Upcoming Seminars:

For further information, please contact Dr Michael Coppins

 

Control of electron injection and acceleration in laser plasma accelerators

6th March 2017, 3.00 - 4.00 pm room 539

Olle Lundh,  Department of Physics, Lund Laser Centre, Lund University, Sweden

Laser wakefield accelerators appear promising as compact sources of highly relativistic electrons and ultrashort pulses of X-rays. However, improving the control of the electron beam parameters is crucially important in order to enable laser plasma accelerators to be efficiently used in applications. We report on our recent experimental studies of controlled trapping of electrons in the accelerating phase of the plasma wave. The experiments are performed using the Ti:Sapphire-based multi-terawatt laser at the Lund Laser Centre. A variety of techniques to achieve stable and tunable electron beams are explored, compared and combined, including density down-ramp injection, ionization-induced injection and colliding pulse injection.

Ultra-intense vortex light for particle acceleration in the plasma

23rd February 2017 3.00 – 4.00 pm room 539

Dr Jorge Vieira, Group for Lasers and Plasmas, Instituto Superior Técnico, Portugal 

Positron acceleration remains a key challenge for a future plasma based linear collider. Here, we show three-dimensional simulations results that suggest how ultra-intense structured light with orbital angular momentum (vortex light) could be used as a driver for plasma accelerators that could accelerate positrons in strongly nonlinear regimes. We also investigate innovative pathways to generate and amplify vortex laser pulses to ultra-high intensities, required to realise this positron acceleration scheme. We show that some of these pathways can also provide mechanisms to produce high orbital angular momentum harmonics.

Full scale modelling simulations of plasma based accelerators

20th February 2017 3.00 – 4.00 pm room 539 Blackett.

Dr Jorge Vieira, Group for Lasers and Plasmas, Instituto Superior Técnico, Portugal

Laser wakefield accelerators have the potential to deliver relativistic electron bunches for several applications. While in the plasma, electrons are subject to strong focusing forces that lead to intense betatron x-ray radiation generation. Using particle-in-cell simulations and radiation post-processing tools, we show that the laser driver polarisation can control the polarisation of betatron x-rays in direct laser acceleration setups. We show that fast electrons flowing out of the plasma can trigger large-scale magnetic fields around the entire plasma accelerator. If the electron beam collides with a high Z target, an electron-positron fireball bunch forms. We show that these beams can lead to magnetic field amplification through the current filamentation instability, relevant in astrophysical conditions. When only a single filament is present, the resulting plasma wave could be used to accelerate positrons to high energies.

Past Seminars 2016: 

 

6th July: Capturing Structural Dynamics in Crystalline Silicon Using Chirped Electrons from a Laser Wakefield Accelerator

Alec Thomas, Lancaster University and Cockcroft Institute

741 Blackett Laboratory 2pm

Recent progress in laser wakefield acceleration has led to the emergence of a new generation of electron and X-ray sources that may have significant benefits for ultrafast science. In this talk, I will describe the use of laser-wakefield-accelerated electron bunches for time-resolved electron diffraction measurements of the structural dynamics of single-crystal silicon nano-membranes pumped by an ultrafast laser pulse. In our proof-of-concept study, we resolved the silicon lattice dynamics on a picosecond time scale by deflecting the momentum-time correlated electrons in the diffraction peaks with a static magnetic field to obtain the time-dependent diffraction efficiency. Our measurements were enabled by the development of a laser wakefield accelerator operating at kHz repetition rate with good stability, delivering electrons in the 100 keV range with the transverse coherence required for electron diffraction. Necessary beam quality improvements were enabled by  feedback-optimized wavefront manipulation using a deformable mirror, which steered the plasma dynamics and resulted in improvement to the charge and transverse emittance of the electron beam. Further improvements to this scheme may lead to femtosecond temporal resolution, with negligible pump-probe jitter. In addition, the feedback techniques may be applied to the next generation of high repetition-rate, high power lasers for laser wakefield acceleration.

