Laser Spectroscopy studies at the TSR Kieran Flanagan The University of Manchester

The splitting of the hyperfine structure results from the presence of a permanent magnetic field associated with the nucleus and/or a non-symmetric electric field associated with a deformed nuclear charge distribution. Nuclear observables from laser spectroscopy F=J+IF=J+I 2 P 3/2 2 P 1/2 2 S 1/2 FjFj FiFi N N S S If we can measure the splitting of the atomic transitions with sufficient resolution it is possible to deduce the nuclear observables (magnetic and electric moments, spin and size) without any model (nuclear) dependence.  IS =  MS +  FS Isotope Shift Isotope Shift ppm shift

Status of laser spectroscopy Between 1995 and 2010 Before 1995 Z N Laser spectroscopy measurements to date J. Phys. G: Nucl. Part. Phys (1995) J. Phys. G: Nucl. Part. Phys. 37, (2010)

Laser Spectroscopy Laser Beam Sensitive Light detector Closed box of atoms at temperature for a vapour to form ( C) The thermal motion of the atoms broadens the transition, masking the hyperfine structure: Doppler Broadening Frequency Doppler Free Spectroscopy Collinear Laser Spectroscopy Ion source V Mass Separation V Neutralization and scanning voltage Light collection region Laser Beam

Applied Doppler tuning voltage Background due to scattered light PMT Charge exchange Relatively low detection efficiency ~ 1: Large background due to scattered light /s Typical lower limit on yield is 10 6 /s (with a couple of exceptions) ISCOOL z End plate potential Accumulate Release Reacceleration potential PMT 10µs gate 200ms accumulation = 10µs gate width Background suppression ~ min With ISCOOL Counts Tuning Voltage 46 K

Example spectrum - 76 Ga Ungated Gated (64μs - 70μs) Time of flight (50ms accumulation) Background suppression 50ms / 6μs = ~10 4

The heavy ion storage ring TSR at MPIK Heidelberg Circumference: 55m TSR Max Planck Institute Heidelberg

Advantages/Possibilities Possible to utilize highly charged ions with simple alkali-like atomic structures. A single ion in the ring will be probed ~10 5 to 10 6 times per second resulting in a large gain in sensitivity. Opens access to elements only available at ISOLDE via chemical separation techniques, which inhibits access at low energy. Extensive R&D already carried out on the TSR and ESR.

Status of laser spectroscopy Between 1995 and 2010 Before 1995 Z N Laser spectroscopy measurements to date J. Phys. G: Nucl. Part. Phys (1995) J. Phys. G: Nucl. Part. Phys. 37, (2010)

Simple electronic structure Odd-Z elements present a current challenge for extracting changes in the mean-square charge radius from isotope shift measurements. By performing laser spectroscopy on lithium-like or helium- like ions it is possible to perform exactly calculate the field and specific mass shift and extract the charge radius of the isotope. In most cases measuring just 2 or 3 additional unstable isotopes are required to construct a King plot for calibrating transitions in the atom or 1+ ion.

Challenges Deep UV to X-ray photons required to excite Li-like transitions in HCI. Life times of metastable states drops dramatically with increasing Z making spectroscopy in He like ions all but impossible. Stripping to Lithium like ions at 10MeV/A at HIE-ISOLDE will be difficult for heavy elements. Low energy of beams limits Doppler shift effect. Resolution ~few GHz

Example case: ESR Demonstration of C 3+ Doppler shift at the TSR will be ~20-30 nm which is still possible with modern pulsed dye laser systems

Ideal situation Ground state Ideal case alkali-like metastable state populated in the EBIS and long-lived Fast decay to ground state emitting VUV or even soft X-rays would allow clean signal (no laser scattered background) Low J, large HFS nm strong Decay to ground state eV-keV Metastable State

Laser spectroscopy of Li-like ions 2 P 3/2 2 P 1/2 2 S 1/2 280 eV ~1 eV ~0.1 eV 4 keV Uranium Li-like Sn atoms will have a splitting of ~40eV for the S 1/2 -P 1/2 transition At the TSR this requires X-ray lasers. Better suited to DR studies for heavier isotopes.

e-e-  L X Normal Compton Scattering the photon has higher energy than the electron The inverse process has the Thomson cross-section when X e The scattered photon satisfies the undulator equation with period L /2 for head-on collisions energy =  e =   m e X = L (1+  2  2 ) 4242 Therefore, the x-ray energy decreases by a factor of 2 at an angle of 1/  EeEe Head-on collision between a relativistic electron and a photon Inverse Compton Scattering Progress in X-ray lasers David E. Moncton, JLab

