Publications by Roman Walczak


EuPRAXIA - A compact, cost-efficient particle and radiation source

AIP Conference Proceedings 2160 (2019)

MK Weikum, T Akhter, PD Alesini, AS Alexandrova, MP Anania, NE Andreev, I Andriyash, A Aschikhin, RW Assmann, T Audet, A Bacci, IF Barna, A Beaton, A Beck, A Beluze, A Bernhard, S Bielawski, FG Bisesto, F Brandi, O Bringer, R Brinkmann, E Bründermann, M Büscher, M Bussmann, GC Bussolino, A Chance, JC Chanteloup, M Chen, E Chiadroni, A Cianchi, J Clarke, J Cole, ME Couprie, M Croia, B Cros, P Crump, G Dattoli, N Delerue, O Delferriere, P Delinikolas, S De Nicola, J Dias, U Dorda, R Fedele, AF Pousa, M Ferrario, F Filippi, J Fils, G Fiore, RA Fonseca, M Galimberti, A Gallo, D Garzella, P Gastinel, D Giove, A Giribono, LA Gizzi, FJ Grüner, AF Habib, T Heinemann, B Hidding, BJ Holzer, SM Hooker, T Hosokai, M Hübner, A Irman, F Jafarinia, DA Jaroszynski, S Jaster-Merz, C Joshi, MC Kaluza, M Kando, OS Karger, S Karsch, E Khazanov, D Khikhlukha, A Knetsch, D Kocon, P Koester, O Kononenko, G Korn, I Kostyukov, K Kruchinin, L Labate, C Lechner, WP Leemans, A Lehrach, FY Li, X Li, V Libov, A Lifschitz, V Litvinenko, W Lu, O Lundh, AR Maier, V Malka, GG Manahan, SPD Mangles, B Marchetti, A Marocchino

© 2019 Author(s). Plasma accelerators present one of the most suitable candidates for the development of more compact particle acceleration technologies, yet they still lag behind radiofrequency (RF)-based devices when it comes to beam quality, control, stability and power efficiency. The Horizon 2020-funded project EuPRAXIA ("European Plasma Research Accelerator with eXcellence In Applications") aims to overcome the first three of these hurdles by developing a conceptual design for a first international user facility based on plasma acceleration. In this paper we report on the main features, simulation studies and potential applications of this future research infrastructure.


Low-density hydrodynamic optical-field-ionized plasma channels generated with an axicon lens

Physical Review Accelerators and Beams American Physical Society 22 (2019) 041302-

RJ Shalloo, C Arran, A Picksley, A Von Boetticher, L Corner, J Holloway, G Hine, J Jonnerby, HM Milchberg, C Thornton, R Walczak, S Hooker

We demonstrate optical guiding of high-intensity laser pulses in long, low density hydrodynamic optical-field-ionized (HOFI) plasma channels. An axicon lens is used to generate HOFI plasma channels with on-axis electron densities as low as $n_e(0) = 1.5\times 10^{17}\, \mathrm{cm}^{-3}$ and matched spot sizes in the range $ 20 \mu \mathrm{m} \lesssim W_M \lesssim 40 \mu \mathrm{m}$. Control of these channel parameters via adjustment of the initial cell pressure and the delay after the arrival of the channel-forming pulse is demonstrated. For laser pulses with a peak axial intensity of $4 \times 10^{17}\, \mathrm{W\,cm}^{-2}$, highly reproducible, high-quality guiding over more than 14 Rayleigh ranges is achieved at a pulse repetition rate of 5 Hz, limited by the available channel-forming laser and vacuum pumping system. Plasma channels of this type would seem to be well suited to multi-GeV laser wakefield accelerators operating in the quasi-linear regime.


