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Charge exchange and spectroscopy with isolated highly-charged ions
1. 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
2. Overview
Goal
Engineer 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)
3. 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)
4. Experiment Region
TOF Detector:
8 mm diameter
Photomultiplier
<1 ns rise time
Tube
Ne10+ Beam Spot Time-of-Flight
on 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
5. Ion Capture and Detection
t=0 t=tcapture ≈ 17 µs t=tstorage ≈ 200ms t ≈ tstorage+1 µs
extract ions pulse trap closed pulse trap open ions arrive at MCP
from EBIT to capture ions to dump ions detector
EBIT MCP
capture
dump
applied voltage
Front Endcap Ring Back Endcap
8. 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
9. Ion Storage: Pressure Dependence
Parameters
Two-Magnet Trap
V0≈ 2.5 kV
∆V=Vring-Vendcap = 25 V
10. 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 comb
nucleus: 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).
11. New Apparatus for Low Charge States
Electron
gun Ion 18 mm
production TOF detector
region
Experiment region
with two-magnet
Penning trap
12. 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.