Horn System Review

1

• Design of NuMI Magnetic Focusing Horns
• Presented by Kris Anderson
• Fermi National Accelerator Lab
• Mechanical Engineer
• August 10, 2001

2
Presentation Outline

• I. Horn Overview and Experiment Requirements
• II. Horn Support Structure (Module and
  Carriage)
• III. Discussion of Design, Loading and Analysis
• IV. Design Methodology
• V. Summary

3
Overview Horn Function in Neutrino Beam
Production
120 GeV protons hit target p produced at 1 to
100 milli-radian angles magnetic horn to focus
p p decay to mn in long evacuated
pipe left-over hadrons shower in hadron
absorber rock shield ranges out m n
beam travels through earth to experiment
Exp.
Decay Pipe
m
Hadron
p
n
p
Absorb.
Target
Rock
Horns
4
Neutrino Beam Requirements Influencing Horn Design

• Produce a wide band muon neutrino beam at the
  MINOS Far Detector with as many muon neutrinos as
  possible, where the energy spectrum is chosen to
  maximize the neutrino oscillation signal in the
  search region (maximize yield)
• Effect Minimize horn inner conductor wall
  thickness while maintaining conductor integrity,
  defines horn shape and beam-line location
• Facilitate accurate (within 2) prediction of
  the spectrum in the MINOS far detector given a
  measurement of the spectrum in the MINOS near
  detector.
• Effect Horn construction tolerances (generally
  within 0.005 or better), field quality
• Center the neutrino beam on the MINOS detector.
• Effect Alignment and survey tolerances, field
  quality, alignment stability

5
Neutrino Beam Requirements Influencing Horn Design

• Accommodate a primary beam intensity of 4x1013
  protons every 1.9 sec, matching the production
  capability of the MI
• Effect Duty cycle, thermal control issues,
  radiation hard materials
• Assure long-term reliability, alignment and
  mechanical stability, and reparability.
• Effect Mounting rigidity and thermal stability,
  hot horn repair/replacement work cell, use of
  horn positioning modules
• Assure personnel safety.
• Effect Radiological considerations (e.g., quick
  release horn support mechanisms, remote
  strip-line connections)
• Provide flexibile design for possible future
  conversions to neutrino beams for defined energy
  search ranges, anti-neutrino beam, narrow band
  beam, etc.
• Effect Horn positioning modules, shielding
  design facilitating component relocation to
  initially accommodate low, medium, and high
  energy beams

6
Magnetic Horn OverviewGeneral Design Features
Outer Conductor
Stripline
B
Inner Conductor
p
I
Spray Nozzle
Focus p toward detector

• Large toroidal magnetic field
• Requires large current, 200 kAmp
• Thin inner conductor, to minimize p absorption
• Water spray cooling on inner conductor
• Most challenging devices in beam design
• Prototype test 1999-2000 to check design

Insulating Ring
Drain
7
PH2 Horn Configurations andNeutrino Spectra
8
NuMI Target Station LayoutSchematic of Horn
Locations
9
Subsystem ComponentsHorn Positioning Module

• Design incorporates requirements such as motion
  capability, potential for relative ease of
  component relocation, radiation aspects of
  handling and replacing hot components, and
  replacement of defective or failed mechanisms

10
Horn Positioning ModuleStripline Remote Clamp
11
Subsystem ComponentsModule Support
Carriage/Girder
Structure Modeled Using Pro-E
at ANL - W14x211 Beam Section - Maximum
deflection 2mm - Beam stress safety factor of
6.5 - Bolted Connections and critical weldments
have been analyzed - FNAL needs to review design
and complete end support hardware
12
Subsystem ComponentsHorn Support Structure in
Beamline
13
Subsystem ComponentsHorn Support Structure in
Beamline
14
Subsystem ComponentsHorn Positioning Hardware in
Shield Pile
15
Design Topics Specific Design Criteria

• NuMI uses 2 horns with parabolic shaped aluminum
  inner conductors driven by 200kA peak damped
  half-sine pulse (horn designed for pulse width of
  5.2 ms for resonant extraction pulse changed to
  2.6 ms for single turn extraction)
• Horn 1designed for 1E7 pulse lifetime with 5.2 ms
  pulse (approximately 1 year integrated run time
  with provisions for accelerator maintenance
  periods)
• Minimize bolted connections and material in
  secondary particle path to minimize the potential
  for pion absorption- dictates welded construction
  with 2mm thick inner conductor for horn 1
• Tolerances Extremely Important
• General alignment budget of 0.020, apportion
  0.010 fabrication, 0.010 alignment accuracy
• Azimuthal wall thickness tolerance variation of
  finished inner conductor of 0.005 called out
  on drawings (IHEP 1999 Task A Report call out
  0.0014 )
• Straightness tolerance of finished conductors
  over 3 meter effective length specified as
  0.010

