Transcript Undulator Physics Update

Undulator Physics Update
Heinz-Dieter Nuhn, SLAC / LCLS
October 12, 2004
FY2004 Parameter Change Summary
Canted Poles
Electromagnetic Quadrupoles
Wakefield Simulations including AC Conductivity
Undulator Physics Update October 12, 2004
Facility Advisory Committee Meeting
Heinz-Dieter Nuhn, SLAC / LCLS
[email protected]
FEL Design Changes Since the May 2003 Lehman Review
Canted Undulator Poles
Remote Undulator Roll-Away and K Adjustment Function
Increase in Undulator Gap
Reduction in Maximum Beam Energy
Reduction in Quadrupole Gradient
Increase in Beta Function
Increase in Break Section Lengths
 Electromagnetic Quadruples
Undulator Physics Update October 12, 2004
Facility Advisory Committee Meeting
Heinz-Dieter Nuhn, SLAC / LCLS
[email protected]
Undulator Pole Canting
Suggested by J. Pflueger, DESY
•Canting comes from wedged
spacers
•4.5 mrad cant angle
•Gap can be adjusted by lateral
displacement of wedges
•1 mm shift means 4.5 microns
in gap, or 8.2 Gauss
•Beff adjusted to desired value
Source: Liz Moog
Undulator Physics Update October 12, 2004
Facility Advisory Committee Meeting
Heinz-Dieter Nuhn, SLAC / LCLS
[email protected]
Undulator Roll-Away and K Adjustment Function
Neutral; K=3.4965; Dx=+0.0 mm
Undulator Physics Update October 12, 2004
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First; K=3.5000; Dx=-1.5 mm
PowerTp; K=3.4804; Dx=+7.0 mm
Last; K=3.4929; Dx=+1.5 mm
RollAway; K=0.0000; Dx=+100 mm
Heinz-Dieter Nuhn, SLAC / LCLS
[email protected]
Effective B field vs. x
Measured slope of 6.6 Gauss/mm agrees with calculations
(~ 5.7 Gauss/mm for 3 mrad cant)
Field variation allowance between segments is DB/B = 1.5x10-4, or
DB = 2 Gauss, which translates to Dx = 0.3 mm ( or 1 micron in gap)
Undulator Physics Update October 12, 2004
Facility Advisory Committee Meeting
SourceSLAC
Liz Moog/ LCLS
Heinz-Dieter Nuhn,
[email protected]
RMS phase error at different x positions
No significant dependence on X
An RMS phase error of ~ 6.5 degree is an upper limit for nearperfect (~100%) performance
Undulator Physics Update October 12, 2004
Facility Advisory Committee Meeting
SourceSLAC
Liz Moog/ LCLS
Heinz-Dieter Nuhn,
[email protected]
Period-averaged horizontal trajectories at 14.1 GeV
(X in mm)
Trajectories are all well behaved and well within the 2 mm tolerance for
maximum walk-off from a straight line
Undulator Physics Update October 12, 2004
Facility Advisory Committee Meeting
SourceSLAC
Liz Moog/ LCLS
Heinz-Dieter Nuhn,
[email protected]
Canting the poles helps in many ways
Facilitates final setting of Beff
Remote control of position allows run-time
adjustment
Allows compensating for temperature effect on
field strength: ±1.0°C temperature error would
require ±1.2 mm lateral shift of undulator
Undulator Physics Update October 12, 2004
Facility Advisory Committee Meeting
SourceSLAC
Liz Moog/ LCLS
Heinz-Dieter Nuhn,
[email protected]
Change in Undulator Quadrupole Technology
LCLS undulator contains 33 quadrupole magnets
located in break sections.
Permanent magnet technology (PMQ) in the past
Now changed to electromagnet technology (EMQ)
Initial cost estimate $740k lower that costs
budgeted for permanent magnet solution
Undulator Physics Update October 12, 2004
Facility Advisory Committee Meeting
Heinz-Dieter Nuhn, SLAC / LCLS
[email protected]
Some of the reasons for using PMQ in the past
Sufficient for focusing of entire operational range
Sufficient for BBA
Small. Fit into small break sections
No heat dissipation. No cooling water requirements.
