1. Linac (WBS 1.2.2) Vinod Bharadwaj April 23, 2002
System Description
Major Technical Challenges
ES&H
Cost Estimates
Construction Schedule & Critical Path Issues
PED Strategy for FY2003, FY2004
LCLS DOE Review, April 23, 2002
Vinod Bharadwaj, SLAC

2. LCLS Linac Overview The function of LCLS Linac (Accelerator) is
Accept 1 nC electron bunch at 150 MeV from the LCLS Injector
Accelerate the beam to 4.54 – GeV ( 15 – 1.5 Å )
Compress the beam to a nominal 22 mm bunch length
Transport beam to the input of the undulator
Preserve beam emittance during the acceleration, compression and transport ( <20% slice, <100 % projected increase for 1.5 Å)
Control energy spread (<0.02 % slice, <0.1 % for 1.5 Å)
Measure beam properties before injection into the undulator to allow for an understanding of the FEL
Take beam from the output of the undulator and dump it
Allow for flexible operation – low charge, range of energies, beam energy chirp …
LCLS DOE Review, April 23, 2002
Vinod Bharadwaj, SLAC

3. LCLS Linac Overview
The LCLS Linac overlays part of the existing SLAC accelerator complex
The use of the existing linac has to be compatible with PEP-II operation
LCLS has to allow for test beams for HEP and other uses at low rates, but on an arbitrary pulse stealing mode – this has a major impact on the LCLS Linac Design
LCLS DOE Review, April 23, 2002
Vinod Bharadwaj, SLAC

4. Nominal Linac Parameters
Parameter Initial 15 Å 1.5 Å Units
Electron energy GeV
Bunch Charge nC
Normalized projected emittance µm rad
Total energy spread %
Slice energy spread %
RMS bunch length mm
Peak current A
Longitudinal slice brightness A
LCLS DOE Review, April 23, 2002
Vinod Bharadwaj, SLAC

5. LCLS Linac – Major Sub-Systems
The LCLS Linac consists of the following sub-systems (the new systems are colored green
L1 – short linac, three 3-m sections in Sector 21-1b,c,d
LX – 60-cm long X-band RF structure
BC1 – 4-magnet chicane bunch compressor
L2 – 330-meter long linac going from Sector 21-3b – 24-6d
SC Wiggler – one period wiggler
BC2 – 4-magnet chicane bunch compressor
L3 – 550-meter long linac going from Sector 25-1a – 30-8d
BSY beamline
DL2 – beamline transport to the undulator
Dump Beamline – dump the electron beam after the Undulator
LCLS DOE Review, April 23, 2002
Vinod Bharadwaj, SLAC

6. SLAC linac tunnel undulator hall (12/01/01) courtesy P. Emma
LCLS Accelerator and Compressor Schematic
7 MeV
z  0.83 mm
  0.2 %
150 MeV
z  0.83 mm
  0.10 %
250 MeV
z  0.19 mm
  1.8 %
4.54 GeV
z  mm
  0.76 %
14.35 GeV
z  mm
  0.02 %
Linac-X
L =0.6 m
rf=180 rf
gun
new
Linac-1
L =9 m
rf = -38°
Linac-2
L =330 m
rf = -43°
Linac-3
L =550 m
rf = -10°
Linac-0
L =6 m
...existing linac
21-1b
21-1d X
21-3b
24-6d
25-1a
30-8c
undulator
L =120 m
BC-1
L =6 m
R56= -36 mm
BC-2
L =22 m
R56= -22 mm
DL-1
L =12 m
R56 0
DL-2
L =66 m
R56 = 0
SLAC linac tunnel
undulator hall
(12/01/01) courtesy P. Emma
LCLS DOE Review, April 23, 2002
Vinod Bharadwaj, SLAC

7. Major Technical Challenges – Beam Quality
Physics challenges – Paul Emma’s presentation
Coherent Synchrotron Radiation in Bends
projected emittance growth
micro-bunching instability
Emittance Preservation in Linacs
transverse wakefields
component misalignments & chromaticity
Machine Stability
jitter tolerance budget
simulation of budget
LCLS DOE Review, April 23, 2002
Vinod Bharadwaj, SLAC

