conclusion and outlook (2) - cern · conclusion and outlook (2) otr (the working horse) will not be...
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Conclusion and Outlook (2)
� OTR (the working horse) will not be as easy to use as it used to be
need to mitigate COTR (experimental demonstration)
� At the present light sources there is a lot of experience with SR diagnostics
for non distracting beam measurements. A lot of that can be applied to ERLs
with emittance ~ 10 times better.
� Beam loss and synchronization (see talk by Florian and Lars)
Other important issues to discuss at the workshop and talk on Friday
will the COTR mitigation work for ERL parameters?� will the COTR mitigation work for ERL parameters?
� for light sources: beam stability, orbit feedbacks – extend experience of 3rd
generation light sources and large scale LINACS
� CW beam monitoring
� Optical Diffraction Radiation (ODR) applicability
� Transfer function (transverse and longitudinal) measurements and monitoring
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ERL Instrumentation Discussions
• Diagnostics of high current CW beams especially at low energies in the injector region
is an area where we have least of experience:
- mostly beam profile measurements
- BPMs for beam position work
- bunch length (longitudinal profile)
• At high energy outside of the LINAC can used SR the same way at the presently operated
high energy rings
- the BIG difference is that LINAC beams are not Gaussians, since they are not in
equilibriumequilibrium
- pin hole cameras
- zone optics systems
- two slit interferometer with visible SR
• Can not do that in the LINAC
- Can ODR be used?
- main question is if the presence of the radiator close to the beam will be acceptable
- Laser wire
• Make use of the fact that the beam is CW – very small modulation + lock-in amp
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Flying wire
• 20 m/s flying carbon
wire
• Applicable with 0.6
MW of beam power
• Two units, one in
dispersive section to
allow studies of long-
April 20, 2010 I.V. Bazarov, Flying wire at Cornell University
allow studies of long-
range wake fields
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Flying wire
April 20, 2010 I.V. Bazarov, Flying wire at Cornell University
signal from a laser test
• Installed on the injector beamline
• Ready to be tested with beam
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test headline
Laser-wire R&D: Intro, results from PETRA II and SNS
• Main focus of R&D studies was to build non-destructive beam profile monitor for ILC-like beams (up to 250 GeV beam energy, several nC bunch charge)
• For beam sizes– in the μm range in the beam delivery systems– down to nm spots at the interaction point
• At low beam energies (< 50 MeV) not yet succesful tested. Opening angle of Compton scatted photons large
T. Kamps
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test headline
PETRA 2D laser-wire: experimental setup to study laser-wire issues for ILC beams
• Use injection seeded Q-switched Nd:YAG laserwith several MW peak power and ns pulse length
• Achieved 2D scans of several 10 μm spot sizes several 10 μm spot sizes within 50 sec measurement time
• Consider faster scans with kHz laser and ps pulses
• Original goal is to achieve full profile measurement within one bunch train of the ILC
Courtesy G. Blair, S. Boogert, NIM A 592 (2008)
T. Kamps
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test headline
Laser-wire at SNS
• Laser-wire photo-neutralizes the H- beam from the SNS linac• Stripped-off electrons flux is measured for each laser position in
bending magnet with electron detector• One Q-switch laser serves 9 laser-wire stations• Measure profiles within one bunch train of 650 ns length
Courtesy T. Shea, Y. Liu, Assad, Proc. of HIB 2008, EPAC 2008 T. Kamps
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Potential nonPotential non--destructive profiledestructive profile
monitors for the Cornell ERLmonitors for the Cornell ERL
Non Destructive Profile Monitors F.Sannibale
•• Pinhole xPinhole x--ray cameraray camera
•• Fresnel optics systemsFresnel optics systems
•• Optical synchrotron radiation 2Optical synchrotron radiation 2--slit interferometerslit interferometer
8
Instrumentation Workshop for ERL @ CSR, Ithaca, NY USA, June 2, 2008
•• Laser wiresLaser wires
•• OthersOthers
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LINAC beams are different from ring beams
JLab FEL transversal beam profile:
