FLS23 / Luzern, CH / 2023-08-28

FLASH: Status & Upgrade. (MO3A5)
Mathias Vogt (DESY/MFL)
Deutsches Elektronen-Synchrotron DESY, Hamburg, Germany, EU

for my co-authors:
S.Schreiber, J.Zemella
and for the complete FLASH- & FLASH2020+ -teams!

FLASH
Free−Electron Laser
in Hamburg

FLS23 / Luzern, CH / 2023-08-28 14:40/ FLASH: Stat+Upgr / MVogt (DESY/MFL) / MO3A5Content.
• FLASH• FLASH2020+• The 2021/22 Shutdown→ Injector Upgrade (FLASH0)−→ Laser Heater−→ BC2→ partial compensation of long.-transv. correlations→ minor FLASH2 changes• The 2024/25 Shutdown . . . a Staged Approach→ FLASH1 : external seeding + . . .
−→ μBunching studies for seeding→ stage-FULL vs. stage-0• Summary / Outlook

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FLS23 / Luzern, CH / 2023-08-28 14:40/ FLASH: Stat+Upgr / MVogt (DESY/MFL) / MO3A5

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FLASH pre FLASH2020+.
BACCA (3 GHz/warm)
RF−stations

RF−station
D−chicane

RF−stations

beam dump

separation/collimation

S−chicane

Xseed experim.
(EEHG seeding)

LOLA

FLASH1
3.9GHz SCRF
1.3GHz SCRF
RF gun (1.3GHz/warm)

1.3GHz SCRF

1.3GHz SCRF

FLASH−INJECTOR

MAIN−LINAC

injector laser (1&2&3)
5.6 MeV

146 MeV

FL2BC

SASE undulators

beam dump
THz undulator

FLASH2350 MeV to 1250 MeV‘‘Albert Einstein’’FEL user halls

450 MeV‘‘Kai Siegbahn’’pre−ionization laser (25 TW)
FLASHForward Exp.

PolariX−TDSFLASH3• superconducting free-electron laser
w/ 2 FEL beamlines run simultane- → for FEL user experiments
ously• exclusively: FLASH2↔ FLASH3• injector/linac → FLASH0→ switch-yard to→ FLASH1→ FLASH2• FLASH3:
plasma wake ﬁeld acc. experi.
FLASHForward>>

PETRA−IIIFLS23 / Luzern, CH / 2023-08-28 14:40/ FLASH: Stat+Upgr / MVogt (DESY/MFL) / MO3A5

FLASH0 pre FLASH2020+.
BACCA (3 GHz/warm)
RF−stations

RF−station

RF−stations

D−chicane

3.9GHz SCRF
1.3GHz SCRF
RF gun (1.3GHz/warm)

S−chicane

1.3GHz SCRF

1.3GHz SCRF

FLASH−INJECTOR

MAIN−LINAC

injector laser (1&2&3)
5.6 MeV

146 MeV450 MeV• injector/linac :→ photo cathode RF gun ∼600 bu 1 MHz
× 10 Hz

350 MeV to 1250 MeV• 1st bunch compr. chicane(now called FL0BC1)• 1st TESLA-type L-band module (ACC1):• 2nd & 3rd TESLA-type L-band module(ACC2 & ACC3)• SC 3.9 GHz linearizer(4 scaled TESLA cav.s) (ACC39)• 2nd bunch compr. chicane(now called FL0BC2)• NC 3.0 GHz long. feedback cavity(BACCA)• “main linac” 4× (TESLA) L-bandmodules (ACC4/5/6/7)

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FLS23 / Luzern, CH / 2023-08-28 14:40/ FLASH: Stat+Upgr / MVogt (DESY/MFL) / MO3A5

FLASH1 pre FLASH2020+.
beam dump

separation/collimation
Xseed experim.
(EEHG seeding)

LOLA

FLASH1

SASE undulators

beam dump
THz undulator
PETRA−III• E–collimation dogleg• seeding experiment Xseed‘‘Albert Einstein’’FEL user halls• main SASE (Self Ampliﬁcation of StimulatedEmission) undulator ← ﬁxed gap :-(• NC 2.865 GHz transverse deﬂect- • spent beam THz undulator(pump-probe experiments)
ing structure (LOLA) from SLAC
• tilted (x/y-coupled) dump line :-(← longitudinal diagnostics5

FLS23 / Luzern, CH / 2023-08-28 14:40/ FLASH: Stat+Upgr / MVogt (DESY/MFL) / MO3A5

FLASH2 & FLASH3 pre FLASH2020+.

FL2BC

beam dump

SASE undulators

FLASH2

FEL user halls‘‘Kai Siegbahn’’

FLASHForward Exp.

