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Ph.D Report

Daniele Palla

Main Ph.D Activities (1° year)

• Being a new field to me, I started to study the basics of laser-plasma interaction and the main plasma diagnostics before starting Ph.D courses.

• I was fully involved in the experimental activities performed at the ILIL laboratory, starting from the setup of the interaction chamber, which include the optical setup, alignments, optics normalizations, vacuum control, radiation and particle detectors setup, etc

• I was also involved in the experimental measurements, primarily in the high energy electron diagnostics including beam transverse profile and energy spectra, from design and construction to data analysis.

I was involved in the measurements and simulations of magnetic fields using Radia, a C++ software package interfaced with Mathematica. I used Radia to simulate several 3-D configurations of the magnetic dipole and quadrupole to design magnetic spectrometers and electron lenses for different applications.

• I created a Mathematica program, called “ConvSpec”, used to retrieve the electron energy spectrum from deflection images. Such a program uses the simulated trajectory of an electron beam passing through the magnetic spectrometer (simulated using Radia).

Main Ph.D Activities (2° year)

During the second year of Ph.D, I also participated to the set up and measurements of a new experiment dedicated to laser interaction with solid targets. This enabled me to gain additional experience in experimental work and data acquisition. However, my main activity was dedicated to the acceleration of electrons by wakefield on underdense gas targets. In mid-year the topic of the thesis was outlined:

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self-injection. A summary of my activity is as follows:

Electrons Acceleration using gas-jet target:

1. Electron energy spectra measurements and analysis for all possible LWFA regimes. Characterization of the spectra as a function of the gas type and plasma density

2. Set up of a Thomson scattering layout, based on a double laser pulse in a counterpropagating configuration. Measurements of the temporal-space synchronization of the two pulse (main and counterpropagating) using plasma shadowgraphy.

3. Collaboration with CPP (Center for plasma Physics) of Belfast for the measurements of the Compton scattering from gamma rays generated by Bremsstrahlung of laser accelerated electrons.

4. Characterization of the electron beam in relation to plasma density, gas properties and polarization of the laser beam

5. Study of a stable regime of laser-plasma acceleration for radiobiology applications, using LWFA in a moderately relativistic regime. Characterization of the electron beam in terms of collimation, stability, absorbed dose on an equivalent water target etc.

6. Radiobiology experiments on biological tissues

Electrons Acceleration using solid target:

1. I have mostly participated in the experiments as a support during the preparation and the carrying out. I also contributed to the analysis of energy energy spectra of fast (MeV) electrons generated during laser-solid interaction experiments.

Radiobiological Activities and Collaboration with the “Istituto di

Bioimmagini e Fisiologia Moleolare IBFM -CNR UOS Cefalù”

1. Design and simulation of a quadrupole lens system and an energy selector in collaboration with the "Istituto di Bioimmagini e Fisiologia Molecolare IBFM". The simulations was performed using mathematica with the Radia package. The goal was to get an electron beam optimized for radiobiological use. This system (selector + quadruples) was simulated in parallel using a Montecarlo method.

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Activities in collaboration with “Azienda ospedaliero Universitaria di

Pisa”

1. In order to obtain a "LWFA" electron beam suitable for radiobiological use, we compared our energy spectrum with the spectrum of a linear radiotherapy accelerator. For this purpose, I designed an optimized diagnostic system for the IORT (Intraoperative RadioTherapy) accelerator. The system was based on an ad hoc collimator, a magnetic dipole, a Lanex scintillating screen and a ccd camera.

2. Data acquisition and analysis in the case of IORT accelerator required a more sophisticated tuning since high spectral resolution was required in a range from 0.5 Mev to 15 Mev. A comparison between LWFA and IORT spectra was also carried out to make quantitative assessments on the absorbed dose.

“Jasmine” Simulations

1. During the second Ph.D year, I was involved in numerical simulation work based on the PIC (GPU) code “Jasmine” developed by Francesco Rossi (University of Bologna). Since I did not have specific competencies in PIC simulations, I was initially involved as a "user". The possibility to perform simulations to model experimental results in “real time” gave me the possibility to identify the main topic of the thesis, i.e. self-injection.

2. After October, I started working on the PIC (CPU) code "AlaDyn" which is based on a CPU architecture. I was also able to carry out a preliminary comparison between Jasmine and AlaDyn numerical results at fixed laser-plasma conditions. While the advantage of using Jasmine in terms of execution time (10 times faster than Aladyn), I experienced some technical issues on Jasmine that forced me to concentrate on ALaDyn code only.

