USPAS - Physics and Technology of Linear Collider Accelerators

972 Pages·2003·21.73 MB·English

An Introduction to the
Physics and Technology
of e+e- Linear Colliders
Lecture 1: Introduction and Overview
Nick Walker (DESY)
Nick Walker
DESY
DESY Summer Student Lecture
USPAS Santa Barbara 16th June, 2003
31st July 2002
Course Content
Lecture:
1. Introduction and overview
2. Linac part I
3. Linac part II
4. Damping Ring & Bunch Compressor I
5. Damping Ring & Bunch Compressor II
6. Final Focus Systems
7. Beam-Beam Effects
8. Stability Issues in Linear Colliders
9. the SLC experience and the Current LC Designs
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This Lecture
• Why LC and not super-LEP?
• The Luminosity Problem
– general scaling laws for linear colliders
• A introduction to the linear collider sub-systems:
– main accelerator (linac)
– sources
– damping rings
– bunch compression
– final focus
during the lecture, we will introduce (revise) some important basic
accelerator physics concepts that we will need in the remainder of
the course.
Energy Frontier e+e- Colliders
LLEEPP aatt CCEERRNN,, CCHH
EE == 118800 GGeeVV
ccmm
PP == 3300 MMWW
RRFF
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Why a Linear Collider?
Synchrotron Radiation from e2c2
P = C E2B2
an electron in a magnetic field:
γ γ
2π
B
Energy loss per turn of a
machine with an average
bending radius ρ:
C E4
∆E /rev = γ
ρ
Energy loss must be replaced by RF system
Cost Scaling $$
• Linear Costs: (tunnel, magnets etc)
$ ∝ ρ
lin
• RF costs:
$ ∝ ∆E ∝ E4/ρ
RF
• Optimum at
$ = $
lin RF
Thus optimised cost ($ +$ ) scales as E2
lin RF
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The Bottom Line $$$
LEP-II Super-LEP Hyper-
LEP
E GeV 180 500 2000
cm
L km 27
∆E GeV 1.5
$ 109 SF 2
tot

The Bottom Line $$$
LEP-II Super-LEP Hyper-
LEP
E GeV 180 500 2000
cm
L km 27 200
∆E GeV 1.5 12
$ 109 SF 2 15
tot

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The Bottom Line $$$
LEP-II Super-LEP Hyper-
LEP
E GeV 180 500 2000
cm
L km 27 200 3200
∆E GeV 1.5 12 240
$ 109 SF 2 15 240
tot

solution: Linear Collider
No Bends, but lots of RF!
e+ e-
5-10 km
• long linac constructed of many RF
accelerating structures
• typical gradients range from 25−100 MV/m
Note: for LC, $ ∝ E
tot
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A Little History
A Possible Apparatus for Electron-Clashing Experiments (*).
M. Tigner
Laboratory of Nuclear Studies. Cornell University -Ithaca, N.Y.
M. Tigner,
Nuovo Cimento 37(1965) 1228
“While the storage ring concept for providing clashing-
beam experiments (1) is very elegant in concept it seems
worth-while at the present juncture to investigate other
methods which, while less elegant and superficially more
complex may prove more tractable.”
A Little History (1988-2003)
• SLC (SLAC, 1988-98)
• NLCTA (SLAC, 1997-)
Over 14 Years of
• TTF (DESY, 1994-)
Linear Collider
• ATF (KEK, 1997-)
R&D
• FFTB (SLAC, 1992-1997)
• SBTF (DESY, 1994-1998)
• CLIC CTF1,2,3 (CERN, 1994-)
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Past and Future
SLC LC
E 100 500−1000 GeV
cm
P 0.04 5−20 MW
beam
σ* 500 (≈50) 1−5 nm
y
δE/E 0.03 3−10 %
bs
L 0.0003 ~3 1034 cm?2s-1

generally quoted as but we have a very
‘proof of principle’ long way to go!
LC Status in 1994
1994 E =500 GeV
cm
TESLA SBLC JLC-S JLC-C JLC-X NLC VLEPP CLIC
f
1.3 3.0 2.8 5.7 11.4 11.4 14.0 30.0
[GHz]
L×1033
6 4 4 9 5 7 9 1-5
[cm-2s-1]
P
beam 16.5 7.3 1.3 4.3 3.2 4.2 2.4 ~1-4
[MW]
P
AC 164 139 118 209 114 103 57 100
[MW]
γε
y 100 50 4.8 4.8 4.8 5 7.5 15
[×10-8m]
σ*
y 64 28 3 3 3 3.2 4 7.4
[nm]
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LC Status 2003
2003 E =500 GeV
cm
TESLA SBLC JLC-S JLC-C JLC-X/NLC VLEPP CLIC
f
1.3 5.7 11.4 30.0
[GHz]
L×1033
34 14 20 21
[cm-2s-1]
P
beam 11.3 5.8 6.9 4.9
[MW]
P
AC 140 233 195 175
[MW]
γε
y 3 4 4 1
[×10-8m]
σ*
y 5 4 3 1.2
[nm]
The Luminosity Issue
n N2 f
Collider luminosity (cm−2 s−1) is
L = b rep H
approximately given by D
A
where:
N = bunches / train
b
N = particles per bunch
f = repetition frequency
rep
A = beam cross-section at IP
H = beam-beam enhancement factor
D
n N2 f
For Gaussian beam distribution: L = b rep H
D
4πσσ
x y
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The Luminosity Issue: RF Power
( )
E n Nf N
Introduce the centre of mass L = cm b rep H
D
energy, E : 4πσσ E
cm
x y cm
n Nf E = P
b rep cm beams
=η P
RF→beam RF
η is RF to beam power
RF
efficiency.
η P N
Luminosityis proportional L = RF RF H
D
4πσσ E
to the RF power for a given
x y cm
E
cm
The Luminosity Issue: RF Power
η P N
Some numbers: L = RF RF H
D
4πσσ E
E = 500 GeV x y cm
cm
N = 1010
P = 8 MW
n = 100 beams
b
f = 100 Hz
rep
Need to include efficiencies:
RF→beam: range 20-60%
linac technology choice
Wall plug →RF: range 28-40%
AC power > 100 MW just to accelerate beams and achieve
luminosity
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The Luminosity Issues: storage ring vs LC
LEP f = 44 kHz η P N
rep L = RF RF H
D
LC f = few-100 Hz 4πσσ E
rep x y cm
(power limited)
⇒factor ~400 in Lalready lost!
Must push very hardon beam cross-section at collision:
LEP: σσ ≈ 130×6 µm2
x y
LC: σσ ≈ (200-500)×(3-5) nm2
x y
factor of 106gain!
Needed to obtain high luminosity of a few 1034 cm-2s-1
The Luminosity Issue: intense beams at IP
 
1 N
L = (η P ) H 
RF RF  D 
4πE σσ
 
cm x y
choice of linac technology: Beam-Beam effects:
• efficiency • beamstrahlung
• available power • disruption
Strong focusing
• optical aberrations
• stability issues and
tolerances
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