8. Major Technical Challenges – Diagnostics
LCLS is a challenging machine to tune and operate
LCLS charge range nC (order of magnitude less than SLC)
Need good diagnostic capabilities, (see PK & DD Talks in Injector/Linac BO)
LCLS is divided into logical pieces
Injector – L1+LX+BC1 – L2+BC2 – L3+DL2
Diagnostics stations at the end of each logical piece so that they can be set up independently
Emittance and Energy Spread measurement using standard SLAC diagnostics – wires, BPMs ..
...existing linac L0 rf
gun L3 L1 X L2
gex,y sE
LCLS DOE Review, April 23, 2002
Vinod Bharadwaj, SLAC

9. Major Technical Challenges – Longitudinal Diagnostics
RF transverse deflecting cavities – TC (slide courtesy PK)
Electro optic systems - EO
Terahertz radiation monitors for bunch length - Tz
Energy and energy spread BPMs and Profile Monitors - DE
CSR measurements from synch light from BC bends
Beam phase measurements - f
Zero phase crossing measurement of bunch length - Zf EO f Tz Zf TC DE
CSR
LCLS DOE Review, April 23, 2002
Vinod Bharadwaj, SLAC

10. Major Technical Challenges – Diagnostics
Feedback systems needed for
bunch length commissioning, tuning and operation
Emittance and orbit control
Helped by SLC operational experience
Need new Beam Position Monitor readout electronics
LCLS charge range smaller than SLC running
BPMs still need to work in HEP mode
LCLS resolution requirements more stringent
LCLS DOE Review, April 23, 2002
Vinod Bharadwaj, SLAC

11. Major Technical Challenges – RF
The LCLS design has very tight tolerances for RF phase stability in the various linacs in order to make the bunch compression work well
Need phase stability of 0.1 degrees S-band in L1, L2
Need amplitude stability of 0.1 %
The present RF has this stability of timescale of order one minute
To achieve this
Install new LLRF (Solid State Sub-Boosters - SSSB, Isolator-Phase-shifter-Attenuator - IPA) + associated controls for critical klystrons – L1, two in L2, two in L3 (and the transverse RF diagnostic cavity)
New timing system will trigger L1 and LX directly
Extensive work needed on RF feedbacks to correct drifts on the one minute time scale
LCLS DOE Review, April 23, 2002
Vinod Bharadwaj, SLAC

12. Major Technical Challenges – timing system schematic
LCLS DOE Review, April 23, 2002
Vinod Bharadwaj, SLAC

13. Major Technical Challenges – HEP test beams
SLAC running in the LCLS era
LCLS is scheduled to run 75% of the time
HEP dedicated runs for the remaining 25%
Low rate test beams for HEP and other uses are required on demand in “pulse stealing” mode during LCLS running
Test beams will not compromise the LCLS beam
Test beams during LCLS running
Arbitrary pulse stealing at low rate (<10 Hz)
Maximum beam energy of 30 GeV – LCLS is just a beam transport
Beam transmission through BC1, BC2 chicanes needs careful design
Pulsed quads needed in order to have optimal test beam quality for the higher energy test beams
( LCLS ~ 150 MeV – 15 GeV ; Test Beams ~ 30 GeV )
LCLS DOE Review, April 23, 2002
Vinod Bharadwaj, SLAC

14. ES&H Issues
The LCLS Linac is a modification of the existing SLAC accelerator complex and all the needed policies, practices and rules are already in place.
Two issues are worth mentioning ..
The maximum credible beam power has been calculated. At injection into the LCLS Linac it is 1.5 kW and at 15 GeV it is 150 kW.
(LCLS-TN J.E. Clendenin, I. Evans, S. Mao, D.T. Palmer, J. Schmerge, and M. Woodley, "LCLS Maximum Credible Beam Power," March 30, 2001)
We are putting a tuneup dump in DL2. This is needed so that the beam quality can be checked and optimized before attempting injection into the undulator. The tuneup dump is located in the part of the FFTB tunnel that is under the berm so there are no associated shielding problems
LCLS DOE Review, April 23, 2002
Vinod Bharadwaj, SLAC

