Transcript Beam collimation and control in the high energy injectors Scenarios for the LHC Luminosity Upgrade. Arcidosso, Italy, 31 August–3 September 2005 N.

Beam collimation and control in the high energy
injectors
Scenarios for the LHC Luminosity Upgrade.
Arcidosso, Italy, 31 August–3 September 2005
N. Catalan Lasheras
Scenarios for the LHC Luminosity Upgrade
Arcidosso, Italy, 31 August–3 September 2005
1
Scenario for the injectors upgrade
Two rings in the SPS tunnel
 25GeV to 150 GeV
– normal conducting
 150 GeV to 1 TeV
Scenarios for the LHC Luminosity Upgrade.
Arcidosso, Italy, 31 August–3 September 2005
– Superconducting 4.5 T
– Bmax = 100 m; D = 4m; en = 7 mm; delta bucket 10-3
– Acceptance 6s
– 20kW tolerable beam losses 5W/m compatible with cryo load
 Only a scenario but representative of all potential problems
2
Outline
 Why do we have to collimate the beam?
– Background for the experiments in colliders (RHIC, Hera,
Tevatron)
– Activation and hands on maintenance (SNS, high power
machines)
Scenarios for the LHC Luminosity Upgrade.
Arcidosso, Italy, 31 August–3 September 2005
– Machine protection, quenches (LHC, Hera, Tevatron II)
 What exactly do we have to collimate?
– Beam halo and Transient losses
– Betatron and longitudinal losses
 How to do it?
– Multi-stage colllimation
– Scrapers, targets, crystals, kickers
3
How much losses can we tolerate?
 Heat load in the cryogenic system of the SC machine
– 20 KW distributed homogeneously 3 W/m
 Activation and residual radiation
– 1-10 W/m. Higher for higher energies
Scenarios for the LHC Luminosity Upgrade.
Arcidosso, Italy, 31 August–3 September 2005
 Quench protection
– 10-50 W/m from LHC magnets
Very similar figures based in still rough approximations
We may have to clean the beam for all these reasons
How much power can we expect to loss?
4
Scenarios for the LHC Luminosity Upgrade.
Arcidosso, Italy, 31 August–3 September 2005
Other machines. What should we expect?
BNL Boos.
BNL AGS
FNALBoos.
FNAL MR
FNAL TEV.
CERN Boos.
CERN PS
KEK Boos.
KEK PS
RAL ISIS
LANL PSR
Cycl. Time
Circumfere
nce
Injection
loss
Accel.
Loss
Transitio
loss
Extraction
loss
Beam
energy
loss
[s]
0.13
3.6
0.07
2.4
60
1.2
1.2
0.05
3
0.02
0.04
[m]
200
800
474
6282
6282
157
628
38
340
163
90
[kJ]
0.4
3.2
0.05
10
0.1
0.24
0.002
0.03
0.006
0.022
[kJ]
0.3
2.5
0.2
5
0.16
0.1
0.004
0.36
0.03
-
[kJ]
2.60(7.4)
0.12(4.3)
4.0(16.7)
0
0.15(5.4)
-
[kJ]
0.3
7.3
0.16
32
0.1
0.4
0.008
0.96
0
0.003
[kJ]
5.4
240
5.1
600
3200
4.8
62
0.16
5.8
2.6
2.9
(H-,0.2)
(B,1.5)
(H-,0.4)
(B,8.0)
(B,150)
(S,0.05)
(B,1.0)
(H-,0.04)
(B,0.5)
(H-,0.07)
(H-,0.8)
(F,1.5)
(S,25)
(F,8)
(F,150)
(S,800)
(F,1)
(F,13)
(F,0.5)
(S,12)
(F,0.8)
(F.0.8)
Fraction
lost
[%]
19
6.5
10.4
3.2
1
7.5
1.2
8.6
25.9
1.4
0.9
The 2nd Mini-Workshop on Particle Losses, December 9-11, 1996, KEK
In the injection loss column the mode of injection (H-:Hinjection, B:Bunch-tobucket transfer, S:Septum injection) and the injection energy in GeV is
listed. In the transition column the transition energy in GeV is listed in
parenthesis. In the extraction column the mode of extraction (F:Fast
extraction, S:Slow resonant extraction) is listed.
5
Scenarios for the LHC Luminosity Upgrade.
Arcidosso, Italy, 31 August–3 September 2005
How much losses can we expect?
# of
bunches
ppb
Energy
[GeV]
Beam
Energy
[MJ]
Cycle time
[s]
Beam
power
[MW]
LHC nominal
2808
1.15e11
7000
362
-
-
LHC ultimate
2808
1.70e11
7000
535
-
-
LHC upgrade
5616
1.70e11
7000
1000
-
-
SPS
288
1.70e11
150
1.2
10
0.2
SSPS
2288
1.70e11
1000
7.8
10
0.8
 15% of the beam is lost from booster to SPS
 Injection losses are in PS and SPS at the level of %
 Same level of losses expected during slow extraction.
