse to the longitudinal confinement strength. Surprisingly, the length of crystalline ion bunches was found to be shorter by a factor of up to three with respect to dedicated models, considerably increasing the luminosity of such beams.
Abstract: Cooling and acceleration of ions by lasers has gained increasing attention over the last years. The common interest is to further increase the luminosity of ion beams, either by shrinking the phase space occupied by the beam, or simply via increasing the number of particles. Recently, laser cooling has demonstrated ion beam crystallization as the ultimate reduction of the beam temperature. On the other hand, acceleration of ions by ultra-intense lasers resulted in the generation of ion beams of unprecedented quality, both in terms of beam power and beam emittance.
Abstract: Recently, the phase transition of a low-energy 24Mg+ ion beam into the Coulomb-ordered ‘crystalline’ state could be realized in the rf quadrupole storage ring PALLAS at the LMU Munich. Thereby, an increase of the phase space density of the beam, subjected to longitudinal laser cooling, by about six orders of magnitude was observed. In this paper, we focus on the systematic experimental investigation of the role of the focusing conditions and of bending shear in the storage ring on the attainment of crystalline beams of different crystal structure.
Abstract: This thesis discusses the probability for the discovery of a Standard Model Higgs Boson at Tevatron and LHC in the mass range of 115 GeV/c^2 to 130 GeV/c^2 in associated production with a Z_0 or W+/-. The final decay channel is characterized by two b-quarks and two leptons.
Abstract: The first part of this thesis summarizes the results of laser-cooling of relativistic C3+ ion beams at the ESR/GSI. It is shown that laser cooling at high beam energies is feasible and that momentum spreads much smaller than those observed for electron cooling can be achieved. Resulty indicate that space-charge dominated beams have been observed, reaching the regime of strong coupling which is an essential prerequisite for beam crystallization. Moderate electron cooling was employed to create three-dimensionally cold beams. With the laser cooled beams it was possible to perform precision VUV spectroscopy of the cooling transition. In the second part results on large-scale realistic simulations on the stopping of highly charged ions in a laser-cooled one-component plasma of 24Mg+ ions confined in a harmonic potential are presented. It is shown that cooling times short enough for cooling unstable nuclei can be achieved and fast recooling of the plasma is possible. With this cooling scheme highly charged ions for precision experiments such as mass spectrometry in Penning traps at millikelvin temperatures can be delivered.