Eupraxia, a step toward a plasma-wakefield based accelerator with high beam quality

Journal of Physics: Conference Series IOP Science 1350 (2019)

D Alesini, A Aschikhin, A Beck, M Chen, E Chiadroni, M Croia, B Cros, A Del Dotto, M Ferrario, RA Fonseca, LA Gizzi, SM Hooker, L Labate, A Martinez De La Ossa, A Mosnier, A Mostacci, D Oumbarek Espinos, A Stella, EN Svystun, D Terzani, P Tomassini, JM Vieira, CP Welsch, SM Wiggins, J Wolfenden

The EuPRAXIA project aims at designing the world's first accelerator based on advanced plasma-wakefield techniques to deliver 5 GeV electron beams that simultaneously have high charge, low emittance and low energy spread, which are required for applications by future user communities. Meeting this challenging objective will only be possible through dedicated effort. Many injection/acceleration schemes and techniques have been explored by means of thorough simulations in more than ten European research institutes. This enables selection of the most appropriate methods for solving each particular problem. The specific challenge of generating, extracting and transporting high charge beams, while maintaining the high quality needed for user applications, are being tackled using innovative approaches. This article highlights preliminary results obtained by the EuPRAXIA collaboration, which also exhibit the required laser and plasma parameters.


Status of the Horizon 2020 EuPRAXIA conceptual design study

Journal of Physics: Conference Series 1350 (2019)

G Fiore, RA Fonseca, M Galimberti, A Gallo, A Ghaith, D Giove, A Giribono, LA Gizzi, FJ Grüner, AF Habib, C Haefner, T Heinemann, B Hidding, BJ Holzer, SM Hooker, T Hosokai, M Huebner, A Irman, FJ Jafarinia, DA Jaroszynski, C Joshi, M Kaluza, M Kando, OS Karger, E Khazanov

© Published under licence by IOP Publishing Ltd. The Horizon 2020 project EuPRAXIA (European Plasma Research Accelerator with eXcellence In Applications) is producing a conceptual design report for a highly compact and cost-effective European facility with multi-GeV electron beams accelerated using plasmas. EuPRAXIA will be set up as a distributed Open Innovation platform with two construction sites, one with a focus on beam-driven plasma acceleration (PWFA) and another site with a focus on laser-driven plasma acceleration (LWFA). User areas at both sites will provide access to free-electron laser pilot experiments, positron generation and acceleration, compact radiation sources, and test beams for high-energy physics detector development. Support centres in four different countries will complement the pan-European implementation of this infrastructure.


Laser-driven high-quality positron sources as possible injectors for plasma-based accelerators

Scientific Reports Nature Research 9 (2019) 5279

A Alejo, R Walczak, G Sarri

The intrinsic constraints in the amplitude of the accelerating fields sustainable by radio-frequency accelerators demand for the pursuit of alternative and more compact acceleration schemes. Among these, plasma-based accelerators are arguably the most promising, thanks to the high-accelerating fields they can sustain, greatly exceeding the GeV/m. While plasma-based acceleration of electrons is now sufficiently mature for systematic studies in this direction, positron acceleration is still at its infancy, with limited projects currently undergoing to provide a viable test facility for further experiments. In this article, we study the feasibility of using a recently demonstrated laser-driven configuration as a relatively compact and inexpensive source of high-quality ultra-relativistic positrons for laser-driven and particle-driven plasma wakefield acceleration studies. Monte-Carlo simulations show that near-term high-intensity laser facilities can produce positron beams with high-current, femtosecond-scale duration, and sufficiently low normalised emittance at energies in the GeV range to be injected in further acceleration stages.


