Electromagnetics and Pulsed Power Laboratories and EMITION Center at UNLV

1
Electromagnetics and Pulsed Power Laboratories
and EMITION Center at UNLV

• Robert A. Schill, Jr., Satya Radhakrishna, Hari
  Krishnan, Shaoru Garner, Brandon Blackstone,
  Greggory Cornell, Richard Kant, Stan Goldfarb,
  and Ved Nayyar
• Department of Electrical and Computer
  Engineering
  
• University of Nevada Las Vegas
• 4505 Maryland Parkway
• Nevada, Las Vegas 89154-4026
• Phone [phone] Email schill_at_ee.unlv.edu
• http//EMandPPLabs.nscee.edu

2
GOALS OBJECTIVES

• Goals
• Motivation to hypothesis driven research
• To display/exhibit/highlight research efforts in
  EM and PP Laboratories
  
• Encourage collaboration
• Objectives
• Expound on a variety of research directions
• Note specialized equipment and modeling
  infrastructure

3
MOTIVATION TO RESEARCH

• What is Pulsed Power?
• Pulsed power is the ability to expend a finite
  amount of energy over miniscule time intervals in
  localized regions in space.
  
• Broad Application Objective
• Pulsed power (electrical, EM, optical, and/or
  charged particle beam) has the potential to
  selectively influence, manipulate and/or
  sculpture particular physical mechanisms. In
  general, physical processes occur over different
  spatial and temporal scales. Therefore, the
  objective is to couple pulsed power energy into
  desired physical processes without inhibiting or
  enhancing other processes that normally exist.
• Consequence
• Managing the electromagnetic spectrum entwined
  with material interactions captivates the essence
  of ones ability to harness ones future.
  
• Experiment

4
NEVADA SHOCKER
Anode
Marx Bank (MB)
Diode
Blumlein (BL)
Cathode

• Understanding the data requires understanding the
  machine

Blumlein Coil
Water/Vacuum Plastic Barrier
5
NOVEL ELECTRICAL SENSOR

• Novel Differential Dot
• Wide bandwidth Matched
• Symmetry
• Natural as a differential B-dot
• Shielded B and D - Dot combined
• No solder connections
• Patent Pending
• Calibrated for Magnetic Field
• Frequency domain
• Sig. Generator 1.5 GHz max.
• Student thesis

Novel Dot
6
NEVADA SHOCKER - ANATOMY

• Experiment/Equipment
• Scopes Marx bank triggered
• 5 Scopes TDS 6604B (6GHz, 22Gb/s)
• Four dot detectors on 1.25 rad 5,6,7,8
• Embedded 1 mm below electrode surf.
• Vac. Press. 7.5X10-6 2.5x10-6 Torr
• Plastic Rexolite 1 dia., 1 and 2 long,
  polished, 30-50 psi exerted on ends

Front Side
Back Side
7
REXOLITE POLISHING HISTORY

• Crazing - Multitude of very fine cracks in the
  matrix material
  
• Stress exceeding tensile strength of plastic
• Ex. Shrinkage, machining, impact shocks,
  temperature
  
• Transition temperature 114oC (Rexolite surface
  gels)
  
• C Lec Plastics Inc. (1 dia. rod stock)
• Cast the plastic - Sample shrinks unevenly
• Wet grounded to 1 dia. (rod surface - opaque
  frost-like)
  
• UNLV Polishing Procedure
• Initial preparation - Band-saw cut
• Rough polishing in lathe (320 rpm) - 2 minute
  procedure
  
• 3M Super Duty rubbing comp. microfiber cloth
  T120o C
  
• Cleaned with water or 200 proof alcohol
• Fine polishing in lathe (320 rpm) - 4-5 minute
  procedure
  
• Light Duty 3M Perfect-It II rubbing compound
  T75o C
  
• Ave. optical opacity - 1.17 with stand. dev.
  0.048 (15 samples)

Grain effect due to polishing
Magnification 20x optical, 150 digital
8
RGA DATA NEVADA SHOCKER

• Water Vapor- Abundant
• 1 H,16 O,17 HO,18 H2O
• Atm.Leak (4 x more N2 than O2)
• 16 O, 28 N2, 32 O2, 40 Ar
• 44 CO2 -- elastomeric O-rings
• Fluorine(Teflon Cleaning Comp.)
• 19 F, 20 HF
• Hydrocarbon Fragments (CiHk)

1
9
1 AND 2 LONG, 1 DIA. REXOLITE SAMPLES, 2.5e-6
TORR
2 SAMPLE
1 SAMPLE
D
D
H
H

• Virgin Sample Distribution (Water switch - normal
  position)
  
• Approx. sixty samples 1 2 long, 7.5e-6
  2.5e-6 Torr
  
• Observed an open circuit charging characteristic
  and then a short circuit behavior. Breakdown
  resulted.

