Transcript Slide 1

Overview of CLIC BDS
Frank Zimmermann
CLIC BDS Day 22.11.2005
Frank Zimmermann, CLIC BDS Day, 22.11.2005
BDS tasks
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focus beams to nm spot size
stably collide two beams
deliver target luminosity
dispose spent beam
ensure adequate background conditions
protect the machine against self-destruction
preserve polarization
control spin orientation
function at different beam energies
handle multiple bunches and nominal intensity
…
Frank Zimmermann, CLIC BDS Day, 22.11.2005
schematic view of beam delivery system
Frank Zimmermann, CLIC BDS Day, 22.11.2005
modular layout
energy collimation
compact
final focus
interaction
region
betatron
collimation
IP switch?
exit line
Frank Zimmermann, CLIC BDS Day, 22.11.2005
dump
optics
Raimondi FF ~0.5 km
CCS length ~2.0 km
only 1 stage
momentum
coll.
final focus.
betatron coll.
with low bx,y
nonzero D’
at IP
F.Z., CLIC-NOTE-551
Frank Zimmermann, CLIC BDS Day, 22.11.2005
beam delivery system & beam parameters
c.o.m. energy
final-focus length
collimation length
3 TeV
0.5 km
2.0 km
hor.,vert. emittance
hor.,vert. beta function
core spot sizes
linear spot sizes
gex,y
bx,y*
sx,y*
0.68, 0.01 mm
7, 0.09 mm
60, 0.7 nm
37, 0.5 nm
bunch length
sz
30.8 mm
crossing angle
bunch population
qc
Nb
20 mrad
2.56x109
# bunches / train
luminosity w/o pinch
nb
L0
220
3.6x1034 cm-2s-1
ideal luminosity w/o pinch
61%
luminosity
L00 loss
Frank Zimmermann, CLIC BDS Day, 22.11.2005
9.3x1034 cm-2s-1
IP distribution
S. Redaelli et al,
CLIC Note 577
(Nanobeam’02)
horizontal
phase-space
distribution
at the IP
calculated
with
Merlin
for a nominal
bunch
particles are
found even
at amplitudes
>1 mm, while
the beam size
is about 40 nm
Merlin, x>3sx: 6.7%, x>6sx: 2.3%, y>3 sy: 15.2%, y>6sy: 7.7%, large tail population
→ for recent studies see talks by T. Asaka & J. Resta Lopez
Frank Zimmermann, CLIC BDS Day, 22.11.2005
what is sx,y?
S. Redaelli et al, CLIC Note 577 (Nanobeam’02)
sx
rms
Gaussian fit
MAD
96.3+/-0.7 nm
55.39+/-0.07 nm
DIMAD
99.0+/-1.4 nm
54.59+/-0.17 nm
Merlin
129.7+/-1.5 nm
57.49+/0.13 nm
PLACET
99.3 +/1.3 nm
54.12+/0.17 nm
sy
rms
Gaussian fit
MAD
3.05+/-0.04 nm
0.680+/-0.001 nm
DIMAD
3.35+/-0.06 nm
0.800+/-0.002 nm
Merlin
4.04+/-0.03 nm
0.688+/-0.002 nm
PLACET
3.42+/-0.03 nm
0.775+/-0.002 nm
linear ideal beam sizes: sx=37.3 nm, sy=0.49 nm
Frank Zimmermann, CLIC BDS Day, 22.11.2005
Gaussian fit
‘loses’ particles
CLIC BDS “footprints” at 3 TeV and 500 GeV
Frank Zimmermann, CLIC BDS Day, 22.11.2005
F.Z., CLIC-NOTE-551
compact FF à la Raimondi & Seryi
advantages:
larger free length l* from last quad to IP,
wider momentum bandwidth,
reduced beam tails
drawbacks:
tighter collimation in x,
sextupoles near final doublet (tuning knobs)
Frank Zimmermann, CLIC BDS Day, 22.11.2005
luminosity performance
luminosity
losses:
SR in bends
→DL~-50%
momentum
spread
→DL~-30%
SR in final
quad’s
→DL~-10%
simulated luminosity w/o pinch & w/o hourglass as a function of full-width
energy spread with & w/o synchrotron radiation for two different values of
bx,y* and assuming gey=10 nm; L0=4.6x1034 cm-2 s-1
Frank Zimmermann, CLIC BDS Day, 22.11.2005
F.Z., CLIC-NOTE-551
system
Length [m] Luminosity w/o pinch
[1034 cm-2 s-1]
total BDS
2557
3.56 28% luminosity
loss from
original long BDS 6186
3.92 collimation
final focus only
548
4.85 system
geometric luminosity without hourglass
and without pinch
(input distribution from PLACET for old linac
pararameters, and taking bx=6 mm, by=70 mm)
numbers refer to new beam parameters: 2.56e9, 150 Hz, 22 bunches/ train
CLIC-NOTE-551
Frank Zimmermann, CLIC BDS Day, 22.11.2005
spot-size limit from SR in final quadrupoles (Oide effect)
O. Napoly
CLIC Note 414,
1999
sx ~30 nm limit
sy~1 nm limit
for gey~20 nm
dependence on
e as sy~e5/7
Frank Zimmermann, CLIC BDS Day, 22.11.2005
top
view
of
CLIC
IR
crab
cavity
crab
cavity
R. Assmann
CLIC-NOTE-551
Frank Zimmermann, CLIC BDS Day, 22.11.2005
final quadrupole
study by M. Aleksa & S. Russenschuck
indicated preference for permanent magnet
CLIC-NOTE-506
stability of magnetic center?