No magnet power supplies required. No wiring.
No problems from cooling water vibrations.
Undulator Physics Update October 12, 2004
Facility Advisory Committee Meeting
Heinz-Dieter Nuhn, SLAC / LCLS
[email protected]
Quadrupole Functionality and PMQ Limitations
Three-fold purpose
(1) Focusing
Method: Focusing strength is reduced with beam energy.
PMQ sufficient because optimum gradient weakly dependent on energy.
(2) Beam steering
Method: Trajectory correction by transverse quad displacement
BBA will work but will leave small local bumps (significant Df)
Beam offsets can not be measured BBA can not be verified
(3) Undulator segment alignment
Method: Mechanical Quad-Undulator coupling is used to keep beam
centered in Undulator.
BBA will leave PMQs ~20 mm (rms) off beam axis adding to the undulator
segment alignment budget
Undulator Physics Update October 12, 2004
Facility Advisory Committee Meeting
Heinz-Dieter Nuhn, SLAC / LCLS
[email protected]
Advantages of EMQ technology become apparent
Provide fast verification and refinement of quadrupole’s alignment with respect
to beam position. Precision 2-3 mm with 20% gradient change. This will
improve undulator segment alignment.
Extra space for EMQs now available due to increase in break section lengths.
EMQ can easily accommodate weak x and y dipole trim coils, removing need
for additional vernier-movers on quadrupole.
Gradient tolerances for the undulator quadrupoles are very loose (4%). No
need to standardize EMQ fields.
The costs of EMQs, including steering trims, power supplies, cooling water,
and controls lower than costs budgeted for PMQs.
Power dissipation in magnets and cables does not present significant load for
the HVAC and LCW system. This thermal load should not present a thermal
stability or uniformity problem in the undulator hall.
Measurements of NLC prototype EMQs have demonstrated magnetic center
stability against gradient changes, water flow, and thermal effects, well below
that needed for the LCLS undulator quads.
EMQs provide beta-function adjustment. Present design will limit minimum
beta-function at 14 GeV to 25 m with nominal value of 30 m.
Undulator Physics Update October 12, 2004
Facility Advisory Committee Meeting
Heinz-Dieter Nuhn, SLAC / LCLS
[email protected]
Limitation of BBA based on PMQs
Standard BBA
leaves small local
bumps
Undulator Physics Update October 12, 2004
Facility Advisory Committee Meeting
Heinz-Dieter Nuhn, SLAC / LCLS
[email protected]
Quad Offset Detection with 20% Gradient Variation
14 mm offset
20% gradient change
Offset prediction from
fit using downstream
BPMs
Undulator Physics Update October 12, 2004
Facility Advisory Committee Meeting
Heinz-Dieter Nuhn, SLAC / LCLS
[email protected]
Improved BBA with EMQs
Undulator Physics Update October 12, 2004
Facility Advisory Committee Meeting
Heinz-Dieter Nuhn, SLAC / LCLS
[email protected]
EMQ Magnet Parameters
Magnet quantity
Magnet core steel length
Effective magnetic length
Magnet bore radius
Max. integrated gradient
Nom. integrated gradient
Max. pole-tip field
Max. excitation current
Turns / coil
Power dissipated in magnet
Power dissipated in cables
Water flow per magnet
Undulator Physics Update October 12, 2004
Facility Advisory Committee Meeting
33
7
7.4
0.4
3.6
3.0
0.195
52
6
27
356
0.5
cm
cm
cm
T
T
T
A
W
W
gpm
Heinz-Dieter Nuhn, SLAC / LCLS
[email protected]
