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15 Νοε 2013 (πριν από 3 χρόνια και 6 μήνες)

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LHC Luminosity Upgrade using Crab Cavities

Rama Calaga,
Yi
-
Peng Sun
, Rogelio Tomas, Frank Zimmermann



Acknowledge: R. Assmann, J. Tuckmantel, S. Fartoukh, D. Schulte, R. de Maria,

C. Bracco, T. Weiler, H. Padamsee, K. Oide, I. Ben
-
Zvi,

and LHC
-
CC collaborators

Presented at Shanghai deflecting cavity workshop, 23~25th April 2008

AB/ABP Group, CERN and BNL/US
-
LARP

Supported by the European Community
-
Research Infrastructure Activity under the FP6 “Structuring
the European Research Area” programme (CARE, contract number RII3
-
CT
-
2003
-
506395)

HHH
HHH
HHH
HHH
Collaborators

23/04/2008, Shanghai

LHC crab cavities

2


AES


M. Cole


Brookhaven National Lab


I. Ben
-
Zvi, R. Calaga, S. Peggs



CERN


F. Caspers, U. Dorda, Y. Sun, R. Tom
a
s, J. Tuckmantel, F. Zimmermann


Daresbury Lab & Cockcroft Institute


C. Beard, G. Burt, P. McIntosh, A. Kalinin, A. Dexter, P. Goudket, L. Ma


FNAL


L. Bellantoni, P. Limon, N. Solyak, G. Wu, S. Yakovlev


Jefferson Lab


H. Wang, R. Rimmer



KEK


K. Akai, K. Oide, K. Ohmi, Y. Morita, K. Yamamoto



LBNL


J. Byrd, D. Li


SLAC


C. Adolphsen, V. Dolgashev, Z. Li, T. Markiewicz, C. Ng, A. Seryi, J. Smith,


S. Tantawi, L. Xiao


ANL, INFN, Tech
-
X
, ...

staged approach to LHC upgrade

“phase
-
1” 2013:


new triplets, D1, TAS,
b
*=0.25 m in IP1 & 5,


reliable LHC operation at ~2x luminosity;


beam from new Linac4

“phase
-
2” 2017:


target luminosity 10x nominal,


possibly Nb
3
Sn triplet &
b
*~0.15 m

complementary measures 2010
-
2017:


e.g. long
-
range beam
-
beam compensation,


crab cavities, new/upgraded injectors, advanced


collimators, coherent e
-

cooling, e
-

lenses


longer term (2020?): energy upgrade, LHeC,…

phase
-
2 might be just phase
-
1 plus complementary measures

+ injector

upgrade

3

Geometric luminosity gain

23/04/2008, Shanghai

LHC crab cavities

4

Good agreements between GUINEA
-
PIG simulations and formulae

Crab Cavities will enhance luminosity for all upgrade phases (including nominal LHC)

-

LHC upgrade paths


ultimate beam (1.7x10
11

protons/bunch, 25 spacing),
b
⨠縱~⁣m=
=

early
-
separation dipoles in side detectors , crab cavities


→ hardware inside ATLAS & CMS detectors,


first
hadron

crab cavities; off
-
d b
=
=
stronger triplet

magnets

D0 dipole

J.
-
P. Koutchouk

early separation (ES)

stronger triplet

magnets


ultimate LHC beam (1.7x10
11

protons/bunch, 25 spacing)


b
* ~10 cm



crab cavities with 60% higher voltage


→ first
hadron

crab cavities, off
-
d b
-
b敡e
=
L⸠.癡v猬
=
W⸠.c慮d慬攬
=
F⸠Z業merm慮n
=
full crab crossing (FCC)

larger
-
aperture triplet magnets



50 ns spacing, longer & more intense bunches


(5x10
11

protons/bunch)



b
⩾㈵*cmⰠn漠o汥len瑳t楮獩se=de瑥c瑯ts
=

long
-
range beam
-
beam wire compensation


→ novel operating regime for
hadron

colliders,


beam generation

F. Ruggiero,

W. Scandale.

F. Zimmermann

large
Piwinski


angle (LPA)

5

LHC parameters

23/04/2008, Shanghai

LHC crab cavities

6

parameter

symbol

nominal

ultimate

Early Sep.