10
SINGLE WIRE IMPLOSIONS

• Motivated by Flashover Studies
• With the large mismatch present in the system, is
  there enough current to vaporize a copper wire?
  
• Typical flashover shot when a 0.25 mm wire is
  attached with nail polish to a 1 polished,
  virgin Rexolite sample.
  
• Unoptimized conditions, the copper wire vaporized
  coating the plastic surface.
  
• UNR Sandia collaboration

11
LASER STIMULATED DESORPTION
Desorption Test Stand

Optically Mag. And Digitally Enhance
d

• Empty Chamber 1e-10 Torr
• Localized excitation NdYAG laser
• Enhance subsurface diffusion of gas contaminants
  leading to desorption
  
• Flashover fine gas layer present between hard
  vacuum and solid

12
ANALYSES
RGA
Laser Beam
Laser Plastic

• MATLAB
• Imaging interrogation tools
• Residual Gas Analyzer (RGA)
• Measures the partial pressure of gas released by
  the medium

13
INTERFEROMETRY SETUP OPTO-MECHANICAL MATERIAL
PROPERTIES
Universal Testing Machine

• Hypothesized Research
• Hardware
• Universal Test Machine
• Optical Components
• CCD Camera
• Optical Modeling Software

Sample Under Test
Mirror
Beamsplitter Cubes
14
LIGHT INTENSITY, SPATIAL POSITION, COLOR
ANALYSIS
Intensity plot superimposed on image
Experiment

• Spatial Intensity Distribution
• VIBGYOR order of intensity profile
• Experimental and computational agreement
• MATLAB
• Imaging interrogation tools
• Shift in fringe corresponds to a mechanical
  pressure

Simulation
15
SEE TEST STAND

• Electron Gun
• Particle Position Detector
• Manipulator Arm
• Cryostat Rotary Table
• RGA Pressure Gauges
• Rough/Turbo/Cryo Pumps

16
SURFACE SAMPLE POLISHING
0.5 mm Reticle
Grid Reflection

• Electropolish Technique
• Cornell Univ. - Two samples
• Surface removal no less than 125 microns
  everywhere except inside grooves

• Buffered Chemical Polish
• LANL - Six samples
• Surface removal - 98 microns
• 112 ratio hydrofluoric acid, nitric acid,
  phosphoric acid
  
• Temp. 8 - 10 oC

17
ELECTRO-POLISHED - 1 keV Prim. Beam
0O Beveled Surf. (Normal Incidence)
15o Beveled Surf.
30o Beveled Surf.
Proc. Count 935
Proc. Count 2136
Proc. Count 604
CG(-4.45,-21.45) SD(7.81,9.01)

• As the angle of incidence increases, the
  distribution of SEE shifts radially outward along
  the detector surface
  
• Aperture opening in the detector may be observed
• 0o 15o incidence - most SEE lost to the
  aperture opening
  
• Aperture masks the SEE spatial distribution
  allowing for study of the tail ends of the
  momentum distribution.
  
• 30o Center of Gravity (CG) of SE distr. and
  standard deviation (SD)

18
DETAILS SEE FROM 1 keV PRIMARY ELECTRON BEAM,
30O EP SAMPLE
19
MONTE CARLO SIMULATION RESULTS

• Monte Carlo Code
• Original Version (valid 50 eV)
• Dr. David Joy, Univ. of Tenn.
• Modified Vers. (added near surf. Effects tracks
  of all SE generations)
  
• Dr. Richard Kant, UNLV
• Microscopic, single scatterer approach to follow
  the primary and all generations of secondaries
  through the collision cascade
  
• Output - Initial energy/mom. dir. cos.
• Logistics
• 100,000 primary electr. launched
• 100 eV large concentration between 40-50 eV
• 1keV large concentration between 0.9 and 1 keV,
  and structure around 50 eV

0.1 keV Primary
30o Beveled Surf.
1 keV Primary
20
SIMULATION vs EXPERIMENT

• Logic
• The SE Monte Carlo code predicts BSE
• Based on specular arguments, exp. data has been
  masked to observe the BSE
  