EMQ Dipole Trim Parameters
Magnet quantity
Effective magnetic length
Maximum dipole field
Maximum excitation current
Turns/coil
Power dissipated in magnet
Power dissipated in cables
33
7.4
50
2
8
0.06
0.12
Equivalent EMQ displacement  123
Undulator Physics Update October 12, 2004
Facility Advisory Committee Meeting
cm
G
A
W
W
mm
Heinz-Dieter Nuhn, SLAC / LCLS
[email protected]
Summary of Undulator Parameter Changes
May 2003
Undulator Type
Magnet Material
Wiggle Plane
Gap
Gap Canting Angle
Period Length
Effective On-Axis Field
Effective Undulator Parameter K
6.0
0.0
1.325
3.630 ± 0.015%
Module Length
Number of Modules
Undulator Magnet Length
Standard Break Lengths
Total Device Length
Lattice Type
Magnet Technology
Quadrupole Core Length
Integrated QF Gradient
Integrated QD Gradient
Average b Function at 1.5 Å
Average b Function at 15. Å
Undulator Physics Update October 12, 2004
Facility Advisory Committee Meeting
Today
planar hybrid
NdFeB
horizontal
6.8
4.5
30.0 ± 0.05
1.249
3.500 ± 0.015%
mm
mrad
mm
T
3.40
33
112.2
m
18.7 - 18.7 - 42.1
121.0
48.2 - 48.2 - 94.9
131.9
cm
m
PMQ
5
5.355
-5.295
18
7.3
FODO
EMQ
7
3.000
-3.000
30
10
cm
T
T
m
m
m
Heinz-Dieter Nuhn, SLAC / LCLS
[email protected]
Performance Impact of Changes (1.5 Å)
Electron Beam Energy
Emittance
Avg. Electron Beam Radius
Avg. Electron Beam Divergence
Peak Beam Power
FEL Parameter (3D)
Power Gain Length (3D)
Saturation Length (w/o Breaks)
Saturation Length (w/ Breaks)
Peak Saturation Power
Coherent Photons per Pulse
Peak Brightness
Average Brightness
Peak Spont. Power per Pulse
May 2003
Today
14.35
0.043
27
1.6
49
0.00033
4.2
82
89
7.4
1.4×1012
1.5×1033
4.6×1022
91
13.64
0.045
35
1.3
46
0.00032
4.3
86
101
7.6
1.5×1012
1.5×1033
4.7×1022
73
Change
GeV
nm rad
µm
µrad
TW
m
m
m
GW
**
**
GW
-5.0 %
+5.2 %
+27.5 %
-17.5 %
-5.0 %
-3.5 %
+3.6 %
+4.9 %
+13.5 %
+2.5 %*
+2.5 %*
+2.5 %*
+2.5 %*
-19.7 %
*Increase due to 3D effects (reduction in diffraction due to beam radius increase)
** [Ph./s/mm2/mr2/.1%]
Undulator Physics Update October 12, 2004
Facility Advisory Committee Meeting
Heinz-Dieter Nuhn, SLAC / LCLS
[email protected]
Resistive Wall Wakefield with AC Conductivity
Revised resistive wall wakefield theory by K. Bane
and G. Stupakov.
Significant impact on bunch wake function
Study of impact on performance is underway using
FEL simulations
Initial results are available.
Undulator Physics Update October 12, 2004
Facility Advisory Committee Meeting
Heinz-Dieter Nuhn, SLAC / LCLS
[email protected]
Past Wake Function (dc Cu)
Start-To-End Simulations
Parmela
space-charge
Charge Distribution
Elegant
compression, wakes, CSR, …
Convolution with Single Electron
Wake Function
Bunch Wake Function
Undulator Physics Update October 12, 2004
Facility Advisory Committee Meeting
Heinz-Dieter Nuhn, SLAC / LCLS
[email protected]
Corrected Wake Function (ac+dc Cu)
Undulator Physics Update October 12, 2004
Facility Advisory Committee Meeting
Heinz-Dieter Nuhn, SLAC / LCLS
[email protected]
Alternative Material : Aluminum (ac+dc Al)
Undulator Physics Update October 12, 2004
Facility Advisory Committee Meeting
Heinz-Dieter Nuhn, SLAC / LCLS
[email protected]
Wake Functions used in Simulations
Wakefield effect equivalent to tapering
Optimum taper when energy
gain over Lsat is about 2 r
ac+dc Cu
dc Cu
Region of
reasonable gain
dc Al
ac+dc Al
Gain for dc Cu and dc Al can be
