Post on 14-Jan-2016
description
Georg.Hoffstaetter@DESY.de
Future HERA High Luminosity Performance
Georg H. Hoffstaetter and Ferdinand Willeke
(DESY, Hamburg)
29 March
2001
H1
ZEUS
HERMES
HERA-B HERA
PETRA
ProtonsElectrons
778 m
6336 m long
920 GeV protons
27.5 GeV electrons/positrons
Georg.Hoffstaetter@DESY.de
pe
HERA: Improvements 1999/2000Start luminosityandBeam currents:
Efficiency%
Average over month
mA
Georg.Hoffstaetter@DESY.de
Development of the Luminosity
Inte
grat
ed L
umin
osity
(1/
pb)
HERA Luminosity 1993-2000
Linear increase of the integrated Luminosity
The time for a luminosity upgrade of HERA has come
Days after start of run
Georg.Hoffstaetter@DESY.de
Th e Detec to r R
e gion
courtesy B.Holzer courtesy B.Holzer
Geo
rg.Hoffstae
tter@D
ES
Y.de
Georg.Hoffstaetter@DESY.de
Superconducting Magnet GO
Geo
rg.H
offs
tae
tter
@D
ES
Y.d
e
Georg.Hoffstaetter@DESY.de
Potential Problems
Dynamic Aperture OK? Polarization OK?, Luminosity OK? Can HERA be handled well?
Polarization OK?, Luminosity OK?
Too strong beam-beam force on p? Too strong beam-beam force on e?
Focusing:
fRF increase:
Georg.Hoffstaetter@DESY.de
The Luminosity was initially too small: Lumiscan
Emittance and Lumi for 72° Optic
)60( sL
)60( sL )72( sL
)72( sL
)(mmx )(mmx)(mmy )(mmy
Bunch has no product distribution: )()( yx coupling
)72( sL
)72( sL
x
y
Luminosity with 72° is large as expected
Georg.Hoffstaetter@DESY.de
Dynamic Aperture for 72° Optic
The kick where half the current is lost leads to a satisfactory dynamic aperture.
Kickx
x´ V2(kV)
Georg.Hoffstaetter@DESY.de
Polarization was in the spin matched 72° optic quickly brought to 63% (one day).
Harmonic bumps were immediately effective Decoupling bumps worked well
60%
PolarizationIe
Polarization for 72° Optic
Georg.Hoffstaetter@DESY.de
6 more measurements indicate For the center frequency , the
luminosity is increased as expected
Luminosity for fRF IncreaseLL
RFf RFf
HzfZentrum 175
HzfZentrum 175
HzfZentrum 175HzfZentrum 0
Georg.Hoffstaetter@DESY.de
Ls is independent of e-current Tp depends on e-current Tails depend on
e-current
Too Strong Beam-Beam Force on p?16mA 73mACorresponding e-current after upgrade
Georg.Hoffstaetter@DESY.de
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
Georg.Hoffstaetter@DESY.de
)(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
Georg.Hoffstaetter@DESY.de
Lumi Reduction by Hourglass Effect
)(cmpy
ep
75.1)5.12(
0L
L cmpyLength 19cm:
12cm: 9.1)5.12(
0L
L cmpy
Luminosity ( )3210
20cm
bunch length: 6cm
30cm
Georg.Hoffstaetter@DESY.de
Tune Shift with Bunch Length Effect
How will the tune shift parameters change and have these been analyzed by accelerator experiments ?
Georg.Hoffstaetter@DESY.de
Resonances with Bunch Length EffectHow will the resonance strength change and have these been analyzed by accelerator experiments ?
All large resonance strength are due to the proton bunch length
Georg.Hoffstaetter@DESY.de
Nominal and Ultimate Parameters
The performance goal of HERA is not unrealistic and should not be too hard to achieve.
A shortfall of beam intensity in the short term can be compensated.