# Presentation: 162855

## Deuterium Heat Flux Measurements on ESP-gun

- Travis K. Gray and David N. Ruzic
- Plasma Material Interactions Group
- University of Illinois at Urbana-Champaign

## Outline

- Upgrades to ESP-gun
- Current Operating Status/Ongoing Experiments
- Single Pulse Operation
- Plasma Parameters
- Measured Heat Flux
- Scaling
- Summary
- Future Experimental Campaigns
- Suggestions?

## ESP-gun

- Bias Field Coils

- Guide Field Coils

- IR Photo-resistor

- Linear motion feedthrough
- (for target holder)

- Triple Langmuir Probe
- (behind)

- Helicon +
- matching network

- -pinch

## ESP-gun Upgrades

- New Helicon Antenna
- Water cooled
- More efficient
- “Helicon” mode _possible_ at 200 W and ~ 250 G
- Stable !
- Guide Magnetic Field
- Lowered downstream magnetic field strength
- ~ uniform 100 G

- Helicon Magnet

- Guide Field Magnets

## Current Operating Status ...

- Typical Operation
- 0.13 mTorr D2
- 400 W RF Power
- With out guide field
- Always w/Helicon magnet

- 12.5  V0  16 kV
-    (300 J  Ecap  750 J)
- 1 kJ @ 22.36 kV
- 7.2 kJ @ 60 kV
- Tin target
- 1 cm DIA, 0.3 cm thickness

## Diagnostics

- Triple Langmuir Probe
- Time resolved Te and ne measurements
- Differential voltage probes used to acquire voltage and current measurements
- IR Thermometry
- PbSe IR Photo-resistor
- Calibrated *in-situ* with target material
- ~ 3_x0015_ s rise time
- Tested against an IR LED @ 100 kHz
- Peak sensitivity at 4 m (cut-off at 4.8 m)

## Plasma Parameters

- _Plasma Parameters_

**Stored Energy, E****dis**** (J)**

## Heat Flux Measurement w/D2 Plasma

- _Heat Flux Measurement w/D__2__ Plasma_

- EM Noise (Cap bank) _10 times greater_ than previously seen!

## Comparison to Argon IR Measurements

- _Comparison to Argon IR Measurements_

- 450 J Argon Discharge:
-  T = 15 C
-  energy flux ~ 90 kJ/m2

## D2 Heat Flux Measurement

- Inconclusive
- Difficulties w/measurement
- Reduced ne compared to Argon plasmas
- Reduced Te compared to Argon plasmas
- Large RF noise pick-up from new Helicon
- Larger than previous noise from Capacitor bank
- How do we improve it?
- Relocation of IR photo-resistor
- More RF/EM shielding?

## Scaling to Higher Energies

- Higher ne pre-ionization plasma _under ____-pinch _
- Higher magnetic fields under -pinch
- Higher RF input power?
- Switch to a DC pre-ionization source?
- Limit on the Capacitor Bank
- Spark gaps can’t go any higher
- Limited by the electrode spacing
- Limited by the charging power supply (20 kV)

## ITER level ELM Simulator

- _ITER level ELM Simulator_

- Multiple combinations are feasible for energy upgrade
-  72, 2 F 60 kV capacitors available for upgrade  250 kJ
- _For Example_

- _Magnetic Field_
- FRC operation of bias
- field  higher densities
- than conical -pinch alone

- _12 ____F PFN (60 kV)_
- twelve PFNs will be fired
- sequentially to achieve 1ms
- total ELM length

## Summary

- ESP-gun operates reliably with Argon
- D2 plasmas pose difficulties
- Helicon operation with D2 is troublesome but possible
- D2 plasmas have low physical sputtered flux unless the incident particle flux is quite large
- Makes low [bank] energy PMI measurements subject to low signal to noise ratio
- Higher Discharge energies are needed to begin studying PMI issues

## Future Upgrades to ESP-gun

- Magnetic Field
- Higher guide fields  Can we maintain uniformity?
- Bias field (Field underneath pinch coil)
- Need uniformity
- High enough field to maintain Helicon through pinch region
- Higher Energy Discharges!
- Problems with corona (mainly in spark gaps)
- Current Design limited to < 20 kV
- Improved spark gap design
- Diagnostics
- QCM
- Optical Diagnostics
- Target line emission during pulse  Single 

## Planned Experimental Campaigns

- IR measurements
- Once noise issue is resolved
- Higher Energy Discharges
- 20 - 40 kV (0.8 - 3.2 kJ)
- Revisit multiple pulses during discharge
- Less jitter in spark gaps at higher V0
- Effect on target temperature rise?
- Required for ultimate goal of full scale ELM simulator

## Acknowledgements

- ALPS/DOE Contract: DEFG02-99ER54515
- PMI Group Members
- Matt Coventry (IIAX)
- Mike Jaworski (IDEAL)
- Ben Schultz (FLiRE / IIAX)
- Undergrads: Patrick Mangan, Michael Sabor, Dan Lossie, Patrick Walsh
- Robert Stubbers @ Starfire Industries