The Heavy Ion Fusion Science Virtual National Laboratory 1 PRoy LINAC06 Neutralized Drift Compression and Related Experiments* P. K. Roy 1, W. L. Waldron 1, S. S. Yu 1, P. A. Seidl 1, E. Henestroza 1, J. Coleman 1, A. Anders 1, D. Baca 1, J. J. Barnard 2, F. M. Bieniosek 1, R. J. Briggs 3, C. Celata 1, R. C. Davidson 4, P. C. Efthimion 4, S. Eylon 1, A. Friedman 2, E. P. Gilson 4, W. G. Greenway 1, D. P. Grote 2, I. Kaganovich 4, M. Leitner 1, B. G. Logan 1, H. Qin 4, L.L. Reginato 1, A. B. Sefkow 4, W. M. Sharp 2, C. Thoma 5 and D. R. Welch 5 1 Lawrence Berkeley National Laboratory, 2 Lawrence Livermore National Laboratory, 3 SAIC, 4 Princeton Plasma Physics Laboratory, 5 Voss Scientific, for HIFS-VNL, USA *This work was supported by the US-DOE

The Heavy Ion Fusion Science Virtual National Laboratory 2 PRoy LINAC06 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

The Heavy Ion Fusion Science Virtual National Laboratory 3 PRoy LINAC06 Beam compression: Why?

The Heavy Ion Fusion Science Virtual National Laboratory 4 PRoy LINAC06 The HIF Driver/WDM experiments require beam compressions to hit mm-sized spot with ns pulse HIF DriverWDM Beam~40 kA (~4GeV) ~200A (~23MeV) Beam number ~1201 Focal spot 2 mm1 mm Pulse length ~10 ns~1 ns HIF Driver One concept of WDM facility: NDCXII

The Heavy Ion Fusion Science Virtual National Laboratory 5 PRoy LINAC06 Beam compression: How?

The Heavy Ion Fusion Science Virtual National Laboratory 6 PRoy LINAC06 Neutralized beam transport (NTX) & drift compression (NDCX) can provide ~mm spot with ~nsec pulse ●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. ●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. NDCX Time Current NTX

The Heavy Ion Fusion Science Virtual National Laboratory 7 PRoy LINAC06 Neutralized Transport Experiment (NTX)

The Heavy Ion Fusion Science Virtual National Laboratory 8 PRoy LINAC06 Neutralized transport experiment completed with quantitative agreement between simulation &experiment FWHM: 2.71 cm Un-neutralized FWHM: 2.14 mm Neutralized (CAP+RF) CAP ONLY 100% neutralized CAP and RF Measurement CAP ONLY 100% neutralized CAP and RF Theory ( LSP) CAP source (Plasma plug) RF source (Volume plasma)

The Heavy Ion Fusion Science Virtual National Laboratory 9 PRoy LINAC06 Neutralized Drift Compression Experiment (NDCX)

The Heavy Ion Fusion Science Virtual National Laboratory 10 PRoy LINAC06 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, n p /Zn b >1, where n p is the plasma density, and n b and Z are the ion beam density and charge state.

The Heavy Ion Fusion Science Virtual National Laboratory 11 PRoy LINAC06 The NDCX experimental setup NDCX uses many components of the former NTX Pulsed cathodic arc plasma (CAP) source Plasma column consists of a 1m long solenoid (~1kG & 7.6 cm diameter). Basic concept of a module Induction core with head to tail voltage ramp (imposing a velocity “tilt” on the beam)

The Heavy Ion Fusion Science Virtual National Laboratory 12 PRoy LINAC06 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.

The Heavy Ion Fusion Science Virtual National Laboratory 13 PRoy LINAC06 3 Fast (ns) diagnostic systems for NDCX Phototube (<1 ns) Faraday Cup (~3ns) Optical imaging (1ns) gating Beam 5 cm Beam Sampling A. Sefkow et al. PRSTAB 9,(2006) F. Bieniosek et al. PAC ‘05

The Heavy Ion Fusion Science Virtual National Laboratory 14 PRoy LINAC06 Plasma is essential for high beam compression

The Heavy Ion Fusion Science Virtual National Laboratory 15 PRoy LINAC06 50-fold * compression measured Phototube signal with & without compression Compression ratio Obtained using phototube 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

The Heavy Ion Fusion Science Virtual National Laboratory 16 PRoy LINAC06 Beam stability test with 2-m drift section 2m ● 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. using phototube ●Longitudinal beam temperature: ~1eV ●No evidence of two- stream degradation or collective instabilities

The Heavy Ion Fusion Science Virtual National Laboratory 17 PRoy LINAC06 Spot size increases at maximal compression due to time dependent defocusing at gap At peak compression Experiment Simulation

The Heavy Ion Fusion Science Virtual National Laboratory 18 PRoy LINAC06 Pulse Line Ion Accelerator (PLIA)

The Heavy Ion Fusion Science Virtual National Laboratory 19 PRoy LINAC06 First beam dynamics validation experiment for the Pulse Line ion Accelerator (PLIA) At peak compression Experimental setup

The Heavy Ion Fusion Science Virtual National Laboratory 20 PRoy LINAC06 Beam energy modulation of -80 to +150 keV was measured using a PLIA input voltage waveform of -21 to +12 kV At peak compression Beam energy: Helix un-powered Marx voltage Longitudinal time-energy Phase-space Beam energy: Helix powered Experiment Simulation Voltage waveform at the exit of the helix Experiment Simulation Beam current amplification

The Heavy Ion Fusion Science Virtual National Laboratory 21 PRoy LINAC06 An example of how the PLIA can accelerate whole bunches, a short pulse was accelerated At peak compression Helix powered Helix un-poweredMarx voltage

The Heavy Ion Fusion Science Virtual National Laboratory 22 PRoy LINAC06 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, (2005)]. ● Significant energy amplification has been achieved with a modest voltage pulse on the PLIA. [Roy et al., Phys. Rev. ST Accel. Beams, 9, (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.

The Heavy Ion Fusion Science Virtual National Laboratory 23 PRoy LINAC06  BACK UP

The Heavy Ion Fusion Science Virtual National Laboratory 24 PRoy LINAC06 NDCX Depends on the simultaneous pulsing of Marx, quadrupoles, tilt core, plasma channel & plasma gun

The Heavy Ion Fusion Science Virtual National Laboratory 25 PRoy LINAC06 Beam bunching observed as tilt voltage waveform turned on Induction module voltage waveforms produced by varying the timing of the modulators The degree of bunching, as well as the pulse shape, is correlated with the voltage waveform.

The Heavy Ion Fusion Science Virtual National Laboratory 26 PRoy LINAC06 Typical NTX ion beam is focused to the final drift section for neutralization and compression (24 mA I b ) Experimental results and simulations of NTX beam profile and phase-space distribution at exit of channel  n =0.050  -mm-mr (measured), from source temperature alone  n  -mm-mr