Hydrodynamic optical-field-ionized plasma channels

Physical Review E American Physical Society 97 (2018) 053203

RJ Shalloo, C Arran, L Corner, J Holloway, J Jonnerby, R Walczak, HM Milchberg, S Hooker

We present experiments and numerical simulations which demonstrate that fully-ionized, lowdensity plasma channels could be formed by hydrodynamic expansion of plasma columns produced by optical field ionization (OFI). Simulations of the hydrodynamic expansion of plasma columns formed in hydrogen by an axicon lens show the generation of 200 mm long plasma channels with axial densities of order ne(0) = 1 × 1017 cm−3 and lowest-order modes of spot size WM ≈ 40 µm. These simulations show that the laser energy required to generate the channels is modest: of order 1 mJ per centimetre of channel. The simulations are confirmed by experiments with a spherical lens which show the formation of short plasma channels with 1.5 × 1017 cm−3 . ne(0) . 1 × 1018 cm−3 and 61 µm & WM & 33 µm. Low-density plasma channels of this type would appear to be well-suited as multi-GeV laser-plasma accelerator stages capable of long-term operation at high pulse repetition rates.


Layout considerations for a future electron plasma research accelerator facility EuPRAXIA

NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT 909 (2018) 111-113

PA Walker, RW Assmann, R Brinkmann, E Chiadroni, U Dorda, M Ferrario, D Kocon, B Marchetti, L Pribyl, A Specka, R Walczak


Layout considerations for a future electron plasma research accelerator facility EuPRAXIA

Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment Elsevier 909 (2018) 111-113

PA Walker, RW Assmann, R Brinkmann, E Chiadroni, U Dorda, M Ferrario, D Kocon, B Marchetti, L Pribyl, A Specka, R Walczak

The Horizon 2020 Project EuPRAXIA (“European Plasma Research Accelerator with eXcellence In Applications”) is preparing a conceptual design for a highly compact and cost-effective European facility with multi-GeV electron beams using plasma as the acceleration medium. The design includes two user areas: one for FEL science and one for High Energy Physics (HEP) detector development and other pilot applications. The accelerator facility will be based on a laser and/or a beam driven plasma acceleration approach. This contribution introduces layout considerations of the future plasma accelerator facilities in the context of EuPRAXIA. It compares conventional and novel plasma accelerator facility requirements and presents potential layouts for the future site. Together with performance analysis, cost effectiveness, and targeted user cases of the individual configurations, such layout studies will later enable a ranking of potential configurations. Based on this information the optimal combination of technologies will be defined for the 2019 conceptual design report of the EuPRAXIA facility.


Reconstructing nonlinear plasma wakefields using a generalized temporally encoded spectral shifting analysis

Physical Review Accelerators and Beams American Physical Society 21 (2018) 103501-

C Arran, NH Matlis, R Walczak, SM Hooker

We generalize the temporally encoded spectral shifting (TESS) analysis for measuring plasma wakefields using spectral interferometry to dissimilar probe pulses of arbitrary spectral profile and to measuring nonlinear wakefields. We demonstrate that the Gaussian approximation used up until now results in a substantial miscalculation of the wakefield amplitude, by a factor of up to two. A method to accurately measure higher amplitude quasilinear and nonlinear wakefields is suggested, using an extension to the TESS procedure, and we place some limits on its accuracy in these regimes. These extensions and improvements to the analysis demonstrate its potential for rapid and accurate on-shot diagnosis of plasma wakefields, even at low plasma densities.


Excitation and control of plasma wakefields by multiple laser pulses

Physical Review Letters American Physical Society 119 (2017) 044802-

J Cowley, C Thornton, CD Arran, RJ Shalloo, L Corner, G Cheung, CD Gregory, SPD Mangles, NH Matlis, Symes, R Walczak, SM Hooker

We demonstrate experimentally the resonant excitation of plasma waves by trains of laser pulses. We also take an important first step to achieving an energy recovery plasma accelerator by showing that unused wakefield energy can be removed by an out-of-resonance trailing laser pulse. The measured laser wakefields are found to be in excellent agreement with analytical and numerical models of wakefield excitation in the linear regime. Our results indicate a promising direction for achieving highly controlled, GeV-scale laser-plasma accelerators operating at multi-kilohertz repetition rates.


