Symposium on Recent Advances in  Plasma Physics June 10-12,  2007 The Plasma-Fil

Symposium on Recent Advances in  Plasma Physics June 10-12,  2007 The Plasma-Fil www.phwiki.com

Symposium on Recent Advances in  Plasma Physics June 10-12,  2007 The Plasma-Fil

Kidd, James, Founder;Editor has reference to this Academic Journal, PHwiki organized this Journal Symposium on Recent Advances in Plasma Physics June 10-12, 2007 The Plasma-Filled Rod Pinch: a Pulsed-Power HED Plasma Radiographic Source D. Mosher, B.V. Weber, in addition to J.W. Schumer Plasma Physics Division, Naval Research Laboratory, Washington, DC 20375, USA Work supported by the U.S. Office of Naval Research, S in addition to ia National Laboratories, in addition to AWE Aldermaston, UK Background NRL has a long-term program to develop intense, mm-diam bremsstrahlung radiography sources driven by 100-ns, 1- to 6-MV, TW-level pulsed-power generators Our star per as long as mer is the plasma-filled rod pinch (PFRP), a sub-mm source concentrating a 0.5-MA, MeV electron beam onto the tip of a 1-mm-diam, tapered tungsten rod1 Tungsten plasma expansion during the x-ray pulse limits the source brightness Underst in addition to ing the dynamics of the high-energy-density tungsten plasma will help to improve this promising radiography source W plasma expansion was studied with holographic interferometry2 These measurements in addition to radiation imaging are compared with the results of simple, self-similar modeling of the plasma expansion Model predictions of the expansion in addition to radiation patterns agree with measurements in addition to indicate peak thermal energy densities of about 2 MJ/cc, corresponding to > 10 Mbar peak pressure 1B.V. Weber, et al., Phys. Plas. 11, 2916-2927(2004). 2D.M. Ponce, D. Phipps, D.D. Hinshelwood, in addition to B.V Weber, Proc. 14th Inter. Pulsed Power Conf. PFRP operation on Gamble II 1-mm-diam rod tapered to a point over 1- to 1.5-cm length Voltage be as long as e x-rays due to d(LI)/dt of the run-down phase About 40% of the 30-kJ diode energy is deposited as electrons in the tip Plasma conducts current Gap opens, MeV electrons deposited at tip Tip explodes, anode plasma exp in addition to s Anode

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X-Ray Radiography 101: Edge Spread x-y view at IP on line of sight tungsten rolled edge x-ray source image plate (IP) Edge Spread Function Y 0 -Y -Y 0 Y X-Ray Radiography 101: Edge Spread x-y view at IP on line of sight tungsten rolled edge x-ray source image plate Y 0 -Y X-Ray Radiography 101: Edge Spread x-y view at IP on line of sight tungsten rolled edge x-ray source image plate Y 0 -Y

X-Ray Radiography 101: Line Spread LSF(y)dy is a measure of x-ray energy emitted in a thin strip along x Source radial distribution: Point Spread Function PSF(r) PSF recovered from LSF by Abel inversion x-ray source PSF(r) x-y view The plasma filled rod pinch diode on GAMBLE II has a line spread with two distinct length scales 0.4-mm FWHM characteristic of conical-rod-tip emission Few-mm “wings” associated with tungsten plasma expansion during the x-ray pulse X-ray pinhole images in addition to interferometry show plasma expansion at the rod tip Use hydro-expansion model to confirm the wing feature cathode Line Spread as long as 1-mm-Diam Tapered W Rod Interferogram in addition to Rod Shadow at the End of the X-Ray Pulse The axial line spread measures the x-ray intensity emitted along the rod The axial line spread is a measure of electron-beam heating vs z Beam heating near the rod tip has a FWHM of about 4 mm This axial heating profile is used in the model to drive tungsten-plasma expansion Hydro-expansion model predictions are compared to 2D, time-dependent interferometry the measured time-integrated LSF Agreement with these measurements will indicate that the tungsten plasma parameters are reasonable in addition to in the HED regime image plate pinhole image

A self-similar expansion model is used to estimate the line spread of the PFRP Tungsten mass in length L of the conical tip is distributed in a cylinder The axial LSF suggests L in the 3- to 5-mm range Ph(t) = 0.4IdiodeVdiode/L Black-body radiation with emissivity e from radius R(t) Tungsten equation of state from SESAME3 Eint = 1.5(1+Z)NkT + ionization Eth = 1.5(1+Z)NkT » 0.4Eint max pressure = 0.67Eth/pR2(t) (r) is the PSF from which the model line spread is calculated Self-Similar Cylindrical Expansion (per cm length of plasma) 3NTIS Doc. DE94-011699, J. D. Johnson, ‘‘SESAME Data Base’’ Self-Similar Expansion of the Rod Tip e = 0.1, L = 3.5 mm Energy Partition Expansion History Self-similar hydro expansion reproduces the PFRP line spread Predicted line spreads are nearly independent of emissivity Best fit to data as long as L = 3 – 4 mm, agrees with axial line spread PSF from Model as long as L = 3.5 mm Line Spreads from Experiment in addition to Model as long as L = 3 in addition to 4 mm

The self-similar expansion model can be generalized to one-dimensional axial variations1 N(z) = pRrod(z)2rW/mW Ph(z,t) from axial line spread Add return-current ohmic heating to the energy balance Iz ~ axial edge spread Spitzer resistivity Expansion Model Variations with z 1B.V. Weber, et al., Phys. Plas. 11, 2916-2927(2004). Schlieren boundary can be calculated from axial hydro in addition to compared to experiment Fringe count determines experimental electron density neS(z,t) at the schlieren boundary RexS(z,t) Axial-expansion equations provide the self-similar expansion radius R(z,t) Determine theoretical schlieren boundary RthS(z,t) from Interferogram in addition to Rod Shadow at 110 ns Axial-cylindrical modeling reproduces expansion Analysis valid as long as dR/dz < 1 Does not predict spherical expansion at z < 2 mm from tip Conclusions For the tapered-rod PFRP on Gamble II, intense beam heating of the low-mass rod tip produces rapid tungsten-plasma expansion leading to extended wings in the line spread Measured Schlieren images in addition to line-spread distributions compare well with self-similar hydrodynamic modeling of rod-plasma expansion Model predictions indicate peak thermal energy densities of about 2 MJ/cc, corresponding to > 10 Mbar peak pressure When axial variations are taken into account, higher energy density is predicted very close to the rod tip early in the expansion, though the assumption of 2D-cylindrical expansion breaks down Future plans include 2-D MHD in addition to PIC simulations of the PFRP Challenges as long as future work include rod return-current-heating effects during the run-down phase the role of adsorbed gases in the rod following the run-down/plasma-opening transition beam- in addition to plasma-current distributions in the exp in addition to ing rod plasma geometries that reduce the wings in the line spread

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Kidd, James Founder;Editor

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