Transcript Slide 1

Linac/BC2 Commissioning
(Dec. 2007 through Sep., 2008)
J. Frisch, et al.
LCLS FAC Meeting
Oct. 30, 2007
LCLS
http://www-ssrl.slac.stanford.edu/lcls/internals/commissioning/index.html
Oct. 30, 2007
LCLS FAC
1
Joe Frisch
[email protected]
LCLS Accelerator Schematic
6 MeV
z  0.83 mm
  0.05 %
4.30 GeV
z  0.022 mm
  0.71 %
Linac-1
L 9 m
rf  -25°
...existing
linac
21-1
b,c,d
DL1
L 12 m
R56 0
Linac-2
L 330 m
rf  -41°
Linac-3
L 550 m
rf  0°
21-3b
24-6d
25-1a
30-8c
X
BC1
L 6 m
R56 -39 mm
Injector Commissioning
BC2
L 22 m
R56 -25 mm
LCLS FAC
undulator
L =130 m
Commission in Jan. 2008
SLAC linac tunnel
Oct. 30, 2007
13.6 GeV
z  0.022 mm
  0.01 %
Linac-X
L =0.6 m
rf= -160
Linac-0
L =6 m
rf
gun
250 MeV
z  0.19 mm
  1.6 %
135 MeV
z  0.83 mm
  0.10 %
2
DL2
L =275 m
R56  0
research yard
Joe Frisch
[email protected]
BC2/Linac
Commissioning Goals
No problems expected
Expect we can run at 1nC
No specific problems expected – but
lots to do
No problems expected
This is the tricky one
No known issues, but there could
be surprises
Oct. 30, 2007
LCLS FAC
3
Joe Frisch
[email protected]
LCLS BC2-Area Layout
OTR screens (3)
Dipole magnets (4)
Kicker magnet (1)
Transverse RF deflector (1)
S-band RF acc. sections
4 wire-scanners “de-scoped”
Can measure gex,y here,
with BC2 OFF
OTR21
BC2
(not to scale)
Oct. 30, 2007
LCLS FAC
4 wire-scanners in sec-28
(300 m downstream)
BXKIK
TCAV3 OTR22
(25-2d) (25-3d)
OTR_TCAV
(25-9)
4.3 GeV
4
Joe Frisch
[email protected]
Linac/BC2 Commissioning Scope
New 4-dipole chicane in 24-7 – 24-8
Adjacent matching quads and new optics
3 new OTR screens, 1 collimator, 1 BPM, and 2
moved wire-scanners in sec-28 (4 wires in sec-24
are “de-scoped”)
Transverse RF deflector at 25-2d + x-kicker 25-3d
Two new coherent radiation-based bunch length
monitors
Energy and bunch length feedback loop and new
SS sub-boosters in 24-1,2,3 + 24-8 (TCAV3)
No new linac BPM electronics in 2008 (or ’09?)
Oct. 30, 2007
LCLS FAC
5
Joe Frisch
[email protected]
Manpower and Scheduling
Ten months of commissioning BC2/Linac (Dec - Sep)
More help with commissioning shifts (H.-D. Nuhn, F.-J.
Decker, Z. Huang, Y. Ding, D. Ratner)
Did 3 shifts per week for 5 months in 2007 - exhausting
No weekend shifts (ops only) after 1st month of startup
Operators now somewhat experienced on injector
Need two physicists/shift for 10 shifts/week (after 1st
month)
Need to cover 20 man-shifts/week - have at least 14
physicists – requires a total of 1.5 shifts/week/man (after 1st
month)
Shutdown LCLS for 2 weeks in March? (new gun probes +
fix GTL)
Oct. 30, 2007
LCLS FAC
6
Joe Frisch
[email protected]
Last Run’s Typical Shift Schedule
Oct. 30, 2007
LCLS FAC
7
Joe Frisch
[email protected]
Schedule
linac/BC2
Install
LTU/Und/Dump
FEE/NEH Install
X-Ray tunnel/FEH Install
Now
1st FEL
Light 1st Users
1st Spont. Light
2008
Controls checkout
& re-commission
injector
…Injector
Commissioning
Oct. 30, 2007
LCLS FAC
2009
Re-commission
Inj/BC2 to SL2
Linac/BC2
Commissioning
FEL
Commissioning
LTU/Und/FEE
Commissioning
8
PPS
2007
PPS
J A S O N D J F M AM J J A S O N D J F M AM J J A S ON D
downtime
commissioning
time
Joe Frisch
[email protected]
BC2 Commissioning Parameters
Parameter
Value
Comments
RF rate
30 Hz
May test 120Hz
Beam rate
≤30 Hz
Drive-laser rate
30 Hz
Bunch charge
Drive-laser pulse length
Final beam energy
250 pC
~6 ps fwhm
13.6 GeV
10 Hz e- beam as baseline – short term 30-Hz
tests (beyond 30 Hz is unnecessary)
Possible 120-Hz late in the run?
