XFEL Project Overview

R. Brinkmann, DESY

S2E Workshop, Zeuthen, Aug. 18, 2003

TESLA TDR, March 2001: integrated XFEL

Considerations leading to XFEL TDR-update, autumn 2002

• Avoid strong “coupling” of XFEL and LC parts of TESLA project during construction, commissioning and operation stages (and: approval)

• Gain flexibility in operation parameter space

XFEL driver linac in separate tunnel• Limitation of additional cost:

Reduce linac length & energy to ~1.5km, 20 GeVDifference in accelerator cost:

(sep. linac – TDR2001) = 196 Mio. € Reduce # of photon beam lines 10 5, # of experiments

30 10

Comparison of parameters (1Å, fixed-gap undulator)

Eb [GeV]

e [10-6m]

sE [MeV]

Ipk [kA]

lU [mm]

KU gap [mm]

Lsat [m]

Ltot

[m] TDR2001 25 1.6 2.5 5 45 4 12 210 311 Update02 20 1.4 2.5 5 38 3.8 10 145 213

Injector: = TTF-II

Simulations (60MV/m cathode field) indicate e < 1 mm*mrad possible

Including BCs (CSR!), phase space structure non-trivial start-to-end simulations

Linac wakefields unlikely a serious problem

Exploration of bunch parameter space (e.g. charge vs. emittance & bunch length) ?

BC-I

BC-II

BC-III

Extractionswitch

CollimationDiagnostics

Vert. bend

0.5GeV

10…20GeV

2.5GeV

20…40GeV

LINAC1st Stage

LINACUpgrade

Injector

beamline #1beamline #2

20 + 2 units

3 + 1 units

2.4

km1.

4 km

0.1

km3.9km

Recent discussions/developments

• Shortening of the accelerator (Injector + linac + collimation/diagnostic etc.) tunnel to ~2km– The “trend” is that arguments towards higher beam energy become

weaker – more aggressive undu’s, perhaps better beam quality (careful: we haven’t seen the 1.4 mm*mrad yet…), h.h. generation; this together with recent achievements in cav. Performance makes linac length extendibility hard to justify (cost!)

• XFEL site layout not anymore linked to LC site explore possible DESY-near sites – No green light from government for an LC site near Hamburg at this point

in time; process in int. community towards LC technology decision, int. funding and site decision likely to take several years

– Synergy/cost saving arguments for Ellerhoop site can’t be used anymore to push the plan approval procedure through

• Linac to be constructed in TTF-like technology: 12m modules with 8 cavities + quad package– R&D effort and investment in infrastructure necessary to develop

17m modules with superstructures not in healthy balance with potential gains for a 1.5km linac (different for 30km LC!)

• Limit average beam power to ~600 kW (max. 300 kW per solid state beam dump in the 1st stage with two dumps)

0.5

km1.

5 km

0.1

km

BC-I

BC-II

BC-IIIExtractionswitch (?)

CollimationDiagnostics

Beam distr.

0.5GeV

10…20GeV

2.5GeV

Main LINAC

Injector

beam lines

100 modules25 RF stations

16 modules4 RF stations

low-E beamline (?)

Start with reference parameter set…

Main linac Section 2 Energy gain 2.5 20 GeV # installed modules 100 # active modules 92 acc gradient 22.9 MV/m # installed klystrons 25 # active klystrons 23 beam current 5 mA powerbeam p. klystron 3.8 MW incl. 10% + 15% overhead 4.8 MW matched Qext 4.6×106 RF pulse 1.37 ms Beam pulse 0.65 ms Rep. rate 10 Hz Av. Beam power 650 kW

Main linac Section 1 Energy gain 0.5 2.5 GeV # installed modules 16 # active modules 12 acc gradient 20.1 MV/m # installed klystrons 4 # active klystrons 3

Comment 1: energy management in case of failure requires reserve RF units in both section 1 and 2 of main linac (maintain 2.5 GeV energy at BC-III)

Comment 2: lower gradient in section 1 can be advantageous in view of desirable rep. Rate flexibility (see below)

...and investigate optimisation towards cost saving, operational flexibility, …

• More modules (6 instead of 4) per 10MW klystron• Duty cycle/rep rate flexibility/limitations

– Cryogenics: frep up to 20Hz/20 GeV possible with cryo plant size of one (of six) TESLA500 plant and unchanged He distribution concept; frep 1/energy2 possible for lower E operation; CW at 20 GeV excluded (3 times entire TESLA500 2K capacity!)

