The Heavy Ion Fusion Virtual National Laboratory Neutralized Transport Experiment (NTX) P. K. Roy, S. S. Yu, S. Eylon, E. Henestroza, A. Anders, F. M. Bieniosek, W. G. Greenway, W. L. Waldron, D. B. Shuman, D. L. Vanecek, B. G. Logan, LBNL D. R. Welch, D. V. Rose, C. Thoma, MRC R. C. Davidson, P. C. Efthimion, I. Kaganovich, E. P. Gilson, A. B. Sefkow, PPPL W. M. Sharp, LLNL 15 th International Symposium on Heavy Ion Inertial Fusion PPPL, Princeton University, New Jersey, USA June 7-11, 2004

The Heavy Ion Fusion Virtual National Laboratory Overview ● Requirements of NTX for Driver ● NTX system and diagnostics ● Keys to a small spot ● Experimental results of neutralization. ● Sensitivity study ● Achievements/conclusion

The Heavy Ion Fusion Virtual National Laboratory NTX and HIF Driver

The Heavy Ion Fusion Virtual National Laboratory The HIF Driver Requires Beam Neutralization in Chamber Transport to Hit mm-sized Spot on Target How and what Neutralized Chamber Transport can do: ●Electrons from external source are entrained by the beam and neutralize the space charge sufficiently that the pulse focuses on the target in a nearly ballistic manner for a small spot. ●Present generation of drivers requires total of ~40 kA divided between perhaps hundred beams, each beam of 2 mm focal spot radius. Driver needs:

The Heavy Ion Fusion Virtual National Laboratory Neutralized Transport Experiment (NTX) Addresses Driver- Relevant Issues Final FocusChamber Transport A schematic of the NTX beam line setup ●Perveance is the key parameter for final focus and neutralization ●NTX covers range of perveance relevant to the driver (K≤10 -3 ).

The Heavy Ion Fusion Virtual National Laboratory NTX System Setup and diagnostics Located at LBNL Gated Camera

The Heavy Ion Fusion Virtual National Laboratory Keys to a Small Spot ●Low source emittance ●Optimal convergence angle Source of emittance growth: ●Geometric Aberration ●Magnetic transport mismatch ●Efficient neutralization —plasma plug —volume plasma

The Heavy Ion Fusion Virtual National Laboratory Low emittance Source

The Heavy Ion Fusion Virtual National Laboratory Extraction of Uniform High Brightness Beam from NTX Injector Increased Source Temperature (~185W) Aperturing Smooth source surface Unapertured beam Lower Temperature source (~160w ) Uneven source

The Heavy Ion Fusion Virtual National Laboratory Aperturing for High-brightness and High Perveance beam Designed by EGN code EGN simulation of NTX diode &beam aperture NTX beam scraper system

The Heavy Ion Fusion Virtual National Laboratory NTX Provides low emittance beam (300kV, 25 mA, 2-cm aperture). Slit-integrated density profile and (x, x’) phase space of a high- brightness apertured beam (300kV, 25 mA, 2-cm aperture).

The Heavy Ion Fusion Virtual National Laboratory Magnetic final focus

The Heavy Ion Fusion Virtual National Laboratory Magnetic Final Focus Transport Final FocusChamber Transport A schematic of the NTX beam line setup ●Perveance is the key parameter for final focus and neutralization ●NTX covers range of perveance relevant to the driver (K≤10 -3 ).

