The Heavy Ion Fusion Virtual National Laboratory 1 NDCX beam experiments and plans Peter Seidl Lawrence Berkeley National Laboratory, HIFS-VNL 11th Japan - US Workshop December 18, 2008 Berkeley, USA …with A. Anders 1, J.J. Barnard 2, F.M. Bieniosek 1, J. Calanog 1,3, A.X. Chen 1,3, R.H. Cohen 2, J.E. Coleman 1,3, M. Dorf 4, E.P. Gilson 4, D.P. Grote 2, J.Y. Jung 1, I. Kaganovich 4, M. Leitner 1, S.M. Lidia 1, B.G. Logan 1, S. Markadis 1, P. Ni 1, P.K. Roy 1, K. Van den Bogert 1, J.L. Vay 1, W.L. Waldron 1, D.R. Welch 5 1 Lawrence Berkeley National Laboratory 2 Lawrence Livermore National laboratory 3 University of California, Berkeley 4 Princeton Plasma Physics Laboratory 5 Voss Scientific, Albuquerque

The Heavy Ion Fusion Virtual National Laboratory 2 Beam requirements Method: bunching and transverse focusing Beam diagnostics Recent progress: longitudinal phase space measured simultaneous transverse focusing and longitudinal compression enhanced plasma density in the path of the beam Next steps toward higher beam intensity & target experiments greater axial compression via a longer-duration velocity ramp time-dependent focusing elements to correct chromatic aberrations Outline

The Heavy Ion Fusion Virtual National Laboratory 3 Explore warm dense matter (high energy density) physics by heating targets uniformly with heavy ion beams Near term: planar targets predicted to reach T ≈ 0.2 eV for two-phase studies. Assumptions for Hydra simulation: E = 350 keV, K +, I beam = 1 A (40X compression) t beam = 2ns FWHM r beam = 0.5 mm, E = 0.1 J/cm 2 E total = 0.8 mJ, Q beam = 2.3 nC Later, for uniformity, experiments at the Bragg peak using Lithium ions

The Heavy Ion Fusion Virtual National Laboratory 4 Approach: High-intensity in a short pulse via beam bunching and transverse focusing The time-dependent velocity ramp, v(t), that compresses the beam at a downstream distance L. Velocity ramp: Induction bunching module (IBM) voltage waveform:, (e  ο = ion kinetic energy.) Measured energy spread is adequate for ~ns bunches. Energy analyzer, unbunched beam IBM voltage waveform Model vs experiment

The Heavy Ion Fusion Virtual National Laboratory 5 Neutralized Drift Compression Experiment (NDCX) with new steering dipoles, target chamber, more diagnostics and upgraded plasma sources Injector Target chamber, beam diagnostics, FCAPS Matching solenoids & dipoles Focusing solenoid IBM & FEPS Beam diagnostics New: steering dipoles, focusing solenoid (8T), target chamber, more diagnostics, upgraded plasma sources FEPS = ferro-electric plasma source CAPS = cathodic-arc plasma sources IBM = induction bunching module

The Heavy Ion Fusion Virtual National Laboratory 6 NDCX-1 has demonstrated simultaneous transverse focusing and longitudinal compression diag. #1 diag. #2 Objectives: Preservation of low emittance, plasma column with n p > n b, (  ni = 0.07 mm-mrad, n b-init ≈ 10 9 /cm 3, n bmax ≈ /cm 3 now, later, ≈ /cm 3 ) E i = 0.3 MeV K + I i = 25 mA IBM Matching solenoids & dipoles K + injector E = keV I = mA FEPS

The Heavy Ion Fusion Virtual National Laboratory 7 Beam diagnostics - improved Fast Faraday Cup: lower noise and easier to modify Requirements: Fast time response (~1 ns) Immunity from background neutralizing plasma Design: 2 hole plates, closely spaced for fast response. Hole pitch (1 mm) & diameter (0.23, 0.46 mm) small  blocks most of the plasma Front plate bias plate collector 0V -150<V<-50 50<V<-150 plasma K + beam v b = 1.2 mm/ns Hole plate front view zoomed view  Metal enclosure for shielding.  Easier alignment of front hole plate to middle (bias) hole plate.  Design enables variation of gaps between hole plates, and hole plate transparency.