7th July: Relativistic Magnetic Reconnection in the Laboratory

Louise Willingale, Lancaster University and Cockcroft Institute

741 Blackett Laboratory 2pm

Magnetic reconnection is a fundamental plasma process involving an exchange of magnetic energy and plasma kinetic energy through changes in the magnetic field topology. In many astrophysical plasmas magnetic reconnection plays a key role in the dynamics, although making direct measurements is obviously challenging. Therefore, laboratory studies of magnetic reconnection provide an important platform for testing theories and characterising different regimes. Until now, the extremely energetic class of astrophysical phenomena - including high-energy pulsar winds, gamma ray bursts, and jets from galactic nuclei - where the energy density of the reconnecting fields exceeds the rest mass energy density (σ ≡ B2/(μ0nemec2) > 1), i.e. relativistic reconnection, have been inaccessible in the laboratory. I will present experimental measurements along with numerical modelling of relativistic magnetic reconnection driven by short-pulse, high-intensity lasers that produce extremely strong magnetic fields. Evidence of magnetic reconnection was identified by the plasma’s X-ray emission patterns, changes to the electron spectrum, and by measuring the time over which reconnection occurs.  Three-dimensional particle-in-cell simulations show the plasma density and magnetic field characteristics in the reconnection region satisfy σ > 1, indicating these experiments are in the relativistic reconnection regime. Accessing these relativistic conditions in the laboratory allows for further investigation that may provide insight into unresolved areas in space and astro-physics.

 

15th July: Two seminars:

Maximizing implosion performance for inertial confinement fusion science

John Kline, Los Alamos National Laboratory

While the march towards achieving indirectly driven inertial confinement fusion at the NIF has made great progress, the experiments show that multi-dimensional effects still dominate the implosion performance. Low mode implosion symmetry and hydrodynamic instabilities seed by capsule mounting features appear to be two key limiting factors for implosion performance. One reason these factors have a large impact on the performance of ICF implosions is the high convergence required to achieve high fusion gains. To tackle these problems, a predictable implosion platform is needed meaning experiments must trade-off high gain for performance. To this end, LANL has adopted three main approaches to develop a 1D implosion platform where 1D means high yield over 1D clean calculations. Taking advantage of the properties of beryllium capsules, a high adiabat, low convergence platform is being developed. The higher drive efficiency for beryllium enables larger case-to-capsule ratios to improve symmetry at the expense of drive. Smaller capsules with a high adiabat drive are expected to reduce the convergence and thus increase predictability. The second approach is liquid fuel layers using wetted foam targets. With liquid fuel layers, the initial mass in the hot spot can be controlled via the target fielding temperature which changes the liquid vapor pressure. Varying the initial hot spot mass via the vapor pressure controls the implosion convergence and minimizes the need to vaporize the dense fuel layer during the implosion to achieve ignition relevant hot spot densities. The last method is double shell targets. Unlike hot spot ignition, double shells ignite volumetrically. The inner shell houses the DT fuel and the convergence of this cavity is relatively small compared to hot spot ignition. Radiation trapping and the longer confinement times relax the conditions required to ignite the fuel. Key challenges for double shell targets are coupling the momentum of the outer shell to the inner shell and mixing of the mid-Z material from the inner shell into the fuel. The primary theme for each of these approaches is reduced implosion convergence with the goal of achieving a 1D implosion. Once established, a systematic approach to solving limiting issues for ICF can be undertaken. This presentation will discuss the approaches, results, and plans for each of these campaigns.

An Overview of the Los Alamos Inertial Confinement Fusion and High-Energy-Density Physics Research Programs

Steve Batha, Los Alamos National Laboratory

The Los Alamos Inertial Confinement Fusion and Science Programs engage in a vigorous array of experiments, theory, and modeling. We use the three major High Energy Density facilities, NIF, Omega, and Z to perform experiments. These include opacity, radiation transport, hydrodynamics, ignition science, and burn experiments to aid the ICF and Science campaigns in reaching their stewardship goals. The ICF program operates two nuclear diagnostics at NIF, the neutron imaging system and the gamma reaction history instruments. Both systems are being expanded with significant capability enhancements.

PLASMA SEMINAR SERIES 2015-16
 
DateNameTitle
15/10 Robert Riedel High power wavelength tunable femtosecond OPCPA
25/11 Ben King Laser-based strong-field QED (under construction)
2/12 Ceri Brenner Laser-driven x-ray and neutron source development for industrial applications of solid-foil plasma accelerators
26/1 Mike Dunne 'A billion times brighter': An overview of the revolution underway in
X-ray science
29/1 Vasily Kharin Temporal laser pulse shape effects in non-linear Thomson scattering
17/2 Charlie Ryan Small and cheap plasma thrusters for the nano and micro-satellite market
30/3 Howard Scott Non-LTE Modeling of Radiatively-Driven Dense Plasmas
20/4 Jeff Colvin Advances in Non-Equilibrium Atomic Physics with Novel Laser Targets
6/7 Alec Thomas Capturing Structural Dynamics in Crystalline Silicon Using Chirped Electrons from a Laser Wakefield Accelerator
7/7 Louise Willingale Relativistic Magnetic Reconnection in the Laboratory
15/7 John Kline Maximizing implosion performance for inertial confinement fusion science
  Steve Batha An Overview of the Los Alamos Inertial Confinement Fusion and High-Energy-Density Physics Research Programs