The coherent combination of fibre lasers - Towards realistic applications

AIP Conference Proceedings AIP Publishing 1812 (2017)

P Tudor, L Corner, R Walczak

To drive a laser-plasma wakefield, high peak-power laser pulses are required. For useful accelerator applications, it is also necessary to have driving lasers with high efficiency, repetition rates, and average power. The coherent combination of Ytterbium-doped fibre laser amplifiers is a promising potential solution, and previous work has demonstrated the successful combination of near-identical ultrafast fibre lasers. We report here the combination of significantly mismatched Ytterbium-doped photonic crystal fibre amplifiers with a combined efficiency of 96%, while the locked power output remained stable for 6 hours. The combined output of the system had a total gain of 12 dB, with no detrimental effect on the compressed pulse width observed.


Excitation and Control of Plasma Wakefields by Multiple Laser Pulses

PHYSICAL REVIEW ACCELERATORS AND BEAMS 20 (2017) ARTN 044802

J Cowley, C Thornton, C Arran, RJ Shalloo, L Corner, G Cheung, CD Gregory, SPD Mangles, NH Matlis, DR Symes, R Walczak, SM Hooker


Horizon 2020 EuPRAXIA design study

Journal of Physics: Conference Series IOP Publishing 874 (2017)

MP Anania, NE Andreev, I Andriyash, A Aschikhin, RW Assmann, T Audet, A Bacci, IF Barna, A Beaton, A Beck, A Beluze, A Bernhard, S Bielawski, FG Bisesto, J Boedewadt, F Brandi, O Bringer, R Brinkmann, E Bründermann, M Büscher, M Bussmann, GC Bussolino, A Chance, JC Chanteloup, M Chen

The Horizon 2020 Project EuPRAXIA ("European Plasma Research Accelerator with eXcellence In Applications") is preparing a conceptual design report of a highly compact and cost-effective European facility with multi-GeV electron beams using plasma as the acceleration medium. The accelerator facility will be based on a laser and/or a beam driven plasma acceleration approach and will be used for photon science, high-energy physics (HEP) detector tests, and other applications such as compact X-ray sources for medical imaging or material processing. EuPRAXIA started in November 2015 and will deliver the design report in October 2019. EuPRAXIA aims to be included on the ESFRI roadmap in 2020.


Production of exclusive dijets in diffractive deep inelastic scattering at HERA

European Physical Journal C Springer Berlin Heidelberg 76 (2016) 1-18

H Abramowicz, I Abt, L Adamczyk, M Adamus, S Antonelli, V Aushev, Y Aushev, O Behnke, U Behrens, A Bertolin, I Bloch, EG Boos, K Borras, I Brock, NH Brook, R Brugnera, A Bruni, PJ Bussey, A Caldwell, M Capua, CD Catterall, J Chwastowski, J Ciborowski, R Ciesielski, AM Cooper-Sarkar

Production of exclusive dijets in diffractive deep inelastic e±p scattering has been measured with the ZEUS detector at HERA using an integrated luminosity of 372 pb-1. The measurement was performed for γ∗–p centre-of-mass energies in the range 90<w<250gev and="" for="" photon="" q2="" virtualities="">25GeV2. Energy flows around the jet axis are presented. The cross section is presented as a function of β and ϕ, where β=x/xIP, x is the Bjorken variable and xIP is the proton fractional longitudinal momentum loss. The angle ϕ is defined by the γ∗–dijet plane and the γ∗–e± plane in the rest frame of the diffractive final state. The ϕ cross section is measured in bins of β. The results are compared to predictions from models based on different assumptions about the nature of the diffractive exchange.</w<250gev>


Generation of laser pulse trains for tests of multi-pulse laser wakefield acceleration

Nuclear Instruments and Methods in Physics Research A Elsevier 829 (2016) 383-385

S Hooker, L Corner, C Arran, J Cowley, G Cheung, C Thornton, R Walczak

In multi-pulse laser wakefield acceleration (MP-LWFA) a plasma wave is driven by a train of low-energy laser pulses separated by the plasma period, an approach which offers a route to driving plasma accelerators with high efficiency and at high pulse repetition rates using emerging technologies such as fibre and thin-disk lasers. Whilst these laser technologies are in development, proof-of-principle tests of MP-LWFA require a pulse train to be generated from a single, high-energy ultrafast pulse. Here we demonstrate the generation of trains of up to 7 pulses with pulse separations in the range 150–170 fs from single 40 fs pulses produced by a Ti:sapphire laser.