Full Crab Xing

L. Piw Angle

transverse emittance

e

[
m
m]

3.75

3.75

3.75

3.75

3.75

protons per bunch

N
b

[10
11
]

1.15

1.7

1.7

1.7

4.9

bunch spacing

D
t [ns]

25

25

25

25

50

beam current

I [A]

0.58

0.86

0.86

0.86

1.22

longitudinal profile

Gauss

Gauss

Gauss

Gauss

Flat

rms bunch length

s
z

[cm]

7.55

7.55

7.55

7.55

11.8

beta* at IP1&5

b*

[m]

0.55

0.5

0.08

0.08

0.25

full crossing angle

q
c
[
m
rad]

285

315

0

0

381

Piwinski parameter

f=q
c
s
z
/(2*
s
x
*)

0.64

0.75

0

0

2.0

hourglass reduction

1

1

0.86

0.86

0.99

peak luminosity

L

[10
34

cm
-
2
s
-
1
]

1

2.3

15.5

15.5

10.7

extent luminous region

s
l

[cm]

4.5

4.3

3.7

3.7

5.3

comment

nominal

ultimate

D0 + crab


crab

wire comp.

for operation at beam
-
beam limit

with alternating planes of crossing
at two IPs










hg
profile
bb
b
b
p
rev
F
F
Q
N
n
r
f
L
D
=
*
1
2
b

↓↓
ES/FCC

↑↑
LPA


LPA


LPA

where (
D
Q
bb
) = total beam
-
beam tune shift;


LPA


ES/FCC

peak luminosity

with respect to ultimate LHC (2.4 x nominal):


ES or FCC: x 6 x 1.3 x 0.86 = 6.7


ES/FCC


LPA: ½ x2 x2.9x1.3 x1.4 = 5.3


LPA

what matters is the
integrated luminosity

23/04/2008, Shanghai

7

LHC crab cavities

Crab crossing

23/04/2008, Shanghai

LHC crab cavities

8

Palmer: linear collider [1]

Oide and Yokoya:

CC in storage rings
(1989)

KEKB: Global CC in rings

Possible LHC crab options: phase 0

23/04/2008, Shanghai

LHC crab cavities

9



One
prototype

crab cavity in one ring for global crabbing



Emphasizes the development and testing of the cavity and cryomodule in LHC
environment.



Luminosity gain (
5
-
7%
) with
β
*=0.55 m.



Limited information about beam
-
beam interactions.



Emittance growth due to effect of crab RF noise together with beam
-
beam tune
spread; Effect of global crab cavities on collimation cleaning efficiency; Effect of
crab


cavity impedance.



Two
prototype

crab cavities in the global crabbing mode, one per
beam



Information on the beam
-
beam interactions in head
-
on collisions.



Possibly
10
-
15%
gain in luminosity (
β

*=0.55 m), in ONE IP.



The increased luminosity would make it more attractive for LHC to support the
installation.



The small increase in luminosity however may be difficult to confirm.

Courtesy BNL workshop summaries

Possible LHC crab options: phase 1

23/04/2008, Shanghai

LHC crab cavities

10



Four crab cavities in the global mode to benefit two interaction
regions



Luminosity gain greater at lower
β
*,
e.g. ~
50%

at
β
*=0.25m.



More expensive than phase 0 and would need more time to implement.



The potential benefit to two interaction regions would probably generate more
support for installation.



Four crab cavities in the local crabbing mode



Luminosity gain greater at lower
β
*, e.g.
~50%

at
β
*=0.25m.



More expensive, as above.



Have to address the tighter space availability near the IPs.


Squashed cell geometry needed for polarization of the crab mode.



Accommodate the crab cavity with vertical crossing angles.


Courtesy BNL workshop summaries

Small crossing angle (0.3~0.6
mrad
)

23/04/2008, Shanghai

LHC crab cavities

11

IP4

IP 6 or 7(8)

IP4 and arc
tunability

(Global CCs)

23/04/2008, Shanghai

LHC crab cavities

12

Possibility of even higher beta
functions with switching polarities
(MQYs) or new hardware.

