Transcript Summary and Final Discussion

Linac Coherent Light Source
Stanford Synchrotron Radiation Laboratory
Stanford Linear Accelerator Center
LCLS Undulator Diagnostics and Comissioning Workshop
Wrap-up
John N. Galayda, Stanford Linear Accelerator Center
20 January 2004
Challenges of Commissioning the FEL
Alignment
Undulator K
Undulator Damage
Undulator Diagnostics
Commissioning
Operation
Charge
LCLS Undulator Diagnostics Workshop
Wrap-up
20 January 2004
1
John N. Galayda, SLAC
[email protected]
Stanford Synchrotron Radiation Laboratory
Stanford Linear Accelerator Center
Linac Coherent Light Source
Beam-Based Alignment, Quad Design
Tolerances on Trajectory are Tight for SASE at 1.5Å
Beam-based alignment, RFBPMs must deliver a good
trajectory
Dispersion-free steering delivers a “straight” trajectory
But beam is not centered in quads at completion
Absolute accuracy is not the crucial requirement- sensitivity is critical
Ability to change quad gradient would be a significant advantage
Iron/copper quads would be longer than 50mm-long permanent magnet
quads
New gradient is ~60 T/m, about 11 mm bore: 3,000 gauss on the pole?
NLC has struggled with “variable” permanent magnet designs
Difficult to vary the gradient without moving the magnetic center
Electromagnets still perform best in this regard
NLC needs beam centered in quads to 1 micron- we don’t
Trim windings may be an acceptable option for LCLS
Trim windings still leave a residual uncertainty about actual location of quad
center
“AC” center is not necessarily the same as the “DC” center
LCLS Undulator Diagnostics Workshop
Wrap-up
20 January 2004
2
John N. Galayda, SLAC
[email protected]
Linac Coherent Light Source
Stanford Synchrotron Radiation Laboratory
Stanford Linear Accelerator Center
Challenges for Diagnostics in the Undulator Channel
Tolerance on K of an undulator is around 1.5 x 10-4
At this time, canted undulator poles provide preferred solution
for K fine-tuning (3 milliradians)
K tolerance equivalent to 300 micron horizontal displacement
K tolerance equivalent to 50 micron vertical misplacement
Piezo tuners may be deleted
This displacement does little to the electron optics
Dispersion-free steering gets beam to within 20 microns of quad centers
If quads and undulators are aligned to within 25 microns, this tolerance is
met
This is not quite impossible; still pretty difficult
This displacement does little to the spontaneous spectrum of 1
und.
No one disputed this
LCLS Undulator Diagnostics Workshop
Wrap-up
20 January 2004
3
John N. Galayda, SLAC
[email protected]
Linac Coherent Light Source
Stanford Synchrotron Radiation Laboratory
Stanford Linear Accelerator Center
Challenges for Diagnostics in the Undulator Channel
Radiation Damage to Undulators is a Concern
Interlocks will be implemented but tolerable losses are low
ANL-APS actively studying radiation damage to storage ring undulators
Can the diagnostics identify a damaged undulator?
No one asserts that the LCLS diagnostics suite can do this
LCLS Undulator Diagnostics Workshop
Wrap-up
20 January 2004
4
John N. Galayda, SLAC
[email protected]
Linac Coherent Light Source
Stanford Synchrotron Radiation Laboratory
Stanford Linear Accelerator Center
Charge – Will the Undulator Diagnostics Serve Commissioning and Operations Needs for the LCLS?
Commissioning
Can diagnostics be used to troubleshoot the new hardware?
Can diagnostics be used to guide path to saturation?
Draft commissioning document emphasizes easier tolerances
at long wavelength
Implication is that achievement of saturation at 1.5 nm will lead
to easier path to 0.15 nm saturation
Implication of implication is reliance on FEE diagnostics
Does the commissioning plan bear this out?
Do simulations show convergence of K-tweaking and steering
to optimum output?