A free-electron laser generated  - ray/X-ray source

Parameters of Source Average flux 10 9 photons/sec Source size 50 microns Courtesy of Ron Ruth David E. Moncton, JLab

MIT Inverse Compton Scattering Concept David E. Moncton, JLab

Conceptual Multi-User Facility based on ICS at MIT Coherent enhancement cavity with Q=1000 giving 1 MW cavity power 1 kW cryo-cooled Yb:YAG drive laser Superconducting RF photoinjector X-ray beamline 2 Inverse Compton scattering X-ray beamline 3 X-ray beamline 4 X-ray beamline 1 Electron beam of mA average current at MeV 10 kW beam dump 6 m 8 m Superconducting RF Linac David E. Moncton, JLab

Parameter High average flux Single-shot Tunable monochromatic photon energy [keV]3 – 12 Pulse length [ps]0.1 – 21 – 10 Flux per shot [photons]5 x x Repetition rate [Hz] Average flux [photons/sec]5 x x FWHM bandwidth [%]25 On-axis bandwidth [%]12 Source RMS divergence [mrad]15 Source RMS size [mm] Peak brightness [photons/(sec mm 2 mrad 2 0.1%bw)] 1 x x Average brightness [photons/(sec mm 2 mrad 2 )]3 x x X-ray Source Parameters David E. Moncton, JLab

Beam cleaning with resonant charge breeding Ground state ~visible wavelength Weak decay Metastable state Continuum keV Ground state Continuum High intensity visible wavelength If high lying metastable states are populated (and long-lived enough) a RIS scheme that avoids any strong transitions to the ground state could work Alternatively a resonant X-ray transition to a high lying state (close enough to the continuum) and a high intensity Nd:YAG pulse to non-resonantly ionize the system.

Possibility of higher energy photons? HIγS facility at Duke Univerisity and TUNL MeV photons with, 10 9 /s (10 10 /s max) currently operational Luminosity of /s/cm -2 with a combined TSR numbers and HIγS. New light source concepts offer possibility of /s allowing /s/cm -2 NRF with mb to b cross sections would have /s Consider (γ,p) and event (γ,α) reactions if /s/cm-2 could be realized.

Chiral Dynamics 2012  S  -ray beam generation Circularly and linearly polarized, nearly monoenergetic  rays from 2 to 100 MeV Utilizes Compton backscattering of FEL light to generate  rays Booster Injector LINAC RF Cavity Mirror Optical Klystron FEL

25 X-ray lab location 12m Electron storage ring, and laser laboratory X-ray beam path

Nuclear Resonance Fluorescence High peak cross sections make this an attractive starting place. Tuneable, narrow bandwidth gamma-ray source opens up many possibilities. Polarized gamma-ray light source allows parity and lifetime measurements down to fs. Would require extensive stable beam access in the TSR.

Outlook Laser spectroscopy (electronic transitions) limited to light cases such as Carbon and Boron. Requires deep UV. Li-like transitions in higher Z nuclei will require a compact X-ray laser source and probably better suited to DR studies. The development of a high intensity, narrow bandwidth and polarized X-ray and γ-ray source offers other possibilities – Isomer selection through resonant charge changing interations (RIS) with an X-ray laser. – γ-ray source would open up access to NRF experiments on radioactive isotopes, allow parity and lifetime measurements – Intense γ-ray source + TSR beam spot could allow (γ,p) and (γ,α) reactions.

Thank for you attention

Space charge limit in TSR Incoherent space-charge tune shift Transverse instabilities Maximum beam intensities intensity limit: E (MeV), I (uA), const=279 calculated from the 12 C 6+ data const valid for e-cooled beams So far highest REX beam intensity for light and medium heavy nuclei: 1.2E7 ions/s 10 Be 3+ => = 5.8 epA 3E7 ions/s 110 Sn 27+ => = 130 epA  for 10 MeV/u,  m =0.8, d dilution =2, T lifetime =5 s I TSR ( 10 Be 3+ )  9 uA and I TSR ( 110 Sn 27+ )  200 uA => below the incoherent tune shift limit of ~1 mA Intensities obtained in TSR M. Grieser presentation