PolariX−TDSFLASH3pre−ionization laser (25 TW)

PETRA−III• switch-yard (FLASH0): kicker/septum • optics matchingw/ Lambertson (DC) septum• 12× planar variable gap undu.:
SASE + advanced extensions:• complicated extraction arc(geometry!!!)→ also extraction to FLASH3(harmonic-lasing-self-seeding,frequency doubler, etc.)• FLASH2’s own post-acceleration, • 12.0 GHz PolariX TDS
post-extraction bunch compressor • electron-photon separation(FL2BC)+ uncoupled dump line

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FLS23 / Luzern, CH / 2023-08-28 14:40/ FLASH: Stat+Upgr / MVogt (DESY/MFL) / MO3A5

FLASH2020+ : Motivation.
• FLASH ([SRF= high rep-rate] + soft X-ray + SASE)×2 beamlines should
stay competitive for the next 10-20 years
1. make lower photon wavelengths possible (“water window”)⇒increase beam energy & afterburner-undulators← but keep the footprint!
2. variable photon polarization ⇒ helical APPLE-III undulators
3.a increase longitudinal photon pulse coherence ⇐ external seeding(HGHG/EEHG)
3.b but keep THz output (⇐ pump-probe) → post compressor
4. high quality beams require improved. . .
. . . operability: transverse matching & reduce long.-2-transv.
intra-bunch-corr.s & long. PS-diagnostics. . . better stability: ameliorate μBunching& remove intra-train orbit slopes

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FLS23 / Luzern, CH / 2023-08-28 14:40/ FLASH: Stat+Upgr / MVogt (DESY/MFL) / MO3A5

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FLASH after the 2021/22 Shutdown.
RF−stations

laser heater

BACCAnewinjector
lasersystem

RF−stationD−chicane

3.9GHz SCRF

FLASH0movable D−chicane

RF−stations

upgraded 1.3GHz SCRF
1.3GHz SCRF
matching (w/ upgr. rf−distribution)
matching

1.3GHz SCRF
RF gun (1.3GHz/warm)

FLASH−INJECTOR

143 MeV

550 MeVbeam dump
THz undulator

XSeed experiment

MAIN−LINAC

old injector lasers (1&2&3)

5.6 MeV

FLASH1
LOLA−TDS

old seed laser

550 MeV to 1350 MeV

matching

photon diag
FLASH2APPLE−III undulator
beam dump

FLASHForward Exp.
PolariX−TDSFLASH3• FLASH0: upgrade towards:→ better beam quality/stability→ higher ﬁnal energy

FEL user halls‘‘Kai Siegbahn’’pre−ionization laser (25 TW)• 2021/22: changes:
only in FLASH0 & FLASH2‘‘Albert Einstein’’• FLASH2: upgrade towards:→ variable photon polarization→ enhanced 3rd harmonics← APPLE-III undulator← prototype for
FLASH1 seed radiators

PETRA

FLS23 / Luzern, CH / 2023-08-28 14:40/ FLASH: Stat+Upgr / MVogt (DESY/MFL) / MO3A5

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FLASH0 after the 2021/22 Shutdown.
RF−stations

laser heater

BACCA

newinjector
lasersystem

RF−station

D−chicane

3.9GHz SCRF

FLASH0movable D−chicane

upgraded 1.3GHz SCRF
matchingmatching

1.3GHz SCRF
RF gun (1.3GHz/warm)

FLASH−INJECTOR

RF−stations

1.3GHz SCRF
(w/ upgr. rf−distribution)
MAIN−LINAC

old injector lasers (1&2&3)

5.6 MeV

143 MeV• new injector laser system prepared• new laser heater installed → space!
⇒ BC1 shifted downstream ← space!
⇒ matching section shrunk& modiﬁed to fulﬁll requirements• ACC2 & ACC3:
new high gradient modules

550 MeV

550 MeV to 1350 MeV• redesign of FL0BC2:
S-type → C-type→ gain space for improved matching• round chamber → quad/BPM/skew-quad packs possible• movable chamber (+ inner dipoles)→ keep variability for simultaneously
seeding (FL1) and SASE (FL2)

FLS23 / Luzern, CH / 2023-08-28 14:40/ FLASH: Stat+Upgr / MVogt (DESY/MFL) / MO3A5

The FLASH0 Laser Heater.

• (LEFT): incoupling chicane for LH laser• overlap bunch w/ laser (green) in undulator (RIGHT)• 1st BC-chicane (FL0BC1): strongly over-folds E-modulation• Increased slice E-spread reduces the μBunching gain (+)
but it also reduces the FEL gain (−)⇒ very sensitive knob for tuning• Commissioning: overlap achieved & μBunching killed & SASE killed
but the sophisticated stuﬀ is still coming!