Main Ph.D Activities (3° year)

The third year of my Ph.D was entirely dedicated to the thesis, which includes the focus on the selected topic, the design of a dedicated experiment, the actual experimental activity, the data analysis and, lastly, the writing of the thesis. The phase of the specific topic selection started in January 2016. At the end of which I decided to base my thesis on the study of a specific electron injection technique, the downramp injection and, in particular, the shock-injection technique, applied to our moderately relativistic LWFA system. A summary of my activity during January-October 2016 is as follows:

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• I performed several 2-D PIC simulation using AlaDyn both to increase the confidence with the “new” code and to model our experimental condition: various gas targets, gas-jet modification, different laser pulse lengths, plasma density scans, etc. I gave several internal seminaries on those points.

• Numerical simulations suggested that a down-ramp density transition mechanism applied on our 1.2 mm long nozzle wound be able to enhance the quality of the accelerated electron beam. For this reason I designed a set up to generate a shock in the gas-jet target, a “shock-driving mechanism” to be applied at the standard gas-jet target, without any modifications

• The preparation of the remotely controllable shock mechanism required an intensive design study to be adapted to the configuration of the gas-jet target. In addition to this, several interferometric measurements were performed, which requires the preparation of a test interaction chamber off-line. After several tests the final shock mechanism design was obtained. Such a mechanism was able to produce a 30-µm wide shock, with excellent reproducibility shot by shot and with a satisfactory mechanical stability. Further 2-D PIC simulations were performed after the first experimental results to confirm (from the numerical point of view) the effects of the real gas-jet profiles on the injection mechanism.

• The experiment dedicated to my thesis took place in 4 days at the end of July, and included, in addition to the shock injection test, a study on electron emittance and a laser polarization scan. The results were encouraging, with experimental evidence of the shock effect on maximum spectrum energy, monochromaticity, emittance, injection threshold, etc. In order to model such a experimental results, 3-D PIC simulation was performed (in addition to the previous 2-D results).

• In September-October 2016, after a deeper analysis of both experimental results and 3-D PIC simulations, we decided that a new experimental run would be required for the correct interpretation of the injection mechanism. Moreover a new shock mechanism and laser setup would be required. Unfortunately, the new experiment could not be scheduled in time for the thesis due to major upgrade work previously planned.

• After careful examination of the results obtained, I started to work on “Self-Injection in a moderately relativistic LWFA regime”; the final topic of my thesis. This works is based on results of the experimental runs discussed above.

Extra Experimental Activities

• Participation, in a LWFA experiment (supported by Strathclyde University), at FLAME facility, Frascati ( April-May 2014)

• Test of the X-ray imaging system “PIXIRAD” in a Thomson Scattering Experiment at the CLF laser system Gemini, RAL, Didcot, UK (10-14 November 2015)

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Ph.D Courses

“Corso interdisciplinare di perfezionamento linguistico e informatico e sulla gestione della

ricerca e conoscenza dei sistemi di ricerca europei e internazional”, Prof. Steven N. Shore.

“Plasmi B”, Prof. Francesco Pegoraro.

“Plasmi C”, Prof. Andrea Macchi (Just Followed, not in study plan).

Corsi avanzati di Fisica della Materia : "Space plasmas: from spacecraft observations to plasma

theory" (P. Henri), "Introduction to modeling and simulations" (F. Puosi), "Pulsed High Power Laser" (M.Galimberti), "Novel aspects of classical and quantum radiation reaction" (A. Di

Piazza), "The 20PW OPCPA laser system" (M. Galimberti), "Laser-driven inertial confinement

fusion: principle, issue, achievements" (S. Atzeni), "Introduzione alla propulsione elettrica" (T.

Andreussi), "Studi di Fisica del Plasma in macchine a confinamento magnetico" (P.Buratti), "Equilibrium and nonequilibrium Green’s functions" (G. Pastori Parravicini).

Conference, Seminary and Course

• INO Annual Symposium, Sezione INO Sensor Lab, Università di Brescia, 1-3 October 2014.

Poster presentation: “Recent development of the diagnostics set up of the laser-driven source of electron at ILIL”

Giornate di Studio sul Piano Triennale & International Day of Medical Physics, Trento , 6-8 November 2014.