Past Seminars 2015:

 

20th April: Advances in Non-Equilibrium Atomic Physics with Novel Laser Targets

Jeff Colvin, Lawrence Livermore National Laboratory

741 Blackett Laboratory 2pm

We have been developing new paths to achieve the higher hard x-ray fluences necessary for radiation hardness testing of military systems and other applications.  The focus of this research has been on development of new ultra-low-density pure metal foams fabricated as self-supporting structures of nanowires, and parallel development of novel metal-nanoparticle-loaded carbon nanotube foams. In this presentation I will discuss the foam development work, review the x-ray spectral emissivity data obtained from Omega and NIF laser experiments with the new foam targets, and compare the experimental results to those predicted by 2D simulations with a radiation-hydrodynamics code incorporating detailed non-LTE atomic models. I will show how this work has opened up two new paths to getting higher x-ray conversion efficiency at high photon energies for the laser-driven x-ray sources needed for radiation hardness testing, and helped to advance our understanding of non-equilibrium atomic physics.

30th March: Non-LTE Modeling of Radiatively-Driven Dense Plasmas

Howard Scott, Lawrence Livermore National Laboratory

741 Blackett Laboratory 3pm

There are now several experimental facilities that use strong X-ray fields to produce plasmas with densities ranging from ~1 to ~103 g/cm3 . Large laser facilities, such as the National Ignition Facility (NIF) and Omega reach high densities with radiatively-driven compression, short-pulse lasers such as XFELs produce solid density plasmas on very short timescales, and the Orion laser facility combines these methods. Despite the high densities, these plasmas can be very far from LTE, due to the large radiation fields and/or short timescales, and simulations mostly use collisional-radiative (CR) modeling which has been adapted to handle these conditions. These dense plasmas present challenges to CR modeling. Ionization potential depression (IPD) has received much attention recently as researchers work to understand experimental results from LCLS and Orion [1,2]. However, incorporating IPD into a CR model is only one challenge presented by these conditions. Electron degeneracy and the extent of the state space can also play important roles in the plasma energetics and radiative properties, with effects evident in recent observations [3,4]. We discuss the computational issues associated with these phenomena and discuss methods for handling them.

[1] O. Ciricosta, S.M. Vinko, H.-K. Chung, et al, Phys. Rev. Lett. 109, 065002 (2012)

[2] D.J. Hoarty, P. Allan, S.F. James, et al, Phys. Rev. Lett. 110, 265003 (2013)

[3] S.P. Regan, R. Epstein, B.A. Hammel, et al, Phys. Rev. Lett. 111, 045001 (2013)

[4] L.A. Pickworth, B.A. Hammel, V.A. Smalyk, et al, submitted to Phys. Rev. Lett.

This work performed under the auspices of U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

29th January: Temporal laser pulse shape effects in nonlinear Thomson scattering

Vasily KharinGSI Helmholtzzentrum für Schwerionenforschung GmbH

630 Blackett Laboratory 2pm

Scattering of the light on high-energy electron beams has become an indispensable tool in providing tunable wide range X-; and gamma-radiation and found applications in various areas of research. In order to obtain higher photon yield, the intensity of the incident pulse can be increased. High values of field lead to non-negligible ponderomotive shift in the emitted frequency varying with the pulse envelope. The present study is devoted to the influence of the pulse shape on the emitted photon spectrum during the non-linear Thomson scattering. We present analytical results on on-axis spectrum of the scattered radiation in the case of symmetric relativistically intense incident pulse and discuss some properties of angular distribution of the emitted radiation. The possibility of incident pulse reconstruction from the scattered spectrum is also discussed.

