Superconducting Thin Films For Levitation of NIF Targets 3 rd - - PowerPoint PPT Presentation

▶

Apr 23, 2023 142 likes •354 views

Superconducting Thin Films For Levitation of NIF Targets 3 rd Workshop on Microwave Cavities and Detectors for Axion Research Alex Baker Post-Doctoral Appointee August 22, 2018 LLNL-PRES-748677 This work was performed under the auspices of the

SLIDE 1

LLNL-PRES-748677

This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under contract DE- AC52-07NA27344. Lawrence Livermore National Security, LLC

Superconducting Thin Films For Levitation of NIF Targets

3rd Workshop on Microwave Cavities and Detectors for Axion Research

Alex Baker Post-Doctoral Appointee August 22, 2018

SLIDE 2

LLNL-PRES-748677

NIF Places Fuel Capsules Inside Hohlraums…

SLIDE 3

LLNL-PRES-748677

▪ Fuel capsule must be supported within center of hohlraum ▪ Tents can cause perturbations that affect the implosion

… but Capsule Supports Cause Perturbations

SLIDE 4

LLNL-PRES-748677

Levitation Offers an Alternative

Earnshaw’s Theorem: a collection of point charges cannot be maintained in a stable stationary equilibrium configuration solely by the electrostatic interaction of the charges

Holding capsule in place without supports would allow fully symmetric implosion

SLIDE 5

LLNL-PRES-748677

Levitation Offers an Alternative

Earnshaw’s Theorem: a collection of point charges cannot be maintained in a stable stationary equilibrium configuration solely by the electrostatic interaction of the charges

Holding capsule in place without supports would allow fully symmetric implosion

SLIDE 6

LLNL-PRES-748677

▪ Expelling the magnetic field enables levitation

Superconducting Levitation

SLIDE 7

LLNL-PRES-748677

Upward Lorentz Force

▪ NIF is already surprisingly compatible with superconducting

levitation:

✓Targets at ~20K within chamber ✓Shape of capsule is favourable for levitation ➢Coat with thin layer of low Z material

Bringing Levitation to NIF

SLIDE 8

LLNL-PRES-748677

▪Simple binary compound ▪Range of fabrication routes ▪Low Z ▪High Tc (39 K), ▪High Jc (~1e9 A/cm2 at 1 T), ▪High Hc2 (>50 T)

Magnesium Diboride

SLIDE 9

LLNL-PRES-748677

Fabrication of MgB2 Thin Films

Film Characterization Glassy Carbon Substrates Boron Sputter Deposition Mg Vapor Anneal at 850ᵒC

Vary film thickness Vary dwell time Vary temperature ramp

Two-step synthesis

SQUID-magnetometry Rutherford Backscattering Raman Spectroscopy

SLIDE 10

LLNL-PRES-748677

Film Thickness and Temperature Profile Matter

▪ Faster temperature ramps and shorter dwell times give higher Tc

and sharper transition

Bulk MgB2

SLIDE 11

LLNL-PRES-748677

Film Thickness and Temperature Profile Matter

▪ Faster temperature ramps and shorter dwell times give higher Tc

and sharper transition

Bulk MgB2

SLIDE 12

LLNL-PRES-748677

Rutherford Backscattering Probes Composition

▪ Films are chemically

homogeneous

▪ Oxygen distributed

throughout the film

▪ Films tend to be

slightly Mg-rich

SLIDE 13

LLNL-PRES-748677

▪ Thinner films have significantly higher oxygen concentrations

Oxygen Depresses Tc

SLIDE 14

LLNL-PRES-748677

▪ Thinner films have significantly higher oxygen concentrations ▪ But this is not the whole story

Oxygen Depresses Tc

SLIDE 15

LLNL-PRES-748677

▪ Defects and inclusions

suppress Tc

▪ Originates in non-epitaxial

growth, mitigated by faster thermal processing

Raman Spectroscopy Reveals Disorder

SLIDE 16

LLNL-PRES-748677

Surface Roughness Must be Controlled

100µm

600 nm, low magnification

1µm

▪ Thicker films are

blister and peel

▪ Needle-like

surface texture

600 nm, high magnification 160 nm, low magnification 160 nm, high magnification

100µm 1µm

SLIDE 17

LLNL-PRES-748677

Surface Roughness Must be Controlled

100µm

600 nm, low magnification

1µm

▪ Thicker films are

blister and peel

▪ Needle-like

surface texture

▪ Thin films are

smooth, < 1nm rms.

