Charge exchange and spectroscopy with isolated

highly-charged ions

Nicholas D. Guise

Samuel M. Brewer, Joseph N. TanQuantum Measurement Division

National Institute of Standards and Technology

Gaithersburg, MD 20899

8 June 20128 June 20128 June 20128 June 2012

� GoalEngineer highly-charged ions (HCI) of interest in metrology, astrophysics, plasma diagnostics, and collision studies

� Basic Scheme1) Extract HCI from EBIT source2) Recapture in Penning trap3) Study recaptured ions

-charge exchange-optical spectroscopy

Overview

CX beam

ions

MCP detector

EBIT(electron beam ion trap)

fs comb

q/manalyzing magnet

ion trap laser

One-Magnet Trap• B field provided by one NdFeB magnet• Magnet also functions as ring electrode• Simple construction with copper endcaps

Two-Magnet Trap• B field more homogeneous near center• Holes in ring provide optical access• Iron electrodes shape field profile

Permanent Magnet Penning Traps

J.N. Tan, S.M. Brewer, and N.D. Guise, Rev. Sci. Instrum. 83, 023103 (2012)

XY Position Sensitive MCP Detector

Time-of-Flight MCP Detector (TOF), on retractable translator

2-MagnetPenning Trap

1-MagnetPenning Trap

PhotomultiplierTube

RF Trap/Lens/Filter

Experiment Region

TOF Detector:8 mm diameter<1 ns rise time

Ne10+ Beam Spoton Position-Sensitive MCP

t=0extract ions from EBIT

capt

ure

dump

t=tcapture ≈ 17 µspulse trap closed to capture ions

t=tstorage ≈ 200mspulse trap open to dump ions

t ≈ tstorage+1 µsions arrive at MCP detector

Ion Capture and Detection

Front Endcap Ring Back Endcap

EBIT MCP

ap

pli

ed

vo

lta

ge

Ion Extraction and Capture Timing

Ion Energy

Ion energy ~ 5.5 eV

Ion Charge Exchange

ParametersTwo-Magnet Trap

V0 ≈ 2.5 kV∆V=Vring-Vendcap = 25 V

Ne10+

only

sum of all charge states

charge state evolutionbare Ne nuclei

H-like Ne

bare Ne nuclei

H-like Ne He-like

Ne

He-like Ne

Ion Storage: Pressure Dependence

ParametersTwo-Magnet Trap

V0≈ 2.5 kV∆V=Vring-Vendcap = 25 V

Electron Probability Distribution

electron state: | n,l,m ›

nucleus: Ze+

|m|=l=n-1

• Theory more accurate than for Hydrogen S states due to:• negligible interactions with the nucleus• accuracy of calculated corrections, including

QED effects

• |n› → |n-1› transitions are accessible to optical frequency comb

U.D. Jentschura, P.J. Mohr, J.N. Tan, and B.J. Wundt,

Phys. Rev. Lett. 100, 160404 (2008).

Long-Term Focus: H-like ions in Circular

Rydberg States

New Apparatus for Low Charge States

Ion production region

Experiment region with two-magnet Penning trap

18 mm TOF detector

Electron gun

Summary

• Unitary architecture NdFeB Penning traps are used to capture andstore highly charged ions extracted from the NIST EBIT.

• Captured ion speciesinclude Ne10+, Ne9+, Ne8+, Ar16+, Ar15+, Ar14+,Ar13+, N7+, and Kr17+.

• Ion storage times of order 1 secondare limited primarily by collisionswith residual gas at 300 K.

• Ongoing experiments include studies of charge exchange, opticalmeasurements of metastable lifetimes(upcoming talk by S. Brewer).

• New apparatus will utilize similar NdFeB construction for a room-temperature “mini-EBIT” source, for planned spectroscopywith low-Zhydrogen-like ions.