AUTHOR=Fan Lulin , Xu Tongjun , Wang Qingsong , Xu Jiancai , Zhang Guoqiang , Wang Putong , Fu Changbo , Ma Zhiguo , Deng Xiangai , Ma Yugang , Li Shun , Lu Xiaoming , Li Jinfeng , Xu Rongjie , Wang Cheng , Liang Xiaoyan , Leng Yuxin , Shen Baifei , Ji Liangliang , Li Ruxin 

TITLE=Enhanced laser-driven backward proton acceleration using micro-wire array targets

JOURNAL=Frontiers in Physics

VOLUME=11

YEAR=2023

URL=https://www.frontiersin.org/journals/physics/articles/10.3389/fphy.2023.1167927

DOI=10.3389/fphy.2023.1167927

ISSN=2296-424X

ABSTRACT=<p>Micro-structured targets can be employed to enhance the coupling of laser energy to the high energy density plasma. Here we report on experimental measurement of enhanced proton beam energy from laser-driven micro-wire array (MWA) targets along the backward direction. An ultra-intense (<inline-formula id="inf1"><mml:math id="m1" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mo>∼</mml:mo><mml:mn>2</mml:mn><mml:mo>×</mml:mo><mml:msup><mml:mn>10</mml:mn><mml:mn>20</mml:mn></mml:msup><mml:mi mathvariant="normal">W</mml:mi><mml:mo>/</mml:mo><mml:msup><mml:mrow><mml:mi mathvariant="normal">c</mml:mi><mml:mi mathvariant="normal">m</mml:mi></mml:mrow><mml:mn>2</mml:mn></mml:msup></mml:mrow></mml:math></inline-formula>) laser pulse of <inline-formula id="inf2"><mml:math id="m2" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mo>∼</mml:mo><mml:mtext> </mml:mtext><mml:mn>40</mml:mn><mml:mtext> </mml:mtext><mml:mi mathvariant="normal">f</mml:mi><mml:mi mathvariant="normal">s</mml:mi></mml:mrow></mml:math></inline-formula> pulse duration interacts with the MWA structure and induces large population of energetic electrons. The enhanced sheath field efficiently accelerates protons both transversely and longitudinally. The spectrometers record proton cut-off energy of around <inline-formula id="inf3"><mml:math id="m3" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mn>16</mml:mn><mml:mtext> </mml:mtext><mml:mi mathvariant="normal">M</mml:mi><mml:mi mathvariant="normal">e</mml:mi><mml:mi mathvariant="normal">V</mml:mi></mml:mrow></mml:math></inline-formula> and temperature <inline-formula id="inf4"><mml:math id="m4" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mn>813</mml:mn><mml:mi mathvariant="normal">k</mml:mi><mml:mi mathvariant="normal">e</mml:mi><mml:mi mathvariant="normal">V</mml:mi></mml:mrow></mml:math></inline-formula> along the backward direction, which is <inline-formula id="inf5"><mml:math id="m5" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mn>20</mml:mn><mml:mo>%</mml:mo><mml:mo>−</mml:mo><mml:mn>60</mml:mn><mml:mo>%</mml:mo></mml:mrow></mml:math></inline-formula> higher than that of a flat target under commensurate laser conditions. Comparison with particle-in-cell simulations suggests that the enhancement originates from the increased temperature and population of the hot electrons within the micro-wires. These measurements provide a direct probe of the high energy density plasma condition in laser-driven solid targets and a useful benchmark for further studies on laser-driven micro-structured targets.</p>