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DNB Program

DNB Program. W.L. Rowan, D. Beals, R.V. Bravenec, M.B. Sampsell, D.M. Patterson Fusion Research Center, University of Texas at Austin G. Schilling, G. Kramer, R. Feder Princeton Plasma Physics Laboratory H. Yuh, D.R. Terry, B. Lipschultz, J. Rice, J. Terry, E. Marmar R. Granetz

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DNB Program

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  1. DNB Program W.L. Rowan, D. Beals, R.V. Bravenec, M.B. Sampsell, D.M. Patterson Fusion Research Center, University of Texas at Austin G. Schilling, G. Kramer, R. Feder Princeton Plasma Physics Laboratory H. Yuh, D.R. Terry, B. Lipschultz, J. Rice, J. Terry, E. Marmar R. Granetz MIT Plasma Science and Fusion Center Alcator C-Mod PAC Meeting 6-7 Feb 2002

  2. Recommendations of last year’s reviews PAC review • – R. Granetz • Appoint C-Mod DNB coordinator • CXRS highest priority (V and Ti) • Measure beam re-ionization and attenuation in duct • Make definitive decision on DNB and diagnostics, and whether to consider deployment of alternate approach • – tried, but signal-to-ambient very low • – not a major problem • – get new beam; upgrade optics DNB review • Condition source & reduce water by increasing source operation time • Add diagnostics in duct (H diodes, pressure gauges) to check for exponential re-ionization. Consider pumped duct. • Add shutters to CXRS to prevent coating • Repair/upgrade MSE/BES optics • – did not help • – pumped duct rejected • – worked well • – repaired, but other components eventually failed

  3. DNB full-energy component unimproved Despite extensive conditioning efforts, • Component fractions: 0.13/0.32/0.48/0.07 • Not understood • Note: no runaway re-ionization observed in duct

  4. 5000 4000 3000 radiance (arbitrary units) 2000 before and after beam 1000 during beam 4944.65, (6-7), B V 0 4936 4940 4944 4948 wavelength (A) CXRS Boron Spectrum • Best result: visible B+4 line shows 2 enhancement with beam • High plasma background line is symptomatic of high density • Fine structure and Zeeman splitting greatly complicate analysis

  5. BES Edge Fluctuation Measurements Beam On: • Dominant features are MSE PEM harmonics and fluctuations in plasma background lines (mostly carbon lines) Beam Off:

  6. MSE Results at Low Density • Blue - Raw (shifted) MSE pitch angles. • Green - EFIT calculated pitch angles • Red - MSE data fitted to EFIT over several shots to obtain “artificial” calibration. • Suffers from low S/N. 2° error still far larger than the 0.1°– 0.2° desired. • Increase in beam full-energy component would greatly improve signals

  7. MSE/BES optics problems • One of the in-vessel mirrors had loosened • Overall transmission efficiency was found to be only 27% , presumably due to glass dust and loose optics

  8. Synopsis of DNB diagnostic difficulties • The difficulties obtaining useful physics from the DNB systems on C-Mod are basically due to the following factors: • Low full-energy fraction in beam (MSE, also BES) • Low overall intensity (CXRS, MSE, BES) • Partly due to problems with optical transmission • Large background plasma line emission (CXRS, BES) • Characteristic of high-density plasmas. • Averaging over longer beam pulse won’t help

  9. The RFX DNBI • Beam parameters (cold cathode source): • 50 kV • 3 A equiv neutral current (~5.5 A ion current) • 1/e diameter of 6 cm at 3.4 m (present beam is  10 cm) • 90+ % full-energy fraction • 50 ms pulse length (possibly extendible to 100 ms) • Built at Budker Institute in Novosibirsk, Russia • Loaned to MIT until Spring 2004 (2 years) • Also involves scientific collaboration with RFX

  10. The RFX DNBI

  11. Planned Installation of RFX beam on C-Mod

  12. Installation of RFX beam on C-Mod • Budker Institute sending a team of 11 staff to install their DNBI hardware (headed by A. Ivanov) • Fee to Budker Institute is $75K for shipping, installation, and commissioning • Schedule: • 24 Jan 2002: injector left Novosibirsk • 6,7 Feb: injector arrives at MIT • 17 Feb: Budker team arrives and begins installation • 2nd week of March: commission DNBI • Texas beam hardware has been dismantled, cannibalized • Visit to Madison last Nov to observe similar installation process

  13. Calculated MSE performance comparison RFX beam Texas beam • RFX beam provides large improvement in MSE signal-to-noise • Improved MSE/BES optics also improves S/N • 0.2° resolution in polarization angle at r/a=0.15 at low density

  14. Expected improvements in CXRS and BES • Improved beam helps, but not as much as for MSE: • CXRS utilizes all beam energy components (Of course, the full-energy component penetrates farther into the plasma.) • BES can utilize any of the beam energy components, although the full-energy peak is not contaminated by carbon lines on C-Mod • Repairs and improvements to optics will increase overall signal levels •  5 for BES  should detect 1% ñ/n for r/a  0.8 •  2-3 for MSE • New spectrometer and detector will increase overall signals levels •  25 for CXRS  enable Ti andV measurements

  15. Additional improvements in progress • Re-design and re-build MSE/BES in-vessel optics • Improve optical throughput 2-3 (new components) • Make MSE polarizer removable(>2 throughput for BES) • Reduce stray polarization characteristics (MSE background) • Reduce vignetting of innermost MSE views • More robust mirror mounts • Ease in-vessel installation • New CXRS spectrometer (improved throughput) • Increase number of edge poloidal views (6  25) • Re-direct CXRS toroidal views to concentrate on outer half (?)

  16. Summary of predicted improvement • The combination of: • Installing the RFX DNBI, and • Improving the optical throughput by a factor of ~3–5 • will greatly improve the performance of all the DNB diagnostics. • We are in the process of doing both of these upgrades in time for the beginning of the next run campaign. • There are still issues concerning • the spatial resolution of the central MSE views, and • the density range for central MSE

  17. 5-Year Plans • Assuming the upgraded DNB systems prove to be successful, • A long pulse DNB injector would be desired: • 1-2 s pulse length • High current density • High full-energy component • About the same energy (50 kV) • Cost would be of order 106 $ • A different view for central MSE (more  to beam), to improve the spatial resolution • Core measurement at high densities would still be problematic

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