600 nm, high magnification 55 nm, low magnification 55 nm, high magnification

100µm 1µm

SLIDE 18

LLNL-PRES-748677

▪ Deposition on spheres will require bounce pan and rotating tube

furnace

▪ Early attempts to measure levitation were a mixed success, but

have plans for custom modification to PPMS in coming year

▪ Studying ion irradiation to enhance critical current

Next Steps

SLIDE 19

LLNL-PRES-748677

▪ L. Bimo Bayu-Aji, Dante O’Hara (summer student), John Bae

(GA), Elis Stavrou, David Steich, Scott McCall, Sergei Kucheyev

Acknowledgments

LDRD 17-ERD-040

Goal: Demonstrate a path to ideal ICF capsule support based on quantum levitation Approach: Thin films of superconducting MgB2

“Vapor annealing synthesis of non-epitaxial MgB2 films on glassy carbon”, A A Baker et al (2018) Supercond. Sci. Technol. 31 055006

Superconducting Thin Films For Levitation of NIF Targets

NIF Places Fuel Capsules Inside Hohlraums…

▪ Fuel capsule must be supported within center of hohlraum ▪ Tents can cause perturbations that affect the implosion

… but Capsule Supports Cause Perturbations

Levitation Offers an Alternative

Earnshaw’s Theorem: a collection of point charges cannot be maintained in a stable stationary equilibrium configuration solely by the electrostatic interaction of the charges

Holding capsule in place without supports would allow fully symmetric implosion

Levitation Offers an Alternative

Earnshaw’s Theorem: a collection of point charges cannot be maintained in a stable stationary equilibrium configuration solely by the electrostatic interaction of the charges

Holding capsule in place without supports would allow fully symmetric implosion

Superconducting Levitation

▪ NIF is already surprisingly compatible with superconducting

levitation:

✓Targets at ~20K within chamber ✓Shape of capsule is favourable for levitation ➢Coat with thin layer of low Z material

Bringing Levitation to NIF

▪Simple binary compound ▪Range of fabrication routes ▪Low Z ▪High Tc (39 K), ▪High Jc (~1e9 A/cm2 at 1 T), ▪High Hc2 (>50 T)

Magnesium Diboride

Fabrication of MgB2 Thin Films

Film Characterization Glassy Carbon Substrates Boron Sputter Deposition Mg Vapor Anneal at 850ᵒC

Two-step synthesis

Film Thickness and Temperature Profile Matter

▪ Faster temperature ramps and shorter dwell times give higher Tc

and sharper transition

Bulk MgB2

Film Thickness and Temperature Profile Matter

▪ Faster temperature ramps and shorter dwell times give higher Tc

and sharper transition

Bulk MgB2

Rutherford Backscattering Probes Composition

▪ Films are chemically

homogeneous

▪ Oxygen distributed

throughout the film

▪ Films tend to be

slightly Mg-rich

▪ Thinner films have significantly higher oxygen concentrations

Oxygen Depresses Tc

▪ Thinner films have significantly higher oxygen concentrations ▪ But this is not the whole story

Oxygen Depresses Tc

▪ Defects and inclusions

suppress Tc

▪ Originates in non-epitaxial

growth, mitigated by faster thermal processing

Raman Spectroscopy Reveals Disorder

Surface Roughness Must be Controlled

100µm

1µm

▪ Thicker films are

blister and peel

▪ Needle-like

surface texture

100µm 1µm

Surface Roughness Must be Controlled

100µm

1µm

▪ Thicker films are

blister and peel

▪ Needle-like

surface texture

▪ Thin films are

smooth, < 1nm rms.

100µm 1µm

▪ Deposition on spheres will require bounce pan and rotating tube

furnace

▪ Early attempts to measure levitation were a mixed success, but

have plans for custom modification to PPMS in coming year

▪ Studying ion irradiation to enhance critical current

Next Steps

▪ L. Bimo Bayu-Aji, Dante O’Hara (summer student), John Bae

(GA), Elis Stavrou, David Steich, Scott McCall, Sergei Kucheyev

Acknowledgments

LDRD 17-ERD-040

“Vapor annealing synthesis of non-epitaxial MgB2 films on glassy carbon”, A A Baker et al (2018) Supercond. Sci. Technol. 31 055006

▪ Measured in plane of film ▪ Good zero field values, but

drops rather precipitously.

▪ Hc2 ~ 20 kOe ▪ Simulations predict

~103A/cm2 required

Critical Current Limits Levitation