Start at this low charge but later up to 1-nC
Optimum not clear yet
13.6 GeV typically with tests down to 4.3 GeV
May 12, 2007
Oct. 30, 2007
LCLS FAC
9
Joe Frisch
[email protected]
Two new OTR screens + LOLA & kicker
BC2 Layout
Oct. 30, 2007
LCLS FAC
10
Joe Frisch
[email protected]
OTR
screen
BPM
Collimator
BC2 Layout
23-m long chicane
Translates horizontally up to 52 cm
Oct. 30, 2007
LCLS FAC
11
Joe Frisch
[email protected]
New construction in BC2 (sector 24/25)
Oct. 11, 2007
Oct. 30, 2007
LCLS FAC
12
Joe Frisch
[email protected]
New construction in BC2 (sector 24/25)
Oct 26
Oct. 30, 2007
LCLS FAC
13
Joe Frisch
[email protected]
New Pre-Beam Tunnel Check List
17 pages
Polarity conventions
Installation orientation
Component bar codes
etc.
Oct. 30, 2007
LCLS FAC
14
Joe Frisch
[email protected]
Magnet Power Supply Modifications
Only QUAD’s 24201-24501 (4 of original 8) remain on sector-24 bulk
supply (keep 0-20 A boost for each)
Q24601 gets its own supply
Doubled-up Q24701A/B gets its own supply
Q24801 quad goes away forever (boost supply is free)
Doubled-up Q24901A/B gets its own supply
New QM21 & QM22 (46-cm FFTB quads) each get own supply
Two new MCOR6 tweaker quads (h-correction) as in BC1
No new correctors here, but all of sectors 20-30 get new MCOR6
corrector supplies to replace old SCOR6 supplies
Control divided between EPICS and SLC
Have software to communicate between systems, but adds complexity.
Still details to work out for LEM, etc .
Oct. 30, 2007
LCLS FAC
15
Joe Frisch
[email protected]
BC2 Dipole Field Quality OK
No quad field and
sextupole is just below tolerance
Oct. 30, 2007
LCLS FAC
16
Joe Frisch
[email protected]
Diagnostics Issues
Can’t tune on something you
can’t measure
Engineering issues with the
wire scanners
Vibration limits us to slow scan
speeds
Can be fixed – but no sure
solution in hand
Physics issues with the OTR
screens
Coherent effects distort image
May be able to fix with short
wavelength filter, but not known.
Oct. 30, 2007
LCLS FAC
17
Joe Frisch
[email protected]
Wire Scanners
Measured beam size
Vs. Motor Steps / second Range is
40-140 microns
With slow scanning, size was
reproducible to 5 microns.
May be able to fix problem by adding
a gear reducer to wires scanner
(cheap), but not tested yet.
For now, limited to slow scans
1 minute / scan,
10 minutes for emittance
measurement.
Oct. 30, 2007
LCLS FAC
18
Joe Frisch
[email protected]
Even “ideal” wire scanner only gives
integrated profiles
Pathological beam shape that would
Not be apparent on wires
Oct. 30, 2007
LCLS FAC
19
Joe Frisch
[email protected]
Coherent Effects in OTRs
OTR12 sum signal as QB is varied. BC1 off, L1X, L1S on crest. Y beam size
Varies with observed intensity
Not clear if effect will be worse after BC2.
