NuMI

FNAL experience withthin beam windows
Issue is:•Survival of window in high power proton beam

Windows described in this talk:•FNAL Anti-proton production target station experience –Information provided by Patrick Hurh and James Morgan•

NuMI prototype-target test window experience•NuMI Decay Pipe Window calculations

NBI03
November 7-11, 2003
FNAL thin beam windows
Jim Hylen / FNAL
Page 1

NuMI

Titanium window
on proton beamline for pbar production

NBI03
November 7-11, 2003
FNAL thin beam windows
Jim Hylen / FNAL
Page 2Tri-clad transition ring and weld backup ring
1.5 mil thick Titanium grade 2 foil

Run I era:• beam sigma of 0.4 mm• 3E12 protons per 1.6 µsec pulse
failure every year or two
Run II era:(~1 – 2 E18 protons/month)• beam sigma 0.3 mm on window• increasing from 4E12 to 5.25E12 per pulse
failures at 3 months, 1 month, 2 weeks

NuMI

Titanium window
on proton beamline for pbar production
Failure mode:• Develop vacuum leak (~ 10-7 torr litre /sec)• See no signs of cracks on the Ti window under a microscope• See some oxidation (similar to picture later in talk)

Failure mechanism not known, but have a supposition• failure is earlier than probably expected from radiation damage• peak temperatures are above "alpha/beta transus" , so high temperatureand rapid cooling could be inducing micro-structural changes,
decreasing ductility, making titanium brittle

Ti window was replaced with Be window last year

NBI03
November 7-11, 2003
FNAL thin beam windows
Jim Hylen / FNAL
Page 3

NuMI

Beryllium window
on proton beamline for pbar production

NBI03
November 7-11, 2003FNAL thin beam windows
Jim Hylen / FNAL
Page 4in beam for about a year now
0.3 mm RMS spot size
~5e12 protons/pulse
accumulated about 1.7E19 protons
with no failures
can see spot where beam heating
has caused oxidation
having to clean-up mixed waste( after a wrench-meets-window
incident NOT at pbar ) induced
installation of a catcher(pair of Ti windows with air breakwhere spot size is 4 mm)
which would limit spread of
Be contamination upstream
in case of catastrophic window failure

NuMI

Beryllium Window
beamline window versus pbar SEM

NBI03
November 7-11, 2003
FNAL thin beam windows
Jim Hylen / FNAL
Page 510 mil thick Be foil in beamline window

Be window used on pbar target SEM is even better test
• has held vacuum longer (for about 7 years )• with spot size about half that listed for Ti window(recently about 5e12 at ~0.2 mm rms spot size)NuMI

NuMI Prototype Target Test
target can Beryllium window

NBI03
November 7-11, 2003
FNAL thin beam windows
Jim Hylen / FNAL
Page 6

During the NuMI target prototype test, an even more intense spot was generated
for a short period of time• 1013 protons/ 10 µsec pulse• 0.21 mm x 0.16 mm spot size
No visible damage to beryllium window( however target was not run at a highvacuum, only a few milli-torr, so asmall leak could have gone unnoticed )NuMI

NuMI Upstream
Decay Pipe Window

NBI03
November 7-11, 2003
FNAL thin beam windows
Jim Hylen / FNAL
Page 7

Steel at large radiusTransition ringAluminum thin window
1/16” thick 6061-T6 Al46 m after target(Downstream window is ¼” steel)NuMI

Decay Pipe Window(accident condition –beam misses target)

NBI03
November 7-11, 2003
FNAL thin beam windows
Jim Hylen / FNAL
Page 8

Accident condition:
4x1013 proton/spill~2.5 mm RMS beam spot
Air pressure pre-stresses
vacuum window
Beam heating temporarily
reduces stress at center of window

Normal running condition:~4x1012 proton/spill through target~11 mm RMS beam spot at window
Expect radiation damage at~ 4x1019 proton/mm2~ one century of runningNuMI

Decay Pipe Window(accident condition –beam misses target)

NBI03
November 7-11, 2003
FNAL thin beam windows
Jim Hylen / FNAL
Page 9Temperature rise after
many beam cycles
is small( 1 pulse / 1.87 seconds)

NuMIConclusions

NBI03
November 7-11, 2003
FNAL thin beam windows
Jim Hylen / FNAL
Page 10

Performance of Beryllium windows is adequate for NuMI near the target,( 4e13 protons/pulse at 1 mm rms spot size) while Titanium would not be
The ES&H aspect of Beryllium has to be dealt with during design(plan for containment and/or clean-up considered)
Aluminum appears adequate for the decay pipe window,
where beam conditions are not as harsh