16
Design Topics Specific Design Criteria

• Design issues to address for implementing a
  robust horn system
• Adequate water cooling to control thermal stress,
  particularly in center conductor region achieved
  using appropriate water nozzles
• Conductor corrosion control measures / fatigue
  life enhancement
• Conductor erosion control and dielectric barrier
  layer coating
• Use of radiation hard materials
• Fabrication techniques to meet design criteria
  (e.g., geometric tolerances)
• Above Concerns Lead to Prototype Cycle
• Validate design through fabrication and
  electrical pulse test of a prototype horn 1
  (i.e., horn with highest mechanical loading) to
  identify and address potential fabrication
  concerns and investigate effectiveness of
  cooling, corrosion measures, and conductor design
  integrity

17
Prototype Horn 1 Isometric Cross-Section View
18
Horn 2 Cross-Section
19
General 2 Horn System Parameters

• Parameter Horn 1 Horn 2
• Neck Radius (cm) 0.9 3.9
• Wall Thickness, Neck (mm) 4.5 5.0
• Outer Conductor Radius to i.d. (cm)
  14.9 32.3
• Inductance (nH) 685-690
  457
• Resistance (µ?) 208 (meas.)
  lt112
• Average Power from Current Pulse (kW) 17.0
  lt7.5
• Power Flux at Neck (W/cm2) 14.5
  lt4.7
• Temperature Rise at Neck (oC) 22.8
  lt7.1

Note Above heat load numbers are from original
design pulse width of 5.2 msec
20
Mechanical Loading and Analysis

• Mechanical Loading of Horn is the Result of
• - Current pulse thermal expansion from resistive
  heating (peak at the
• end of the pulse)
• - Magnetic forces (peak at the mid-pulse)
• - Beam heating from particle interaction in
  material
• Horn 1 Horn 2
• Inner conductor resistive heating 17 kW
  lt7.5 kW
• Inner conductor beam energy deposition 1045
  W 371 W
• Outer conductor beam energy deposition 14.5 kW
  5.4 kW
• (1 thick) (1 thick)

Note Above numbers from original design pulse
width of 5.2 msec
21
Mechanical Loading and Analysis

• Mechanical Loading
• During the current pulse length of 5.2 ms,
  mechanical load disturbances travel the following
  lengths
• Structural l1 t(E/r)1/2 25.2m
• Thermal l2 (tk/rcp)1/2 0.6 mm
• Where
• E Youngs modulus 69 GPa
• t pulse width 5.2 ms
• r density 2713 kg/m3
• k thermal conductivity 180 W/mK
• cp specific heat 963 J/kgK

22
Mechanical Loading and Analysis

• Loading and Analysis Summary
• Current pulse is mechanically a very slow load
  and thermally a very rapid load
• Analyze thermal stresses at beginning, middle,
  and end of pulse (quasi steady-state) to
  determine magnitude of cyclic loading for fatigue
  analysis
• ANSYS shell element FEM modeling conducted by Z.
  Tang
• Magnetic loading (vector cross-product J x B) is
  greatest during mid-pulse this force is
  superimposed with thermal loading and results in
  axial and hoop stress components, as well as
  significant end wall loading

23
Mechanical Loading and AnalysisAreas of Highest
Mechanical Loading

High Stress Areas Identified by ANSYS
Upstream Endcap
Neck of Horn
24
Mechanical Loading and AnalysisFactors Affecting
Fatigue Life

• Fatigue strength is dependent upon stress ratio
• To compute stress ratio R, whole stress cycle
  must be known.
• Stress Ratio, R, is defined as the ratio of the
  minimum to maximum stress.
• Tension is positive, compression is negative
• RSmin/Smax varies from -1R1
• For 6061-T6 Aluminum
• R -1 Þ (alternating stress) smax16 ksi
• R 0 Þ (Smin0) smax24 ksi, (1.5X at R-1)
• R .5 Þ smax37 ksi, (2.3X at R-1)
• These values are for N107 cycles, 50 confidence