• Anticipate- SEs favor emission in specular dir.
• All initial particle trajectory conditions
  (energy/ mom. dir. cos.) for the standard
  deviation extrema from the average final position
  of the SEE distr. as measured on the detector are
  determined with a particle tracking code.
• Initial conditions of final extrema positions are
  plotted. All possible initial conditions should
  lie in between these curves. If SEE is uniformly
  distributed about the detected specular electron,
  the ave. initial conditions of the Monte Carlo
  BSE distri. should be central to experimental
  curves.
• Good agreement shown

30o Beveled Surf.
EP (similar for BCP)
Ave. initial condition stand. deviation from
Monte Carlo Sim.
EP
21
ANTENNA ANALYSIS

• Dielectric encapsulated antenna 2.45 GHz. at 10
  bandwidth 30 x 30 x 15 mm

• Theory - Near and far fields with dielectric
  material
  
• Computational modeling

22
MODELING SOFTWARE
SEE Matlab

• LSP MAGIC
• WAVICA RAYICA (Optica Inc.)
• MICROWAVE OFFICE - New
• ELECTRONIC WORKBENCH
• MONTE CARLO SECONDARY ELECTRON EMISSION
• MATLAB
• FIELD PRECISION EM SOFTWARE

30 million Incident Primary Electrons
Magic 3D
Wavica
Matlab Data Acquisition Software of Detector
RGA on, ion gauge off, grid 150 V
RGA off, ion gauge off, grid 150 V
RGA off, ion gauge on, grid 150 V
23
Energy Material Interaction Technology Initiative
of Nevada Center - EMITION Center

• Focal Areas
• Pulsed power device technology
• Applications of pulsed power Materials science,
  Biological/Medical science, Environmental
  science
  
• The EMITION Center is dedicated to the study of
  pulsed power (both the electromagnetic type and
  the particle beam type) and its interaction on
  materials with these focal interests in mind.
• It is anticipated that a modest, dynamic, user
  research facility with unique capabilities will
  attract on-site experimentation of non-university
  entities while simultaneously enhancing the
  centers expertise and usefulness to the pulsed
  power community.

24
RESEARCH COLLABORATION OPPORTUNITIES?

• Pulsed power computing and communication
• Burst of information condensed in a single pulse
• Optical and Pulsed Wideband Microwave Imaging
• Charged particle imaging
• Optical Computing

25
CONCLUSION

• Cool Page (Motivation, Target, Strategy)
• Gen. community, Grade High School (HS)
  College
  
• Story Line -
• Xenon (from Zaro II) visits UNLV EM Lab
• Tools for Travel
• Four fundamental forces introduced
• HS phys. - calculations conversions
• Microwave, Visible, and EM spectrums
• Plasmas, Lightning in Box (Nevada Shocker),
  Materials, and Sensors
  
• Tour the EM and Pulsed Power Labs
• Community Service
• Webpage
• http//EMandPPLabs.nscee.edu , http//emandpplabs.
  nscee.edu/cool/coolpage.htm

26
COMMUNITY SERVICE / TEACHING

• Scouts
• Childrens Leid Museum
• Interesting Web Page with Cool Stuff
  http//EMandPPLabs.nscee.edu , http//emandpplabs.
  nscee.edu/cool/coolpage.htm
  

27
National Visibility

• Seven-minute news clip on Academic Café regarding
  the Nevada Shocker pulsed power device. Academic
  Café broadcasts high profile research and events
  on public television to the community Robert A.
  Schill, Jr. and William Culbreth. Filmstrip
  may be viewed at the bottom of the webpage
  http//emandpplabs.nscee.edu/communtyservice/pro/p
  resenats/realpresentons.htm
• High Profile National Visibility - UNLV
  visibility in a Multidisciplinary University
  Research Initiative (MURI) program, ranking UNLV
  with MIT, Berkeley, and the University of
  Wisconsin Madison. Please refer to the webpage
  at http//cathwinmuri.ece.wisc.edu .

28
NEVADA SHOCKER - PROBES UPGRADES

• Sensor Locations
• Machine Upgrades
• Water switch
• Diode electrodes

Fiber Sensor B/D-Dot
Resistive Probe Upgrades
29
NS CHARGING/DISCHARGING DIODE PHYS.

