LCLS-IISC Undulator Options Present Status 08/24/2013

LCLS-IISC Undulator OptionsPresent Status 08/24/2013Heinz-Dieter Nuhn, Tor Raubenheimer, Juhao Wu

2Insert Presentation Title in Slide Master

Outline

1. Assumed beam parameters and undulator requirements2. Baseline undulator parameters3. LCLS performance with HXR4. Short gain length options for SXR5. SCU options and benefits6. Genesis simulations

Caveats: not all simulation/calculations are done for exactly the same period devices and parameters but they are similar and can be scaled to understand parameter the space


Assumed FEL Configuration

• High rep rate beam could be directed to either of two undulators HXR or SXR bunch-by-bunch• 120 Hz beam could be directed to the HXR at separate times• The SC linac would be located in Sectors 0-10 and would be transported to BSY in the 2km long Bypass Line. It would use a dual stage bunch compressor.• A dechirper might be used to further cancel energy spread for greater flexibility in beam parameters• The high rep rate beam energy would be 4 GeV and the HXR would fill the LCLS hall with ~144 m while the SXR would be <75 m so that it could be fit into ESA• Both undulators would need to support self-seeding as well as other seeding upgrades


Assumed Beam Parameters

The assumed emittance of 0.43 at 100 pC is roughly 25% larger than the LCLS-II baseline. It is more conservative than the NLS or the scaled NGLS values (the latter are consistent with the LCLS-II baseline) however a gun has not yet been demonstrated that achieves the desired emittances. Reduced emittances will decrease gain lengths.Peak current is consistent with higher energy beams and BC’s

NLS NGLS LCLS-IISCBeam energy [GeV] 2.25 2.4 4

Bunch charge [pC] 200 300 100

Emittance [mm-mrad] 0.3 0.6 0.43

Energy spread [keV] 150 150 keV 300 keV

Peak current [kA] 0.97 0.5 1

Useful bunch fraction [%] 40 50 50


High Level Parameters from David Schultz Table

Preliminary machine parameters v0.4 8/21/2013

Line SXR HXR HXRRepetition rate 100 kHz 100 kHz 120 HzElectron Energy 4 GeV 4 Gev 14 Gev

Electron Energy spread 300 keV 300 keV 1000 keVTransverse slice emittance 0.4 μm 0.4 μm 0.3 μm @ 100pCPeak current 1 kA 1 kA 3 kA

Pulse charge 100 pC 100 pC 20-200 pCPhoton energy 0.2-1.3 keV 1.3-5 keV 0.25-20 keVPhoton pulse energy 200 μJ 200 μJ <10mJPhoton beam power < 30W < 50W < 0.01W limit

Photon beam power (DF) 20 W 20 W 1.2 W


Undulator Requirements

Requirements:1. SXR self-seeding operation between 0.2 and 1.3 keV

in ESA tunnel (<75 meters) with 2.5 to 4 GeV beam2. HXR self-seeding operation between 1.3 and 4 keV in

LCLS tunnel (~144 meters) with 4 GeV beam3. HXR SASE operation up to 5 keV with 4 GeV beam4. Primary operation of SXR and TXR at constant beam

energy large K variation5. HXR operation comparable to present LCLS with 2 to

15 GeV beam


Undulator Parameters

1. To cover the range of 0.2 to 1.3 keV using SASE in less than 50 meters (to allow for seeding) lw ~ 40 mm• A conventional hybrid undulator with 40 mm and a 7.2 mm

minimum gap would have Kmax ~ 6.0 which easily covers the

desired wavelength range at 4 GeV2. To achieve 5 keV using SASE with less than 144 meters

at 4 GeV TXR lw <= 26 mm• A conventional hybrid undulator with 26 mm and a 7.2 mm

minimum gap would have Kmax ~ 2.4 which covers desired wavelength range at 4 GeV

• Provides reasonable performance with LCLS beam

Baseline Tuning Range for 4 GeV

HXR: lw = 26 mm, L = 144 m

SXR: lw = 41 mm, L = 75 m

SASE

Self-Seeding

Self-Seeding

Kmax = 6.0

Kmin = 1.6

Kmax = 2.44

Kmin = 0.91

Kmin = 0.55

Kmin is chosen to saturate within given length for SASE or Self-seeding

Kmax is set to the maximum value for a 7.2 mm gap variable gap undulator

Ebeam [GeV]

Eph

oton

[keV

]


X-ray pulse energy at High Rate

More than enough FEL poweralthough results assume fullbeam and are ~2x optimistic


Comparison of HXR with LCLS performance at 120 Hz (1)

26 mm HXR covers 2 keV at ~4 GeV to 30+ keV at 14 GeV – beam energy might be reduced futher ifdesired


Comparison of HXR with LCLS performance at 120 Hz (2)

26 mm HXR provideslower pulse energy than 30 mm LCLS


Options for HXR: SCU, IV, or 30 mm period (1)