asymmetric DT=1 K (9 kJ/m)→ Dy=286 nm
Frank Zimmermann, CLIC BDS Day, 22.11.2005
or should we
reconsider s.c.
quadrupole?
Frank Zimmermann, CLIC BDS Day, 22.11.2005
synchrotron radiation in solenoid (fringe) field together with
vertical dispersion due to crossing angle & solenoid causes
vertical beam blow → crossing angle limited to 20 mrad
D. Schulte, F. Zimmermann, CLIC-NOTE-484
Frank Zimmermann, CLIC BDS Day, 22.11.2005
spent beam & exit line
at 3 TeV
wide energy
spread
D. Schulte,
CLIC-NOTE-391
F.Z., CLIC-NOTE-551
conceptual
layout of
quadrupoleless
exit line
water dump at 4oC
Frank Zimmermann, CLICB.
BDSJeanneret
Day, 22.11.2005
& E. Wildner, CLIC-NOTE-421
polarization
spin rotation angle ag~ 3404 times bend angle
polarization
vector
must be
matched
into the
BDS
to ensure
longitudinal
polarization
at the IP
Frank Zimmermann, CLIC BDS Day, 22.11.2005
R. Assmann, F. Zimmermann,
CLIC-NOTE-501
collimation requirements:
• remove beam halo to suppress detector background
arising from synchrotron radiation and beam loss
• provide minimum distance from collimators to
collision point for muon suppression
• ensure collimator survival and machine protection
against errand beam pulses
• not be excessively long
• not amplify incoming trajectory fluctuations via
collimator wake fields
Frank Zimmermann, CLIC BDS Day, 22.11.2005
SR fans with beam envelopes at 14 sx & 83 sy
O. Napoly
Frank Zimmermann, CLIC BDS Day, 22.11.2005
CLIC-NOTE-446
collimator survival?
surface of 20-mm
gold-plated Ti-alloy
collimator at the end
of SLC linac after
damage; CLIC beam
is ~104 times more
intense!
Frank Zimmermann, CLIC BDS Day, 22.11.2005
LC collimation concept: thin spoilers followed
by thick absorbers [H. DeStaebler & D. Walz];
spoiler increases angular divergence, reduces
risk of fracture and/or melting
Frank Zimmermann, CLIC BDS Day, 22.11.2005
nominal
beam
sizes at
CLIC
spoilers
superposed
on ‘FJP’
damage
threshold
diagram
‘FJP’ = S. Fartoukh, B. Jeanneret & J. Pancin
Frank Zimmermann, CLIC BDS Day, 22.11.2005
CLIC-NOTE-477
CLIC failure modes & machine protection
• large betatron oscillations are not easily generated
from pulse to pulse; and in the linac they rapidly filament
& emittance increases by ~2 orders of magnitude
• energy errors will occur much more frequently, e.g.,
due to missing or mis-phased drive beams, injection
phase errors, or charge fluctuation
CLIC philosophy: demand passive survival for momentum
errors; but allow sacrificial betatron collimators
(shorter length)
failure mode study by Daniel Schulte & F.Z. at PAC2001
Frank Zimmermann, CLIC BDS Day, 22.11.2005
simulated effective beam size sr=(sx sy)1/2 at 1st
spoiler; error bar indicates minimum and maximum over
10 random seeds
various failure modes
CLIC-NOTE-492
Frank Zimmermann, CLIC BDS Day, 22.11.2005
various failure modes
simulated centroid
betatron oscillation
amplitudes at the
first spoiler, normalized to unperturbed
rms beam sizes;
error bars show
min. and max. over
10 random seeds
these pulses would destroy
these pulses might destroy the betatron collimators
the betatron collimators
tighten momentum collimation depth to intercept
all dangerous pulses by the momentum spoiler!
