SCUs for the LCLS-II HXR FELP. Emma, et. al.
July 9, 2014
Hard X-Ray (HXR) FEL for LCLS-II must cover 1-5 keV (4-GeV)SASE to 5 keV is just possible (with no margin)Self-seeding with PMU not possible beyond 4 keVRadiation dose at 1 MHz threatens PMU fields (DK/K ~ 0.01%)SCU can extend photon range toward 8 keV (1 MHz), and beyond, can allow TW peak-power levels (120 Hz), and with much less sensitivity to radiation dose
L2-Linac L3-Linac
HXU
SXU
Sec. 21-30
LH BC1 BC2
BC3
D2
D10
m-wall
0.65 m0.93 m
2.50 mL1
“kicker”LTUH
LTUSLCLS-ILinac
Pe 120 kW
Pe 120 kW
Pe 250 kW Lu 145 m
PMUNbTi Nb3Sn
g = 5 mm
g = 4 mmg = 4 mm
E = 4.0 GeV (nominal)
145 m
gex,y = 0.40 mmIpk = 1 kAsE = 500 keVb = 16 m20% Lu margin3.4-m seg’s1.0-m breaks1 und. missing1.5 keV low-lim.
magnetic gap is 2.3 mm larger than vac. gap, g
7.6 keV SASE4.8 keV SASE6.8 keV
SASE
lu = 25.6 mm, 18.4 mm, 16.8 mmK = 0.6-2.4, 1.1-3.0, 1.3-3.2B = 0.2-1.0 T, 0.6-1.8 T, 0.8-2.0 T
PMUNbTi Nb3Sng = 5 mm
g = 4 mmg = 4 mm
E = 4.2 GeV (stretch)
8.2 keV SASE145 m
lu = 25.6 mm, 18.4 mm, 16.8 mm
~7 keV HXRSS limit
gex,y = 0.40 mmIpk = 1 kAsE = 500 keVb = 16 m20% Lu margin3.4-m seg’s1.0-m breaks1 und. missing
magnetic gap is 2.3 mm larger than vac. gap, g
E = 4.8 GeV (20% upgrade)
10 keVSASE
PMUNbTi
Nb3Sn
g = 5 mm
g = 4 mm
g = 4 mm
145 m
lu = 25.6 mm, 18.4 mm, 16.8 mm
8.3 keV HXRSS limit
magnetic gap is 2.3 mm larger than vac. gap, g
P (T
W)
z (m)
Add field taper to SCU
TeraWatt Peak Power Possible
C. Emma, C. Pellegrini, Z. Huang
1.2 TW
Nb3Sngm = 7.2 mmge = 0.4 umE = 7.8 GeVf = 120 HzIpk = 4 kA
Possible SCU Layout in LCLS-II (HXR)
Joel Fuerst, ANL
Joining Three 1.5-m Magnets into a Single 4.5-m Device
• Magnets conduction cooled through gap separation extrusion
• Gap separation ensures “seamless” core-to-core joint
• Core center channels may be omitted
End corrector End correctorPhase shifter dipole
Alignment verification quadsand Bx correction
Lb
Lb
Second Field Integral with phase shifter
+k +k
-2k
• Compact phase shifter uses one end corrector from each undulator and one extra dipole magnet in between
• Distance between the undulator cores ~13 cm for this layout (could be reduced if alignment quadrupoles are not necessary)
• Joint sections for Nb3Sn undulator are 4 cm long for each core
Joining Two 1.5-m Segments (13 cm extra)
Cold Break (quadrupole magnet)Conceptual design of a compact quadrupole magnet at breaks
– Directly attached to undulator cold mass– Integrated quadrupole strength of 4 T (LCLS-II) can be obtained– Independently powered coils can be used for x-field correction
End correctorQuadrupole Magnet
Vertical Alignment with Alignment Quadrupoles• Use reference quads at each end of ~3-m structure
– Tuning and calibration based on line between magnetic center of two quads
– Fiducialization performed with stretched wire measurement and referenced to fiducials on outside of cryostat
– Allows for beam based alignment by moving cryostat to find center of quads with electron beam
Small Alignment QuadFull Length Quadrupole
DC Resistive-Wall Wakefield (cold bore & warm)
cold bore
warm boreCu Al
Cu
Al
Parameter NbTi (ANL) Nb3Sn (LBNL) unitsPhoton Energy (4 GeV) 1.5 - 5.0+ 1.5 - 5.0+ keVUnd. Segment Length ~2 ? ~2 ? mUnd. Break Length (cold) 0.5 - 0.7 0.5 - 0.7 mUnd. System Length 145 145 mMissing Segments (HXRSS) 1-2 1-2 -Number of Segments 54 ? 54 ?Magnetic full gap 6.3 6.3 mmVacuum full gap 4.0 4.0 mmUndulator period 18.4 16.8 mmOn-axis field 0.6 - 1.8 0.8 - 2.0 TK parameter 1.1 - 3.0 1.3 - 3.2 -Cryo Power Required ~250 ~250 W
Undulator Parameters (4 GeV)
SCU Advantages
• Dramatically improved HXR-FEL performance (~7 keV with SC-Linac & 1-TW with Cu-Linac)
• Orders of magnitude less radiation dose sensitivity (1 MW!)• No mechanical motion (DC power supply drives each
segment)• Less tunnel space required – looks like LCLS-I und. (?)• Can easily be arranged as vertical polarizer (hor. fields)• Cryo-plant (4.5K, 280 W) might serve as injector stand-in at 2K
(7.5M$) – cryo-dist. system not incl. • Might drop 5 linac CM’s (3.4 GeV) and still get 5 keV (Ti or Sn)?• Or drop 10 linac CM’s (2.8 GeV) and still get 4 keV (Sn only)?
1. What decision criterion should be used to make this technology decision in 2015.
2. What is the impact on the LCLS-II project schedule and what additional
resources are needed to develop production SCUs and install them by the same April 2018 date presently planned for the PMUs?
3. What other subsystems would have to be developed / designed / specified
and become part of the baseline? How would they fit into the facility / tunnel?
4. What other reviews would we have to organize before this could become
baseline? 5. What other assurance would you want as the project director before you
can support the change?
Questions