# Presentation: 092092

## Fabrication of Capsules with Angle Dependent Gold shims for Hohlraum Drive Symmetry Correction 

**Fabrication of Capsules with Angle Dependent Gold shims for Hohlraum Drive Symmetry Correction **

**15th International Symposium on Heavy Ion Fusion**
**PPPL**
**Princeton, New Jersey**
**June 7-11, 2004**

**Work performed under General Atomics Internal R&D program**

## Innovation in target design and fabrication can be used to compensate for drive asymmetry

**In the HIF hybrid target, most of the energy is deposited behind a shine shield**
**Radiation flows around the shield and results in a bright source around the shield**
**This causes a large P****4**** asymmetry**
**The P****4**** asymmetry can be corrected using a shim to remove excess radiation**
** ****Initial examination of this concept was done on a target shot in SNL’s double ended Z-pinch**

**Shims can be used to fix asymmetries in all **
**indirect drive targets (heavy ion, laser, z-pinch) **

**equator XY**

**Au shim**

**Ge-CH**

**Z-axis**

## Summary of angle dependent gold shim fabrication process

** ****Ge-CH mandrels were made using well developed ICF capsule fabrication techniques**
** ****Gold shim coating was deposited by magnetron sputtering**
** ****Using masks patterned coatings were produced**
** ****Coatings on flats were used as initial guidelines**
** ****Gold thicknesses on shells were determined by x-ray transmission (contact radiography)**
** ****Profile similar to desired profile was produced**
** ****Adjustments to process is necessary to obtain desired profile**

## The decomposable mandrel technique was used to fabricate Ge-CH shells

** ****Process allows fabrication of shells with:**
** ****Desired diameter (~ 5 mm)**
** ****Wall thickness (~ 20-30 μm)**
** ****Sphericity (>99.9%)**
** ****Wall thickness uniformity (<0.2 μm)**
** ****Dopant content (germanium- ~ 2 at.%) **

**High aspect ratio- fragile**

## The desired gold shim profile was a combination of P2 and P4 Legendre polynomials

**The desired gold shim profile was a combination of P2 and P4 Legendre polynomials**

** ****The relative contribution of P2 and P4 needed to be an adjustable  parameter**
** ****Shim coating process had to be flexible enough to accommodate such changes:****	**
** ****Use of multiple masks**
** ****Adjustment of mask-shell distance**

**XZ Projection**
**vs. polar angle**

**Designed to zero out P2, P4 double ended Z-pinch asymmetry  **

## Gold coating was deposited using physical vapor deposition via magnetron sputtering

**Gold coating was deposited using physical vapor deposition via magnetron sputtering**

** ****Sputtering provides an important processing knob**
** ****Background argon pressure determines mean free path of gold atoms **
** ****Affects scattering and deposition pattern of gold atoms**
** ****Masks were used to pattern gold coating**

**Sputter system**

## Combination of coatings through two different masks could be used to obtain different profiles

**Combination of coatings through two different masks could be used to obtain different profiles**

** ****Aluminum plate with precision milled slots was used as mask**
** ****Varying slot dimension varied coating profile**
** ****Single and double slot masks could be combined to fine tune pattern**

**Coatings on flat substrates**

**Combination mask**

## Gold coating pattern could also be changed by varying the mask-substrate distance 

**Movable mask**

**1mm**

**2mm**

** ****For a given mask the separation between mask and substrate could be changed**
** ****Coatings spread with separation of mask from substrate**
** ****This allowed obtaining various profiles by adjusting mask-substrate distance **

**Coatings on flats**

## The desired profile could be produced on flats very closely

** ****Coatings using:**
** ****~ 2mm mask-substrate distance**
** ****0.8* single slot + 1.0 double slot**
**   ****produced desired pattern on *****flats***

** ****Coatings on *****shells***** were likely to be deficient near the poles**
** ****This, however, was used as a starting point for producing the shim on shells**
** ****Coating rate on shells needed to be determined **