The Heavy Ion Fusion Virtual National Laboratory 8 Beam diagnostics in the target chamber: Fast faraday cup Biased hole plate collector 4 Al plasma sources = 1.7 K + beam v b = 1.2 mm/ns window front hole plate Example waveform I beam = I collector x (transparency) -1 = 35 mA x 44 = 1.5 A peak.

The Heavy Ion Fusion Virtual National Laboratory 9 Beam diagnostics in the target chamber: scintillator + CCD or streak camera, photodiode Biased hole plate scintillator V≈-300 V Al 2 O 3 4 Al plasma sources = 1.7 K + beam v b = 1.2 mm/ns PI-MAX CCD camera window 10mm 10ns gate pixels/mm typ. photodiode Streak camera Optical fiber Al 2 O 3 wafer with hole plate: a Hole plate to preduce beam flux: less damage pprevent charge buildup. Image intensified CCD camera using 2 <  t <500 ns gate.

The Heavy Ion Fusion Virtual National Laboratory 10 Simultaneous longitudinal compression and transverse focusing, compared to simulation. 7.5 mr 13.5 mr Net defocusing in gap due to energy change, E r Angle at entrance to bunching module ExperimentLSP Calculation (m) z (m) B (T) WARP Calculation

The Heavy Ion Fusion Virtual National Laboratory 11 Uncompressed Preliminary analysis of latest measurements show a smaller focused spot: R(50%) = 1 mm. 6mm 10ns gate 400 ps slices ≈10 mJ/cm 2 (compared to previous 4 mJ/cm 2 ) 2 ns fwhm Higher plasma density near the focal plane. 5 Tesla --> 8 Tesla final focusing solenoid.

The Heavy Ion Fusion Virtual National Laboratory 12 LSP simulation of drift compression

The Heavy Ion Fusion Virtual National Laboratory 13 With the new bunching module, the voltage amplitude and voltage ramp duration can be increased > 20 induction cores --> higher ΔVΔt Beam experiments in etraps FEPS FEPS = ferro-electric plasma source New bunching module

The Heavy Ion Fusion Virtual National Laboratory 14 It is advantageous to lengthen the drift compression section by 1.44 m via extension of the ferro-electric plasma source ~2x longer drift compression section (L=2.88 m), Uses additional volt- seconds for a longer ramp and to limit  V peak & chromatic effects 2.24 m Ferroelectric plasma source L = 2.88 m New plasma source built

The Heavy Ion Fusion Virtual National Laboratory 15 Calculations support a longer IBM waveform with twice the drift compression length Comparison of LSP, the envelope-slice model, and the simple analytic model. (a) no final focusing solenoid. (b) New IBM, the final focusing solenoid (B max = 8 Tesla) L drift =144 cm, present setup (c) with twice the drift compression length (L=288 cm) as the present setup. etra ps IBM Velocity ramp Drift compression in Ferro-electric plasma source 8 T solenoid FCAPS plasma

The Heavy Ion Fusion Virtual National Laboratory 16 The improved cathodic arc plasma source (CAPS) injection has led to a higher plasma density near the target Plasma density > / cm 3 after modifications to CAPS: straight filters, 2 --> 4 sources, increased I discharge Plasma density beam density Target plane

The Heavy Ion Fusion Virtual National Laboratory 17 Recent simulations show how insufficient plasma density affects the beam intensity at the target Schematic near the target chamber, showing regions where lower plasma density exists in the experiment.

The Heavy Ion Fusion Virtual National Laboratory 18 Warp simulation of plasma injection from Cathodic-Arc Plasma Sources Warp t = 7.5  s B max = 8 T includes calculated Eddy fields (Ansys transient model). Warp Experiment

The Heavy Ion Fusion Virtual National Laboratory 19 Parametric variation of plasma density distributions and the effect on the beam fluence Energy fluence (time integral of beam power over a 10 ns window) from idealized Warp simulations of unbunched beam, showing effects of gap and limited radius plasma.

The Heavy Ion Fusion Virtual National Laboratory 20 Possible changes to the plasma source configuration to improve intensity on target (1) Reducing the gap between the FEPS and the FFS (12 cm  5 cm) (2) compact plasma sources on the beam pipe wall, near the end of the solenoid (3) Collective focusing, Reducing B  0.05 T, & only FEPS plasma (I. Kaganovich talk).