15. Cost Estimate – 1.2.2 WBS – Summary Parts list
LCLS DOE Review, April 23, 2002
Vinod Bharadwaj, SLAC

16. 1.2.2 Accelerator Cost Estimate (FY02 Dollars, Thousands)
Name
PED
Construction
Contingency
Total
% Contingency
1.2.2
Accelerator
$ 6,269
$ 11,909
$ 4,874
$ 23,052
27%
$ 1,954
$ 8,222
31%
Mechanical
$ 1,238 $
$ 1,598
29%
Vacuum
$ 1,079
$ 1,440
33%
Diagnostics
$ 1,070 $
$ 1,332
24%
Power Conversion
$ 2,724 $
$ 3,094
14%
Magnets
$ 1,720 $
$ 2,150
25%
Controls
$ 1,876 $
$ 2,356
26% RF
$ 2,201 $
$ 2,860
30%
LCLS DOE Review, April 23, 2002
Vinod Bharadwaj, SLAC

17. Construction Schedule
LCLS Linac construction milestones –
Magnets to bid Oct 2004
SC wiggler to bid Oct 2004
BC-1 Magnets award Jan 2005
SC wiggler award Jul 2005
Start of BC-1 shutdown Oct 2005
BC-1 Magnets received Dec 2005
X-band installed Jan 2006
BC-1 installed Jan 2006
First beam to BC-1 Mar 2006
SC wiggler received May 2006
Start BC-2/DL2 shutdown Oct 2006
BC-2 installed Jan 2007
DL2 installed Jan 2007
Start BC-2 commissioning Mar 2007
LCLS Linac commissioned Oct 2008
LCLS DOE Review, April 23, 2002
Vinod Bharadwaj, SLAC

18. Technical Risk in the LCLS Linac
Emittance control
Emphasis on diagnostics
SLC and SLAC operational experience
Understanding physics effects such as CSR
Bunch length optimization
Fast relative bunch length measurement
Beam temporal structure measurements
Bunch length feedback
Stability issues
Control of input parameters such as charge, timing
RF improvements for phase, amplitude stability
Feedbacks
Start-to-end simulations of the system
LCLS DOE Review, April 23, 2002
Vinod Bharadwaj, SLAC

19. Critical Path Issues Goals: Commission up to BC1 – Spring 2006
Commission Linac – Summer 2007
BC1 system design
Fast bunch length monitoring needed for BC1 commissioning
Timing, RF modifications for L1, and LX needed for BC1 commissioning (RF mods in Injector PED)
LCLS DOE Review, April 23, 2002
Vinod Bharadwaj, SLAC

20. PED Milestones in FY2003 December 2002 March 2003 June 2003
Dipole magnet modelling finished
March 2003
Quadrupole magnet modelling finished
Fast bunch length monitor design complete
June 2003
X-band structure design complete
September 2003
SC wiggler magnet specs finished
BC1 magnet design, vacuum and articulation finished
High resolution BPM electronics designed
LCLS DOE Review, April 23, 2002
Vinod Bharadwaj, SLAC

21. PED Milestones in FY2004 December 2003 March 2004 June 2004
Magnet power supplies defined
March 2004
BC2 magnet, vacuum chamber and articulation design complete
Fast bunch length monitor prototype testing complete
June 2004
Vacuum system design complete
High resolution BPM electronics prototyping finished
Magnet and wiggler design complete
RF systems design complete
September 2004
Designs finished & reviewed
Bid packages for all systems ready
LCLS DOE Review, April 23, 2002
Vinod Bharadwaj, SLAC

22. CD-2 Preparations
LCLS Linac is a modification of the existing SLAC accelerator complex, the majority of equipment is already in place and operational
By April 2003
New magnet modelling complete
Fast bunch length monitor design complete
X-band RF system design started
LCLS DOE Review, April 23, 2002
Vinod Bharadwaj, SLAC

23. Conclusions LCLS Linac physics is well understood
Needed modifications to the SLAC accelerator complex well understood
System is well instrumented
PED plans for FY03, FY04 presented
Construction milestones are set to provide first beam at the end of DL2 in spring 2007
LCLS DOE Review, April 23, 2002
Vinod Bharadwaj, SLAC