 Power quickly exceed the 20 KW
 And we still have to make sure it is homogeneously lost
6
Loss mechanisms
 Slow continuous losses (Beam halo)
– Space charge (Bunch intensity, energy, emittance, acceptance)
– IBS & Touscheck effect (Intensity, energy, transverse and longitudinal
emittance, transverse and longitudinal acceptance)
– Beam gas scattering (Intensity, vacuum conditions)
Scenarios for the LHC Luminosity Upgrade.
Arcidosso, Italy, 31 August–3 September 2005
– Beam-beam (Intensity, emittance, crossing angle, acceptance)
– Slow resonant extraction (acceptance)
 Transient (still slow) losses
– Capture loss and ramping (Bdot, RF voltage)
– Transition (Uff!)
– Instabilities (…)
 Accidental (fast) losses
– Misinjection
– Kicker failures
– They have to be treated separately but kept in mind all the time!!
7
Acceptance needs
 Losses will be caused by multiple mechanisms not all of them
known
 BUT, for all halo formation mechanisms, an halo remains an halo if
no beam tube is present!!
 Losses will be quantified by the acceptance of the machine
Scenarios for the LHC Luminosity Upgrade.
Arcidosso, Italy, 31 August–3 September 2005
 Both the aperture of the magnets and the optics functions have to be
optimized
 If losses occur (and we know they will) then collimators are
necessary and they will further reduce the aperture of the machine
 Need sufficient magnet aperture, small betas and small dispersion
 Should be easier than in a collider but space is restricted
 Very difficult to fit in an old machine
8
Collimation principles
 Collimators are material blocks
limiting the aperture of the ring.
 Lattice functions determine the
resolution and phase space cuts
Ax
Transverse collimator h=0
Scenarios for the LHC Luminosity Upgrade.
Arcidosso, Italy, 31 August–3 September 2005
 Three main mechanisms capture
the beam
– Ionization
– Multiple Coulomb scattering
– Nuclear interactions (Elastic +
inelastic)
dp/p0
 Hadronic showers are created after an inelastic interaction and power is
deposed along the way
 Typically power is spread along one meter
9
Energy loss by ionization
Cu
Fe
Pt
Pb
Be
C
Al
Si
W
10.00
 Continuous process inside the
collimator
 Well known (Bethe-Bloch
 Lighter materials are more
1.00
1.E-01
1.E+00
1.E+01
1.E+02
1.E+03
bg
1.E+04
1.E+05
ionizing (but less dense)
Closer look to the interesting
range 25, 150 and 1000 GeV
Be
C
Al
Si
Fe
Cu
W
Pt
Pb
4
3
Practically constant across
energies!
-dE/dx
[MeVcm2/g]
Scenarios for the LHC Luminosity Upgrade.
Arcidosso, Italy, 31 August–3 September 2005
equation)
- dE/dx
[MeVcm2/g]
Energy loss or stopping power
2
1
0
0
200
400
T [GeV]
600
800
1000
10
Energy vs. momentum acceptance at 25 GeV
MCs angle and nuclear interaction 25 GeV
0.10
6.00
Be
CAl Si
4.00
2.00
Fe
Cu
W
0.00
Pt
Pb
Scattering angle
[mrad]
Length [cm]
8.00
PtPb
W
0.08
0.06
0.02
Be
Al Si
C
0.1
0.05
0.00
0
20
40
60
80
0
0
20
Atomic number (Z)
Scenarios for the LHC Luminosity Upgrade.
Arcidosso, Italy, 31 August–3 September 2005
0.2
0.15
Fe Cu
0.04
0.25
Fraction removed
Scraper length for dp/p0=0.001 @ T 25 GeV
40
60
80
Atomic number (Z)
 Energy loss is very important for almost any size collimator.
 Protons are outside the momentum acceptance with a weak nuclear
absorption. Jaws are most effective in spreading the beam.
 Primary scrapers could be used with a preference for heavier
elements with downstream longer collimators.
– Secondary jaws need to be very efficient
– One to few turns process.
– Local losses around magnetic elements
11
Energy vs. momentum acceptance at 1 TeV
Scraper length for dp/p0=0.001 @ T 1 TeV
Length [cm]
Be
150.00
CAl Si
100.00
50.00
Fe
Cu
W
0.00
0
20
40
60
Pt
Pb
80
Scattering angle
[mrad]
200.00
1.4E-02
1.2E-02
1.0E-02
8.0E-03
6.0E-03
4.0E-03
2.0E-03
0.0E+00
Atomic number (Z)
PtPb
W
Fe Cu
Be
0
Al Si
C
20
40
60
1
0.995
0.99
0.985
0.98
0.975
0.97
0.965
Fraction removed
MCs angle and nuclear interaction 1TeV
80
Scenarios for the LHC Luminosity Upgrade.
