Recirculating pass optics V.Ptitsyn, D.Trbojevic, N.Tsoupas.

Recirculating pass optics

V.Ptitsyn, D.Trbojevic, N.Tsoupas

Recirculation passes in eRHIC designRecirculation passes in eRHIC design

At present design of eRHIC the beam passes the main linac five times during acceleration. Four of the beam recirculation passes will be placed in the tunnel. Lower energy pass can be put locally.

Possible location of therecirculation passes in the tunnel

Four recirculation passes

PHENIX

STAR

e-ion detector

eRHIC

Main ERL (1.9 GeV)

Low energy recirculation pass

Beam dump

Electronsource

Possible locationsfor additional e-ion detectors

The RHIC tunnel curvature defines average orbit radiusfor the passes. The dipole magnet strength is limited bysynchrotron radiation loss power.

Beam power loss due to synchrotron radiation for 0.26 A beam at 10 GeV versus dipole filling factor.

0

1

10

100

0 0.2 0.4 0.6 0.8 1 1.2

Dipole filling factor

Po

we

r lo

ss

, M

W

10 GeV pass

All 5 passes

Longitudinal transportLongitudinal transport

3rd harmonic cavities are used in both main and pre-accelerator linacs

R56=500 mm R56=20 mm

For acceleration on the crest the recirculating passes should be isochronous enough in order to have acceptable momentum spread after deceleration

-1.5

-1

-0.5

0

0.5

1

1.5

-15 -10 -5 0 5 10 15

z0, mm

dp

/p, 1

e-3 de/e_0

de/e_5

de/e_10

de/e_f

z, mm-30

-20

-10

0

10

20

30

40

-15 -10 -5 0 5 10 15

z0, mm

dp

/p, 1

e-3 de/e_0

de/e_5

de/e_10

de/e_f

z, mm

dp/p

, 1e-

3

dp/p

, 1e-

3

Basic cell for the recirculating passesBasic cell for the recirculating passes

FMC cell (D.Trbojevic)Dipole filling factor: 54%Reduced lengthTuned to ~0 momentum compaction

For 10GeV:Largest gradient: 7.7 T/mDipole field: 1.6 kGs

Dipole length: 5.5 mQuad length: 0.6 m

81 m

Summary of synchrotron radiationSummary of synchrotron radiation

I, mAI, mA E loss E loss on top on top pass,pass,

MeVMeV

E loss E loss on 5 on 5

passespasses

MeVMeV

Power Power loss on loss on

top top pass, pass, MWMW

Power Power loss on loss on

5 5 passespasses

MWMW

((p/p) p/p) rad,rad,

1e-31e-3

rad, rad, nmnm

10 GeV10 GeV 260260 4.34.3 6.76.7 1.11.1 1.71.7 0.020.02 0.040.04

20 GeV20 GeV 2626 6969 107107 1.81.8 2.82.8 0.130.13 1.31.3

Tunable RTunable R5656 parameter parameter

Should give at least +-0.3m tuning range for R56 on the whole pass.Beta_max change within 15%.

R56 versus gradient of QD2 quad (central quad)

For this basic cell there are also some other ways to tune R56.

-1.5

-1

-0.5

0

0.5

1

1.5

-0.25 -0.23 -0.21 -0.19 -0.17 -0.15

K(QD2),1/m^2

r56

per

cel

l,cm

Basic cell: beta-functionsBasic cell: beta-functions

Phase advances:_x = 1.6_y = 1.4

Arc latticeArc lattice

4 basic FMC cells+ matching sections

The whole arc transfer is achromatic.R56=0 and adjustable.

One sextantOne sextant

Arc+ straights with no IR

Separated functions:• R56 tuning: arcs• Phase trombone: straights• Path length tuning: in area of IR insertion (IR12)

Achromatic SpreaderAchromatic Spreader

N.Tsoupas

Beam parameters and dispersion for each line of the separatorBeam parameters and dispersion for each line of the separator

Interaction Straight LayoutInteraction Straight Layout

-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

-100 -50 0 50 100

H-plane V-plane

-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

-100 -50 0 50 100

Presently considered geometry of the interaction region straight.Ongoing work on the optics to minimize (or eliminate) dispersion at the IP.

SummarySummary

Optics of recirculation passes has been modified, Optics of recirculation passes has been modified, from FODO cell to FMC-cell based optics. from FODO cell to FMC-cell based optics. Isochronous lattice. Provides the flexible control of Isochronous lattice. Provides the flexible control of RR5656 parameter. parameter.

Initial separator/merger design has been Initial separator/merger design has been developed.developed.

Ongoing work: Ongoing work: Finalizing interaction region straight design.Finalizing interaction region straight design. Tracking with magnet errors/misalignments to study Tracking with magnet errors/misalignments to study

tolerances.tolerances.