# Presentation: 695666

## Towards a High Gradient Lithium Collection Lens for the Fermilab Anti-proton Source

- P. Hurh
- Fermilab BDMS
- 9/9/03
- High Power Targetry Workshop 2003

## Presentation Overview

-  Introduction to Lens
-  Identified Problems and Issues
-  Possible Solutions
-  Conclusion and Future Work

## Introduction - Anatomy of a Lens

## Introduction - Anatomy of a Lens

## Introduction - Operating vs Design Parameters

- Original Design Parameters (1000 T/m)

-  670 kA, 350 μs half-sine pulse
-  5E12 ppp on target every 2 seconds

- Current Operating Parameters (745 T/m)

-  500 kA, 370 μs half-sine pulse
-  5.2E12 ppp on target every 2.4 seconds

## Introduction - Fatality

- Lens 21

## Introduction - Fatality

- Lens 20

## Introduction - Fatality

- Lens 17

## Introduction - Fatality

- Lens 18

## Introduction - Fatality

- Lens 22

- Lens 22

## Introduction - Fatality

- Subsequent analyses (FEA) have shown that these failures are not consistent with predicted loads.
- This indicates:

-  Material degradation
-  Actual loads more severe than predicted by analyses

## Identified Problems & Issues -Overview

- Ongoing analyses and investigations have revealed the following issues with the current lens design:

-  Overheating (melting lithium)
-  Material Degradation (embrittling titanium)
-  Li/Ti Separation (moving lithium)
-  Fatigue (cracking titanium)
-  Fabrication & Assembly Difficulties

## Thermal Results - TemperatureJust after 400th pulse, High Gradient

- Thermal Results -** ****Temperature**Just after 400th pulse, High Gradient

- Li Melts @ 454  ̊K

## Thermal Results - TemperatureJust before 401st pulse, High Gradient

- Thermal Results -** ****Temperature**Just before 401st pulse, High Gradient

## Thermal Results - TemperatureJust after 400th pulse, Low Gradient

- Thermal Results -** ****Temperature**Just after 400th pulse, Low Gradient

## Thermal Results - TemperatureJust before 401st pulse, Low Gradient

- Thermal Results -** ****Temperature**Just before 401st pulse, Low Gradient

## Identified Problems & Issues -Overheating

- High Gradient pulse appears to create local melting
- Low Gradient pulse does not appear to create local melting
- Structural portion of FEA analysis does not currently model phase transition effects

## Identified Problems & Issues -Material Degradation

- Crack profiles exhibit brittle and ductile fracture regions consistent with fatigue

## Identified Problems & Issues -Material Degradation

- Identified Problems & Issues -**Material Degradation**

- Load at final fracture was estimated from crack depth and is consistent with models

## Identified Problems & Issues -Material Degradation

- However at those low loads a crack would have to be at least 200 microns deep initially before propagating

## Identified Problems & Issues -Material Degradation

- In addition, inner tube wall shows micro-cracks (25 microns deep).

## Identified Problems & Issues -Material Degradation

- Hydrogen Embrittlement?
- Liquid Metal Embrittlement?
- Other Contamination?
- Radiation Damage?

## Identified Problems & Issues -Li/Ti Separation

- Magnetic pinch effect pulls lithium inward away from septum conductor tube.
- If lithium motion is large and pre-load is insufficient, voids instantly form and close.
- This may cause detrimental arcing and/or shock effects along the septum conductor tube wall.

## Identified Problems & Issues -Li/Ti Separation

## Identified Problems & Issues -Li/Ti Separation

- Identified Problems & Issues -**Li/Ti Separation**

## Structural Results - U Sum 1st Pulse, Max Mag Forces, High Gradient

- Structural Results -** ****U Sum**** **1st Pulse, Max Mag Forces, High Gradient

## Structural Results - Ux 1st Pulse, Max Mag Forces, High Gradient

- Structural Results -** ****Ux**** **1st Pulse, Max Mag Forces, High Gradient

## Structural Results - Hoop Stress 1st Pulse, High Gradient

- Structural Results -** ****Hoop Stress**** **1st Pulse, High Gradient

## Structural Results - Hoop Stress 400th Pulse, High Gradient

- Structural Results -** ****Hoop Stress**** **400th Pulse, High Gradient

## Structural Results - Hoop Stress 1st Pulse, Low Gradient

- Structural Results -** ****Hoop Stress**** **1st Pulse, Low Gradient

## Structural Results - Hoop Stress 400th Pulse, Low Gradient

- Structural Results -** ****Hoop Stress**** **400th Pulse, Low Gradient

## Structural Results - Hoop Stress 400th Pulse, Extremes, High Gradient

- Structural Results -** ****Hoop Stress**** **400th Pulse, Extremes, High Gradient