LCLS Undulator Diagnostics Workshop
Wrap-up
20 January 2004
5
John N. Galayda, SLAC
[email protected]
Linac Coherent Light Source
Stanford Synchrotron Radiation Laboratory
Stanford Linear Accelerator Center
Charge – Will the Undulator Diagnostics Serve Commissioning and Operations Needs for the LCLS?
Operations
Will the diagnostics permit simple and speedy
troubleshooting?
Reliability/Availability goals of the LCLS will be those of a light
source
Progressive installation of undulators may work for
commissioning, but
In operation, this would require automated “removal” of
undulators
Routine replacement/measurement of undulators must be part
of plan
Operations troubleshooting needs attention
LCLS Undulator Diagnostics Workshop
Wrap-up
20 January 2004
6
John N. Galayda, SLAC
[email protected]
Linac Coherent Light Source
Stanford Synchrotron Radiation Laboratory
Stanford Linear Accelerator Center
Charge – Will the Undulator Diagnostics Serve Commissioning and Operations Needs for the LCLS?
Light diagnostics are crucial
Can the Inter-undulator diagnostics survive at high power?
No good solution for 800 eV
If not, are we placing too heavy a reliance on data taken with
low charge?
Will optimization at low charge allow us to reach optimum at higher charge
40 cm looks very tight
A lot of work required to develop inter-undulator diagnostics
Inter-undulaor diagnostics that work at all wavelengths are
challenging
Even at shorter wavelength, variable geometry of diagnostics is a
mechanical challenge
Rollaway undulators?
How far must they move to be useful?
Variable Gap would require a lot of R&D
LCLS Undulator Diagnostics Workshop
Wrap-up
20 January 2004
7
John N. Galayda, SLAC
[email protected]
Linac Coherent Light Source
Stanford Synchrotron Radiation Laboratory
Stanford Linear Accelerator Center
Charge – Will the Undulator Diagnostics Serve Commissioning and Operations Needs for the LCLS?
Do we have redundant diagnostics capability where
appropriate?
Diagnostics that check the diagnostics
We are heavily dependent on FEE diagnostics
I don’t see much redundancy yet
FEL/Spont is very bad for the 0.15nm case
Nothing to tune on in the first 40 meters
What is the smallest PROJECTED energy spread we
can produce at any (lower) charge? Can spontaneous
radiation serve as our diagnostic?
Do we need a hi-res monochromator on day 1?
LCLS Undulator Diagnostics Workshop
Wrap-up
20 January 2004
8
John N. Galayda, SLAC
[email protected]
Linac Coherent Light Source
Stanford Synchrotron Radiation Laboratory
Stanford Linear Accelerator Center
Conclusions
Gain versus z can be measured by turning off gain with
an orbit kink
In early commissioning there may be no measurable
gain signal for 40-50 meters when attempting to lase at
0.15 nm
10-3 energy resolution is a must, to get rid of
spontaneous
LCLS Undulator Diagnostics Workshop
Wrap-up
20 January 2004
9
John N. Galayda, SLAC
[email protected]
Linac Coherent Light Source
Stanford Synchrotron Radiation Laboratory
Stanford Linear Accelerator Center
Issues to be Addressed
It is important to estimate how many gain lengths
needed to produce a gain signal above spontaneous
background
~10-3 energy resolution is a must, to get rid of
spontaneous
investigate whether spontaneous radiation become a
diagnostic for undulator alignment and quality
Investigate whether roll-away undulators provide a
useful degree of freedom for diagnosing problems in
commissioning or operations
10
LCLS Undulator Diagnostics Workshop
Wrap-up
20 January 2004
John N. Galayda, SLAC
[email protected]
Linac Coherent Light Source
Stanford Synchrotron Radiation Laboratory
Stanford Linear Accelerator Center
Point of No Return
LCLS Undulator Diagnostics Workshop
Wrap-up
20 January 2004
11
John N. Galayda, SLAC
[email protected]
Linac Coherent Light Source
Stanford Synchrotron Radiation Laboratory
Stanford Linear Accelerator Center
End of Presentation
LCLS Undulator Diagnostics Workshop
Wrap-up
20 January 2004
12
John N. Galayda, SLAC
[email protected]