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Enhancements to NDCX-II Design: Precision Tweaks for Improved Beam Performance

This paper outlines recent adjustments to the NDCX-II design aimed at optimizing beam performance through precision tweaks. Key modifications include the correction of the lattice period to 27.94 cm, adjustment of beam-pipe radius to 3.9675 cm, and synchronized ramping of cathode and extractor voltages. The redesign of the injector waveform has led to enhanced initial beam profiles, with current output reaching 43.3 nC and energy increased to 1.22 MeV. The results indicate that these refinements bring the design nearly on par with the original specifications while addressing low-current source longevity issues.

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Enhancements to NDCX-II Design: Precision Tweaks for Improved Beam Performance

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  1. NDCX-II Tweaks • W M Sharp, A Friedman, D P Grote - LLNL • L L Reginato, W L Waldron, J-L Vay - LBNL • 12 January 2011

  2. Aren’t we done already? • ASP initially used approximate sizes • NDCX-II lattice period is 27.94 cm, not 28 cm • beam-pipe radius is 3.9675 cm, not 4 cm • engineers have made minor adjustments to the NDCX-II baseline • cathode and extractor voltages are now ramped together • space has been added between final gap and plasma for solenoid and gate valve • neutralized-drift section design requires beam to focus 1.57 m beyond last gap • all waveforms must be realizable • previous designs assumed low-voltage tailored waveform on first cell to correct energy • ASP obtains good results with the first cell removed... • but • leaving the first cell off degrades the final pulse • changing the 12-cell baseline is problematic at this point

  3. So what’s been done? • the NDCX-II baseline design has had many small tweaks • lattice period and radius have been corrected • plasma neutralization now begins at the proper position • the initial beam profile in ASP is now obtained using the redesigned injector waveform • an realizable approximation to the first-cell waveform has been developed • 3 kV has been added to the cathode voltage • a voltage ramp obtained from low-voltage test circuitry is applied at the first cell gap 1 voltage fitted voltage voltage offset

  4. How well have we done so far? • new baseline appears nearly as good as the original one • current reaching target is 43.3 nC vs 37.3 nC for baseline • duration is 0.65 ns vs 0.52 ns for baseline • energy is 1.22 MeV vs 1.2 MeV for baseline baseline tweaked

  5. What about low-current cases? • a usable low-current design is needed to prolong source lifetime • lithium sources to date require a 1280oC temperature to produce 1 mA/cm2 • the source lifetime is less than 50 hours at that temperature • designs using a 0.5 mA/cm2 source have been developed for alignment and testing phases unaltered baseline fields rescaled fields

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