Arcidosso, Italy, 31 August–3 September 2005
Atomic number (Z)
 Energy loss in the collimator is negligible for practical size jaws.
 MCs angle is very small. Definitely a multi-turn process
 Absorption in a single jaw could be done very efficient. Limited by
heat concerns and by out-scattering.
 Shorter jaws of lighter materials are more resistant
 Collimator length needs to be adapted to the expected level of
losses or vice versa.
 Very challenging in the extraction channel
12
Energy vs. momentum acceptance at 150 GeV
0
0.040
CAl Si
Fe
20
Cu
W
40
60
Pt
Pb
0.7
PtPb
W
0.030
0.6
Fe Cu
0.020
0.010
Be
0.5
0.45
0.4
0
20
Atomic number (Z)
Scenarios for the LHC Luminosity Upgrade.
Arcidosso, Italy, 31 August–3 September 2005
0.55
Al Si
C
0.000
80
0.65
Fraction removed
35.00
30.00 Be
25.00
20.00
15.00
10.00
5.00
0.00
MCs angle and nuclear interaction 150 GeV
Scattering angle
[mrad]
Length [cm]
Scraper length for dp/p0=0.001 @ T 150 GeV
40
60
80
Atomic number (Z)
 Somewhere in the middle. Momentum loss is important but particles
stay in the bucket after one passage.
 Momentum acceptance needs to be high to allow multi-turn cleaning
 Injection & ramping losses in the high energy ring
– Assume short injection and fast ramping. Insignificant halo
growth (?)
– Only momentum cleaning would be necessary. Could use thin
scrapers of heavy materials to induce energy loss
13
Nuclear interaction. Optimal jaw length.
 To capture 99.9 % of protons 44 cm of copper are necessary
 Includes both inelastic and elastic nuclear interaction (10% Nuclear
elastic will be lost in the vicinity of the collimator)
 We may not want to absorb that much in a single jaw for the shake
of collimator integrity
100
Fraction of protons absorbed [%]
Scenarios for the LHC Luminosity Upgrade.
Arcidosso, Italy, 31 August–3 September 2005
90
E=1 TeV
80
E=150 GeV
70
E=25 GeV
60
50
40
30
20
99.9% nuclear
absorbtion
10
0
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
Jaw length [m]
 In practice, the final efficiency is less than that but no significant gain
afterwards
14
Out-scattering
 Multiple Coulomb scattering (mCs) as well as ionization is a
continuous process.
 Proton stays on the beam acceptance but it is deflected by the
collimator material
 Protons close to the edge are “out-scattered”
Scenarios for the LHC Luminosity Upgrade.
Arcidosso, Italy, 31 August–3 September 2005
 Out-scattering due to mCs reduces the effective length of the jaw
 One or more secondary collimators located at larger aperture are
necessary to capture the out-scattered particles
15
Maximum efficiency with a single collimator
 Efficiency of the jaw depends on out-scattering
 Out-scattering depends on the impact parameter (diffusion speed
and loss mechanism).
 For continuous losses we assume a 6s halo and a normalized
emittance en=7mm
Scenarios for the LHC Luminosity Upgrade.
Arcidosso, Italy, 31 August–3 September 2005
 Maximum impact parameter estimated from
bmax=3/2(rp2Dr2)1/3
using r=0.3 mm estimated from SPS experiments (T. Risselada, JB.
Jeanneret)
 Beam divergence for 7um emittance and an average b=40m
bmax
6s’
[mm]
[mrad]
25 GeV
0.04
0.5
150 GeV
0.03
0.2
1 TeV
0.02
0.08
16
Out-scattering vs.energy
100
25 GeV
14000
150 GeV
1 TeV
12000
10000
8000
6000
4000
80
Small impact parameter
b=1m, b'=1mrad
70
60
50
40
2000
0
Scenarios for the LHC Luminosity Upgrade.
Arcidosso, Italy, 31 August–3 September 2005
Large impact parameter
90
Fraction of protons absorbed [%]
5
scaping protons (out of 10 )
16000
30
0
0.05
0.1
0.15
s [m]
0.2
0.25
0.3
0
100
200
300
400
500
600
700
800
900
1000
Beam Energy [GeV]
 For a copper block 0.3 m long
 At high energy out-scattering is less important and efficiency is
higher.
 Not strongly dependent on the jaw length. After the out-scattering
length no gain for longer jaw
 Increasing the efficiency implies catching the secondary halo
 We need to have a closer look to their distribution.
