Measuring magnetic fields in laser-driven coils with dual-axis proton deflectometry

TY - JOUR

T1 - Measuring magnetic fields in laser-driven coils with dual-axis proton deflectometry

AU - Bradford, P.

AU - Dearling, A.

AU - Ehret, M.

AU - Antonelli, L.

AU - Booth, N.

AU - Carroll, D. C.

AU - Clarke, R. J.

AU - Glize, K.

AU - Heathcote, R.

AU - Khan, M.

AU - Moody, J. D.

AU - Pikuz, S.

AU - Pollock, B. B.

AU - Read, M. P.

AU - Ryazantsev, S.

AU - Spindloe, C.

AU - Ridgers, C. P.

AU - Santos, J. J.

AU - Tikhonchuk, V. T.

AU - Woolsey, N. C.

N1 - © 2021 The Author(s). Published by IOP Publishing Ltd.

PY - 2021/8

Y1 - 2021/8

N2 - By driving hot electrons between two metal plates connected by a wire loop, high power lasers can generate multi-tesla, quasi-static magnetic fields in miniature coil targets. Many experiments involving laser-coil targets rely on proton deflectometry directed perpendicular to the coil axis to extract a measurement of the magnetic field. In this paper, we show that quantitative measurements using perpendicular probing are complicated by the presence of GV m-1 electric fields in the target that develop on sub-ns timescales. Probing parallel to the coil axis with fiducial grids is shown to reliably separate the electric and magnetic field measurements, giving current estimates of I ≈ 5 kA in 1 mm- and 2 mm-diameter wire loops. An analytic model of proton deflection in electric and magnetic fields is used to benchmark results from the particle-in-cell code and help deconvolve the magnetic and electric field deflections. Results are used to motivate a new experimental scheme that combines a single-plate target with axial proton probing and direct current measurements. This scheme has several important advantages over the traditional target and diagnostic set-up, enabling the robust measurement of coil magnetic fields and plasma properties, as well as making it easier to validate different theoretical models at a range of laser intensities.

AB - By driving hot electrons between two metal plates connected by a wire loop, high power lasers can generate multi-tesla, quasi-static magnetic fields in miniature coil targets. Many experiments involving laser-coil targets rely on proton deflectometry directed perpendicular to the coil axis to extract a measurement of the magnetic field. In this paper, we show that quantitative measurements using perpendicular probing are complicated by the presence of GV m-1 electric fields in the target that develop on sub-ns timescales. Probing parallel to the coil axis with fiducial grids is shown to reliably separate the electric and magnetic field measurements, giving current estimates of I ≈ 5 kA in 1 mm- and 2 mm-diameter wire loops. An analytic model of proton deflection in electric and magnetic fields is used to benchmark results from the particle-in-cell code and help deconvolve the magnetic and electric field deflections. Results are used to motivate a new experimental scheme that combines a single-plate target with axial proton probing and direct current measurements. This scheme has several important advantages over the traditional target and diagnostic set-up, enabling the robust measurement of coil magnetic fields and plasma properties, as well as making it easier to validate different theoretical models at a range of laser intensities.

KW - coils

KW - fields

KW - laser

KW - magnetic

KW - plasma

KW - proton deflectometry

KW - proton radiography

UR - http://www.scopus.com/inward/record.url?scp=85109807803&partnerID=8YFLogxK

U2 - 10.1088/1361-6587/ac0bca

DO - 10.1088/1361-6587/ac0bca

M3 - Article

AN - SCOPUS:85109807803

SN - 0741-3335

VL - 63

JO - Plasma Physics and Controlled Fusion

JF - Plasma Physics and Controlled Fusion

IS - 8

M1 - 084008

ER -