• Resistive Coil (Displays 4 distinct stages)
• Charging stage (Low Freq.)
• Transition stage (Increase Freq.)
• Firing stage (Relatively Const.)
• Recover stage (High Freq. - reflections)
• Sums Diff. Dot (Rate of change ROC)

30
NULL TEST
NULL TEST
2 SAMPLE
D
D
H
D
H
H
H

• Null Test
• A 0.185 thick aluminum plate covers anode.
• 2 long, 1 dia. Rexolite sample betw. cathode
  null cover
  
• Compare Null Test to 2 Sample Test
• Overall ampl. of D H decreased by a factor
  betw. 4 8.
  

31
CONCLUSIONS

• Based on electrical diagnostics, flashover has
  been observed.
  
• Gross 10s to 100s ns resolutions show
  tendencies
  
• Nanoseconds and subnanoseconds resolutions will
  offer information on relative time displacements
  of signals
  
• This provides more localized information of the
  flashover event lending itself to statistical
  analysis of the position and time of the event.

32
EXPERIMENTAL PROCEDURE

• Sample placement
• Crudely by hand
• Pumps on
• Finer placement with manipulator arm, electron
  gun (EG) Faraday cup at 5e-9 Torr
  
• Cryostat on at 5e-9 Torr
• Diagnostic measurement on primary electron beam
• RGA measurements pressure measurements
• RGA pres. gauges off - particle position
  detector (PPD) on
  
• Determined location of each bevel surface using
  PPD EG - position recorded
  
• Perform exp. on virgin sample surf. at particular
  beam energy
  
• Between each change in primary beam energy - PPD
  turned off and RGA, pressure, and beam
  characteristics recorded
  

33
LUMPED CIRCUIT PARAMETERS
34
TYP. OPEN AND SHORT-CIRCUITED DIODE SIGNATURES
FIRST 1.75 mS
2 long, 1 dia. Cyl. Al short
OPEN
SHORT
D
D
H
H
2 Gap

• 8 samples 32 field histories
• High freq. riding on low freq. (water switch
  fired early electrodes too close)
  
• Shark tooth signature observed for D
• Definite phase relation
• Const. charging/discharging pattern t310ns
• Short surf. current order of mag. larger open
• Ave. charge density for open short same
• Note opposite polarity for surf. currents

• 6 samples - 24 field histories
• Surf. charge builds up 1.6 ms
• Small diode capacitor charges faster than
  Blumlein coil discharges
  
• Marx bank supplying sign. amount of energy
  water switch fired early
  
• Surface current max 5e5 to 1.75e6 A/m
• Low freq. signal vs high freq. signal

35
TYP. OPEN AND SHORT-CIRCUITED DIODE SIGNATURES
AT TRANSITION

• Electric Flux Density
• Zero until MB fires (circled region) - transition
  to rel. constant charge
  
• At transition pnt, large energy surge from BL to
  MB by passing BL coil
  
• Radial Magnetic Field Intensity
• MB and BL transition points obvious

• Electric Flux Density
• Slow init. charging leads to const. rs
• 270 ns large D rs (20 ns fall time)
• Radial Magnetic Field
• From 0 to 100ns Approx. zero
• 100 to 280 ns Grows slowly
• 280 to 500 ns Rel. rapid growth

36
OPEN CIRCUITED DIODE - RESISTIVE PROBE
H
D
RP
RP

• As MB charges, diode appears to charge
• MB fires - Blumlein (BL) charges the diode
  charge density remains approximately constant
  
• Water switch fires Coil blocks forefront of
  pulse
  
• Roughly 5-6 ns later - large Drs on diode
  constant change in radial surface current
  density
  
• About 20 ns later (transition point) the surface
  current density grows faster

37
1 LONG REXOLITE SAMPLE SHORT-CIRCUITED DIODE
SIGNATURES-WATER SWITCH SHORTED
1 SAMPLE
SHORT
D
D
D
D
H
H
H
H

• One Inch Sample
• The diode cap. is small enough to charge to the
  level of the discharge through the inductor in
  series with the resistor probe as if it (CD)
  where not present on the time scale of the
  discharge of the MB through the BL coil.
• Short
• Resistance of the diode short is much smaller
  than that of the resistor probe such that the MB
  is discharging directly through the diode
  
• The dist. of sep. of the water switch electr. in
  normal position is far from optimal. Low freq.
  signal content in earlier figs. is due to the MB.

