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F. Willeke, Snowmass HERA Luminosity Constraints & Limitations Limitations: N p / N proton beam brightness = 1 x / 4 m (injector, ibs, bb-e) I e total lepton beam current = 60mA (rf power, bb-p) p proton relativistic factor = 981 (max field, circumference) x,y p hor.& vert. Betafunctions at the IP = 2.45m/0.18m (ir layout, p ) Constraints: mr (beam-beam tracking Sen‘95) => set 0(head on coll.) x,yp =~ x,ye (Brinkmann, Willeke PAC’93) e not (yet) limiting L = 7 x cm -2 sec -1 To what extend are these fundamental?
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F. Willeke, Snowmass 2001 1
Luminosity Limitations of e-p Colliders
•Extrapolation from HERA Experience•Examples for IR Layout•LINAC-Ring Limitations•HERA Limitations
F. Willeke, Snowmass 2001 2
HERA Luminosity
222222
0
4 yeypspxexp
bep fnNNL
2001 PARAMETERS
Np number of protons per bunch = 1 x 1011
Ne number of leptons per bunch = 3 x 1010
nb number of bunches = 174
f0 revolution frequency = 47.3kHz
x,y,p,e hor./vert. beam dimensions of leptons & protons = 114m/ 30m
half crossing angle = 0
L luminosity = 7 x 1031cm-2sec-1
F. Willeke, Snowmass 2001 3
HERA Luminosity Constraints & Limitations
**2 xpypN
pep
e
INL
Limitations: Np / N proton beam brightness = 1 x 1011/ 4m (injector, ibs, bb-e)
Ie total lepton beam current = 60mA (rf power, bb-p)
p proton relativistic factor = 981 (max field, circumference)
x,y p hor.& vert. Betafunctions at the IP = 2.45m/0.18m (ir layout, p)
Constraints: mr (beam-beam tracking Sen‘95) => set 0(head on coll.)
x,yp=~ x,ye (Brinkmann, Willeke PAC’93)
e not (yet) limiting
L = 7 x 1031cm-2sec-1
To what extend are these fundamental?
F. Willeke, Snowmass 2001 4
Proton Beam Brightness Limitations
Present design Np / N =1 x 1011 / 4 x 10-6 m
Laslett Tuneshift in DESY III Booster Synchrotron 50MeV (kin.energy) injection
sc ~ R Np / ( N B ) = 0.6 @ 1.3 1011 & N=2mCan be overcome by smaller ring are higher injection
energy in the booster
No principal limitation `just´ costs
Example:
DESYIII Inj. Energy from 50MeV120MeV @ 10M$
F. Willeke, Snowmass 2001 5
Proton Beam Brightness Limitations:IBSScaling from HERA
N p 1 1011 E 920 GeV E A 1 920 GeV
3.17 10 4 s 0.12 e volt sec N 4 mrad mm x 0.419 mm
e 7.392 10 5 s 168.386 mm 4.079 nm y 0.419 mm
0.562 ns
longitudinal s h
2
2 e2A ib F c 1 c 2 c 3
1
s 8.238 hour
A ib1
64 2r 0
2 c
s e x y xp yp 4
N p F c1 c2 c3( ) 8
0
1
x2 ln c32
1
p x c1( )1
q x c2( ) 0.577 1 3 x2
p x c1( ) q x c2( ) d
p x c1( ) c 12 x2 1 c 1
2 q x c 2 c 22 x2 1 c 2
2
h1
e2
D x2
x2
D y2
y2
1
d 1 x c 1 h
xpc 2
h yp
c 3 2 h dr 0
F. Willeke, Snowmass 2001 6
F. Willeke, Snowmass 2001 7
Scaling IBS
Increasing Np/N increases growth time:
larger s Larger s larger * (hourglass effect)
Luminosity almost independent of Np/N
Possible Cure: More RF Voltage
ibs~URF0.25 however e ~ URF
0.25
L / L0 = (e / e )2= (URF/ URF0)1/2 (expensive)
HERA Experience: Running with 2x nominal e still ok but effect already noticeable (increased backgrounds)
s~N1.42~s
1.52~URF1/4
F. Willeke, Snowmass 2001 8
Cooling
Bunched Beam Stochastic Cooling at High Energy
Not very promising perspective
Bunched e-Beam Cooling:
-May be cost effective way to provide bright beams
-Doesn‘t look promising for high energies
-May work for ions
See K.Balewski‘s presentation
F. Willeke, Snowmass 2001 9
Lepton Beam-Beam Effect
This is already a rather large value which potentially limits the proton beam brigthness.
