A comparison of optical trains based on a GIMM or a Dielectric Mirror final optic

Malcolm W. McGeoch

PLEX LLC280 Albany St.

Cambridge MA 02139

617-621-6300

HAPL San Diego, 9th Aug. 2006

Baseline HAPL final optical parameters:

1. 2.5MJ at 5Hz, 40 illumination beams each 62.5kJ

2. 2 Jcm-2 in optical distribution ducts.

3. Duct aspect ratio 6:1, each beam 3x18 beamlets (area of one beam = 3x18x(0.24)2 = 3.1m2)

4. Focal length 39m (GIMM) or 42m (all-Dielectric case)

5. Vertical “slits” in blanket, total 0.6% of 4(slit size 1.35m high x 0.22m wide for GIMM case)

24cm x 24cm beamletfrom de-multiplex array

The final optics must function to attenuate the neutron flux:

target

laser building3x1024 /beamline /FPY n

< 1x1019 /beamline /FPY

= < 1mrem/hr/dayat one day after shutdown

Attenuation factor of 106 !(M. Sawan, this meeting)

We can encase the optical path with 1.5m - 3m of concreteand attenuate using the angles that are needed in any casefor distribution around the sphere

target

3x1024 neutrons/beamline /FPY n

< 1x1019 /beamline /FPY

Concrete + ferritic steel + H2O coolant

View from above “North Pole”

40 port arrangement: 3 tiers, 8 longitudes each hemisphere

Elevation

Uniformity for 9-element “basket”: N = 3,4,5 with = 0.8, 0.9, 1.0

2.0

1.5

1.0

0.5

0.0

Mean uniformity of basket (% rms)

80706050403020Number of Beams

icosahedron 30 beam 3-6-6 + offset 40 beam 4-8-8 + offset 50 beam 5-10-10 +offset 60 beam 6-12-12 + offset truncated icosahedron 72 beam 6-6-12-12 + offset

all 3-tier cases have 24 / 52 / 79 o polar angles

Elevation sketch of beams for all-dielectric final optics

entry mirrors (turn beams from horizontal to vertical propagation)

(hollow)

66 deg

38 deg

11 deg

blanket

22.5m

20m

10.75m

11.85m

32.5m

main containment wall

plane mirror M1

"Ground Level"

focusing mirror M2

turning mirror M3

(3J cm-2)

11.85m10.75m

20m

(upper hemisphere)

(lower hemisphere)

10 beams, vertical aspect ratio

Equatorial plane

(upper hemisphere)

(lower hemisphere)

22.5m

blanket

main containment wall32.5m

set of 4 beams 11 deg to horizontal shown here

Plan sketch of beams in one quadrant for all-dielectric final optics

30cm 46cm

6.0m

1.6m

77cm

10m12.25m

20m

22.5m

vacuum duct main containment   (concrete) blanket

3m

plane dielectric turning mirror, M4

plane dielectric turning mirror, M3

70cm

32.5m

focusing dielectric mirror M2, f=42m

plane dielectric turning mirror, M1

HAPL Dielectric design of 4-8-06: Plan view of one beamline

(access)

15.5m

9.5m

Mirror location total n/FPY/cm2 n >0.1MeV/cm2 n>1MeV/cm2 gamma/cm2

M1 32.5m from target 2.3e20 2.3e20 2.3e20 8e19M2 9.5m from M1 6e17 4.5e17 3.5e17 3e17M3 15.5m from M2 1e16 5e15 3e15 1e16M4 1.6m from M3 2e14 3e13 1.5e13 2e14M4 6m from M3 2e13 2e12 1e12 2e13Estimates courtesy of M. Sawan.

Radiation loads in all-dielectric design

Radiation resistance of multilayers compared to requirements

Category: layer mixing reflectivity damage resistance

Dose:

1e19cm-2 OK OK (vis*) ?(4% of FPY)

1e20cm-2 OK anneal? ?(44% of FPY)

1e21cm-2 4nm? anneal? ? (4 FPY)

*I. I Orlovskiy and K. Yu. Vukolov, “Thermal and neutron testsof multilayered dielectric mirrors” Fus. Eng. Des. 74, 865-869 (2005)

Mixing of layers was thought (*) to be a showstopper fordielectric mirrors, but data on irradiated multilayers forX-ray optics and superconductors eases this concern

(*) R. L. Bieri and M. W. Guinan, “Grazing incidence metal mirrors as the finalelements in a laser driver for inertial confinement fusion”, Fusion Technology19 673-678 (1991).

Layer mixing? (248nm mirror layers are about 35nm thick)

Exposure of XUV mirrors to 1.1e19cm-2 (1-2MeV neutrons)

N bilayers

“d” spacing

high index: Mo or W

low index: Si or B4C, or C

S. P. Regan et al. “An evaluation of multilayer mirrors for the soft X rayand extreme ultraviolet wavelength range that were irradiated with neutrons”Rev. Sci. Instrum. 68(1), 757-760 (1997)

XUV mirrors tested by Regan et al. (exposure temp 270-300C)

Composition “d” (nm) substrate N

Mo/Si 8.78nm Zerodur 50

W/B4C 2.28nm Si wafer 100

W/C 2.53nm Si wafer 100

Mo/Si 18.7nm Si wafer 25

Results:Mo/Si mirrors had slight shift in peak and slight reflectivitydecrease, exactly consistent with 270-300C known thermal effects.

