Position of the 3rd Harmonic System

T. Limberg

Position of the 3rd Harmonic System


Injector (with first Bunch Compression Stage)2

European XFEL MAC May 2010T. Limberg


Injector Hall 3


Start Linac Tunnel

XTIN: Length = 48m, accommodates Gun, ACC1, 3,9GHz, Laser Heater, Diagnostics, Dump Line. XSE: Length = 22.55m, accommodates Shielding, Dogleg


Optical Restraints4


Laser Heater

Diagnostics

Shielding Dogleg BC0 Phase Shifter

LH: - round and as stable as possible beam size required

Diagnostics: - consists of TDS and 4 OTR screens - Optics at OTR screens is implemented by means of a 1.5 FODO cell with the phase advance of 76° - Fixed phase advance between TDS and OTR screens - Optics after LH is fixed. Entrance into the Diagnosticsdescribes the boundary conditions for optics functionsShielding: - Concrete solid wall of 5.1m thickness with a spare place for the beam pipe. However two quadrupoles inside are needed to control the beta function. Dogleg: - Combination of two four cell arcs (8 cell system) - Provides a vertical displacement of the beam for a distanceof 2,75m over the length of 20m. - First order momentum compaction r56 is zero.Phase Shifter:- Two 4m long FODO cells- Allows to adjust the phase advance by +-36°


After Chromatic Optimization5


Assumed: - ideal installation of the quadrupoles without any offsets.- Energy spread of the bunch is 2% RMS

Results:- Emittance growth due to chromaticityeffects over the first 80m is about 5-10%

LH BC0

DOGLEG


Laser Heater6


Horizontal Vertical

, m 4.65 18.33

1.6 -2.6

D, m 0.03 0

, m 615 271

Off-crest acceleration in ACC1 energy spread of 2%

22 D

27,2y

x

at the moment the best possible ratio

Length, mm

BL.1 200

BL.2 200

OTR, BPM 300

UNDULATOR 800

Total 2600

Optics and beam parameters in the undulator

Length of the elements in LH

BL.1

BL.2 BL.2

BL.1

OTR OTRUNDULATOR


MAC Proposal

Avoid energy chirp in laser heater and dogleg:

• Shift 3rd harmonic rf system downstream of dogleg

• Provide chirp for compression with 3rd harmonic

7

European XFEL MAC January 2010T. Limberg


Compression System Overview8



Relation between rf sum shape and amplitudes and phases of fundamental and harmonic rf systems (normalized to beam energy)

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Running fundamental on crest 10


nn

nn

a

a

a

nkk

nk

p

p

p

sin

cos

0)(

00

011

''

'1

22

Control of third derivative (tail control) is lost

For given energy a1 in dogleg, energy p upstream of BC0 will

vary for different working points (or otherwise)

Beam-based rf feedbacks might get simpler


First checks (0.1 nC case) look o.k.11


Longitudinal phase space

Current Profile


Effort and cost: Kryo

Feedcap & endcap

Knees for transfer line

Tight installation

(Very) rough estimate for extra kryo cost: 1 M€

12



RF and LLRF Issues

Klystron will be installed underneath module

LLRF system will be installed close to 3rd harmonic rf

→ no additional problems for these systems at the linac tunnel position

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Summary for Shifting 3rd Harmonic rf and Running First Module on Crest

Plus: Relaxed conditions in dogleg and laser heater Might simplify beam-based rf feed-backs

Minus: Reduced tunability of bunch compression system ~1 M€ extra cost Tight installation Independent and early commissioning not possible

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Position of the 3rd Harmonic System

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