January 13, 2004 D. Rubin - Cornell 1

CESR-c

BESIII/CLEO-c Workshop, IHEP

January 13, 2004

D.Rubin

for the CESR operations group

January 13, 2004 D. Rubin - Cornell 2

CESR-cEnergy reach 1.5-6GeV/beam

Electrostatically separated electron-positron orbits accomodate counterrotating trains

Electrons and positrons collide with ±~3.5 mrad horizontal crossing angle

9 5-bunch trains in each beam(768m circumference)

January 13, 2004 D. Rubin - Cornell 3

CESR-c IR

Summer 2000, replace 1.5m REC permanent magnet final focus quadrupole with hybrid of pm and superconducting quads

Intended for 5.3GeV operation but perfect for 1.5GeV as well

January 13, 2004 D. Rubin - Cornell 4

CESR-c IR* ~ 10mm

H and V superconducting quads share same cryostat

20cm pm vertically focusing nose piece

Quads are rotated 4.50 inside cryostat to compensate effect of CLEO solenoid

Superimposed skew quads permit fine tuning of compensation

At 1.9GeV, very low peak => Little chromaticity, big aperture

January 13, 2004 D. Rubin - Cornell 5

CLEO solenoid 1T()-1.5T()

Good luminosity requires zero transverse coupling at IP (flat beams)

Solenoid readily compensated even at lowest energy

*(V)=10mm E=1.89GeV*(H)=1m B(CLEO)=1T

January 13, 2004 D. Rubin - Cornell 6

CESR-c Energy dependence

Beam-beam effect• In collision, beam-beam tune shift parameter ~ Ib/E• Long range beam-beam interaction at 89 parasitic

crossings ~ Ib/E (for fixed emittance) (and this is the current limit at 5.3GeV)

Single beam collective effects, instabilities• Impedance is independent of energy• Effect of impedance ~I/E

January 13, 2004 D. Rubin - Cornell 7

CESR-c Energy dependence(scaling from 5.3GeV/beam to 1.9GeV/beam)

Radiation damping and emittance Damping Circulating particles have some momentum transverse to design orbit (Pt/P) In bending magnets, synchrotron photons radiated parallel to particle momentum Pt/Pt = P/P RF accelerating cavities restore energy only along design orbit, P-> P+ P so that transverse momentum is radiated away and motion is damped Damping time ~ time to radiate away all momentum

January 13, 2004 D. Rubin - Cornell 8

CESR-c Energy dependence Radiation damping

In CESR at 5.3 GeV, an electron radiates ~1MeV/turn ~> ~ 5300 turns (or about 25ms)

SR Power ~ E2B2 = E4/2 at fixed bending radius 1/ ~ P/E ~ E3 so at 1.9GeV, ~ 500ms

Longer damping time• Reduced beam-beam limit• Less tolerance to long range beam-beam effects• Multibunch effects, etc.• Lower injection rate

January 13, 2004 D. Rubin - Cornell 9

CESR-c Energy dependence

Emittance• L ~ IB2/ xy

= IB2/ (xyxy)1/2

• x~ y (coupling)

• IB/ x limiting charge density • Then IB and therefore L ~ x

CESR (5.3GeV), x = 200 nm-radCESR (1.9GeV), x = 30 nm-rad

January 13, 2004 D. Rubin - Cornell 10

CESR-c Energy dependence

Damping and emittance control with wigglers

January 13, 2004 D. Rubin - Cornell 11

CESR-c Energy dependence In a wiggler dominated ring

• 1/ ~ Bw2Lw

~ Bw Lw

E/E ~ (Bw)1/2 nearly independent of length (Bw limited by tolerable energy spread)Then 18m of 2.1T wiggler -> ~ 50ms -> 100nm-rad < <300nm-rad

January 13, 2004 D. Rubin - Cornell 12

Optics effects - Ideal Wiggler

πλϑ20

0 w

E

ceB=

Bz = -B0 sinh kwy sin kwz

Vertical kick ~ Bz

€

′ y = −B0

2L

2(E0 /ce)2y +

2

3

2π

λ

⎛

⎝ ⎜

⎞

⎠ ⎟2

y 3 + ... ⎛

⎝ ⎜ ⎜

⎞

⎠ ⎟ ⎟

January 13, 2004 D. Rubin - Cornell 13

Optics effects - Ideal Wiggler

Vertical focusing effect is big, Q ~ 0.1/wiggler But is readily compensated by adjustment of nearby quadrupoles

Cubic nonlinearity ~ (1/ λ)2

We choose the relatively long period -> λ = 40cm

Finite width of poles leads to horizontal nonlinearity

January 13, 2004 D. Rubin - Cornell 14

7-pole, 1.3m 40cm period, 161A, B=2.1T

Superconducting wiggler prototype installed fall 2002

January 13, 2004 D. Rubin - Cornell 15

Wiggler Beam Measurements-Measurement of betatron tune vs displacement consistent with modeled field profile and transfer functon