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FLS23 / Luzern, CH / 2023-08-28 14:40/ FLASH: Stat+Upgr / MVogt (DESY/MFL) / MO3A5

FL0BC2.
• replace old 6-dipole S-type chicane by new 4-dipole C-type chicane⇒ gain some space for matching• round vacuum chamber allows quad/BPM/skew-quad packaround the chamber⇒ partial compensation of systematic longitudinal-to-transverse correlations
inside the bunches⇐ bunch has E-chirp, chicane has hor. dispersion→ head sees diﬀerent kick through quad/skew-quad than tailpg of deﬂection angleg• movable chamber and the inner dipoles
to enable change11

FLS23 / Luzern, CH / 2023-08-28 14:40/ FLASH: Stat+Upgr / MVogt (DESY/MFL) / MO3A5

Compensating Long.–Transv. Correlation w/ FL0BC2.
• Idea by Guetg, Beutner, Prat, Reiche;
Decker, Ding, Huang, Maxwell; (2015/16)
• η⊥ (τ ) := R5 ηΨ(z⊥ , η, τ ) d4 z⊥ d η⇒ η⊥ (τ ) = h τ +O(τ 2 )← bunch compression
z⊥ Ψ(z⊥ ,η, τ )d4 z⊥ dη• z⊥ ⊥ (τ ):= R5 ⇒z⊥ ⊥ (τ ) = ξ τ + O(τ 2 )LL(Qcbf1)τηE−chirp+ transv. disp.
corr−quads/skewquads

τx,y,...

magneticchicaneτ• solve exactly for δ = 0,then solve O(δ) f. δ > 0

Qs2

Qs1
mchirpedRF• thin lens model (IPAC21/TUPAB102)

m−ϕ −ϕ Qu2+ϕx,y,...

ττ

nQu1

correlation correction

η• long.-to-transv. correlation← compensate in chicaneδ δηbunchcompression+ϕδδ(Qcbf2)• gives quad/skew quad strengths
for given correlation and E-chirp
comes at a prize: disp⊥ leaks & M56 modiﬁed

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FLS23 / Luzern, CH / 2023-08-28 14:40/ FLASH: Stat+Upgr / MVogt (DESY/MFL) / MO3A5

The Energy Upgrade.

• pics: FLASH0→ w/o old ACC2 & ACC3 in Jan. 2022 (left)←the weakest modules in FLASH: beam energy at 2nd BC was 450 MeV→ w/ the new ACC3 already placed on supports Feb. 2022 (right)• replaced by refurbished, XFEL-type modules PXM2.1 and PXM3.1• cav’s new ACC2 : from 29MeV/m to 34MeV/m; cav’s new ACC3 : from 24MeV/m to 34MeV/m+ optimized power distribution through ACC23 wave guides⇒ E-gain of > 417 MeV possible even 25◦ oﬀ-crest• great success: Beam energy at 2nd BC immediately up to 550 MeV,
recently even 560 MeV ⇒ E-upgrade save to > 1300 MeV

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FLS23 / Luzern, CH / 2023-08-28 14:40/ FLASH: Stat+Upgr / MVogt (DESY/MFL) / MO3A5

FLASH2 after the 2021/22 Shutdown.

matchingphoton diag
FLASH2APPLE−III undulator
beam dump

FEL user halls‘‘Kai Siegbahn’’

PolariX−TDSPETRA• last undulator ex-FL2SASE14 moved • APPLE-III 3rd harmonic a-burner
to FL2SASE2 (ex-FL2SEED7)⇒ down to 1.3 nm• space for afterburner undulator in exFL2SASE14 (now FL2BURN)→ beam diagnostics shifted upstream &shorter→ new matching into undulator& variable photon polarization• 6 mm diameter chamber already installed in FL2BURN• parts for APPLE-III delayed:
installation end of September?

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FLS23 / Luzern, CH / 2023-08-28 14:40/ FLASH: Stat+Upgr / MVogt (DESY/MFL) / MO3A5

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FLASH after the 2024/25 Shutdown : Stage-FULL.
RF−stations

laser heater

BACCA

newinjector
lasersystem

RF−station

D−chicane

3.9GHz SCRF

FLASH0movable D−chicane

RF−stations

matching &collimation

upgraded 1.3GHz SCRF
1.3GHz SCRF
matching (w/ upgr. rf−distribution)
matching

1.3GHz SCRF
RF gun (1.3GHz/warm)

FLASH−INJECTOR

MAIN−LINAC

old injector lasers (1&2&3)

5.6 MeV

143 MeV

550 MeV

FLASH1beam dump
THz undulator
LOLA−TDS

quasi−DBA
seed lasers
post−compr.
photon diagmatching

FLASH2APPLE−III undulator

550 MeV to 1350 MeVbeam dump‘‘Albert Einstein’’FEL user halls‘‘Kai Siegbahn’’pre−ionization laser (25 TW)
FLASHForward Exp.
PolariX−TDSFLASH3PETRA• 2024/25: only FLASH1• the old FLASH1 will be com- → disentangle photon beamline fromdump line
pletely removed→ moved dump
• FLASH1: upgrade towards:→ uncoupled dump line!
→ HGHG/EEHG seeding• 4 new chicanes: 3 for seeding→ variable polarization& 1 as post-compressor for THz(helical APPLE-III undulators)

FLS23 / Luzern, CH / 2023-08-28 14:40/ FLASH: Stat+Upgr / MVogt (DESY/MFL) / MO3A5

EEHG Seeding at Xseed Experiment in FLASH1.

