4/22/2011  1 

The 3MV Dust Accelerator at the Colorado Center for Lunar Dust

and Atmospheric Studies Anthony Shu

University of Colorado Colorado Center for Lunar Dust and

Atmospheric Studies CIPS Seminar April 22nd, 2011

4/22/2011  2 

Outline • Why a dust accelerator? • Goals of the CCLDAS accelerator • Couple of projects that require dust

accelerator • Examples of possible use by other users

• The CCLDAS Dust Facility • How the accelerator works • Performance of the dust accelerator • Current and future work

4/22/2011  4 

Why a dust accelerator?

It’s not just a vacuum cleaner run in reverse…

4/22/2011  5 

Goals of CCLDAS Accelerator • Instrument development for lunar and

interplanetary/interstellar dust • What is the composition of impact-generated

vapor (molecular and/or elemental)? • Does the composition of vapor depend on

impact energy or soil grain size distribution? • What is the angular/energy distribution of

vapor? • What is the angular/velocity distribution of

particulate debris? • User Facility - for any imaginable use

4/22/2011  6 

Dust Accelerators in the World

A. Max Planck Institut fur Kernphysik, Heidelberg, Germany

B. Colorado Center for Lunar Dust and Atmospheric Studies, Boulder, CO, USA

4/22/2011  7 

Lunar Environment

4/22/2011  8 

Evidence of Dust on the Moon Horizon Glow 

LEAM Excess Solar Brightness 

4/22/2011  9 

LDEX

4/22/2011  10 

Polyvinylidene Fluoride detectors

• Used on New Horizons as dust detector

• Light weight and low power

• Fast recovery time allows high density measurements

http://www.curbellplastics.com/engineering‐plastics/pvdf.html 

4/22/2011  11 

Materials Testing

• Hypervelocity impacts can cause significant damage

• High speeds make most materials appear liquid

• Reduce efficiency of reflectors and solar cells

http://www.nasa.gov/centers/wstf/laboratories/hypervelocity/gasguns.html 

http://www.spaceacademy.net.au/watch/debris/gsd/gsd.htm 

http://www.spaceacademy.net.au/watch/debris/gsd/gsd.htm 

Space Shuttle Window damage from Micrometeorite  Light Gas gun impact on Glass 

Hubble Telescope Solar Panel 

4/22/2011  12 

Lunar Retro-reflectors • Findings: • Moon is spiraling

away at 38 mm/yr • Liquid core 20% of

moons radius • G is very stable,

variation of 1 in 1011

• Verification of strong equivalence principle

• Reflectivity allows return of 1 photon out of 1017

http://physics.ucsd.edu/~tmurphy/apollo/lrrr.html 

(Samples courtesy of D. Currie) 

4/22/2011  13 

Impact Light Flashes • Intensity

correlated to particle and target parameters

• THz detection can allow better specificity in material detection

• Characterize time-dependent behavior of radiating debris

• Can be used to look at secondary ejecta

http://en.wikipedia.org/wiki/File:Hypervelocity_Impact_Demonstration.jpg 

4/22/2011  14 

Impact Generated Plasmas

• Mobilize small areas generating impact craters • Generate transient impact plasma cloud

• Expand and possibly enhance secondary ejecta yield

4/22/2011  15 

Interstellar and Interplanetary Dust

http://www.eso.org/public/images/eso0812c/ 

4/22/2011  16 

Dust Telescope

0 50 100 150

10-3

10-2

10-1

Ni (58,6

0)

C 2 (24

)

Ag (107,

109)

C (12)

H (1)

Ampli

tude

Mass [amu]

DTS Signals

Dust mass, velocity vector and chemical, and isotopic composition M/DM > 200

4/22/2011  17 

Aerogel Sample Returns

http://newscenter.lbl.gov/feature‐stories/2005/08/05/it‐came‐from‐outer‐space/ 

• Aerogel may alter chemical composition, size, and shape • Can experimentally test what happens to dust particle and aerogel due to dust impacts 

4/22/2011  18 

Micrometeorite Impact Studies

http://www.sciencephoto.com/images/download_lo_res.html?id=823460026 

4/22/2011  19 

Space Weathering • Space weathering

from solar wind, cosmic rays, and micrometeorites

• Effects found on moon, Mercury, asteroids • Reddening of

reflected spectrum • Reduction in

reflectivity • Depth of absorption

bands are reduced

http://www.lpl.arizona.edu/~shane/PTYS_395_MOON/presentations/Justice_space_weather.ppt 

4/22/2011  20 

Dust in Fusion Devices

https://fusion.gat.com/conferences/psi2010/files/talks/Tuesday/Session%206/PSI19_presentation_Smirnov.pdf 

Dust in DIII‐D penetration port 

Titanium dust in Alcator C‐Mod waveguide 

4/22/2011  21 

Dust Issues in Fusion Devices

• Safety issues

• risk of explosion in Loss of Vacuum Accident, Loss of Coolant Accident events

• radiological hazard • chemical toxicity

• Operational issues • tritium retention • impairment of diagnostic

instruments • plasma contamination

Dust Sparks in LHD 

Li dust in NSTX 

R.D. Smirnov, 19th Conference on Plasma Surface Interactions 

4/22/2011  22 

Dust Injection in Fusion Devices • Aims of dust

injections • Calibration of

diagnostics • Benchmark

modeling of dust dynamics

• Testing of wall materials

• Edge Localized Modes mitigation studies

Sample of DIII‐D wall tile material for dust impact studies at CCLDAS (Courtesy of D. Rudakov) 