17
Energy vs. one passage efficiency
5
8
14
25 GeV
4.5
7
150 GeV
12
6
25 GeV
150 GeV
1 TeV
Collimator
14
10
5
8
Beam
side
Collimator
side
Beam
side
6
12
10
2
Scenarios for the LHC Luminosity Upgrade.
Arcidosso, Italy, 31 August–3 September 2005
-0.001
3
Beam
side
side
0.001
0.003
Beam
0.005
side-0.001
8
-0.0005
Collimator
side
2.5
2
1.5
2
1
1
0
-0.003
3.5
3
4
-0.005
4
1 TeV
4
Collimator
0.0005
side 0.001
0
0
0.5
-0.00025
-0.00015
0
-0.00005
0.00005
0.00015
0.0002
6
4
2
0
-0.005
•
•
-0.003
-0.001
0.001
0.003
0.005
Out-scattering decreases with energy as well as deflected angle
Absorption decreases with energy for the same collimator length
18
Multi-stage collimator system
 Reducing the losses implies catching the secondary halo out-scattered from
the jaw
Residual Halo
Scenarios for the LHC Luminosity Upgrade.
Arcidosso, Italy, 31 August–3 September 2005
Primary Halo Secondary Halo
 Secondary collimators have to be retracted from primary jaws and located
at optimized phase advance.
 To increase efficiency the secondary halo has to circulate freely in the
machine
Collimation efficiency depends of machine acceptance as well!!
19
Scenarios for the LHC Luminosity Upgrade.
Arcidosso, Italy, 31 August–3 September 2005
What do we find in other machines?
Low energy high intensity machines
20
What do we find in other machines? High energy
 Main injector FERMILAB 8 - 150 GeV
 Hera p 40 – 820 GeV
– Two stage collimation system
 Tevatron 150 Gev - 1TeV
Scenarios for the LHC Luminosity Upgrade.
Arcidosso, Italy, 31 August–3 September 2005
– Single collimation system.
– Two stage system for Tevatron II
 SPS 26 - 450GeV
– Single collimation/scrapping system
 AGS 33 GeV
– No collimation system. High activation
 RHIC 100 GeV/n Au.
– Crystal assisted collimation system
– Two stage collimation system from Run 4
21
Very first ideas
 Momentum cleaning at low energy in the SPS
– a heavy material scraper
– local collimators at the right phase advance
 Protection absorbers in the transfer line
Scenarios for the LHC Luminosity Upgrade.
Arcidosso, Italy, 31 August–3 September 2005
 Momentum and betatron cleaning at injection and extraction energy
for the SSPS
– If possible using the same secondary collimators but different
scrapers for different energies to save space
– Separate function scrapers betatron/momentum
– Common absorbers. Special optics with high dispersion
– Could share location with warm injection?
22
Do collimators work?
Dec,5 2003
 Fermilab 980 GeV proton beam. Quench on 2/3 of the machine
 Tungsten target 5mm
 Stainless steel collimator 1.5m long
Scenarios for the LHC Luminosity Upgrade.
Arcidosso, Italy, 31 August–3 September 2005
 Could be considered a success
23
Collimator damage
 Collimators in Hera have
grooves but still protected the
machine
Scenarios for the LHC Luminosity Upgrade.
Arcidosso, Italy, 31 August–3 September 2005
 Studies are on-going (SPS,
FERMILAB) to help predict
the damage
 Still very difficult to predict
the geometry
24
Remaining issues
 Jaw damage studies depending on the energy and beam spot size
may be necessary. Good progress with the LHC studies
 Jaw length definition based on these studies
 Study different jaw cooling, Composite materials
Scenarios for the LHC Luminosity Upgrade.
Arcidosso, Italy, 31 August–3 September 2005
 The typical length of an hadronic shower is 1m. Losses in SPS will
be seen by the SSPS. Cross-talk between machines when in the
same tunnel
 Injection and extraction lines are too short for anything?
 Impedance of the collimators needs to be weighted
 Residual radiation and hands on maintenance requirements to be
defined
 Shielding and maintenance procedures are better considered soon
than later
25
Conclusions
 Collimation is necessary for heat load, machine protection and
activation concerns
 Enough aperture is essential for low losses and high cleaning
efficiency. Do not forget it when defining the magnets
 Most losses are expected at injection energy.
Scenarios for the LHC Luminosity Upgrade.
Arcidosso, Italy, 31 August–3 September 2005
 Collimation system very dependent on the energy
 Two stage collimation is necessary at all energies
 Collimation system needs to be integrated from the beginning but it
is feasible
 More difficult to implement in an old machine
 A lot to learn from LHC specially for 1 TeV
 Either the beam defines the collimation system or the collimation
system will define the beam!!
26