Oct. 30, 2007
LCLS FAC
20
Joe Frisch
[email protected]
OTRs - Plans
Installing diffraction gratings in front of OTR cameras
Hope to find that coherence is only in long wavelength signals
If signal is incoherent below ~400nm can easily add filters to
cameras
Installing UV (200nm) and IR (2.5um) detectors on OTRs
IR detectors to understand coherence (not seen yet at DESY /
FLASH or Spring-8 / SCCS)
UV detectors to look for coherence at hard UV
If no coherence at 200nm, can use UV cameras (but $$)
Can not show from beam parameters that we don’t have
coherence as short at 100nm – beyond the range of
conventional cameras.
In future “Laser Heater” will probably fix this problem – but
would like to be able to diagnose beam without heater.
Oct. 30, 2007
LCLS FAC
21
Joe Frisch
[email protected]
Diagnostics – BPMs
Existing linac BPMs have 30 – 100 micron resolution
depending on beam charge (300pc – 1nC).
Readout is through SLC – EPICS communication – slow ~5
seconds.
Will need good linac orbit tuning algorithms.
Work underway.
Need initial accuracy ~1mm. OK
Then tune on emittance – should work but slow.
May wish to tune at high charge (~1nC)
Increase effect of wakefields
Better BPM resolution
Oct. 30, 2007
LCLS FAC
22
Joe Frisch
[email protected]
Diagnostics – where are we?
Wire scanners work but:
For now, just slow scans – hope for a mechanical fix soon
First wires located in S28, 300 meters downstream of BC2
OTRs
So far can not be used for quantitative measurements
Some plans that may fix the problem, but not clear a solution exists
Discussed at 3-way collaboration meeting at Spring-8 this month.
Work underway at other labs.
BPMs
Using old LINAC BPMs.
Should be OK, but readout slow
Next year (?) replace with epics BPMs.
Oct. 30, 2007
LCLS FAC
23
Joe Frisch
[email protected]
Emittance Preservation and Measurement
Measure emittance after L2:
In BC2 (with compressor straight) using OTR
If we do not have coherent effects – otherwise:
Wire scanner in Sector 28 (300M downstream)
Orbit Tuning
Minimize orbit on Linac BPMS
Then Tune orbit on emittance
In OTR21, or in S28 wires
Might be slow to converge
Then optimize BC2 emittance
This is probably our most serious technical
challenge.
Oct. 30, 2007
LCLS FAC
24
Joe Frisch
[email protected]
Bunch Length measurement
In much better shape than transverse measurements
TCAV in S24 will let us resolve bunch length.
Old cavity in new installation.
No problems anticipated.
Cross check with direct compression measurement using
phase cavities
Demonstrated in injector
On line mm-wave bunch length monitors similar to injector
monitors
Shorter mm wavelengths, but should work
Unique beam conditions – can always have surprises!
Oct. 30, 2007
LCLS FAC
25
Joe Frisch
[email protected]
Other Issues
LINAC controls split between EPICS and SLC
systems.
We have tools in place to make this work, but could be
slow to get going
Limited LINAC tunnel access – B-factory running.
Limited time to make changes or repairs
Systems designed for “Production”, not R+D.
Compact, reliable, and high performance, but difficult ot
modify.
Oct. 30, 2007
LCLS FAC
26
Joe Frisch
[email protected]
Additional Run Plans
Improve performance of injector
Better BC1 magnet field quality
X-band cavity moved to reduce steering
Try programmable phase ramp in L0A to reduce bunch length /
improve emittance
New RF system for phase stabilization over ~1km beamline
New temperature stabilized transmission lines
Need to compare with beam timing and MDL.
Complexities due to path length changes in bunch compressors.
Commission new beam feedbacks
Energy and bunch length throughout machine
Energy at 3 points, bunch length at 2, beam time.
Transverse feedbacks throughout machine
Optimize orbit on emittance, then stabilize
Oct. 30, 2007
LCLS FAC
27
Joe Frisch
[email protected]
Summary
Linac/BC2 e- commissioning starts in early Dec.
’07
Large amount of commissioning time available
(fewer shifts/week & no weekends after 1st month?)
Main ’07 goal is to verify full functionality of
linac/BC2 beamline, plus diagnostics and controls
Optimizing performance may take longer
Will need some linac access in first 1-2 months
Oct. 30, 2007
LCLS FAC
28
Joe Frisch
[email protected]