The Heavy Ion Fusion Virtual National Laboratory 21 We are studying time dependent lenses to compensate the chromatic aberrations Ramped electric quadrupole or Einzel lens correction, close to the IBM. Example: V(t) = [100 kV](t/1  s) 1/2 4 periods, P = 6 cm, R = 2 cm 300 kV K + Modulates envelope by ≈20 mr in 1  s. V= 0 +V 0 +V 0 +V 0 +V 0 Beam R P Insulators Electrodes

The Heavy Ion Fusion Virtual National Laboratory 22 Example of envelope model approach to time- dependent corrections to chromatic aberrations Target plane = 572 cm

The Heavy Ion Fusion Virtual National Laboratory 23 The beam characteristics are now satisfactory for target diagnostic commissioning and first target experiments Energy spread of initial beam is low (130 eV / 0.3 MeV = 4 x ) --> good for sub ns bunches. Simultaneous axial compression (≈50x) to 1.5 A and 2.5 ns Beam diagnostics enhanced plasma density in the path of the beam PIC simulations of plasma and beam dynamics Next steps: greater axial compression via a longer velocity ramp while keeping ∆v/v fixed. Additional plasma sources, approaches to overcome incomplete neutralization. time-dependent focusing elements to correct considerable chromatic aberrations

The Heavy Ion Fusion Virtual National Laboratory 24 backup slides

The Heavy Ion Fusion Virtual National Laboratory 25 Example field modifications under consideration to increase plasma transport to the beam path near the target An additional coil near target might increase plasma density just upstream of the target plane.

The Heavy Ion Fusion Virtual National Laboratory 26 Minimum spot same time as peak compression 2X reduction in the spot size (4X increase in beam intensity) brings the peak beam density to the range n b ≈ cm -3.

The Heavy Ion Fusion Virtual National Laboratory 27 Alignment: Beam centroid corrections are required to minimize aberrations in IBM gap & for beam position control at the target plane Alignment survey: mechanical structure aligned within 1 mm. Manufacturing imperfections (coil w.r.t support structure) not included. Observe < 5 mm, <10 mrad offsets at exit of 4 solenoid matching section without steering dipole correction. We can correct the centroid empirically with steering dipoles at the exit of the solenoid matching section. 3 dipole pairs between solenoids I max ~ 200 A B max ~ 0.5 kG Beam Y dipole (inside)

The Heavy Ion Fusion Virtual National Laboratory 28 All Errors: Solenoids: Dispacements +tilts Solenoids: tilts only Solenoids: displacements only. Initial conditions only (ion source) Average centroid orbit Next step: Minimization of the centroid betatron amplitude. Requires knowledge of the absolute offsets. Ensemble of 10,000 random error combinations to estimate sensitivity, Lund, Po-24 Beam centroid measured without dipoles will be used to solve for beamline offsets Beam distribution J(x,y) at exit of 4 solenoid matching section. We plan more measurements to verify this method

The Heavy Ion Fusion Virtual National Laboratory 29 Increasing velocity tilt increases the peak current. Chromatic effects --> larger spot radius. Transversely, spot radius determined by emittance + chromatic aberrations Higher momentum trajectory Lower momentum trajectory Envelope (average) Minimum Spot radius Tilt imposed z VV Drift Compression Length of beam prior to compression Length of beam after compression  v tilt Velocity spread before compression Longitudinally, phase space undergoes rotation during drift compression; 1/2 limits final bunch length rr  =  v/v, e  = beam energy, f = final solenoid focal length Energy deposition (J/cm 2 ):

The Heavy Ion Fusion Virtual National Laboratory degree view -- zoomed field lines only Plasma sources target Solenoid coil B lines

The Heavy Ion Fusion Virtual National Laboratory 31 Uncompressed mm mm Uncompressed radii Optical Analysis 10ns gate 6mm 10ns gate

The Heavy Ion Fusion Virtual National Laboratory 32 Spot size variations with camera gate

The Heavy Ion Fusion Virtual National Laboratory 33 10ns Gate Totals (over 20ns) 1.70 mJ 22.1 mJ/cm mJ/cm 2

The Heavy Ion Fusion Virtual National Laboratory 34 2ns Gate Totals (over 20ns) 1.12 mJ mJ/cm mJ/cm 2

The Heavy Ion Fusion Virtual National Laboratory 35 Beam fluence from lineout 10mm 10ns gate2ns gate

The Heavy Ion Fusion Virtual National Laboratory 36 Beam Steering Jitter 0.75mm1.0mm2.5mm 50% radius