• High Powered Lasers (HPL) Training Course, STFC Rutherford Appleton Laboratory, Harwell Oxford, Didcot, 16-27 March 2014. Seminary: “The Laser Wake-Field Acceleration"

• IFAE, Facoltà di Scienze, Università di roma Tor Vergata, 8-10 April 2015. Poster Presentation: “Studio Sperimentale nell'Accelerazione Laser-Plasma”

Internal Seminary, Istituto Nazionale di Ottica, Pisa, 4 May 2015. Seminary: “Laser-plasma

acceleration: A close view on self-injection mechanisms”

• 2nd EAAC, La Biodola, Isola D'elba, 13-19 September 2015. Seminary: “Laser-plasma

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• 101° Congresso Nazionale SIF, Dipartimento di Fisica, La Sapienza, Roma, 21-25 September 2015. Seminary: “Laser-plasma acceleration: A close view on self-injection mechanisms” • Extreme Light Infrastructure, Aula Convegni, CNR, Roma, 9 October 2015.

Internal Seminary, Istituto Nazionale di Ottica, Pisa, 28 January 2016. Seminary: “An

Overview of AlaDyn; a Particle in cell Code”

Internal Seminary, Istituto Nazionale di Ottica, Pisa, 16 february 2016. Seminary: “Investigation about the new 30fs ILIL regime”

Internal Seminary, Istituto Nazionale di Ottica, Pisa, 3 March 2016. Seminary: “Gas-Jet

Length Optimization (30fs regime)”

Internal Seminary, Istituto Nazionale di Ottica, Pisa, 16 March 2016. Seminary: “Energy

Spectrum Analysis for 40fs and 30fs regime”

Internal Seminary, Istituto Nazionale di Ottica, Pisa, 12 April 2016. Seminary: “Energy

Spectrum Analysis for 30fs regime with Density Ramp”

Internal Seminary, Istituto Nazionale di Ottica, Pisa, 20 May 2016. Seminary: “Introduction to

Emittance”

Internal Seminary, Istituto Nazionale di Ottica, Pisa, 15 July 2016. Seminary: “Gas Jet Profile

Characterization”

• 102° Congresso Nazionale SIF, Polo Multifunzionale, Università degli studi di Padova, 26-30 September 2016. Seminary: “Role of shock-front and ionization in self-injecion of

laser-plasma acceleration”.

INO Annual Symposium, Polo Scientifico e Tecnologico, Trento, 9-10 February 2017. Poster

presentation: “Self-Injection in a Moderately Relativistic LWFA Regime”.

Publications:

• D. Lamia a, G.Russo, C.Casarino, L.Gagliano, G.C.Candiano, L.Labate, F.Baffigi, L.. Fulgentini, A.Giulietti, P.Koester, D.Palla, L.A.Gizzi, M.C.Gilardi. “Monte Carlo application

based on GEANT 4 tool kit to simulate a laser–plasma electron beam line for radiobiological studies”. Nuclear Instruments and Methods in Physics Research A786, 113– 119 (2015)

• L.A. Gizzi, L. Labate, F. Baffigi, F. Brandi, G.C. Bussolino, L. Fulgentini, P. Koester, D. Palla, F. Rossi. Laser–plasma acceleration of electrons for radiobiology and radiation sources”.

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• S. Tudisco, C. Altana, G. Lanzalone, A. Muoio, G. A. P. Cirrone, D. Mascali, F. Schillaci, F. Brandi, G. Cristoforetti, P. Ferrara, L. Fulgentini, P. Koester, L. Labate, D. Palla and L. A. Gizzi. “Investigation on target normal sheath acceleration through measurements of ions

energy distribution”. Review of Scientific Instruments 87, 02A909 (2016)

• L.A. Gizzi, b, C. Altana, F. Brandi, e, P. Cirrone, G. Cristoforetti, A. Fazzi, P. Ferrara, L. Fulgentini, D. Giove, P. Koester, L. Labate, G. Lanzalone, P. Londrillo, D. Mascali, A. Muoio, D. Palla, F. Schillaci, S. Sinigardi, S. Tudisco, G. Turchetti. “Role of laser contrast and foil

thickness in target normal sheath acceleration”. Nuclear Instruments and Methods in Physics ResearchA829, 144–148 (2016)

• C. Altana, A. Muoio, G. Lanzalone, S. Tudisco, F. Brandi, G.A.P. Cirrone, G. Cristoforetti, A. Fazzi, P. Ferrara, L. Fulgentini, D. Giove, P. Koester, L. Labate, D. Mascali, D. Palla, F. Schillaci, L.A. Gizzi. “Investigation of ion acceleration mechanism through laser-matter

interaction in femtosecond domain”. Nuclear Instruments and Methods in Physics Research A829, 159–162 (2016)

• D. Palla, F. Baffigi, F. Brandi, L. Fulgentini, P. Koester, L. Labate, P. Londrillo, L.A. Gizzi.

“Comparison of self-injection thresholds in He and N2 and role of self-focusing in LWFA”. Nuclear Instruments and Methods in Physics Research A829, 408–412 (2016)

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