CASA Collider Design Review RetreatCASA Collider Design Review Retreat

HERAHERA The Only Lepton-Hadron The Only Lepton-Hadron Collider Ever Been Built Collider Ever Been Built

WorldwideWorldwide

Yuhong ZhangYuhong Zhang

February 24, 2010February 24, 2010

OutlineOutline

Overview, baseline design and Overview, baseline design and parametersparameters

Polarization and coolingPolarization and cooling

Luminosity upgradeLuminosity upgrade

Interaction regionInteraction region

e-p

e-p

Proton on wire target

electron on polarized gas

target

•Construction started in April 1984, ended on Dec. 1990

•Commissioning took place in 1991 (First collision on Oct. 14, 1991)

•Data taken in June. 1992

HERA Collider RingsHERA Collider RingsDesign requirements• head-on collisions

• Energy range

• p: up to 300 to 820(920) GeV (lower limit by maximum path length adjustment for preserving e and p synchronism)

• e: up to 30 GeV

• RF power (SR loss) limit 7.2 MW

HERA Collider RingsHERA Collider Rings• Ring circumference: 6336 m

(determined by maximum p energy)

• Four quadrants: north, east, south, west

• Quadrant = two mirror symmetric octants

• Each octant has 18 FODO cells

• Ion FODO: 47 m, phase advance 60°

• 416 SC dipoles (4.6 K), 8.83 m, 4.68 T, radius 584m, 75 mm aperture

• 6 vertical dipoles, 3.356 m

• 224 SC quads, 1.5 to 1.86 m, 90 T/m

• e FODO: 23.5 m, phase advance 60°

• half of ion FODO cell length• Four 360 m straights for four IRs• Straights also for injection/ejection, RF, beam dump, collimators, etc• Electron straight also includes spin rotators (interleafed vertical & horizontal

bending magnets)• Small electron betatron functions (strong focusing) in RF sections for reducing bad

orbit-RF coupling (eg. single and multiple bunch instabilities) • Minimizing dispersion in RF sections for avoiding synchro-betatron resonances

Arc

Straights

HERA InjectorsHERA Injectors Electron/positron (polarized)Electron/positron (polarized)

– An S-band warm linac An S-band warm linac 450 450 MeV pulsed currentMeV pulsed current

– Accumulator ring PIA (also Accumulator ring PIA (also bunching) into single bunchbunching) into single bunch

– Synchrotron DESY II Synchrotron DESY II 7 GeV 7 GeV– e-P storage ring PETRA e-P storage ring PETRA 12 12

GeV, filling with 60 bunchesGeV, filling with 60 bunches– HERA collider ring HERA collider ring 27.5 GeV 27.5 GeV

– Self-polarizationSelf-polarization

Proton/ionsProton/ions– An HAn H-- sources, a 750 KeV RFQ sources, a 750 KeV RFQ– A 50 MeV HA 50 MeV H-- linac linac– Synchrotron DESY III Synchrotron DESY III 7.5 7.5

GeV (transition energy is 9 GeV (transition energy is 9 GeV)GeV)

– Striping at injection of DESY IIIStriping at injection of DESY III– e-P storage ring PEREA e-P storage ring PEREA 40 40

GeV (transition energy is 6.5 GeV (transition energy is 6.5 GeV)GeV)

– HERA collider ring HERA collider ring 920 GeV 920 GeV

Synchrotron DESY II and IIISynchrotron DESY II and III

Proton emittance determined by Proton emittance determined by space charge effect in proton space charge effect in proton injectorinjector

Beam spot size (and luminosity) Beam spot size (and luminosity) at IP is determined byat IP is determined by– Beam emittanceBeam emittance– Chromaticity & dynamical Chromaticity & dynamical

apertureaperture

smallest acceptable smallest acceptable ββ* at IP* at IP

HERA HERA Design Design

ParameterParameterss

Polarized Lepton BeamsPolarized Lepton Beams

(Unrealized) Electron Cooling(Unrealized) Electron Cooling

120 m

• Continuous cooling

• Cooling bunch dimensions can be smaller than ion bunch

• Wiggler with 1 T

• A high-β (~500 to 2000) insertion

e Ring Lattice & chromaticity e Ring Lattice & chromaticity CorrectionCorrection Change of FODO cell betatron phase advanceChange of FODO cell betatron phase advance

– Increasing focusing in FODO lattice reduces electron beam equilibrium emittance, Increasing focusing in FODO lattice reduces electron beam equilibrium emittance, reaching minimum at 135reaching minimum at 135° phase advance per cell ° phase advance per cell

– Strong focusing (large betatron phase advance per FODO cell) causes big Strong focusing (large betatron phase advance per FODO cell) causes big chromaticitychromaticity

– Needs strong sextupole strengths to correct chromaticity, but reduces dynamical Needs strong sextupole strengths to correct chromaticity, but reduces dynamical aperturesapertures a compromise: 90a compromise: 90° for horzontal and 75° for vertical° for horzontal and 75° for vertical

equilibrium emittance for 27.5 GeV is 22 nmequilibrium emittance for 27.5 GeV is 22 nm (In the north, south and east straight sections, (In the north, south and east straight sections, high dispersion caused by bends in spin rotators high dispersion caused by bends in spin rotators contribute significantly to the emittances)contribute significantly to the emittances)

Interleaved Chromaticity correction Interleaved Chromaticity correction schemescheme– Two families in the horizontal plane, three Two families in the horizontal plane, three

families in the vertical planefamilies in the vertical plane– Chromatic correction adequate but worse in Chromatic correction adequate but worse in

the horizontal planethe horizontal plane

Non-interleaved chromaticity correction Non-interleaved chromaticity correction scheme scheme – Requires stronger sextupole strengthRequires stronger sextupole strength

Electron Dynamics Study for Luminosity Electron Dynamics Study for Luminosity UpgradeUpgrade

Goal: reducing beam emittance throughGoal: reducing beam emittance through– Change of RF frequencyChange of RF frequency– Increase focusing (phase advance)Increase focusing (phase advance)

Dynamics aperture study (G. Hoffstatter)Dynamics aperture study (G. Hoffstatter)

Synchrotron RadiationSynchrotron Radiation

Detector shielded by 3 movable Detector shielded by 3 movable upstream collimatorsupstream collimators

Two fixed collimators near IP against Two fixed collimators near IP against back scatteringback scattering

Background conditions very lowBackground conditions very low

No upstream collimatorsNo upstream collimators Radiation fan must pass through IRRadiation fan must pass through IR Main background sources: back-scattering Main background sources: back-scattering

from absorbers 11 to 27 m right of IPfrom absorbers 11 to 27 m right of IP Small central beam pipeSmall central beam pipe

Total power 18 kW (26 kW at 30 GeV)Total power 18 kW (26 kW at 30 GeV) Critical energy up to 115 keV (150 at 30 Critical energy up to 115 keV (150 at 30

GeV)GeV)

Special MagnetsSpecial Magnets

Things Still Bother Them at Last Days of Things Still Bother Them at Last Days of HERAHERA

2007

End of a Great Machine & EraEnd of a Great Machine & Era