January 13, 2004 D. Rubin - Cornell 16

January 13, 2004 D. Rubin - Cornell 17

January 13, 2004 D. Rubin - Cornell 18

January 13, 2004 D. Rubin - Cornell 19

January 13, 2004 D. Rubin - Cornell 20

6 wigglers installed spring 2003

January 13, 2004 D. Rubin - Cornell 21

6 Wiggler Linear Optics

Lattice parameters

Beam energy[GeV] 1.89*

v[mm]

*h[m]

Crossing angle[mrad]

Qv

Qh

Number of trains

Bunches/train

Bunch spacing[ns]

Accelerating Voltage[MV]

Bunch length[mm]

Wiggler Peak Field[T]

Wiggler length[m]

Number of wigglers

x[mm-mrad]

E/E[%]

12

0.56

3.8

9.59

10.53

9

4

14

10

9

2.1

1.3

6

0.15

0.08

January 13, 2004 D. Rubin - Cornell 22

Machine Status

Commissioning with 6 wigglers beginning in August 2003-Measure and correct linear optics-Characterize

- wiggler nonlinearity-Injection-Single beam stability

-Measure and correct “pretzel” dependent /sextupole differential optics

January 13, 2004 D. Rubin - Cornell 23

Wiggler Beam Measurements

Beam energy = 1.89GeV

-Optical parameters in IR match CESR-c design

-Measure and correct betatron phase and transverse coupling

- Measurement of lattice parameters (including emittance) in good agreement with design

January 13, 2004 D. Rubin - Cornell 24

Wiggler Beam Measurements

-Injection

1 sc wiggler (and 2 pm CHESS wigglers) -> 8mA/min

6 sc wiggler -> 50mA/min

1/ = 4.5 s-1

1/ = 10.9s-1

January 13, 2004 D. Rubin - Cornell 25

Wiggler Beam Measurements 6 wiggler lattice

-Injection

30 Hz 68mA/80sec 60 Hz 67ma/50sec

January 13, 2004 D. Rubin - Cornell 26

Wiggler Beam Measurements

-Single beam stability

1/ = 4.5 s-1 1/ = 10.9s-1

2pm + 1 sc wigglers 6 sc wigglers

January 13, 2004 D. Rubin - Cornell 27

Measurement and correction of linear lattice

Measured - modeled

Betatron phase

and transverse coupling

January 13, 2004 D. Rubin - Cornell 28

Sextupole optics

Modeled pretzel dependence of betatron phase due to sextupole feeddown

Difference between measured and modelled phase with pretzel after correction of sextupoles

January 13, 2004 D. Rubin - Cornell 29

Beam profiles due to horizontal excitation Best luminosity

Solenoid compensation Coupling parameters in the interaction region

January 13, 2004 D. Rubin - Cornell 30

CESR-c Peak Luminosity

January 13, 2004 D. Rubin - Cornell 31

CESR-c integrated luminosity

January 13, 2004 D. Rubin - Cornell 32

1-jan-2004

January 13, 2004 D. Rubin - Cornell 33

2.5pb-1/day28-Dec-2003

January 13, 2004 D. Rubin - Cornell 34

CESR-c parameters

Parameter Measured (Design)

Beam energy[GeV] 1.88 (1.88)

Luminosity[1030/cm2/s] 45 (300)

Ib[ma/bunch] 1.7 (4)

Ibeam[ma/beam] 55 (180)

v 0.025 (0.04)

h 0.036

Wigglers 6 (12)

E/E[10-4] 0.8 (0.81)

[ms] 110 (55)

Bw[T] 2.1(2.1)

*v[mm] 13 (10)

h[nm] 160 (220)

January 13, 2004 D. Rubin - Cornell 35

CESR-c StatusRemaining 6 (of 12) wigglers will be installed is spring 2004 Double damping decrement -> Faster injection -> Higher single beam current -> Reduced sensitivitiy to current limiting parasitic crossings -> Higher beambeam current limit -> Increased tune shift parameter

Machine studies/beam instrumentation in progress -> Improved correction of linear and nonlinear optical errors -> More precise and reliable correction of coupling errors -> Improved tuning “knobs” and algorithms

January 13, 2004 D. Rubin - Cornell 36

CESR-c design parameters

January 13, 2004 D. Rubin - Cornell 37

Machine modeling-Wiggler transfer map

-Compute field table with finite element code

-Tracking through field table -> transfer maps

January 13, 2004 D. Rubin - Cornell 38

Machine modeling

- Fit analytic form to field table

January 13, 2004 D. Rubin - Cornell 39

Machine modeling-Wiggler map

Fit parameters of series to field table

Analytic form ofHamiltonian -> symplectic integration -> taylor map

January 13, 2004 D. Rubin - Cornell 40

Simulation

-Machine model includes:-Wiggler nonlinearities-Beam beam interactions (parasitic and at IP)-Synchrotron motion-Radiation excitation and damping

-Weak beam -200 particles - initial distribution is gaussian in x,y,z - track ~ 10000 turns