17th February: Small and cheap plasma thrusters for the nano and micro-satellite market

Charlie Ryan, University of Southampton

741 Blackett Laboratory 3pm

Currently the propulsion of satellites is undergoing a revolution, with a move away from chemical propulsion to electric propulsion; i.e. propulsion using electrical energy to accelerate propellant. Many types of electric propulsion techniques rely upon the creation of low-density plasma, and the acceleration of the ions created to km/s velocities. This talk will introduce the various different types of plasma thrusters and their operational characteristics. The electric propulsion concepts being experimentally investigated at the University of Southampton will be introduced. Further the drive to smaller and cheaper electric propulsion options will be outlined, motivated by the large growth in nano and micro-satellites, and the need for electric propulsion to be applicable within the smaller constraints of these platforms. The work being completed at the University of Southampton to reduce the cost, size and mass of electric propulsion for spacecraft will be demonstrated, putting it into the context of the significant growth in the microsatellite market.

26th January: 'A billion times brighter': An overview of the revolution underway in X-ray science

Mike Dunne, Director of LCLS, SLAC National Accelerator Laboratory

539 Blackett Laboratory 3pm

This talk will provide an introductory overview of the world’s first “hard x-ray free electron laser facility”, known as LCLS, operated by Stanford University on behalf of the US Department of Energy.  The x-rays produced by LCLS are a billion times brighter than can be produced by conventional sources, such as a synchrotron, and are delivered in ultrafast bursts - typically a few tens of femtoseconds (10-15 seconds). This opens up revolutionary opportunities for the study of novel states of matter, quantum materials, ultrafast chemistry, and structural biology. 

Since its initial operation in 2009, LCLS has enabled a remarkable series of studies, via its ability to provide atomic resolution information, with freeze-frame ‘movies’ of how atomic, chemical and biological systems evolve on ultrafast timescales.  Based on this success, a major upgrade project is now underway that will increase the repetition rate by 4 orders of magnitude and open up entirely new scientific opportunities. Access to LCLS is open to everyone, based purely on the scientific merit of the proposed experiments. Hopefully this talk will help engender further ideas and opportunities for future use of this remarkable new science facility.

2nd December: Laser-driven X-ray and neutron source development for industrial applications of solid-foil plasma accelerators 

Ceri Brenner, Application Development Scientist, STFC Central Laser Facility 

741 Blackett Laboratory 3pm

Pulsed beams of energetic X-rays, electrons and neutrons from intense laser interactions with solid foils are promising for applications where bright, small emission area sources are ideal. Possible end users of laser-driven sources are those requiring advanced non-destructive and non-invasive inspection techniques in industry sectors of high value commerce such as aerospace, nuclear, defence and advanced manufacturing. 

In collaboration with the UK’s Defence Science Technology Laboratory the CLF’s Gemini laser was used to generate an electron beam, via the Wakefield acceleration method in a high pressure gas jet, to drive a source of backscattered X-rays at the test object plane. An X-ray backscatter image of an array of different density and atomic number items is demonstrated for the first time from a laser-generated electron beam. 

Results from an experiment with the Vulcan laser in March 2015 demonstrate the key features of laser-driven Bremsstrahlung beams for imaging applications and show neutron yield enhancement during pitcher-catcher generation. Active detector radiographic imaging of industrially relevant sample objects with a 10 ps drive pulse is also presented, demonstrating that features of 200 micron size are resolved when projected at high magnification.

25th November: Laser-based strong-field QED (under construction)

Ben King, University of Plymouth 
741 Blackett Laboratory 3pm

Since the advent of the laser in the early 1960s, quantum electrodynamics (QED) has been used to predict a variety of new phenomena when charged particles interact with intense laser pulses.

Recent progress in high-intensity laser technology has put several of these phenomena in reach of near-future experiments. Unlike the technology, the progress of theory understanding beyond what was calculated by the 1970s has been limited. In this talk, I will outline some of the theory successes of laser-based strong-field QED and discuss the main challenges and potential benefits of solving them.

15th October: High power wavelength tunable femtosecond OPCPA

Robert Riedel, Class 5 Photonics GmbH/DESY 
1004 Blackett Laboratory 11am

Optical parametric chirped-pulse amplication (OPCPA) is the most promising method for providing compact, wavelength-tunable, high power, femtosecond lasers. We have recently achieved a 112 W OPCPA with wavelength-tunability around 800 nm and 30 fs pulse duration in burst mode (100 kHz in a 800 µs burst at 10 Hz). In this seminar, we discuss the various laser architectures and the critical parameters in achieving similar laser parameters but in continuous operation. Further, energy scaling to the terawatt level is discussed.

For further information on this seminar, contact Christos Kamperidis