4/22/2011  23 

The CCLDAS Dust Facility

Capabilities and future work

4/22/2011  24 

Overview •Pelletron 3 MV Electrostatic Generator •Particle velocities:  100 km/s •Active selection of particles (charge/velocity) •Particle materials: Fe, Ag, Latex, ??? •Particle sizes: 0.2 – 2.5 m 

SF6 Tanks 

3MV Pelletron 

Beamline 

Target Chamber 

4/22/2011  25 

Dust Head •Pre‐accelerator for Pelletron •Particle charging to surface electric fields of ~3x109 V/m (~ 30% of field emission limit) •Needle kept at 20kV DC •Reservoir pulsed from 20kV to Ground •Extraction plate held at ground •Fires particles at random rate 

4/22/2011  26 

Pelletron Charging System

E‐Field 

‐ ‐ ‐ ‐ ‐ ‐ ‐ 

+ + + + + + + 

• Similar to Van der Graaf generator • Metal pellets form chain instead of band • No contact between chain and charging 

system • More stable voltage difference maintained • No belt dust creation • No ultimate terminal potential limit • Systems up to 25MV 

4/22/2011  27 

Detector

•Passive Detection •Detect image charge induced on cylinder •20 cm detector  2‐200 s square pulse (SNR≥2.5) •Smallest and fastest particles can be lost in noise 

4/22/2011  28 

Detector Signal - Good

4/22/2011  29 

Full Beam Line Signal

4/22/2011  30 

Comparison to Heidelberg

4/22/2011  31 

Comparison to Heidelberg

4/22/2011  32 

Lunar Environment Impact Lab UV Lamp  Solar Wind Simulator Port  Cryo Pump 

UV Lamp ports 

Beamline port 

• High Intensity UV Lamps • 1A/cm2 

• 9W of UV emission 

• Sheath scale length ~5cm 

• 14UV lamp ports • Solar wind simulation 

port • Maglev turbo for 

vibration isolation • Cryo pump for fast 

pumping • Capable of simulating 

lunar environment • Vacuum pressures 

down to 10‐6 torr 

Maglev turbo 

4/22/2011  33 

Ultra-High Vacuum Chamber

Beamline ports 

Lid Lifting points 

Feet 

• Arrived at lab, still needs to be unpacked and sealed • Vacuum tested to 10‐9 torr, hoping for < 10‐10 torr • Used for impact generated plasma and neutrals 

detection   

Mount Points 

Inside of UHV Chamber 

4/22/2011  34 

Particle Selection Unit

• Uses Ortec TAC/SCA to calculate timing • Uses Ortec SCA to calculate pulse height • Determines appropriate delay for any speed of particle 

• High speed clock (~10MHz) for counting  up between two pulses • Low speed delay clock (variable) for counting down to determine delay • Ratio of clock frequencies determines distance:𝑙" = 𝑙$ ×

&'(&)(

 

4/22/2011  35 

Real-Time Filtering •Signal embedded in noise can be extracted through cross correlation. •Known signal shape allows precise choice of filter shape •Maximum of correlation directly proportional to pulse height and width •Threshold detection of central peak and timing from zero crossing to next signal zero crossing gives velocity •Charge can be derived 

4/22/2011  36 

SIMION Modeling

•Using SIMION to model beam line characteristics •Modeling Dust head pre‐accelerator, Einzel focusing lens, and Pelletron Accelerator 

Electrostatic Potential 

Z X 

Red equi‐potential lines are spaced every 10kV 

4/22/2011  37 

Pre-acceleration with No Focusing Dust Reservoir  Extraction Plate  Einzel Lens (off)  Pelletron Entrance 

•Einzel focusing lens is turned off •Red lines are equi‐potential lines •Blue lines are trajectories of dust particles 

•Dust is modeled as a point source fired in a 30o cone from tip of needle in dust reservoir •Charge to Mass Ratio is ~17 C/Kg 

Ground  ‐75kV +20kV 3.128in 

4/22/2011  38 

Pre-acceleration with Focusing Dust Reservoir  Extraction Plate  Einzel Lens (off)  Pelletron Entrance 

•Einzel focusing lens is turned on •Red lines are equipotential lines •Blue lines are trajectories of dust particles •Charge to Mass Ratio is ~17 C/Kg 

•Dust is modeled as a point source fired in a 30o cone from tip of needle in dust reservoir •Particles are roughly parallel after entering Pelletron 

Ground +20kV 

+16kV 

‐75kV 3.128in 

4/22/2011  39 

Final Beam Spot

•Without focusing lens, beam is not collimated •Final spot is larger than size of beam line ~6” •With lens on, beam is collimated  •Spot size: ~0.5mm diameter 

Walls of Beam line  Dust particles hitting wall 

Einzel off 

Einzel on 

1mm 

4/22/2011  42 

Current Beamline

3MV Pelletron Detectors 

Particle Selection Unit 

4/22/2011  43 

Future Work

• Attach beam line to LEIL target chamber • Prepare for first user on May 1st • Lunar Retroreflector material studies

• Finish PSU testing and implement FPGA • Prepare stand for UHV chamber and

connection to beam line • Start shooting dust at stuff! • CCLDAS Website - lasp.colorado.edu/ccldas • Lab Webcam - dustcam.colorado.edu

4/22/2011  44 

Timelapse

4/22/2011  45 

Detector Signals - Bad

• Bad Signals are hard to filter out • Noise • Unexplained upside signals • Particles hitting detectors • Slow particles do not appear as square 

waves 

4/22/2011  46 

Distributions

4/22/2011  47 

Distributions