1 / 25

The polarized target for G E n

The polarized target for G E n. Gordon D. Cates, Jr. University of Virginia Professor of Physics and Radiology. G E n , - October 24, 2003. Target issues. Snuggling up close to Bigbite’s fringe fields. Magnetic shielding No room for the laser hut. More compact laser system.

phiala
Télécharger la présentation

The polarized target for G E n

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. The polarized target for GEn Gordon D. Cates, Jr. University of Virginia Professor of Physics and Radiology GEn, - October 24, 2003

  2. Target issues • Snuggling up close to Bigbite’s fringe fields. • Magnetic shielding • No room for the laser hut. • More compact laser system. • Maintaining performance with high beam current. • Improving polarimetry

  3. The solutions • Field clamp around Bigbite • Magnet based around an iron box • Laser system based around a “5-to-1” combiner. • Cell design with larger pumping chamber. • Perhaps utilize K/Rb hybrid pumping • Electromagnetic shielding (from the iron box) and vibration insulation.

  4. Top view of magnet concept

  5. Bigbite and target/magnet on beamline

  6. Bigbite and target/magnet

  7. Cutaway view showing some elements of the target

  8. Close-up on some elements of the target

  9. The laser system • Existing system • Provides both longitudinal and transverse pumping. • Four fiber array packages (FAPS) for longitudinal pumping. • Three FAPS for transverse pumping. • Total of (4+3)x2=14 beam lines. • Optics in laser hut. • New system • Only one pumping direction required. • System based on “5-to-1” combiner. • Only two beam lines, with all optics housed on the target itself.

  10. Similar laser system on noble-gas polarirzer used for medical imaging

  11. Laser system

  12. View showing laser system together with oven and coils

  13. Laser system

  14. Overview of medical polarizer

  15. Performance summary • Maximum input power without excessive heating: around 3x40=120 Watts. • Power on oven: 93 Watts. • Homogeneity: ok, but not great. • “Diffuser” made by Newport Corp. may be good alternative to Coherent’s new homogenizer. • 200 Watt input power not yet achieved.

  16. Polarimetry issues • Field in iron-box magnet will not be easy to scan. • AFP scans will need to be done scanning the rf frequency and not the field. • This means, among other things, that the lock-in will need to track a changing frequency. • Kentucky system seems to work well, but line-shape is somewhat asymmetric. • Need to convince ourselves we understand the signal if we want to trust it at the 2-3% level.

  17. Kentucky NMR apparatus

  18. Average of 50 water sweeps at Kentucky

  19. Average of 500 water sweeps at Kentucky

  20. Single helium sweep at Kentucky

  21. Rb spin destruction is a major issue when polarizing 3He • Slow spin exchange necessitates very high Rb number densities: 2-10 x 1014 cm-3. • Spin destruction rates mean high laser power. • Laser power itself is less of an issue. • High laser power brings its own problems • Significant heating. • Chemical effects? • Other problems? • New direction: take advantage of slower spin-destruction rates for K, which hence has higher spin-exchange efficiency.

  22. Hybrid (K and Rb) spin-exchange optical pumping • Potassium (K) is about ten times more efficient than rubidium (Rb) at transferring angular momentum from photons to 3He nuclei. • Cells containing a mixture of mostly K and a little Rb greatly improve the efficiency with which the light is used. Data showing dramatically higher spin-exchange efficiency for K (Baranga et al., PRL 80, Pg. 2801 (1998))

  23. What does it all mean? • The spin-exchange rate of K with 3He is about the same as Rb with 3He, but….. • For a given amount of laser power, you can polarize many more alkali-metal atoms using hybrid pumping. • It is unclear how much better performance will be when other effects are taken into account. • But it looks promising!

  24. Where hybrid pumping stands • 1998: Romalis clearly showed indirectly that K efficiency is much better than Rb efficieny. • 2003: Walker and co-workers showed directly K efficiency is much better than Rb efficiency. • A practical target has yet to be demonstrated.

  25. Status and responsibilities • Magnet components will arrive soon. • Assembly and testing: everyone? • Most design work remains on target’s “internal” components, ladder, movement mechanism, etc. • Al Gavalya working with Gordon and Bogdan • Laser system, some questions remain, ready to order some components. • Gordon, Jian-Ping, Bogdan • Polarimetry: many tests remain. • Todd, Wolfgang • Cells: work just beginning. • Jaideep, Gordon

More Related