Measurement of the cross-section ratio σψ(2S)/σJ/ψ(1S) in deep inelastic exclusive ep scattering at HERA

Nuclear Physics B Elsevier (2016)

H Abramowicz, I Abt, L Adamczyk, M Adamus, S Antonelli, V Aushev, Y Aushev, O Behnke, U Behrens, A Bertolin, I Bloch, EG Boos, K Borras, I Brock, NH Brook, R Brugnera, A Bruni, PJ Bussey, A Caldwell, M Capua, CD Catterall, J Chwastowski, J Ciborowski, R Ciesielski, AM Cooper-Sarkar

The exclusive deep inelastic electroproduction of ψ(2S) and J/ψ(1S) at an ep centre-of-mass energy of 317 GeV has been studied with the ZEUS detector at HERA in the kinematic range 2 &lt; Q2 &lt; 80 GeV2, 30 &lt;W&lt; 210 GeV and |t| &lt; 1 GeV2, where Q2 is the photon virtuality, W is the photon–proton centre-of-mass energy and t is the squared four-momentum transfer at the proton vertex. The data for 2 &lt; Q2 &lt; 5 GeV2 were taken in the HERA I running period and correspond to an integrated luminosity of 114 pb−1. The data for 5 &lt; Q2 &lt; 80 GeV2 are from both HERA I and HERA II periods and correspond to an integrated luminosity of 468 pb−1. The decay modes analysed were μ+μ− and J/ψ(1S)π+π− for the ψ(2S) and μ+μ− for the J/ψ(1S). The cross-section ratio σψ(2S)/σJ/ψ(1S) has been measured as a function of Q2, W and t. The results are compared to predictions of QCD-inspired models of exclusive vector-meson production.


Generation of laser pulse trains for tests of multi-pulse laser wakefield acceleration

Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment Elsevier 829 (2016) 383-385

R Shalloo, L Corner, C Arran, J Cowley, G Cheung, C Thornton, R Walczak, SM Hooker

In multi-pulse laser wakefield acceleration (MP-LWFA) a plasma wave is driven by a train of low-energy laser pulses separated by the plasma period, an approach which offers a route to driving plasma accelerators with high efficiency and at high pulse repetition rates using emerging technologies such as fibre and thin-disk lasers. Whilst these laser technologies are in development, proof-of-principle tests of MP-LWFA require a pulse train to be generated from a single, high-energy ultrafast pulse. Here we demonstrate the generation of trains of up to 7 pulses with pulse separations in the range 150–170 fs from single 40 fs pulses produced by a Ti:sapphire laser.


Combination of differential D*(+/-) cross-section measurements in deep-inelastic ep scattering at HERA

Journal of High Energy Physics Springer Berlin Heidelberg 2015 (2015)

S Mikocki, FM Idris, A Morozov, NM Nasir, K Mueller, V Myronenko, K Nagano, T Naumann, PR Newman, C Niebuhr, T Nobe, D Notz, G Nowak, RJ Nowak, JE Olsson, Y Onishchuk, D Ozerov, P Pahl, C Pascaud, GD Patel, E Paul, E Perez, W Perlanski, A Petrukhin, I Picuric