W mirrors had opposite shift in peak and slight increase in reflectivity,again consistent with known thermal effects.

No effects attributable to fast neutron exposure of 1.1e19cm-2 (10-2 dpa/atom)

Layered superconductors have been tested for fusion reactor use

20 bilayers

R. Herzog et al. “Radiation effects in superconducting NbN / AlN multilayer films”J. Appl. Phys. 68, 6327-6330 (1990).

2nm AlN layers

9 - 26nm NbN layers (not to scale)

Results: Jc>108Am-2 at 4.2K and 20T, before and after irradiation

No degradation of 2nm AlN layers at 1x1019 neutrons/cm2 (>0.1MeV)

XUV reflectivity and enhanced Jc are both sensitive to the roughnessof the surfaces of layers, and the above results both indicate less than about 1nm of induced roughness after irradiation to 10-2 dpa.

Bieri and Guinan (*) estimated mixing of roughly 3nm/(dpa)1/2, where1dpa = 5x1020 (14MeV) n/cm2 for most dielectrics

For “low” doses (much less than1 dpa), this diffusion approach does not apply (for example, at 10-2 dpa, 99% of layer remains undisturbed).

A more critical test will occur at > 0.1dpa (5x1019 neutrons cm-2)(20% of FPY)

(*) R. L. Bieri and M. W. Guinan, “Grazing incidence metal mirrors as the finalelements in a laser driver for inertial confinement fusion”, Fusion Technology19 673-678 (1991).

Lack of layer mixing is consistent with expectations

Dielectric mirrors are being evaluated for the final optic

1.00.80.60.40.20.0

Reflectivity

40302010Number of interfaces

alumina/silica hafnia/silica hafnia/alumina30 layers = 1.9µm …short absorption path

Neutron-stable sapphire substrate

500C anneal cycle removesneutron-induced absorption

25

20

15

10

5

0

Log(I0/I) for 1cm path

1016 1017 1018 1019 1020 1021Fast neutron flux (cm-2)

Al2O3 Abdukadyrova Al2O3 Evans and Stapelbroek 1cm SiO2 (248nm) (Latkowski and Abdukadyrova)

Optical density in 1cm path at 257nm (4.8eV)Neutron irradiation produces optical absorption in dielectrics

248nm neutron-induced absorption is annealed out at 500C

0102030405060708090

100

200 300 400 500 600 700 800

Wavelength (nm)

Corrected transmission (%)

Initial1 hr4 days2 hr @ 500C1 day @ 500C2 days @ 500C3 days @ 500C4 days @ 500C

Data from J. Latkowski, HAPL meeting, Rochester, Nov. 2005

Sample 0.6cm SiO2, 6.6e20 neutrons cm-2. --> post anneal loss in 2µm dielectric path is negligible

Planned neutron irradiation of mirrors

All the reported multilayer exposures have been to about 1019/cm2

The key near term need is for exposure to 1020/cm2 (44% FPY)

A variety of KrF mirrors and GIMM quality aluminum mirrors will beexposed to up to 1021 neutrons cm-2 at ORNL (>1FPY).

Some mirrors will be irradiated at high temperature (250C and 500C)

(K. J. Leonard et al. 14th laser IFE progm. wkshp, ORNL, March 2006)

Two options considered for GIMM materials and thicknessesBoth options have 50 microns thick Al coating

Option 1: Lightweight SiC substrate• The substrate consists of two SiC face plates surrounding a SiC foam with

12.5% density factor• The foam is actively cooled with slow-flowing He gas• Total thickness is 1/2" • Total areal density is 12 kg/m2

Option 2: Lightweight AlBeMet substrate• The substrate consists of two AlBeMet162 (62 wt.%Be) face plates

surrounding a AlBeMet foam(or honeycomb) with 12.5% density factor• The foam is actively cooled with slow-flowing He gas• Total thickness is 1" • Total areal density is 16 kg/m2

GIMM design options (slide courtesy M. Sawan)

Mirror location total n/FPY/cm2 n >0.1MeV/cm2 n>1MeV/cm2 gamma/cm2

GIMM(M1)24m from target 4.2e20 4.0e20 3.6e20 1.4e20M2 14.9m from M1 1.0e18 9e17 8e17 4e17M3 1.6m from M2 2e16 6e15 2.8e15 1.3e16M3 6m from M2 2e15 4e14 2e14 1.3e15

Estimates courtesy of M. Sawan.

Radiation loads in SiC GIMM design

3m

GIMM, M1

focusing dielectric, M2

plane dielectric turning mirror, M3

10deg closest location of M3

furthest location of M3

blanketmain containment   (concrete) vacuum duct

22.5m

20m

12.25m10m

24m

33m

14.9m

71cm

81cm

77cm

1.6m

6.0m

60cm

46cm30cm

5.2m

HAPL GIMM design of 3-31-06 5Jcm-2

Unknowns remain for both the GIMM and dielectric approaches:

After neutron exposure:

Laser-induced damage has not been measured in either case

Reflectivity at 248nm (KrF) has not been measured in either case

Substrate optical quality has not been measured (except to 1019 cm-2)

Other considerations:

The GIMM requires polarized light => less random illumination

The GIMM area is 14m2 vs dielectric area 1.9m2 => cost is high

The neutron maze is much more effective in the dielectric case