Frank Zimmermann, CLIC BDS Day, 22.11.2005
CLIC-NOTE-492
transverse collimation depth:
from synchrotron radiation & beam loss in final
quadrupoles on incoming side only
bx from SR fan in final doublet: about +/- 10 sx
by from SR fan in final doublet: about +/- 80 sy
momentum collimation depth:
failure modes & machine protection
d from linac failure modes: about +/- 1.5%
Frank Zimmermann, CLIC BDS Day, 22.11.2005
collimator parameters
cm energy
d spoiler gap
bx spoiler gap
by spoiler gap
spoiler material
spoiler length
absorber
material
absorber length
no. of d spoilers
no. bx,y spoilers
3 TeV
+/- 4 mm (1.5%)
+/- 80 mm (10 sx)
+/- 104 mm (80 sy)
Be
177 mm (0.5 r.l.)
Ti (Cu coated)
500 GeV
+/- 4.8 mm (1.5%)
+/- 300 mm (9 sx)
+/- 215 mm (69 sy)
Be
177 mm (0.5 r.l.)
Ti (Cu coated)
712 mm (20 r.l.)
1
4, 4
712 mm (20 r.l.)
1
4, 4
scattered beam size on d-absorber: sr ~1.1 mm!?
should sr>r.l.?
Frank Zimmermann, CLIC BDS Day, 22.11.2005
muon background
Geant-4
simulation
size of magnets
for
10000
matters!
e- lost on
first spoiler
(H. Burkhardt)
magnetized cyl.
unmagnetized cyl.
radius 20 cm
unmagnetized cyl.
& only 1st photon
unmagnetized cyl.
radius 50 cm
(H. Burkhardt, Nanobeam 2002)
Frank Zimmermann, CLIC BDS Day, 22.11.2005
max. jitter enhancement from collimator wake
carbon
spoiler
seems not
acceptable;
Be spoiler
possible;
absorbers
from
Cu-coated
Ti & pure
Cu both ok
(Redaelli)
CLIC-NOTE-579
nominal
4 spoilers & 4 absorbers
Frank Zimmermann, CLIC BDS Day, 22.11.2005
alternative nonlinear collimation system
better optical performance
reduced wake fields
shorter?
basic scheme
→ talks by A. Faus-Golfe & J. Resta Lopez
Frank Zimmermann, CLIC BDS Day, 22.11.2005
laser wire as beam-size monitor?
energy distribution along
old CLIC BDS from 1000
laser-wire Compton scatters
total energy loss per bunch
train along the CLIC BDS
due to 0.1% flat halo
backgrounds completely swamp laser-wire signal!
G.A. Blair, BDSIM simulation, Nanobeam2002
Frank Zimmermann, CLIC BDS Day, 22.11.2005
margins & overheads?
S. Redaelli’s simulations indicate 25-30% luminosity
loss due to fast ground motion
1996 NLC ZDR estimated 20% luminosity loss due
to limited beam-based tuning precision for 16
important IP aberrations (Irwin et al)
we could expect a total luminosity loss >50% due to
these effects
Frank Zimmermann, CLIC BDS Day, 22.11.2005
Frank Zimmermann, CLIC BDS Day, 22.11.2005
open questions & outstanding tasks
 simulate luminosity performance with errors,
ground motion, component jitter, feedback, and
realistic tuning, and noisy diagnostics
 integrated simulation, including realistic beam
distribution from linac with its own errors and tails
 improve performance of present system, especially
collimation (→shorter, wider bandwidth, higher
luminosity), characterize collimation efficiency
 fully master design of compact final focus
 Be spoilers acceptable? beam size at absorber?
 wake field effects, electron cloud, etc.
Frank Zimmermann, CLIC BDS Day, 22.11.2005
thank you for your attention!
Frank Zimmermann, CLIC BDS Day, 22.11.2005