One arc has 23 cells→
Δ
Ø
x

= [
-
0.60,0.11] and
Δ
Ø
y

= [
-
0.16,0.46]

Switching polarities may increase beta up to
800m,
idea by K. Oide

Wide range tunability in arc, to get good phase advance between CC and IP.


LHC Main RF status

23/04/2008, Shanghai

LHC crab cavities

13

P. Baudrenghien &
T. Linnecar



Two independent rings


4 cryostats (2/beam) plus 1 reserve, each
module 4 SC cavities


Super Conducting SW 400 MHz cavities,


V
RF

= 2 MV (nominal max.)



Tuner: mechanical (range > 200 kHz

), large
tuning range (180 kHz @ 9kHz/s) for beam
-
loading compensation


Movable Main Coupler, 300 kW full reflection,
(12000 < Q
L

< 180000)


1 MV /cavity at injection with Q
L

= 20000


2 MV/cavity during physics with Q
L

= 60000

Local scheme: space challenge

23/04/2008, Shanghai

LHC crab cavities

14

D2

New approach: separation between D1
-
D2, after phase 1

23/04/2008, Shanghai

LHC crab cavities

15


Approximate 10 sigma beam envelope.


New idea from
S. Fartoukh
: Move D2, Q4 and Q5 towards the arcs to improve matchability and
LSS aperture (space between D1 and D2 is increased).


Separation of beams to 27cm for 20m longitudinally achievable with present technology.


D11&D12

Local CC

Noise tolerances

23/04/2008, Shanghai

LHC crab cavities

16

White noise, very pessimistic, below 10^
-
3 deg tolerance, at the edge of
technology?!

Modulated jitter

23/04/2008, Shanghai

LHC crab cavities

17

assuming noise spectra measured at KEKB crab cavities, LHC transverse
emittance growth is negligble

Synchro
-
betatron resonances with Global CCs

23/04/2008, Shanghai

LHC crab cavities

18

CCs enhance the 3
rd
, 5
th
, 6
th
, 7
th

Qs sidebands

Dangerous synchrobetatron resonances could be: Qx
-

Qy + 6Qs, Qx + 2Qy + 30Qs, ...


CCs will suppress Synchro
-
betatron resonances induced by the crossing angle (not included
in the FFT shown).

ongoing study

10
5

Turns DA with CCs

23/04/2008, Shanghai

LHC crab cavities

19

initial momentum offset = 2.5 sigma (standard LHC value), beam energy 7TeV

Collimation

23/04/2008, Shanghai

LHC crab cavities

20

Ralph Assmann


The LHC
collimators must sit very tight
on the beam
to provide good passive protection and cleaning.


As a consequence, the
6D phase space must be well
defined
. Tolerances on relative settings (retraction)
are critical.


Off
-
momentum beta beat is important
and is being
addressed (S. Fartoukh). Larger off
-
momentum beta
beat with upgrade optics.


A
global crab cavity scheme will further complicate
the situation
.


Tests with a global crab scheme can be performed
with a few nominal bunches (increase of specific
luminosity).


Further work is ongoing and required. Interference
local crab cavities and collimation in experimental
insertions.

Off
-
momentum beta
-
beat a big problem, global CC only add a small fraction

Global CC’s impact on collimation

23/04/2008, Shanghai

LHC crab cavities

21

Ralph Assmann

-

0.5
s
x


Set
-
up errors of collimators and transient
changes of beam:


Estimate: ~ 0.3
s

(60
m
m)



Off
-
momentum beta beat
mixes up the 6D
phase space

and can
corrupt collimation
performance

(e.g. loss of horizontal retraction for
tertiary tungsten collimators):


Estimate for tertiary collimators (margin 0.8
s
): ~ 0.5
s


Estimate for absorbers (margin 2.5
s
):


~ 1.5
s


Global crab cavity further reduces
horizontal
retraction
:


Estimate:

ongoing, in the order of 0.5
s





Off
-
momentum beta beating
must be fixed
before installing
global crab cavities
(solution
with complete correction in progress for
nominal LHC and upgrade phase 1, by S.
Fartoukh)



