Ultra-thin Gas Jet for Non-Invasive
Beam Halo Measurement
Adam Jeff
CERN & University of Liverpool
Workshop on Beam Halo Monitoring
19th September 2014
adam.jeff@cern.ch
Contents
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The CLIC Drive Beam
Jet monitor principle
Jet generation & shaping
Test Stand @ the Cockcroft Institute
Experimental Results
Quantum focusing
Prospects (sieve)
1 / 17
The CLIC Drive Beam
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Beam Energy
Beam Current
Pulse Length
to 2.4 GeV
4.2 A
140 μs
2 / 17
Principle of the gas jet monitor
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• Generate thin atom gas
curtain,
• Ionize atoms with primary
particle beam,
• Extract ions via electric
field,
• Monitor on MCP, P screen.
Y. Hashimoto et al., Proc. Part. Acc. Conf., Chicago (2001)
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Thanks to M. Putignano
Test Setup @ Cockcroft Institute
3 / 17
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Test Setup @ Cockcroft Institute
4 / 17
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Test Setup @ Cockcroft Institute
5 / 17
e- beam
Gas Jet
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Test Setup @ Cockcroft Institute
Residual
Gas Ions
Gas Jet
Ions
E
Gas Jet
e-
6 / 17
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Test Setup @ Cockcroft Institute
5 / 17
7 / 17
Vacuum Effects
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V. Tzoganis, A. Jeff, C. Welsch , “Gas dynamics considerations in a non-invasive profile monitor for charged particle beams”,
Vacuum (2014), dx.doi.org/10.1016/j.vacuum.2014.07.009
8 / 17
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Pulsed Jet
Valve
Control
Jet
Brightness
Chamber
Pressure
9 / 17
Gas Jet Scanner
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Shaping of gas
curtain possible
through sole
manipulation of
Pressure and
Temperature of
Gas Reservoir.
1 order of
magnitude density
difference
between core and
side strands
M. Putignano, C.P. Welsch, “Numerical study on the generation of a planar supersonic gas-jet”, NIM A 667 (2012)
10 / 17
• Need to separate beam / halo:
– Spatial separation
Gas Jet Scanner
• Filter out beam-rest gas
– Temporal separation
• Time-of-flight 𝑡 =
2𝑑𝑚
𝐸𝑞
• Total tof ≈ 10 µs, time difference <0.5≈ µs
halo
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beam
– Energy Spectrum
• Linear with vertical position
• Space Charge?
halo
E
11 / 17
Gas Jet Scanner
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• Alternative Solution: Gas Jet Scanner
– Generate a thin pencil jet and scan it
through the beam
– Like a wire scanner but non-interceptive
– Still collect ions but position not
important: not affected by space charge
– Slow scan through halo region, fast
through main beam
– Need a way to generate a thin jet…
12 / 17
Matter-Wave Focusing
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Matter-Wave Focusing for a Thin Neutral Jet
Smallest zone 100 nm
FWHM at focus 2μm !
T. Reisinger, S. Eder, M.M. Greve, H.I. Smith, B. Holst, “Free-standing silicon nitride
zoneplates for neutral-helium microscopy”, Microelectronic Engineering 87 (2010)
13 / 17
Fresnel Zone Plates
• The path difference between each successive
light ring is equal to 1 wavelength (at the focal
point) constructive interference.
• Each zone is equal in area
• Focal spot size is roughly the width of the
narrowest (outer) zone
• Compared to traditional lens: no spherical
aberration, large chromatic aberration
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DeBroglie wavelength ≈ 0.05 nm
for room temperature Helium
Focal length of zone plate 𝑓 =
radius of outer zone
width of outer zone
2𝑟𝑁 ∆𝑟𝑁
λ
Resolution ≈ width of smallest zone (ignoring chromatic effects)
14 / 17
Photon Sieve replaces clear zones of an FZP with a series of holes
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Photon Sieves
+ Sharper focusing
- Lower transmission
+ Easier to manufacture
Apodised Photon Sieve reduces higher order
diffraction, increases central maximum
L. Kipp et al, “Sharper images by focusing soft X-rays
with photon sieves”, Nature 414 (2001)
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ZEMAX Simulations
15 / 17
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The Atomic Sieve
16 / 17
The Atomic Sieve
17 / 17
Conclusions
Conclusions
• The test setup at the Cockcroft Institute has demonstrated
reliable gas jet operation, and can be used for profile
measurement in both continuous and pulsed mode.
• Thanks to efficient dumping of the jet and differential
pumping in the jet generator, the effect on the beam vacuum
system is small.
• A split jet can be generated for halo imaging
• Additional discrimination would be needed to achieve high DR
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• An alternative solution is a gas jet scanner
• A focusing method based on the deBroglie wavelength of the
neutral gas atoms will be tested.
• The ‘atomic sieve’ is under production and will be tested later
this year.
Thank you for your Attention
Adam Jeff1,2, Barbara Holzer1, Thibaut Lefèvre1,
Vasilis Tzoganis2,3, Carsten Welsch2,3 and Hao Zhang2,3
1CERN 2University
of Liverpool 3Cockcroft Institute
Workshop on Beam Halo Monitoring
19th September 2014