1. CW Energy Recovery Linac for Next Generation of XFELs
General Thoughts based on TESLA XFEL-TDR
TJNAF: A. Bogacz
INFN: M. Ferrario, L. Serafini
DESY: D. Proch, J. Sekutowicz, S. Simrock
BNL: I. Ben-Zvi
LANL: P. Colestock
UCLA: J. B. Rosenzweig
TESLA_TTF Meeting
Frascati, May 26-28, 2003
TTF Meeting , May 26-28, 2003

2. Motivation XFEL pulsed linac, present layout: Emax = 20 GeV L = 1.4 km
78 Cryomodules each housing 12 sc cavities
936 cavities at Eacc = 23.5 MV/m
Cryoplant kW at 2 K (safety margin ~50%)
capital cost: 336 M€
includes m of active length ~ 0.34 M€/m
TTF Meeting , May 26-28, 2003

3. What do we buy for this money ?
up to 1 nC bunches /s at 20 GeV up to 1 nC bunches /s at 10 GeV (add. costs)
The questions are:
can we buy much more in the future after pulsed XFEL ?
and
is there a major change in the technology needed ?
TTF Meeting , May 26-28, 2003

4. An alternative possible future layout of the linac driving XFEL
Technical assumptions, towards cw operation :
I cavities @ Qo ~ 2E10 @ Eacc  15 MV/m
II. 46 2K cryoplant
III. energy recovery
Are these assumptions very challenging ?
TTF Meeting , May 26-28, 2003

5. • cavities : • cryoplant = ~45÷55 M€ • energy recovery 95 %:
we have good chance after experiment at CEBAF : 1 GeV 20 MeV (98 %) with sc cavities
TTF Meeting , May 26-28, 2003

6. Possible layout can be very similar to the present pulsed linac
1.8 km
~3 km
Dump (0.5 MW)
3xSASE 2xUndulators
RF-Gun ?
BC I : 0.14 GeV
BC II : 0.50 GeV
En = 10÷20 GeV
R~150 m
BC III : 2.50 GeV
TTF Meeting , May 26-28, 2003

7. A very preliminary and not optimized list of parameters
TTF Meeting , May 26-28, 2003

8. Example: 1 mA= 1 nC @ spacing 1 µs
Any combination of the bunch charge and the spacing of bunches giving nominal current is OK
Example: mA= 1 nC @ spacing 1 µs
TTF Meeting , May 26-28, 2003

9. Length of the pulse and power/FPC vs. En
bunches/s
But this requires additional RF
TTF Meeting , May 26-28, 2003

10. How much does the RF cost ?
We have here practically 2 solutions:
Solid state amplifiers ~ 5 kW/FPC  6 M€ (Simrock)
16 kW klystrons (CEBAF 12 GeV upgrade)  16 M€
TTF Meeting , May 26-28, 2003

11. • suppression of microphonics
Conclusion
Needed R&D :
• cw RF gun
• suppression of microphonics
• more experience with the energy recovery
Total cost without experiments should be < 400 M€
Total AC power for Cryoplant + RF < 10 MW
But we will have :
6 x more bunches /s
very flexible time structure of the beam.
TTF Meeting , May 26-28, 2003