NDCX-II Tweaks

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