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NDCX beam experiments and plans Peter Seidl Lawrence Berkeley National Laboratory, HIFS-VNL

NDCX beam experiments and plans Peter Seidl Lawrence Berkeley National Laboratory, HIFS-VNL.

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NDCX beam experiments and plans Peter Seidl Lawrence Berkeley National Laboratory, HIFS-VNL

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  1. NDCX beam experiments and plansPeter SeidlLawrence Berkeley National Laboratory, HIFS-VNL …with A. Anders1, J.J. Barnard2, F.M. Bieniosek1, J. Calanog1,3, A.X. Chen1,3, R.H. Cohen2, J.E. Coleman1,3, M. Dorf4, E.P. Gilson4, D.P. Grote2, J.Y. Jung1, I. Kaganovich4, M. Leitner1, S.M. Lidia1, B.G. Logan1, S. Markadis1, P. Ni1, P.K. Roy1, K. Van den Bogert1, J.L. Vay1, W.L. Waldron1, D.R. Welch5 1Lawrence Berkeley National Laboratory 2Lawrence Livermore National laboratory 3University of California, Berkeley 4Princeton Plasma Physics Laboratory 5Voss Scientific, Albuquerque 11th Japan - US Workshop December 18, 2008 Berkeley, USA

  2. Outline • 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

  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+, Ibeam = 1 A (40X compression) tbeam = 2ns FWHM rbeam = 0.5 mm, E = 0.1 J/cm2Etotal = 0.8 mJ, Qbeam = 2.3 nC • Later, for uniformity, experiments at the Bragg peak using Lithium ions

  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

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

  6. NDCX-1 has demonstrated simultaneous transverse focusing and longitudinal compression • Ei = 0.3 MeV K+ • Ii = 25 mA K+ injector E = 280-350 keV I = 26-37 mA FEPS IBM diag. #1 diag. #2 Matching solenoids & dipoles Objectives: Preservation of low emittance, plasma column with np > nb, (ni = 0.07 mm-mrad, nb-init ≈ 109 /cm3, nbmax ≈ 1012 /cm3 now, later, ≈ 1013 /cm3)

  7. Beam diagnostics - improved Fast Faraday Cup: lower noise and easier to modify Front plate • 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 bias plate plasma collector • 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. K+ beam vb = 1.2 mm/ns 0V -150<V<-50 50<V<-150 Hole plate front view zoomed view

  8. Beam diagnostics in the target chamber: Fast faraday cup window Biased hole plate collector front hole plate K+ beam • Example waveform vb = 1.2 mm/ns 4 Al plasma sources <Z> = 1.7 • Ibeam = Icollector x (transparency)-1 • = 35 mA x 44 = 1.5 A peak.

  9. 10ns gate 10mm Beam diagnostics in the target chamber: scintillator + CCD or streak camera, photodiode • Al2O3 wafer with hole plate: • Hole plate to • reduce beam flux: less damage • prevent charge buildup. • Image intensified CCD camera using 2 < t <500 ns gate. window Biased hole plate scintillator Al2O3 PI-MAX CCD camera K+ beam • 10-20 pixels/mm typ. Optical fiber vb = 1.2 mm/ns V≈-300 V Streak camera 4 Al plasma sources <Z> = 1.7 photodiode

  10. Simultaneous longitudinal compression and transverse focusing, compared to simulation. Net defocusing in gap due to energy change, Er WARP Calculation LSP Calculation Experiment (m) Angle at entrance to bunching module 7.5 mr 13.5 mr (m) B (T) 2.6 1.4 0.6 2.3 z (m)

  11. Preliminary analysis of latest measurements show a smaller focused spot: R(50%) = 1 mm. 10ns gate 6mm ≈10 mJ/cm2 (compared to previous 4 mJ/cm2) Uncompressed Higher plasma density near the focal plane. 5 Tesla --> 8 Tesla final focusing solenoid. 2 ns fwhm 400 ps slices

  12. LSP simulation of drift compression

  13. With the new bunching module, the voltage amplitude and voltage ramp duration can be increased. FEPS etraps New bunching module 12 --> 20 induction cores --> higher ΔVΔt FEPS = ferro-electric plasma source Beam experiments in 2009.

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

  15. Calculations support a longer IBM waveform with twice the drift compression length 8 T solenoid FCAPS plasma IBM Velocity ramp • Comparison of LSP, the envelope-slice model, and the simple analytic model. • no final focusing solenoid. • New IBM, the final focusing solenoid (Bmax = 8 Tesla) Ldrift =144 cm, present setup • with twice the drift compression length (L=288 cm) as the present setup. etraps Drift compression in Ferro-electric plasma source

  16. The improved cathodic arc plasma source (CAPS) injection has led to a higher plasma density near the target • Plasma density > 1013 / cm3 after modifications to CAPS: straight filters,2 --> 4 sources, increased Idischarge Plasma density beam density Target plane

  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.

  18. Warp simulation of plasma injection from Cathodic-Arc Plasma Sources Warp Warp t = 7.5 s Bmax = 8 T Experiment includes calculated Eddy fields (Ansys transient model).

  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.

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

  21. Insulators R Beam V= 0 +V 0 +V 0 +V 0 +V 0 P Electrodes 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.

  22. Example of envelope model approach to time-dependent corrections to chromatic aberrations Target plane = 572 cm

  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 10-4 ) --> 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

  24. backup slides

  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.

  26. Minimum spot size @ same time as peak compression 2X reduction in the spot size (4X increase in beam intensity) brings the peak beam density to the range nb ≈1011-1012 cm-3.

  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. Y dipole (inside) 3 dipole pairs between solenoids Beam Imax ~ 200 A Bmax ~ 0.5 kG

  28. 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 Errors: Average centroid orbit All Solenoids: Dispacements +tilts Solenoids: tilts only Solenoids: displacements only. Initial conditions only (ion source) 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

  29. Increasing velocity tilt increases the peak current. Chromatic effects --> larger spot radius. Longitudinally, phase space undergoes rotation during drift compression; <(dv/v)2>1/2 limits final bunch length Transversely, spot radius determined by emittance + chromatic aberrations DV Higher momentum trajectory Drift Compression Lower momentum trajectory Envelope (average) r Tilt imposed Velocity spread before compression z Minimum Spot radius Dvtilt Energy deposition (J/cm2): Length of beam prior to compression Length of beam after compression  = v/v, e = beam energy, f = final solenoid focal length

  30. 45 degree view -- zoomed field lines only Solenoid coil B lines Plasma sources target

  31. Optical Analysis Uncompressed Uncompressed radii + 2.55mm + 1.71mm 10ns gate 6mm 10ns gate

  32. Spot size variations with camera gate

  33. 10ns Gate Totals (over 20ns) 1.70 mJ 22.1 mJ/cm2 14.1 mJ/cm2

  34. 2ns Gate Totals (over 20ns) 1.12 mJ 10.46 mJ/cm2 6.23 mJ/cm2

  35. Beam fluence from lineout 10ns gate 2ns gate 10mm 10mm

  36. Beam Steering Jitter 50% radius 0.75mm 1.0mm 2.5mm

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