The Heavy Ion Fusion Virtual National Laboratory Good agreement between Experimental and Theoretical Beam profile at Entrance of Final Drift Section Simulation Experiment 191keV 401keV 265 keV 283 keV (1.5 mA beam, 5 mm initial radius, Ne ~ 1.2x10 11 /cm 3, 20mm-20mr)

The Heavy Ion Fusion Virtual National Laboratory Measured and Calculated Beam Profiles Agreed Well 265keV 283keV Horizontal density profile Vertical Horizontal Vertical

The Heavy Ion Fusion Virtual National Laboratory Typical NTX Ion Beam is Focused to the Final Drift Section for Neutralization (24 mA Beam Current) Experimental results and simulations of NTX beam profile and phase-space distribution at exit of channel

The Heavy Ion Fusion Virtual National Laboratory Neutralized drift

The Heavy Ion Fusion Virtual National Laboratory LSP predicted Neutralized Reduces Beam Spot No neutralization 1.5 cm Plasma Plug 1.4 mm Plasma Plug + Volume 1 mm 300 keV, 25 mA, 0.1 pi-mm- mrad, K + beam

The Heavy Ion Fusion Virtual National Laboratory Unexpected Partial Beam Neutralization in the Final Drift Section was controlled by a Radial Bias Mesh 6 inch pipe3 inch pipe Unwanted neutralization for “vacuum” propagation in small pipe Electron current collected in the radial mesh Radial mesh suppresses beam- Generated secondary electron Phase III Phase II Phase I

The Heavy Ion Fusion Virtual National Laboratory Electron Suppression provided beam for controlled Neutralization Simulation Experiment 6 inch pipe Experiment 3 inch pipe Mesh (+1kV) 260 – 300keV

The Heavy Ion Fusion Virtual National Laboratory MEVVA Plasma Plug and RF Volume Plasma Source Neutralized Ion Beam for Small Spot Size MEVVA plug RF Plasma system a) b) c) Neutralization drift section

The Heavy Ion Fusion Virtual National Laboratory High Density Plasma Obtained from MEVVA Plasma plug and RF Plasma (~10 11 cm -3) Argon Plasma 3.7<t<4.0mS N>10 11 cm -3 P<10 -5 Torr Neutral Pressure and RF Plasma Density Each point on the IV characteristic for MEVVA plug. The ion saturation current is used for plasma density. Density ~10 11 cm -3

The Heavy Ion Fusion Virtual National Laboratory Reduction of Spot Size Using Plasma Plug & Volume Plasma (24 mA beam, 20 mm initial radius) FWHM: 2.71 cm FWHM: 2.83 mm FWHM: 2.14 mm Non-neutralized transport Effect of plasma plug on spot size Effect of plasma plug and volume plasma on spot size

The Heavy Ion Fusion Virtual National Laboratory 100% Current Transmission Through Neutralized Drift Section (24 mA Beam)

The Heavy Ion Fusion Virtual National Laboratory *Image taken after pinhole sample has drifted 1 meter Vertical Pinhole Scan Full 2-D Pinhole Scan 7 mm Pinhole scan at Entrance to Neutralization* and Neutralized beam (6 mA beam, Ne ~ 2x10 11 /cm 3 ) Neutralized beam rms size ~ 1.0 mm rms size ~ 1.4 mm Plasma density ~ 2x10 11 /cm 3 Movable Pinhole Measurements of 4-D Phase Space

The Heavy Ion Fusion Virtual National Laboratory Beam profile at focal plane for three neutralization methods (6 mA beam, 10mm initial radius) MEASUREMENT SIMULATIONS With plasma plug and RF Plasma 100% neutralization MEVVA ONLY 100% neutralized MEVVA and RF Fluence MEVVA ONLY 100% neutralized MEVVA and RF

The Heavy Ion Fusion Virtual National Laboratory Sensitivity Study: Beam Spot Size Dependency on Convergence Angle Non neutralized beam radius as a function of convergence angle calculated using WARP code Measured neutralized beam radius as a function of convergence angle at the end of final focus

The Heavy Ion Fusion Virtual National Laboratory Sensitivity Study of Neutralization Head to tail variationVariation with beam energy Beam envelope variation with axial position Beam envelope variation with plasma discharge voltage

The Heavy Ion Fusion Virtual National Laboratory Summary ●We have completed a detailed study of neutralized final transport. ● The experimental results are in good agreement with simulations. ● The NTX experiments have significantly increased our confidence for a variable driver final focused scenario.