Charge exchange and spectroscopy with isolated highly-charged ions
Charge exchange and spectroscopy with isolated highly-charged ions Nicholas D. Guise Samuel M. Brewer, Joseph N. Tan Quantum Measurement Division National Institute of Standards and Technology Gaithersburg, MD 20899 8 June 2012
Overview GoalEngineer highly-charged ions (HCI) of interest in metrology, astrophysics,plasma diagnostics, and collision studies q/m Basic Scheme analyzing magnet fs comb 1) Extract HCI from EBIT source ion 2) Recapture in Penning trap trap laser ions 3) Study recaptured ions -charge exchange -optical spectroscopy CX beam MCP detector EBIT (electron beam ion trap)
Permanent Magnet Penning Traps One-Magnet Trap Two-Magnet Trap• B field provided by one NdFeB magnet • B field more homogeneous near center• Magnet also functions as ring electrode • Holes in ring provide optical access• Simple construction with copper endcaps • Iron electrodes shape field profile J.N. Tan, S.M. Brewer, and N.D. Guise, Rev. Sci. Instrum. 83, 023103 (2012)
Experiment Region TOF Detector: 8 mm diameter Photomultiplier <1 ns rise time TubeNe10+ Beam Spot Time-of-Flighton Position-Sensitive MCP MCP Detector (TOF), on retractable translator XY Position Sensitive MCP 1-Magnet Detector Penning Trap 2-Magnet RF Trap/ Penning Trap Lens/Filter
Ion Capture and Detectiont=0 t=tcapture ≈ 17 µs t=tstorage ≈ 200ms t ≈ tstorage+1 µsextract ions pulse trap closed pulse trap open ions arrive at MCPfrom EBIT to capture ions to dump ions detectorEBIT MCP capture dump applied voltage Front Endcap Ring Back Endcap
Ion Charge Exchange sum of all bare Ne charge state evolution charge states nuclei H-like Ne He-like Ne10+ Ne bare Ne only nuclei Parameters H-like Two-Magnet Trap Ne He-like Ne V0 ≈ 2.5 kV∆V=Vring-Vendcap = 25 V
Ion Storage: Pressure Dependence Parameters Two-Magnet Trap V0≈ 2.5 kV ∆V=Vring-Vendcap = 25 V
Long-Term Focus: H-like ions in Circular Rydberg States • Theory more accurate than for Electron Probability Hydrogen S states due to: Distribution • negligible interactions with the nucleus • accuracy of calculated corrections, including QED effects • |n› → |n-1› transitions are accessible to optical frequency combnucleus: Ze+ electron state: | n,l,m › |m|=l=n-1 U.D. Jentschura, P.J. Mohr, J.N. Tan, and B.J. Wundt, Phys. Rev. Lett. 100, 160404 (2008).
New Apparatus for Low Charge StatesElectrongun Ion 18 mm production TOF detector region Experiment region with two-magnet Penning trap
Summary• Unitary architecture NdFeB Penning traps are used to capture and store highly charged ions extracted from the NIST EBIT.• Captured ion species include Ne10+, Ne9+, Ne8+, Ar16+, Ar15+, Ar14+, Ar13+, N7+, and Kr17+.• Ion storage times of order 1 second are limited primarily by collisions with residual gas at 300 K.• Ongoing experiments include studies of charge exchange, optical measurements of metastable lifetimes (upcoming talk by S. Brewer).• New apparatus will utilize similar NdFeB construction for a room- temperature “mini-EBIT” source, for planned spectroscopy with low-Z hydrogen-like ions.