• Obtained in a specially setup measurements to show how much beam is non Gaussian
• It in not how we have it during standard operation
• There is no Halo shown in this measurements in sense that all of it participates in FEL
interaction
• The techniques we can borrow from rings assume Gaussian beam and therefore
are concentrating on beam size (RMS) measurements �
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Optical Diffraction Radiation
)(10 rK
v
qEr ⋅
⋅
⋅= α
π
αω βγλ
πα
⋅⋅
⋅=
2
amplitude of a Fourier componentof transversal Coulomb field of anelectron
),( yxfb - transverse beam distribution
intensity of the ODR from the beam
unpolarized
vertically polarized
horizontally polarized∫∫ ⋅⋅−−⋅=
beam
rbbeam ddyxEfI ψξψξλγψξπ
ω2)],,,([),(
8
1
intensity of the ODR from the beamIs 2D convolution of the fb and Erω
2
Example assuming
4.597 GeV;
σx=215 µm; σy=110 µm;
λ=550 nm; h=1.1 mm
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5µµµµA tune beam; OTR
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10µµµµA CW beam; ODR V. polarized
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Fig. 1
Fig. 3Fig. 4
Fig. 5
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Diagnostics
and and
Machine Protection from WG2
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X-Band Cavity BPM Designed for LCLS (R. Lill, ANL)
� Each BPM has Dipole and Monopole cavity for
measuring position and beam intensity
� Design strengths
– Sub-micron resolution
– Inherent centering accuracy and reproducibility
– Very successful in LCLS commissioning
� Challenges for ERL
– Fast response for machine protection– Fast response for machine protection
– Multiple beams in linac
– High dynamic range needed for ramp-up
– Complex installation and need for z space
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X-ray BPM Development: Pinhole Camera XBPM (B. Yang, ANL)
� Pinhole camera used as an x-ray beam position monitor
� Transverse resolution ~ 30 nm with 0.1 Hz filter
� Observed horizontal beam motion: 300 nm @ 1-minute interval
� Observed vertical beam motion:
1 µm peak-peak related with
0.1 deg water temperature change
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Diagnostics @ ALICE
Susan Smith Daresbury
Quick review diag
ALICE to EMMA TL
EO, beam arrival, timing and synchronisation
EMMA BPMs
EO, beam arrival, timing and synchronisation
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Collimation and Tomography Systems for NLS (D. Angal-
Kalinin, ASTeC)
• Collimation needs : Machine protection, Undulator demagnetisation,
photoinjector
3rd harmonic cavity
BC1 BC2 BC3
laser heater
accelerating modules
collimation
diagnostics
spreader
FELs
IR/THz undulators
gas filters
experimental stations
• Collimation needs : Machine protection, Undulator demagnetisation, radiation levels
• Collimation immediately after the gun and considerations for the post Linac collimation
• Simple post Linac collimation system need ~40m of length and thus a collimation system is foreseen to be before the beam switchyard
• Collimation wakefields and emittance degradation can be important
• Tools and experience available from linear collider
• 6D Tomography section proposed to be included in additional branch of the switchyard to mimic the effect of switchyard
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Discussion Points and Comments
• Cost of cavity BPMs was a concern (20k$/channel), but can
be reduced with design improvements
– Could use for undulator locations only
• Must think carefully about how to implement cavity BPM
with CW beam at high rep rate
– Any beam impedance issues?
– Should try such a BPM on existing ERL
• X-ray pinhole is sensitive to position, whereas in light
sources we need to control angle as well
– Can be paired with more standard x-ray BPM
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� Method for halo detection: coronagraph (high energy) / ? (low
energy)
� Beam-loss monitors for human/machine protection:
� Need to install them close to beams
� How fast can they be without being unreliable? (A few-µs response is
desirable)
Collimation at low-energy (e.g., in merger)
Discussion: Diagnostics and Machine Protection
� Collimation at low-energy (e.g., in merger)
� Does the collimator degrade the beam quality?
� Halo prevention is better than collimation.
• How to protect SC-cavities from beam impact?
� How to distinguish x-rays from cavity from beam losses near cavity?
� Start-up process including verification of beam orbit will be necessary.