BNL E951 BEAM WINDOW EXPERIENCE

Nicholas Simos, PhD, PE
Neutrino Working GroupBrookhaven National Laboratory

OVERVIEW of E951 Experimental Studies

WHY Beam Studies ?
Simulation Studies
Benchmark Studies

Assessment

Liquid Jet Target Configuration for Neutrino Factory

BackgroundAll studies suggest that, to push frontier in proton drivers to an order higher
than the existing ones, one must maximize the yield at the source

Proton drivers with beam power up to 4 MW could become reality

Challenge in finding suitable materials that will withstand intense heating,shock waves and radiation damage

Experience suggests that without R&D surprises have a way of coming backStudy Goals• Find best possible materials that can be used
as beam windows under extreme conditions• Experiment with selected materials, measureresponses• Validate prediction models against
measurements to gain confidence inpredicting material response and/or failure atanticipated extreme conditions

E951 WINDOW TEST Station Set-Up
Fiber-optic Strain Gauges & Double window vacuum monitoringE951 WINDOW TEST Station Set-Up
Fiber-optic Strain Gauges & Double window vacuum monitoringWhat Triggered the Window Experimental Effort

Figure above depicts the tight beam spot requirement (0.5 x 0.5 mm rms) fortarget experiment at AGS
Induced shock stress in a window structure by 16 TP intensity beam and thespot above will likely fail most materials in a single short pulse ( ~ 2 ns)
Figure (right) depicts prediction of vonMises stress in a stainless steel
window for the above conditions. Initial shock stress is ~ 3 x yield strength ofmaterial !!

Mechanism of induced shock stress in windows•No matter how thin the window is, thereverberation of stress between surfaces is
the key issue• vonMises stress amplitude depends on
the spot size (initial compressive loadamplitude), thickness of window, speed ofsound and pulse shape• the measurement of strain on the surface
is to be used as benchmark of the ability ofthe model to predict the stress field in theheated zone
• the radial response (stress/strain) and theability of the pulse to relax depends on thespot size and the pulse structure• smaller spot size does not necessarilymean larger response at a distance• smaller spot size definitely means higher
stress field in the vicinity of the heatedzone

Mechanism of induced shock stress in windows

Issues and Material Matrix selection•••••FAST proton beam interacting with window and depositing energy in small spot
inducing shock waves
Based on a 24 GeV/16 TP/0.5 mm rms beam MOST materials could fail with asingle pulse
Though thin, failure in window governed by through-thickness responseSound speed - material thickness & pulse structure critical elements
Material search combined with analytical predictions led to the followingmaterials for testing––––•Inconel 718 (1mm and 6mm thickness to study the effect)
Havar
Titanium Alloy (highest expectation of survivability)
AluminumAluminum (3000 series) selected as the one that COULD fail underrealistic expectations of AGS beam during E951 (~ 8 TP and 1mm rms)

Finite Element Models to Capture the Dynamic Response of Windows

Aluminum Window Strain Waves(beam spot ~ 0.3 x 1mm)

Aluminum Window Strain Wave Simulation

Aluminum Window Strain Data
Experimental data vs. prediction using the new beam spot (0.3 x 1mm)

Recorded Aluminum Window Strain Data in back-to-back pulses

Measured and predicted strains in the 1mm thick Inconel-718

RECORDED strains in the Havar Window (back-to-back pulses)

Data Acquisition Considerations
Aluminum Window Strain Data - Raw(100 KHz) vs. Processed (500 KHZ)30
AL-01-57
Al-01-57 raw

200-10-20-30-40-0.0001

0.00010.00030.00050.00070.0009E951 - Recorded Strain in the Aluminum Window - Raw Strains (100 KHz) vs. Processed (500 KHz)

secs

30

2010

micro-strain

microstrains

100-10-20-30-400.00002

0.0000250.00003

0.000035

0.00004
secs

0.000045

0.00005

0.000055

Illustration of sampling rate on data prediction

BNL E951 Window Study Assessment
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•••

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Examination of the actual windows revealed that beam spot was tighter
than originally thought (~ 0.3mm x 0.8mm)
Therefore, energy density same order as one expected for 16 TP 0.5mm
RMS
Orientation of elliptical spot and offset KEY parameters for PHASE IIof benchmarking exercise
ANSWERS to some of the QUESTIONS:
There was no loss of vacuum in any of the double windows, indicatingthat no FAILURE has occurred !!
The utilized model also predicts that no window material (given theintensity achieved < 2.7 TP and the pulse length ~ 100 ns base) would
approach yield
BUT failure means different things to different people !!!

SUMMARY•

Based on close examination of activation in the E951 windows beam spot size wassmaller than originally estimated leading to desired energy densities•Materials are more resilient than we give them credit for !!!

•Irradiation may have more to do with life limit•

There is need to go thinner in beam window applications => thus new materials must
be tested