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Neutralized Drift Compression and Related Experiments*

Neutralized Drift Compression and Related Experiments*.

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Neutralized Drift Compression and Related Experiments*

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  1. Neutralized Drift Compression and Related Experiments* P. K. Roy1, W. L. Waldron1, S. S. Yu1, P. A. Seidl1, E. Henestroza1, J. Coleman1, A. Anders1, D. Baca1, J. J. Barnard2, F. M. Bieniosek1, R. J. Briggs3, C. Celata1, R. C. Davidson4, P. C. Efthimion4, S. Eylon1, A. Friedman2, E. P. Gilson4, W. G. Greenway1, D. P. Grote2, I. Kaganovich4, M. Leitner1, B. G. Logan1, H. Qin4, L.L. Reginato1, A. B. Sefkow4, W. M. Sharp2, C. Thoma5 and D. R. Welch5 1Lawrence Berkeley National Laboratory, 2Lawrence Livermore National Laboratory, 3SAIC, 4Princeton Plasma Physics Laboratory, 5Voss Scientific, for HIFS-VNL, USA *This work was supported by the US-DOE

  2. Overview ● Beam compression: Why ? --For HIF Driver & Warm dense matter (WDM) experiments ● Beam compression: How ? 1. Neutralized Transport Experiment (NTX) (for transverse beam compression) 2. Neutralized Drift Compression Experiment (NDCX) (for longitudinal beam compression) ● New beam acceleration technique --Pulse Line Ion Accelerator (PLIA) --First beam dynamics validation experimental results

  3. Beam compression: Why?

  4. The HIF Driver/WDM experiments require beam compressions to hit mm-sized spot with ns pulse HIF Driver One concept of WDM facility: NDCXII

  5. Beam compression: How?

  6. Neutralized beam transport (NTX) & drift compression (NDCX) can provide ~mm spot with ~nsec pulse ●NTX: In beam neutralization, electrons from a plasma or 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 to a small spot. NTX ●NDCX: In neutralized drift compression beam is longitudinally compressed by imposing a linear head-to-tail velocity tilt to a drifting neutralized beam and producing a pulse duration of several ns. NDCX Current Time

  7. Neutralized Transport Experiment (NTX)

  8. Measurement Theory ( LSP) 100% neutralized 100% neutralized CAP and RF CAP and RF CAP ONLY CAP ONLY Neutralized transport experiment completed with quantitative agreement between simulation &experiment Un-neutralized Neutralized (CAP+RF) FWHM: 2.14 mm FWHM: 2.71 cm CAP source (Plasma plug) RF source (Volume plasma)

  9. Neutralized Drift Compression Experiment (NDCX)

  10. Concept of longitudinal beam compression Induction module voltage waveform Plasma neutralization Compressed beam bunch has higher space charge density than uncompressed beam bunch section. This higher space charge can contribute to beam blow-up before reaching the target or diagnostic location. Therefore, the compressed beam must be neutralized with an appropriate plasma density. Typically, np/Znb>1, where np is the plasma density, and nb and Z are the ion beam density and charge state.

  11. The NDCX experimental setupNDCX uses many components of the former NTX Basic concept of a module Induction core with head to tail voltage ramp (imposing a velocity “tilt” on the beam) Plasma column consists of a 1m long solenoid (~1kG & 7.6 cm diameter). Pulsed cathodic arc plasma (CAP) source

  12. NDCX setup & induction module voltage waveform Theory specifies the ideal voltage waveform required to produce an exactly linear longitudinal velocity ramp. The induction module voltage waveform is optimized to obtain a rather close approximation to the ideal waveform.

  13. Beam 3 Fast (ns) diagnostic systems for NDCX Phototube (<1 ns) F. Bieniosek et al. PAC ‘05 Sampling Faraday Cup (~3ns) 5 cm A. Sefkow et al. PRSTAB 9,(2006)052801 Beam Optical imaging (1ns) gating

  14. Plasma is essential for high beam compression

  15. 50-fold* compression measured Compression ratio Obtained using phototube Phototube signal with & without compression Compression ratio obtained using Faraday cup Compression ratio Obtained using LSP simulation The maximum compression is observed by fine tuning the beam energy to match the voltage waveform and precisely positioning the longitudinal focal point at the diagnostic location. *Slightly different diagnostic and data reduction yield a factor of 60

  16. 2m Beam stability test with 2-m drift section using phototube ● As the drift length is increased, the compression is more sensitive to: -the degree of neutralization and -intrinsic longitudinal temperature. ● If there are any instabilities, e.g. two-stream, they may become evident with longer drift length. ●Longitudinal beam temperature: ~1eV ●No evidence of two- stream degradation or collective instabilities

  17. Spot size increases at maximal compression due to time dependent defocusing at gap At peak compression Simulation Experiment

  18. Pulse Line Ion Accelerator (PLIA)

  19. First beam dynamics validation experiment for the Pulse Line ion Accelerator (PLIA) At peak compression Experimental setup

  20. Beam energy modulation of -80 to +150 keV was measured using a PLIA input voltage waveform of -21 to +12 kV Beam energy: Helix un-powered Voltage waveform at the exit of the helix Longitudinal time-energy Phase-space At peak compression Marx voltage Beam current amplification Beam energy: Helix powered Simulation Experiment Experiment Simulation

  21. An example of how the PLIA can accelerate whole bunches, a short pulse was accelerated At peak compression Marx voltage Helix un-powered Helix powered

  22. Summary ● Radial compression of a neutralized ion beam achieved, increasing current density by a factor of 100 over un-neutralized beam in the Neutralized Transport Experiment (NTX) [One of many references: Roy et al., Phys. of Plasmas 11, 2890 (2004)]. ● 50-fold longitudinal compression of a velocity-ramped, intense neutralized beam to 3ns has been demonstrated. [Roy et al., Physical Review Letters, 95, 234801(2005)]. ● Significant energy amplification has been achieved with a modest voltage pulse on the PLIA. [Roy et al., Phys. Rev. ST Accel. Beams, 9, 070402(2006)]. -We are preparing for experimentally exploring simultaneous transverse and longitudinal compression experiments. -Vacuum flashover, which presently limits the acceleration gradient to ≤150 kV/m, is being investigated.

  23. BACK UP

  24. NDCX Depends on the simultaneous pulsing of Marx, quadrupoles, tilt core, plasma channel & plasma gun

  25. Beam bunching observed as tilt voltage waveform turned on The degree of bunching, as well as the pulse shape, is correlated with the voltage waveform. Induction module voltage waveforms produced by varying the timing of the modulators

  26. Typical NTX ion beam is focused to the final drift section for neutralization and compression (24 mA Ib) n=0.050 -mm-mr (measured), from source temperature alone n 0.030 -mm-mr Experimental results and simulations of NTX beam profile and phase-space distribution at exit of channel

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