What are the margins? beam-beam experiments
*
*
*
**
*
2zp
yp
zp
xpzppNe
zepeez
Nr
ey=0.045
F. Willeke, Snowmass 2001 10
Too Strong Beam-Beam Force on e?
No reduction of Ls by the second experiment
No reduction of Ls by a larger -funktionen
Ls
Ippb
So far no reduction of Ls by the bunch
current
F. Willeke, Snowmass 2001 11
)(mey
measureds ,L
Where are the Beam-Beam Limits?
Upgrade and Ip=140mA: emittance starts to grow
)(mey
yQ2
xQ2
)(mey
emeasuredx,
emeasuredy ,
)(mey
)( ,ecalcys L
measureds,L
)( ,emeasuredys L
F. Willeke, Snowmass 2001 12
Conclusion of Proton Beam Brightness Limitation
For a machine with the circumfrence and the energy range
of HERA there is no large increase factor in p beam brightness possible.
A factor of >2 might be compatible with lepton beam beam effect and controlling IBS
Lepton Beam-Beam Effect: Could be mitigated
By smaller beta, however: D.A. limitations
present HERA optics DA=~15-20 x
F. Willeke, Snowmass 2001 13
Electron Beam Current LimitationsRF RF installation costs, operation costs Not fundamental Now: RF power 12 MW, RS1.5GW 60mA @ 27.5GeVCost example: prov RF to increase I by factor 1.6 5M$
Vacuum costs, not fundamentalSR losses 5.2MW @ 1000W/m (~B-Factories ) Presumably no big current increase factor reasonable! (factor 2-3?) costs!
Feedback System: designed for 60mA, upgrade no technical problem
Proton Beam Beam Effect (stability, background, lifetime concerns)
N
beppx ef
Ir
2
b=96ns, unproblematic
For IR design & paras. Resonancespx=1.4 x 10-3 limit?f: fill factor
F. Willeke, Snowmass 2001 14
Ls is independent of
e-current
Tp depends on e-current
Tails depend one-current
Too Strong Beam-Beam Force on p?16mA 73mACorresponding e-current after upgrade
F. Willeke, Snowmass 2001 15
Conclusions: Electron Beam Current Limitations
Educated guess:
Besides COSTS, the beam current is limited by
IR design considerations and beam-beam effects.
For HERA, the e-beam current could be increased by a factor ~2 if costs could be disregarded
F. Willeke, Snowmass 2001 16
Limitations to Focussing
•Chromatic effects Dynamic Aperture Limitations
•Hourglass Effect
•Interaction Region Layout and IR Magnet Design:
Need e & p lenses close to IP
Crossing angle
separate quickly beam dynamics, geometry
Magnetic Separation
Concern about SR
F. Willeke, Snowmass 2001 17
Lumi Reduction by Hourglass Effect
)(cmpy
ep
75.1)5.12(
0LL cmpyLength
19cm:
12cm: 9.1)5.12(
0LL cmpy
Luminosity ( )3210
20cm
bunch length: 6cm
30cm
F. Willeke, Snowmass 2001 18
New HERA Inter Action Region (==>see M. Seidel)strong magnetic combined function separation
Half Quadrupoles Superconducting Separator/Quads
p-focusing
sc sc
p-beam
e-beam
e-focusing DF p-focusing D-F-D-F
F. Willeke, Snowmass 2001 19
Superconducting Magnets in the Detectors
F. Willeke, Snowmass 2001 20
Ring Linac ColliderBecome interesting at Lepton Energies beyond capability of Storage Rings Ee>100GeV
Np 10-6m p 10cm Pe 250GeVL= 4.8 x 1030cm-2sec-1
1011 N 1066 * 26.6MW Ee
High Energy bunched beam Cooling! Energy Recovery
F. Willeke, Snowmass 2001 21
THERA LINAC-Ring Lattice (proposed) small crossing angleprotons focussed by 2 electron low beta triplets, *=10cm max 8kmprotons deflected from e-orbit by a long off-center quadrupoleelectron orbit straightenergy range Ep/Ee: 4/1 - 1/1
Proton Optics
1TeV
Electron Optics
250GeV-800GeV
F. Willeke, Snowmass 2001 22
Conclusions
• Ring-Ring HERA L=~1032cm-2sec-1 New Collider in the range of HERA
Energies: L=1033cm-2sec-1 is an ambitious goal and may be considered as a target for new designs
• Ring-LINAC L>1031cm-2sec-1 :only feasible witg bunched beam cooling