To recover the LCLS performance, we need to increase K. Can (1) increase the period, (2) adopt an in-vacuum design, or (3) consider a planar or helical SCU. Example of ahelical SCU below howeverhave not incuded poorerSCU fill factor results areoptimistic


Options for HXR: SCU, IV, or 30 mm period (2)

Example of a 30 mm period hybrid undulator below. Nearly recovers LCLS performance (reduction due to slightlylarger gap with VG undulator) however the maximum photon energy at highrate, i.e, 4 GeVis now 4.3 keV not 5 keV as with 26 mm period


Short Gain Length Options for SXR

The full length of 75 m will be tight in ESA at the maximum photon energy of 1.3 keV and provides little margin. There are three options: (1) lower the beam emittance through either a better injector (LCLS comparable – see slide 4), (2) decrease the SXR period and increase K, or (3) decrease the beam energy and the SXR period.

Example 1: decrease to 26 mm with K=2.4 gain length roughly ½ but almost all tuning is done with energyExample 2: decrease to 30 mm with K=2.0 self-seeding at 1.6 keV and 4 GeV requires ~65 meters

Problem: a shorter period conventional hybrid SXR will not cover the full wavelength range at constant energy SCU


SCU options

An SCU has a number of benefits:1. Would attain comparable performance as LCLS even

while achieving 5 keV at 4 GeV at high rate by operating with high K

2. Would reduce allow shorter SXR period to reduce SXR beam energy and gain length to ensure space in ESA while still covering full wavelength range at constant energy.

J. Wu (SLAC), [email protected], 08/05/2013 16

GENESIS SIMULATION ELECTRON PARAMETERS

Centroid energy 4 GeV; 100 pC compressed to 1 kA; normailized emittance: 0.45 mrad; slice energy spread: sE =

300 keV except for LCLS case with 15 GeV6 cases – details in following pages

Case 1: HXR Kmin = 0.91; lw = 26 mm; Lw = 144 m (study SS 4keV)

Case 2: SXR Kmin = 1.6; lw = 41 mm; Lw = 75 m (study 1.6 keV)

Case 3: SXR Kmax = 6.0; lw = 41 mm; Lw = 75 m (study 200 eV)

Case 4: SXR K = 1.9; lw = 41 mm; Lw = 75 m (study 1.3 keV)

Case 5: SXR K = 2.0; lw = 30 mm; Lw = 75 m (short gain len.)

Case 6: HXR in LCLS TW parameters but K too high for hybrid undulator

Bad

Barely

Good

Good

GoodOK


Summary

Present parameters based on:HXR: 26 mm, 144 meters hybrid VGSXR: ~40 mm, 75 meters hybrid VG (simulations for

41 and 39 mm – either work).

Both choices have limitations: SXR gain length is too long to guarentee self-seeded operation at 1.6 keV in ESA (barely works at 1.3 keV)HXR does not reproduce LCLS performance

Shorter period SXR and longer period HXR fix some issues but introduce others. SCU solves many limitations.


CASE 1: HXR SHORTEST SEEDING WAVELENGTH

Case 2: HXR Kmin = 0.91; lw = 26 mm; Lw = 144 m

SASE: saturates around 70 m


CASE 1: SELF-SEEDING OK AT 4 KEV

Case 1: HXR Kmin = 0.91; lw = 26 mm; Lw = 144 m

Self-seeding: will saturates

Monochromator


CASE 2: SXR 1.6 KEV

Case 2: SXR Kmin = 1.6; lw = 41 mm; Lw = 75 m



CASE 2: SXR SELF-SEEDING NOT OK AT 1.6 KEV


Self-seeding: won’t saturates

Monochromator


CASE 3: SXR AT 200 EV – SHORT GAIN LENGTH

Case 3: SXR Kmax = 6.0; lw = 41 mm; Lw = 75 m



CASE 3: 200EV SELF-SEEDING FINE



Monochromator


CASE 4: SXR AT 1.3 KEV




CASE 4: SXR AT 1.3 KEV BARELY OK FOR SELF-SEEDING


Self-seeding: barely saturates

Monochromator


CASE 5: ALTERNATE SXR FOR SHORTER GAIN LENGTH




CASE 5: ALTERNATE SXR FOR SHORTER GAIN LENGTH



Monochromator


CASE 6: HXR WITH 15 GEV BEAM – K NOT REALISTIC

Case 1: HXR K = 4.2; lw = 26 mm; Lw = 144 m


Centroid energy 15 GeV; 150 pC compressed to 3 kA; normailized emittance: 0.4 mrad; slice energy spread: sE = 1.3 MeV


CASE 6: HXR AT 15 GEV BUT K NOT REALISTIC

Case 1: HXR K = 4.2; lw = 26 mm; Lw = 144 m

Self-seeding: reaching about 500 GW

Monochromator

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LCLS-IISC Undulator Options Present Status 08/24/2013