25
Mechanical Loading and AnalysisAreas of Highest
Mechanical LoadingValues for 5.2 msec Pulse Width

• US end cap minimum stress before pulse is -1030
  psi maximum stress at mid-pulse is -9020 psi
  mean stress is -5025 psi with an alternating
  stress of 3995 psi Stress ratio R0.11
• Under the above calculated stress levels,
  allowable maximum stress for 107 cycles at endcap
  is 26.5 ksi resulting in fatigue safety factor of
  2.9
• Neck of horn stress at mid-pulse is 4351 psi
  stress at end of pulse is
• -3742 psi mean stress is 304 psi with
  alternating stress 4047 psi Stress ratio R
  -0.86 (Note Negative value of R results in lower
  value of fatigue stress limit)
• Under the above calculated stress levels,
  allowable maximum stress for 107 cycles at neck
  is 15.3 ksi resulting in fatigue safety factor of
  3.5
• Stress in conductor weldment regions is very low
  (ltlt4 kpsi)
• Fatigue data from Aerospace
  Structural Metals Handbook

26
Inner Conductor Support Modal Analysis Summary

• Conducted modal analysis of prototype horn 1
  using IDEAS Master Series v6.0
• Objective is to determine the appropriate number
  of spider supports such that the first mode is
  above excitation pulse frequency
• Finite Element Model generated using 8 node brick
  elements
• Excitation pulse frequency 100 Hz
• Unsupported inner conductor first mode (bending)
  natural frequency 65 Hz
• Single support DS of neck - 165 Hz
• Two spiders either side of neck - 175 Hz
• Three spider support system - 358 Hz
• Additional supports contributed little to
  increasing first mode frequency - diminishing
  returns

27
WBS 1.1.2 Technical Progress Inner Conductor
Supports
Belleville Spring Washers
Zirconia Ceramic
6061-T6 Al Electroless Nickel Coated Support
Struts
28
Horn Test Stand MeasurementsInitial Vibration
Measurements

• Conducted Inner and Outer Conductor Modal
  Measurements
• Used miniature accelerometers and shaker (white
  noise) to excite and measure first 15 modes in
  inner and outer conductor
• General Summary of Results
• First mode, global system mode
• Inner and outer conductor simple bending, 120 Hz,
  highly damped
• Higher order modes (from 198 Hz to 678 Hz) are
  associated with the inner conductor, are
  generally local, and are reasonably well damped
  from conductor supports
• Areas exhibiting maximum modal deflections do not
  occur in high stress regions identified by ANSYS
  (i.e., upstream end cap and neck of horn)

29
Discussion of Design MethodologyCooling

• Initial ANSYS analysis was conducted assuming a
  heat transfer coefficient h 1700 W/m2K
• Note that equilibrium conductor temperature and
  resultant thermal stress is a function of cooling
  effectiveness (i.e. heat transfer coefficient)
• We conducted cooling nozzle tests simulating horn
  neck geometry to ensure that measured values for
  the heat transfer coefficient exceeded the above
  value
• Actual measured values for h at 20 psig with
  110-005 (.5 gpm) nozzles result in lower bound h
  values of 4300-4800 W/m2K
• Actual measured values for h at 20 psig with
  110-010 (1 gpm) nozzles result in lower bound h
  values of 5800-6500 W/m2K

30
Discussion of Design MethodologyCooling

• Nozzle Heat Transfer Coefficient Measurement

31
Corrosion ConsiderationsFactors Affecting
Fatigue Life

• Moisture reduces fatigue strength
• For R -1, smooth specimens, ambient
  temperature
• N108 cycles in river water, smax 6 ksi
• N107 cycles in sea water, smax 6 ksi
• Hard to interpret this data point
• N5107 cycles in air, smax 17 ksi
• The above data is motivation for utilizing
  corrosion/encapsulating barrier layer over
  aluminum substrate

32
Design MethodologyCandidate Corrosion Barrier
Layer

• Two Possible Candidates
• Electroless nickel reasonable corrosion barrier
  properties, non-dielectric, more expensive,
  limited vendor base with large tank capacity
• Conducted fatigue test of nickel coated aluminum
  samples at the 107 fatigue limit and compared
  results with equivalent non-coated aluminum
  specimens coated samples survived 1.7x 107
  cycles, non-coated samples failed at 0.6x 107
  cycles
• Use high phosphorus electroless nickel (0.0005 -
  0.0007 thick) on inner conductor and conductor
  supports
• Anodizing best solution for lower stress thick
  cross-section areas Type III (hard coat sulfuric
  acid, 0.0023), Rc 60-65, dielectric strength of
  800 V/mil
• Type III hardcoat anodize is selected for outer
  conductor and thick lead in portion of inner
  conductor not suitable for thinner/higher
  stress areas of inner conductor due to
  approximate 60 reduction of fatigue strength