38
1 LONG, 1 DIA. REXOLITE SAMPLE WATER SWITCH
REMOVED
D
D
H
H

• Low Freq. MB Charging Removed
• Open Circuit Charging and Short Circuit Breakdown
  Characteristics Observed
  
• Continued effort

39
ACOUSTIC WAVE STUDIES

• Correlate flashover based on acoustic and dot
  studies
  

40
Optical Modeling Tools

• Optical Software
• Ray Optics - Geom. Optics
• Wave Optics - Physical Optics
• Diffraction modeling
• 3-Dimensional
• Ability to custom build components and system
• Spatial intensity profiles and more

41
Light Intensity and ColorAnalysis
Intensity plot superimposed on image

• MATLAB
• Analyze both color and intensity results obtained
  from experiment.
  
• MATLAB programming capabilities to analyze
  Wavica/Rayica in different ways for clearer
  understanding and interpretation

42
THEORY

• Governing Eqs.
• Static approximation (dh/dt 0)
• Duration of experiment and acoustic wave
  determines number of monolayers.

b - brass p - Rexolite plastic
mn mass of nth monolayer hn displacement of nth
layer FEM Electromagnetic force on top layer of b
rass
43
SEE TEST STAND SCHEMATIC DRAWING

• Gun-Detector Geometry
• Electron beam passes through center of particle
  detector via beam drift tube
  
• Grid (72 transmission)
• 75x200mm wire 1mm2 hole
• Covers MCP of detector
• Cryostat
• First stage of cryostat partially surrounded by a
  second stage oxygen free high conductivity (OFHC)
  copper shield
  
• Mounted on rotary table
• Transfer Engineering Inc.
• Built vacuum system manipulator arm with diagn.

44
TYPICAL OPERATING CONDITIONS

• Pressure (RGA - 5e-9 Torr)
• Water Vapor- Abundant
• 1 H,16 O,17 HO,18 H2O
• Atm.Leak (4 x more N2 than O2)
• 16 O, 28 N2,32 O2,40 Ar
• UHV epoxy used on pin-hole in welded bellows
• 44 CO2 elastomeric O-rings
• Typ. Pres.-5e-9 to 9e-10Torr
• Cryostat Temp. (Grease)
• Side 9oK Top 23oK(no pressure)
• Electron Beam Parameters
• Energies 0.1-3 keV (1 keV typ.)
• Dia. / Duration - 150 mm / 100ms
• Current 80pA-3.7nA (2.2nA typ)
• Grid Potential 100 150 V
• Alignment and Sample Geom.

Cryostat axis 2 mm off beam axis
Cylindrical sample - 4 beveled surfaces
45
Specular Backscattered Electron Location

• Motivation
• Quantum mechanics - electron is treated as a wave
  function
  
• Wave function has properties of an
  electromagnetic (EM) wave
  
• An EM wave obeys Snells law of reflection
• Backscattered electron (BSE) energy is nearly the
  same as the incident primary electron
  
• Location of Specular BSE for Different Beveled
  Surfaces
  
• 0o and 15o beveled surface
• Lost in aperture opening (r12 detector units or
  6.8 mm for 15o)
  
• 30o beveled surface
• Location r26.6 detector units or 15 mm, nearly
  in middle of cluster

Specular Reflection qr qi
46
DATA PROCESSING PRESENTATION

• Scattered Plots - Color and Location
• Detected SE count over a 281mm x 281mm sq.
• Pixel color signifies the number of electrons
  detected in a bin 1 pixel is 281 x 281 mm sq.
  
• Aperture opening visible in scattered plots
• Data Processing - Count
• One is subtracted from all bins bins with counts
  less than one are omitted
  
• Enhance the visibility of the BSE
• Removes dark counts (sparse random)
• Negligible dark counts due to short pulse
  duration (2 - 6 total count)
  
• Total count detected offers information on
  relative change in SEE
  
• Other forms of measure
• Center of gravity (CG) of SEE spatial distr.
• Standard deviation(SD) from CG

Before Processing Total Count 3137
NOTE 20 bins 10 det. units Dect. Length
45 mm
Approx. Det. Boundary
After Processing Proc. Count 1244
47
SURFACE CONDITIONING BCP - PULSE WIDTHS NUMBER
SHOTS

• Pulse Width vs Rep. Rate
• Five 200 ms pulses yield a similar min.
  conditioning effect as ten 100 ms pulses
  
• Ten 50 ns pulses yield a conditioning minimum
  slightly higher than ten 100 ns pulses
  
• Fall and rise rates for a particular pulse width
  is similar.
  