– RF system: can trade rep rate vs peak power model calculation taking into account properties of 10MW MBK, but not other possible limitations (modulator power switch, RF drive, etc.)

– Injector needs special consideration (e.g. shorter pulses in RF gun at higher frep, laser limitations?)

rep rate vs. acc gradient, 4 modules/klystron

0

20

40

60

80

100

120

0 10 20 30

E_acc [MV/m]

f_re

p [

Hz]

0

200

400

600

800

1000

1200

1400

1600

f_rep

<P_beam>/kW

rep rate vs. acc gradient, 6 modules/klystron

0

20

40

60

80

100

120

0 10 20 30

E_acc [MV/m]f_

rep

[H

z]

0

200

400

600

800

1000

1200

1400

1600

f_rep

<P_beam>/kW

Remark: av. Beam power is maximum possible - because of beam dump (solid absorber option) we wanted to limit Pav 600kW

Max rep rate and beam power, four vs. six modules/klystron

rep rate and max av. power vs. acc gradient, Q_ext varied with E_acc (I_beam=const.), 6

modules/klystron

0

20

40

60

80

100

120

140

0 5 10 15 20 25 30

E_acc [MV/m]

f_re

p [

Hz]

0

200

400

600

800

1000

1200

1400

1600

f_rep

<P_beam>/kW

What can we gain from variable Qext? Example (6 modules):

• Keep Ib = 5 mA const., scale Qext Eacc

• Attractive option: shorter pulses/higher frep (RF gun!)

for this example: assumed variation of pulse length vs. E_acc

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

0 5 10 15 20 25 30

E_acc [MV/m]

T_

pu

lse

[m

s]

T_pulse

T_beam

Options, not part of 1st stage

• Adding more beam lines: in principle straight forward, need to take additional beam distribution requirements into account (facilitate civil construction, leave space for kicker magnets etc.)

• Site dependent: do not exclude using the linac as injector for PETRA and/or HERA

• Do not exclude the far future possibility of operating in CW/ERL mode– Can’t work out a full detailed design for this, but have to avoid “stupid

mistakes” (like non (2n+1)/2 l cavity and module spacing or a fixed Q_ext which can’t be changed without taking the entire linac apart)

– Possible at any site, but has site-dependent aspects

• Challenge is to avoid too much entropy in the project preparation process without missing important future opportunities!

XFEL – Linear Collider Synergies

Working towards getting ready for start of construction of 20 GeV s.c. linac in ~2 years from now is a big step forward for making TESLA technology available for large-scale projects

The issues in common for developing the 500-800 GeV LC s.c. linac and getting ready for constructing the XFEL linac (by far) outweigh those issues which may be different and may require potential priority conflict discussions

There is also overlap between LC and XFEL for a number of other design issues and sub-systems (e.g. failure handling/operational reliability, beam size and profile monitoring, fast orbit feedback, LLRF…)

Example 1: Tunnel Layout

E.g.:

Electronics in tunnel/radiation environment ( test in DESY-LINAC-II)

Handling of RF and cavity failures

Stray fields?

Supports and alignment

520

cm

190

cm

440 cm

80 cm

90

cm

30 cm

125

cm

210 cm2

75 c

m

Figure 3. Main LINAC, Damping Ring & Klystron Station

Example 2: fast kicker systems

• Damping ring: re-distribute the train of bunches in time (compress/de-compress at injection/ejection)

• XFEL user beam lines: distribute bunches within a train to different beam lines (possibly extraction points at different energies, etc…)

• Technology for both applications may also be similar to fast orbit feedback requirements

XFEL Project Group at DESY – 1st meeting Aug. 6group leaders: R. Brinkmann (mainly accelerator), A. Schwarz (mainly user facility)

• Structure the work necessary to prepare for start of project construction in ~ two years total of 38 work packages (reasonable break down of work to start with – not necessarily 100% static, may want to re-define in some cases later)

• WPs cover all categories for complete project definition:– Overall design & parameters, beam physics– Major technical components– Sub-systems– Other issues like “site and civil construction”, “safety”, etc.

• Try to (ideally) have one DESY representative for each WP (WP leader at DESY)

• To avoid mis-understanding: this does not mean to imply that DESY wants to take over all tasks! Leadership and/or participation from other labs is already present, especially for s.c. linac technology

participation from outside will grow in the future and have to be integrated in the Project Group

http://xfel.desy.de