Nominal LHC

LHC
-
CC08

joint BNL/CARE
-
HHH/US
-
LARP


workshop,
BNL, 25
-
26 Feb. 2008

use KEKB experience

plan R&D for crab cavities

phased approach: (1) prototype construction [SBIR]



(2) “global” crab cavity test in IR4,



(3) “local” crab cavities in IR1 & 5

international collaboration

RF Deflector
( Crab Cavity )
Head-on
Collision
Crossing Angle
(11 x 2 m rad.)
Electrons
Positrons
LER
HER
1.41 MV
1.41 MV
1.44 MV
1.44 MV
K. Oide

B. Palmer

22

BNL LHC
-
CC workshop Charge and conclusions

23/04/2008, Shanghai

LHC crab cavities

23



Choice of Freq


800 MHz may be best for Phase 0, lower frequencies if compact cavities are
available (space challenges and more crab voltage). BB simulations with RF
curvature NEEDED




How much free space


10m for Phase 0 (IP4) & 20m for Phase I (IP5/1 with new optics)




Global or Local Phase I


Collimation has to evaluate the exact loss maps and additional heat
deposition from oscillating bunch. Configuration to allow for the extra 0.5
σ

orbit


Can we optimize the existing collimators to exploit oscillating bunch
(
longitudinal collimation
) and reduce impedance




Noise Effects


Need more
S
-
S simulations

to understand any issues but current estimates and
RF jitter suggests that LLRF can keep the jitter within required tolerances


BNL LHC
-
CC workshop Charge and conclusions (con’t 2)

23/04/2008, Shanghai

LHC crab cavities

24


R&D Objectives



Adapt from previous R&D: LLRF, Couplers (LOM), Cryostat(LHC), Tuners



Focus priorities: Collimation, Impedance, Final cavity design and couplers,
Common cryostat,
Simulations
& Measurement on models



Cavity Impedance
needs careful evaluation to establish single bunch & coupled
bunch effects. Start with assumptions used for existing narrow band impedances in
the LHC



RF Control



Q
ext

10
5

− 10
6

? Power Amplifiers: IOT (50
-
100 kW) ?



Power handling
-

beam pipe coax + ferrites robust for high currents



Phase jitter control easily possible ≤ 1
×

10
−2

deg, need ≤ 1
×

10
−3

degree slightly
challenging (800 MHz)


BNL LHC
-
CC workshop:
http://indico.cern.ch/conferenceDisplay.py?confId=24200

BNL LHC
-
CC workshop Charge and conclusions (con’t 3)

23/04/2008, Shanghai

LHC crab cavities

25



Design, Fabrication & Processing



Gradient of 2.5
-
3 MV for 2 cell 800 MHz cavity (E
peak
= 40 MV/m, B
peak
= 120mT)



1
-
2 crab structures/beam should be sufficient. Additional degrees of freedom from optics



0.75 squash ratio is reasonable to fabricate and will fit in new optics with VV crossing
(exotic structures in parallel)



Cavity aperture > 10 cm diameter (smallest aperture 8 cm) (HOM extracting)



Various designs of couplers available, beam pipe coax + waveguide may be most effective
and robust


• Use TWiki as the central repository for design & simulation results


https://twiki.cern.ch/twiki/bin/view/Main/LHCCrabCavities

• Identify various people involved in different studies and consolidate

• What are current resources available & what is needed

BNL
-
AES prototype crab cavity

23/04/2008, Shanghai

LHC crab cavities

26

M. Cole

Preliminary cavity design

23/04/2008, Shanghai

LHC crab cavities

27

Conclusions

23/04/2008, Shanghai

LHC crab cavities

28

1.
Phased crab cavity program in place for LHC

2.
Crab cavities decoupled from the rest of LHC upgrade; they would boost
luminosity for all LHC stages

3.
Global collaboration, and synergy with ILC, CLIC and light sources

4.
First prototype beam testing approximately in 2011
-
2012

5.
KEKB experience is critical

6.
New coupler designs for robust damping needed

7.
Collimation, impedance and noise issues require new simulations, tests,
and developments

8.
LHC constraints could benefit from novel compact cavity

Your collaboration is welcome!