• EP Conditioning Rate is Slower than BCP but SEE
  Minimum are Similar

1 keV Prim. Beam
200 ms
100 ms
50 ms

• Repeated beam impacts on
• single spatial location
• 30 s between each impact
• 1 keV primary beam, pulse current 2.2 nA

48
SIMULATION LIMITATIONS

• SEE Monte Carlo Code-Limitations
• Model provides estimates for energies between 50
  eV and 1 keV in the collision cascade
  
• Once below 50 eV, the charge is no longer
  tracked
  
• If near the surface and the SE energy is betw. 20
  eV and 50 eV, a random generator decides if the
  particle is emitted from the surface
  
• Important Observations
• Literature suggests that true secondary electrons
  typically have energies less than 50 eV
  
• SEE Monte Carlo Code in its present form may not
  adequately predict the true secondary electron
  emission
  
• Since the primary electron beam is low, tracking
  results obtained from the SEE Monte Carlo code
  should provide reasonable estimates for the
  backscattered secondary electron (BSE) (Note BSE
  have energies comparable to primary electron)

49
OTHER INFRASTRUCTURE OF INTEREST

• Subnanosecond risetime pulser with pulse
  sharpener
  
• Pulse widths 10 ns, 50 ns, 200 ns into 50 Ohm
  load
  
• sharpener
  
• Shot log database
• Documentation is important
• Technician and scientist What are the real
  environmental and experimental conditions?
  
• Secure Website for data transfer to offsite
  location
  
• Polycold - more shots per day
• Safety Precautions
• New Hire
• Subcontract - K-Tech ?

50
NEVADA SHOCKER DATA BASE LOG
51
INVITED WORKING RELATIONSHIP

• To promote a long term research oriented working
  relationship with proposal development roots.
  
• Talents exist and infrastructure is now in
  place.
  
• EMITION pools multi-disciplinary researchers
  under a single umbrella to push the state of the
  art in a number of fields. Offers new ideas and
  research resources.
• Possible Funding Mechanism
• More cost effective to work as a consortium where
  the funding agency would support each entity
  independent of the other
  
• We would be the lead institution and all other
  partners are subcontractors
  
• Overhead is charged for each subcontract up to
  the first 25k, thereafter UNLV does not charge
  overhead

52
BUFFERED CHEMICAL POLISHED (BCP) - 1 keV Primary
Electron Beam
0O Beveled Surf.
15o Beveled Surf.
30o Beveled Surf.
Proc. Count 414
Proc. Count 164
Proc. Count 790
CG(-5.65,-20.32) SD(5.25,8.44)

• Observations - (Same trends as from the EP
  sample)
  
• Significant loss of count for 15o incidence
  compared to normal.
  
• 30o Beveled Surface
• On ave., proc. EP count is 2.3 times larger than
  proc. BCP count
  
• Based on six BCP and five EP shots
• Lit. - rough surf. on a micro. level min. SEE.
  Electr. emitted from the surf. inside of a micro.
  groove may be recaptured by its walls.

53
TRACKING SEE DISTR. VARYING GRID VOLT.
displacement
200 V
Approx. Aperture Boundary
1 keV Primary Beam 15o Beveled Surface BCP Samp
le
100 V
150 V
50 V
0 V

• Controlling Grid Properties - BCP
• Specular cal. indicate the CG of the SEE
  distri. for the 100 V higher grid pot. is lost
  to the detector aperture.
  
• At 50 V, the entire distribution is visible to
  the detector.
  
• D200 V-displaced by 40 bin / 11.3 mm

• Controlling Grid Properties - EP
• Increasing the pot. displaces the center of
  gravity of the distribution towards the detector
  center.
  
• For a 150 V change, the distribution traverses 16
  bins or 4.4 mm

54
CONCLUSION

• A SEE test stand has been designed to study the
  initial conditions of secondary electrons emitted
  from niobium in cryogenic state.
  
• Secondary electron particle distributions have
  been studied for 0o, 15o, and 30o beveled
  surfaces
  
• BCP and EP samples have been compared showing
  that the EP count is over twice as large as the
  BCP count
  
• Electron beam surface conditioning was examined.
  Conditioning appears to be sensitive to pulse
  duration and the number of impacts
  
• Good comparison have been shown between
  experiment and simulation
  

55
INITIAL DIODE CHARGING
D
56
NEVADA SHOCKER - TRANSIT TIME STUDY
57
DIODE PHYSICS - JS AND rs
(ns)