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FLS23 / Luzern, CH / 2023-08-28 14:40/ FLASH: Stat+Upgr / MVogt (DESY/MFL) / MO3A5

μBunching Simulations using SelaV1D .
• LSC(+CSR) induced
μbunching• MP sim.: overestimating the intrinsic shot-noise→ massive one-to-one simulations (extremely t-consuming!), or:• potentially degrades
FEL performance• SelaV1D , based on backward tracking the PSD on
tree-grid covering only the support of PSD

not always:

semi-Lagrangian tracking / Method of Characteristics /Perron Frobenius Operators→ SpaceChargeAmpliﬁer!!!

⇒ w/ optimized compression WP and moderate LH amplitude → negligible• gain mechanism wellstudied(Stupakov;

Venturini;

10-1
amplitude / DC

known to be more
severe for external
seeding

p3 keV
5 keV
7 keVa) WP1

10-2
10-3
10-4
10-5
2

5

Shneid-10
wavelength / m20

miller, Saldin; Amstutz; . . . )• seed mechanism
mostly unclear →one thing is shotnoiseamplitude / DC10-1

p
3 keV
5 keV
7 keVb) WP2

10-2

30

10-3
10-4
10-52

510
wavelength / m20

30

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FLS23 / Luzern, CH / 2023-08-28 14:40/ FLASH: Stat+Upgr / MVogt (DESY/MFL) / MO3A5

FLASH1 after the 2024/25 Shutdown : Stage-FULL.
matching &collimation

FLASH1beam dump
THz undulator
LOLA−TDSquasi−DBAseed lasers• incoupling of seed laser L1• 1st modulator• over-folding chicane(+ out-coupling L1 + incoupling L2)• 2nd modulator• bunching chicane (+ out-coupling L2)

post−compr.
photon diag‘‘Albert Einstein’’PETRA

FEL user halls• seed radiators:
variable polarization APPLE-III• new location of LOLA
• quasi-DBA (5◦ ) & post-compressor
chicane & THz radiator• new dump line
• but then. . . the staged approach. . .

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FLS23 / Luzern, CH / 2023-08-28 14:40/ FLASH: Stat+Upgr / MVogt (DESY/MFL) / MO3A5

FLASH1 FL1RADI Stage-FULL (top) vs. Stage-0 (bott.).

• 6 instead of 11 APPLE-IIIundulators• No wire scanners/ only WS-chambers• replace 3 of 5 w/ Xseed, P2Ntype undulators as bunchers• otherwise :• leave 2 of 5 empty(FODO-layout is kept)

intersections stay as designed

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FLS23 / Luzern, CH / 2023-08-28 14:40/ FLASH: Stat+Upgr / MVogt (DESY/MFL) / MO3A5

FLASH1
LASH1 FL1PARC Stage
Stage-FULL
FULL (top) vs. Stage
Stage-00 (bott.).

• only OTR station for LOLA
• No post-compression chicane • x-dispersion from messing withFL1CH4
quasi-DBA ⇒parasitic use = bunch length only
• i.e. No post-compression for(full long. PS only in destructiveTHz undulatormode)20

FLS23 / Luzern, CH / 2023-08-28 14:40/ FLASH: Stat+Upgr / MVogt (DESY/MFL) / MO3A5

Summary & Outlook.
• FLASH is undergoing a substantial upgrade/refurbishment program(FLASH2020+).
• If we’re quick, then FLASH will be the only seeded soft X-ray FEL
capable of ∼ 5000 bu/sec.
• 1st upgrade shutdown (2021/22) went well:user-run after quick beam commissioning.
→ Commissioning still ongoing whenever there’s time. . .
• E-upgrade: two new very nice high-gradient modules for ACC2&3⇒ 100-110 MeV more at end of the injector (FL0BC2)• 2nd upgrade shutdown being prepared. Everything within schedule.
• However, in 2024/25 only reduced version possible =“stage-0”.
• Full upgradability to “stage-FULL” is guaranteed be design of stage-0.
• Seeded operation still uncompromised goal of stage-0.
• We are looking forward to the shutdown in 2024/25!

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FLS23 / Luzern, CH / 2023-08-28 14:40/ FLASH: Stat+Upgr / MVogt (DESY/MFL) / MO3A5

Thank you for Listening!

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