improved by actual undulator tapering
Undulator Physics Update October 12, 2004
Facility Advisory Committee Meeting
Heinz-Dieter Nuhn, SLAC / LCLS
[email protected]
FEL Power Predicted by GENESIS
Power at End:
no wake: 12 GW
dc Cu: 10 GW
ac Cu:
8 GW
ac Al:
5 GW
no wake
ac Cu
ac Al
dc Cu
Start-To-End Simulations
Parmela
space-charge
Undulator Physics Update October 12, 2004
Facility Advisory Committee Meeting
Elegant
compression, wakes, CSR, …
Genesis
SASE FEL with wakes
Heinz-Dieter Nuhn, SLAC / LCLS
[email protected]
X-Ray Pulse Profile for Cu DC Model
Deviation from earlier
results due to accidental
coarse phase space
reconstruction
Undulator Physics Update October 12, 2004
Facility Advisory Committee Meeting
Heinz-Dieter Nuhn, SLAC / LCLS
[email protected]
X-Ray Pulse Profile for Cu AC Model
Undulator Physics Update October 12, 2004
Facility Advisory Committee Meeting
Heinz-Dieter Nuhn, SLAC / LCLS
[email protected]
X-Ray Pulse Profile for Al AC Model
Undulator Physics Update October 12, 2004
Facility Advisory Committee Meeting
Heinz-Dieter Nuhn, SLAC / LCLS
[email protected]
Alternate Vacuum Chamber Cross Sections
Parallel plates reduce wakefield effect by 30-40%
(as shown by K. Bane)
Elliptical or rectangular chamber with ratio 2:1 or
larger is reasonable approximation.
This will be investigated with simulations.
Undulator Physics Update October 12, 2004
Facility Advisory Committee Meeting
Heinz-Dieter Nuhn, SLAC / LCLS
[email protected]
Alternate Vacuum Chamber Radius ?
Present case:
en
ID Gap Period Energy Lsat
[mm] [cm] [cm] [cm] [GeV] [m]
1.20 0.5 0.68 3.00
1.65 0.5 0.68 3.00
13.64
13.64
101
130
Psat
[GW]
7.6
4.9
Maximum gap and period adjusted to keep the same power and keep the
saturation length for 1.65 microns under 170 m:
Maximum gap case (Estimates):
en
ID Gap Period Energy Lsat
[mm] [cm] [cm] [cm]
[GeV] [m]
Psat
[GW]
1.20 1.0 1.20 3.85
1.65 1.0 1.20 3.85
7.6
4.6
14.05
14.05
127
167
Extra 40 m of installed undulator needed, which will increase the impact from
wakefields. [Under investigation] Requires redesign of the strongback
assembly.
Undulator Physics Update October 12, 2004
Facility Advisory Committee Meeting
Heinz-Dieter Nuhn, SLAC / LCLS
[email protected]
Wake Function Dependence on Radius (ac+dc Cu)
Undulator Physics Update October 12, 2004
Facility Advisory Committee Meeting
Heinz-Dieter Nuhn, SLAC / LCLS
[email protected]
Wake Function Dependence on Radius (ac+dc Al)
Undulator Physics Update October 12, 2004
Facility Advisory Committee Meeting
Heinz-Dieter Nuhn, SLAC / LCLS
[email protected]
Conclusions
Several Undulator Parameters have been Changed.
New K Adjustment and Roll-Away Option will aid undulator
and FEL commissioning.
Move to EMQ technology to improve trajectory straightness
The newly recognized ac conductivity aspect of resistive
wall impedance impacts the LCLS FEL performance.
Initial simulations with GENESIS 1.3 illustrate the expected
effects:
Power Reduction
X-Ray Pulse Shortening
X-Ray Pulse Dependence on Electron Bunch Distribution Increased
Alternate Material Choices and Chamber Cross Sections
are Investigated
Undulator Physics Update October 12, 2004
Facility Advisory Committee Meeting
Heinz-Dieter Nuhn, SLAC / LCLS
[email protected]
End of Presentation
Undulator Physics Update October 12, 2004
Facility Advisory Committee Meeting
Heinz-Dieter Nuhn, SLAC / LCLS
[email protected]