H1 and ZEUS have published single-differential cross sections for inclusive D<sup>∗±</sup>-meson production in deep-inelastic ep scattering at HERA from their respective final data sets. These cross sections are combined in the common visible phase-space region of photon virtuality Q<sup>2</sup>&gt; 5 GeV<sup>2</sup>, electron inelasticity 0.02 &lt; y &lt; 0.7 and the D<sup>∗±</sup> meson’s transverse momentum p<inf>T</inf>(D<sup>∗</sup>) &gt; 1.5 GeV and pseudorapidity |η(D<sup>∗</sup>)| &lt; 1.5. The combination procedure takes into account all correlations, yielding significantly reduced experimental uncertainties. Double-differential cross sections d<sup>2</sup>σ/dQ<sup>2</sup>dy are combined with earlier D<sup>∗±</sup> data, extending the kinematic range down to Q<sup>2</sup>&gt; 1.5 GeV<sup>2</sup>. Perturbative next-to-leading-order QCD predictions are compared to the results.


Combination of measurements of inclusive deep inelastic e±p scattering cross sections and QCD analysis of HERA data: H1 and ZEUS Collaborations

European Physical Journal C Springer Verlag (2015)

AM Cooper-Sarkar, RCE Devenish, B Foster, C Gwenlan, R Walczak

A combination is presented of all inclusive deep inelastic cross sections previously published by the H1 and ZEUS collaborations at HERA for neutral and charged current (Formula presented.) scattering for zero beam polarisation. The data were taken at proton beam energies of 920, 820, 575 and 460 GeV and an electron beam energy of 27.5 GeV. The data correspond to an integrated luminosity of about 1 fb(Formula presented.) and span six orders of magnitude in negative four-momentum-transfer squared, (Formula presented.), and Bjorken x. The correlations of the systematic uncertainties were evaluated and taken into account for the combination. The combined cross sections were input to QCD analyses at leading order, next-to-leading order and at next-to-next-to-leading order, providing a new set of parton distribution functions, called HERAPDF2.0. In addition to the experimental uncertainties, model and parameterisation uncertainties were assessed for these parton distribution functions. Variants of HERAPDF2.0 with an alternative gluon parameterisation, HERAPDF2.0AG, and using fixed-flavour-number schemes, HERAPDF2.0FF, are presented. The analysis was extended by including HERA data on charm and jet production, resulting in the variant HERAPDF2.0Jets. The inclusion of jet-production cross sections made a simultaneous determination of these parton distributions and the strong coupling constant possible, resulting in (Formula presented.). An extraction of (Formula presented.) and results on electroweak unification and scaling violations are also presented.


Combination of measurements of inclusive deep inelastic e±p scattering cross sections and QCD analysis of HERA data

European Physical Journal C: Particles and Fields Springer Berlin Heidelberg 75 (2015) 580

A Cooper-Sarkar, C Gwenlan, RCE Devenish, R Walczak

A combination is presented of all inclusive deep inelastic cross sections previously published by the H1 and ZEUS collaborations at HERA for neutral and charged current e±p scattering for zero beam polarisation. The data were taken at proton beam energies of 920, 820, 575 and 460 GeV and an electron beam energy of 27.5 GeV. The data correspond to an integrated luminosity of about 1 fb−1 and span six orders of magnitude in negative four-momentum-transfer squared, Q2, and Bjorken x. The correlations of the systematic uncertainties were evaluated and taken into account for the combination. The combined cross sections were input to QCD analyses at leading order, next-to-leading order and at next-to-next-to-leading order, providing a new set of parton distribution functions, called HERAPDF2.0. In addition to the experimental uncertainties, model and parameterisation uncertainties were assessed for these parton distribution functions. Variants of HERAPDF2.0 with an alternative gluon parameterisation, HERAPDF2.0AG, and using fixed-flavour-number schemes, HERAPDF2.0FF, are presented. The analysis was extended by including HERA data on charm and jet production, resulting in the variant HERAPDF2.0Jets. The inclusion of jet-production cross sections made a simultaneous determination of these parton distributions and the strong coupling constant possible, resulting in αs(MZ)=0.1183±0.0009(exp)±0.0005(model/parameterisation)±0.0012(hadronisation)+0.0037−0.0030(scale). An extraction of xFγZ3 and results on electroweak unification and scaling violations are also presented.

Pages