## Characterization of coatings on shells provided a difficult challenge

** ****Interferometry or profilometry were not possible**
** ****X-ray transmission detected by contact radiography was readily available and used:**
** ****Convolution of x-ray source, coating, x-ray film signal was calibrated on flats **
** ****X-ray signals was linear for the range of interest**
** ****Uncoated shell signal was subtracted**
** ****Shell signal was corrected for cord length in ZX projection**
** ****Data near poles suffers from saturation due to large cord length**

## Coatings on flat substrates were used to calibrate x-ray transmission signal

**Coatings on flat substrates were used to calibrate x-ray transmission signal**

** ****Coatings through single and double slots on flats were measured by interferometry**
** ****Coatings were duplicated on thin CH film (~ zero substrate signal)**
** ****X-ray signals were recorded using various tube voltage and exposure times**
** ****The settings that led to highest x-ray vs. interferometry linearity were used for measuring shells**
** ****It also allowed thickness determination on shells**

**Single mask coating**

**8 bit digitized line out**

## X-ray signal was linear in most of the range of interest

**X-ray signal was linear in most of the range of interest**

** ****X-ray signal measures projection of shells thickness on ZX plane**
** ****Cord length for desired profile is ~ 0.5-1.2 μm**
** ****X-ray signal is linear vs. thickness for this range**
** ****Proper exposure and source voltage settings are required!**
** ****Region of linearity could be changed by changing settings**

**ZX profile cord length of desired profile**

## Shells were precisely positioned under the masks

**Shells were precisely positioned under the masks**

** ****Shells were mounted on ~ 200 μm tungsten stalks**
** ****Stalk was attached to motor shaft with wobble of < ~ 50 μm**
** ****Interferometer was used to determine position of top of shell to < 1 μm**
** ****Measuring microscope was used for lateral position determination (~1 μm)**
** ****XYZ micrometer stage was used to move mask over shells to within ~ 2 μm**

**Tungsten stalk**

**Shell mounting**
**for coating**

## X-ray signal from shells coated through single mask was used to determine coating thickness

**X-ray signal from shells coated through single mask was used to determine coating thickness**

** ****Single slot pattern on shell was very similar to that on flats**
** ****X-ray exposure settings were changed for these thinner coatings**

**Uncoated shell**

**Au coated shell**

**ZX thickness projection**

## X-ray signals from double slot mask indicated lower rate near equator 

** ****Coatings using double slot mask were thicker near equator and thinner at the poles than expected from flat data**
** ****Shell curvature and larger distance between poles and mask are responsible**
** ****Data analyzed after shells were delivered for shots**
** ****We will make adjustments for next series**

**Au coated shell**

**ZX thickness projection**

## A profile similar to the desired profile was produced on target shells

** ****Final profile was not exactly as desired on shells delivered for shots**
** ****Coating near equator was thicker than desired- would it reverse P2 asymmetry?**
** ****Coating near poles was thinner  **
** ****Adjustment of the double slot mask is needed **
** ****Shells were assembled and shot at SNL **

**P2 symmetry was reversed in shot on SNL Z-pinch as expected**

## We hope to simulate process using Monte Carlo simulation to obtain better predictive capability

**We hope to simulate process using Monte Carlo simulation to obtain better predictive capability**

** ****Direct Monte Carlo simulation program DS2V of G. Bird**
** ****Initially determine gold atom distribution near masks**
** ****Use that distribution to simulate coating under masks as function of distance on flat and *****spherical***** substrates**

## We have produced angle dependent gold shim targets

** ****This innovative target can compensate for driver asymmetry**
** ****Targets were produced using ICF target fabrication infrastructure  at General Atomics**
** ****Gold coating thickness could be patterned by coating shells through:**
** ****Various masks **
** ****Adjusting mask-substrate distance **
** ****The desired pattern was nearly produced**
** ****However, adjustments are needed to faithfully produce desired profile **
** ****Other characterization techniques also need to be examined in the future**