## Structural Results - Hoop Stress 400th Pulse, Extremes, Low Gradient

- Structural Results -** ****Hoop Stress**** **400th Pulse, Extremes, Low Gradient

## Identified Problems & Issues -Li/Ti Separation

- FEA model does not simulate lithium failure (void production).
- FEA model can be used to predict onset of Li/Ti separation.
- Li/Ti Separation is evident in High Gradient pulse.
- Li/Ti Separation is not evident in Low Gradient pulse.
- Insufficient or loss of pre-load aggravates phenomenon

## Identified Problems & Issues -Fatigue

- Identified Problems & Issues -**Fatigue**

## Identified Problems & Issues -Fatigue

- Identified Problems & Issues -**Fatigue**

## Identified Problems & Issues -Fatigue

- FEA model predicts maximum stress of about 68 ksi in areas with R=-.05 (closer to R=0.1 w/o Li/Ti separation).
- Real world testing of Ti alloy (6 Al-4V) shows endurance limit of 70 to 80 ksi.
- Environmental and quality control factors could reduce lifetime significantly.

## Identified Problems & Issues -Fabrication and Assembly Difficulties

- Current design relies on work intensive and high quality electron beam welding of the septum.
- Multiple etching and machining steps invite quality control errors (hydrogen absorbtion, contamination, weld defects, etc.)
- Multiple lithium seals are difficult to make and could lead to lithium pre-load loss.
- Poor instrumentation during lithium filling led to uncertainty in pre-load values (error bars of 50%).
- Cost and time for construction are relatively high (historically have made new lenses at a rate of 2 per year).

## Possible SolutionsOverview

- Diffusion bonding fabrication technology -(addresses fabrication difficulties, overheating, and loss of pre-load issues)
- New seal technology & refined Li filling process- (addresses fabrication difficulties and insufficient pre-load issues)
- New septum alloy (Ti 6Al-4V to Ti 10V-2Fe-3Al) - (addresses fatigue issue)
- Coating of septum interior surface (anodizing) - (addresses material degradation issue)
- Re-shaped Li end regions to reduce Li motion - (addresses Li/Ti separation issue)

## Possible SolutionsDiffusion Bonding

- Drastically reduces fabrication difficulties (all joints made at one time, eliminates body/septum seals, reduces number of etches)
- Easily accommodates body cooling
- Requires body to be made from Ti alloy

## Possible SolutionsDiffusion Bonding

- Possible Solutions**Diffusion Bonding**

## Possible SolutionsDiffusion Bonding

## Possible SolutionsDiffusion Bonding

- Fatigue testing of critical joint show Ti 6Al-4V joint samples endurance limit = 65 ksi, R=0.1 (same as parent material samples)
- Proof-of-principle prototype complete and in process of lithium filling
- Fatigue testing of Ti 10V-2Fe-3Al joint samples in process

## Possible SolutionsNew Septum Material

- Ti 10V-2Fe-3Al exhibits better fatigue and fracture toughness properties than Ti 6Al-4V.
- Ti 10V-2Fe-3Al is a near Beta alloy that is generally used for forging.
- Heat treatment can be easily combined with diffusion bonding run to obtain optimum properties (not easily done with Ti 6Al-4V).
- Fatigue testing of heat treated material show endurance limit of 110 ksi, R=0.1. Fatigue testing of joint samples underway.

## Possible SolutionsRe-shaped Li End Regions

- FEA Model (E-M, Thermal, and Structural) is almost ready to use as design tool
- Alternate geometries of end regions will be explored to find effect on Li/Ti separation and stresses
- Also effect of lithium pre-load with various geometries will be explored.

## Possible SolutionsRe-shaped Li End Regions

- Possible Solutions**Re-shaped Li End Regions**

## Conclusion & Future Work

-  Many problems and issues have been identified for the current lens design that may be responsible for failures at high gradient.
-  Some possible solutions are being aggressively investigated.
-  The proof-of-principle prototype should be pulsing within 2 months.
- Final prototype should be completed within 1 year.

## Conclusion & Future Work

-  From recent DOE “Lehman” Review findings:
- “Lithium lens improvements look promising: good chance of lifetime and/or gradient improvements”-Fritz Caspers, CERN-G. Dugan, Cornell-Flemming Pedersen, CERN