33
Prototype Horn 1 Hardcoat Anodize
34
Horn Fabrication Precision Welding

• Single pass, full penetration CNC weld is
  required to minimizing conductor distortion,
  assure repeatability, and control internal weld
  porosity
• Proper cleaning, handling, fixtures, and weld
  parameters are crucial to minimize
• conductor distortion and internal weld porosity
• NuMI approached welding solution via parallel
  paths
• 1) Identify vendor base to subcontract critical
  horn conductor welding
• - Vendor base for CNC TIG welding extremely
  limited and expensive less
• flexible fabrication path than in-house
• - Prototype horn 1 fabricated in this manner
  using Sciaky as prime contractor,
• ANL as subcontractor
• 2) Investigate the development of welding
  capability in-house
• - Have specified, benchmarked, purchased, and
  commissioned a Jetline fully
• automated TIG welding system for producing
  controlled conductor weldments
• - System installed at MI-8 horn facility
• - Long term solution for welding 4 initial horns
  (production and spare horn 1
• and horn 2)

35
Horn Fabrication Precision Welding
36
Horn Fabrication Precision Welding
37
Technical Progress Prototype Horn 1 Design Summary

• Conductor Fabrication
• Inner conductor fabricated from 6061-T6 billet
  per QQA 200/8
• Relatively good strength (UTS 45 ksi, YS 40
  ksi, R-1 FS 16 ksi)
• Available in variety of sizes and shapes
• Welds readily
• Relatively good corrosion resistance
• All prototype horn inner conductor parts CNC
  machined by Medco to tolerances better than
  0.002
• Inner conductor welding complete - CNC TIG -
  Overall tolerances held to 0.010 over 133.375
  length (straightness and radial deviation from
  ideal)
• Outer conductor overall tolerances better than
  0.010
• Outer conductor anodized, inner conductor uses
  electroless Ni coating
• Stripline contact surfaces use 0.0005 silver
  brush plating

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WBS 1.1.2 Technical Progress Prototype Horn 1
Design Summary

• Water Seals
• - Total of 64 water seals in horn
• - Utilize EVAC aluminum delta seals on KF style
  flange
• Bolted Connections
• - Utilize TimeSert threaded inserts, pullout
  exceeds 9600 lb. on 3/8 insert
• - As a reference, maximum end wall reaction is
  approximately 4270 lb.
• Current Contact Surfaces
• - Current surfaces have 32 µin finish,
  0.0003-0.0005 silver plate finish
• - Interface clamping pressure exceeds 1400 psi
• - As reference, lithium lens secondary contact
  lead is 5.01 in2 for 6285 Arms
• Prototype horn 1 contact area is 9.2 in2 for
  7250 Arms.
• Corrosion/Erosion Control
• - Outer conductor and thick lead in section of
  inner conductor employs 0.0023
• thick Type III hard coat anodize followed by
  mid-temp nickel seal
• - Inner conductor utilizes 0.0007 thick high
  phosphorus electroless nickel
• Inner Conductor Spider Support Columns
• - Design has been experimentally tested to 36
  million cycles at defections of 0.031
• with 80 lbs. axial preload with no failures

39
Prototype Horn 1 at MI-8
40
Prototype Horn Test Summary

• - Have successfully operated prototype horn for
  2,152,352 pulses at 200 kA peak, 850µsec pulse
  width
• - Magnetic field mapping, powered vibration, and
  cooling measurements are complete with excellent
  results
• - Experienced two small NW16 water nozzle leaks
  (one stopped after tightening EVAC clamp, the
  other resulted in a cracked flange after several
  polishing/tightening attempts)
• - Pulse testing resulted in mild redesign of
  water lines (samples)
• - Recently operated for 1000 pulses at full
  production pulse of 200 kA peak, 2.6ms pulse
  width

41
SummaryProduction Horn Status

• Design of production horn 1 and horn 2 complete
  except
• - Mild design iteration of horn 1 based on MI-8
  pulse test results
• - Integration of outer conductor cooling for
  both horn 1 and horn 2
• Production Horn Fabrication
• - Outer conductor rough forgings in fabrication
  for production and spare horns 1 and 2 (Vendor
  Scot Forge)
• - Inner conductor rough forgings (including weld
  samples) in fabrication for horn 2 (Vendor
  Lenape Forge)
• - Horn 2 parts to final vendor fabrication this
  fall