IR Upgrade Overview

Y. Funakoshi (KEK)Choice of machineparameters

Design parameters of KEKB andSuperKEKBKEKB (design)

SuperKEKB

LER

HER

LER

HER

I [A]

2.6

1.1

9.4

4.1

βy*[mm]

101033

ξy0.0520.052

L

1 x 1034[/cm2/sec]

σl [mm]50.14~0.28 0.14~0.28
2.5~5 x 1035

533

IR basic parameters
KEKB (design)

SuperKEKB

LER

HER

LER

HER

βy*[mm]10103

3

βx*[cm]33332020εx [nm]18182424

φ [mrad]1115

βy* : basic assumption of SuperKEKB designβx*, εx : from beam-beam simulations
φ : assumption for IR design

Choice of β∗x, εxβ∗x=30, 20, 15 cm
εx=24, 18, 12 nm

Strong-Strong Beam-BeamSimulations by K. Ohmi

Our choice
Achievable beam-beam parameters depends on β∗x and εx.

Crossing angle (φ)

Physical apertureof IR magnets
Power of SR fromQCS magnets
Required voltageof crab cavities
Parasitic collisioneffects±11mrad± 15mradvery tight

tight

lower

higherlower

highermaybe o.k.

maybe o.k.

IssuesIssues of IR Design
Issues

CausesMeasuresDynamic aperture

Lower beta’s at IP

Place QCS magnets
closer to IP.

Physical aperture

Lower beta’s at IP
Energy switch

Damping ring

Heating of IRcomponents

High beam currents.
High power of SR fromQCS magnets.
Short bunch length.

To be studied.

Detector beam
background

High critical energy of
SR from QCS magnets.
High beam currents.

Under study in BelleGroupDesign Work
Overview

IR Design Works
 We have to concurrently pursue the following design

works until we find a consistent set of solutions.

Estimation of required physical aperture from theviewpoint of beam injection
 IR Magnet Design (Talks by Tawada and Ohuchi) IR Optics (Talk by Koiso)
 RequirementsTo realize the required machine parameters.
 βy*, βx*, φTo keep enough dynamic and physical aperture.

Place QCS magnets closer to IP
SuperKEKBKEKBThe boundary between KEKB and Belle is the same.
ESL and ESR will be divided into two parts (to reduce E.M. force).
QCSL (QCSR) will be overlaid with (the one part of ) ESL(ESR).

Crossing angle (φ)
 QCS (defocusing quadrupole) magnets are placed

closer to IP.
 βx* is smaller.

 The maximum value of βx around IP becomes verylarge.

 Physical aperture will be an issue particularly in thehorizontal direction.
 To mitigate this problem, the crossing angle will beincreased from ±11mrad to ±15mrad.

IR magnet layout

QC2RE
QC2LP
QC1RE

HER
beam
QC1LE
QC2LE

QCSL

QCSR
QC2RP

LER
beam

QC1 magnet design
 Severe physical aperture requirement
 Two options (-> Ohuchi and Tawada’s talk) Normal quadruple
 Superconducting
 If we find a solution of the normal quadruple

magnets, we will take this solution.

IR Lattice Design

H. KoisoTracking studies showed
acceptable dynamic aperture.

LERHER

Geometrical Relationship between
SuperBelle and SuperKEKB!"./0!1232)
7516:51644516-

8!65$0,0!$69,+!#$%&'($)!**!$+&*!%&,!#$./0!1232)

Belle Solenoid will not rotate.
The HER axis will not change.
The LER axis will rotate by 8mrad.
The beam pipe (and SVD) have a finite angle of 7mrad withrespect to Belle Solenoid.
QCS magnets will be set parallel to Belle Solenoid.

Estimation of required ringacceptance

Required ring acceptance isdetermined by the beam
injection conditions.
Required acceptance isdetermined by the followingparameters.
Ring emittance: εxr
 nr
 ws
 ns
 ni
 Ring β at the injection point: βxr
 Linac beam emittance : εxi
 Injection line β: βxiOf the parameters above, Ring β and Linac beam emittance can bechosen relatively freely or can be changed with our efforts.

Ring β function
 A higher ring beta function atthe injection point reduces
required ring acceptance.
 However, with higher βx thanabout 100m, required ring
acceptance does not changevery much.
We took Ring βx of 90.4m
which is the same value ofthe KEKB design.

Linac beam emittance Required acceptancedepends strongly on the
Linac beam emittance.
 In our present situation,required ring acceptance isalmost determined by the
Linac beam emittance.

Strategy on ring acceptanceIn our present strategy, beam energy switch between e+ and e- will
be done at some time after the IR upgrade.
 This means that both rings have to accept the beam which has higheremittance.
 We considered two cases.
Case 1: Estimate the Linac beam emittane based on the values
achieved at the present Linac.

The positron beam determined required ring acceptance of both rings.
 The positron beam emittance is 3.5 x 10-7m at 3.5GeV.
 We could not find solutions of the IR magnet design with this condition.


Case 2: We will introduce a damping ring for the e+ beam.

The electron beam determined required ring acceptance of both rings.
 The electron beam emittance is 2.0 x 10-8m at 8GeV.
 We found solutions of the IR magnet design with this condition.
We need a damping ring for the positron beam.

Required Ring AcceptanceWithout damping ringWith damping ringIssues related to SR from QCS
magnets
 Fan of SR

Effects of COD and beam size
 We found that the dynamic beta and dynamic emittance effect due

to the beam-beam interaction are important for the estimation.
 The smaller βx* and the larger emittance make the angulardivergence of beam very large.
 How to deal with the power of SR

Much higher power than KEKBDynamic β and emittance" x = 45.51!

Calculations with analytic formula and by using SAD (KEKB)Fan of SR
QC1R-cryostat-bore

QC1L-cryostat-bore

150

3800

2800
QCSR-cryostat-bore

100

HER

QCSL-cryostat-bore
969.4

501163.3

0[mm]
LER

-50

-100
central beam orbit
beam envelop
SOR from the IP or arc sides of each QCS
deviation of SOR from the central routePower of SOR from QCS Magnets
QCSR

QCSL

Magnet length [m]

0.33

0.42

Δx [mm]

34.5

29.1

G [T/m]

37.2

35.4

B [T]

1.28

1.03

Eb [GeV]

8.0

3.5

I [A]

4.1

9.4

P [kW]

179 (27)64.6 (10)(): present KEKB DesignSummary of Future
worksSummary
 Prior to starting the IR design, we determined somemachine parameters related to the IR design.
 Main issues of the IR design are dynamic and physicalaperture.
 To keep enough dynamic aperture, the QCS magnets will
be placed closer to the IP and overlaid with theESR(ESL).
 A damping ring for the positron beam is vital to reduce
the required value of ring acceptance.
 We found a consistent set of solutions of the IR magnet
design, the IR optics design and the injecting beam
quality which provide sufficient physical aperture andacceptable dynamic aperture.
 Feasibility of SuperKEKB IR has been confirmed.

Future works
 How to deal with very high power of SR from QCS’s
 Heating of IR components
 Design of vacuum system
 3D design of IR magnets
 Estimation of HOM power and its counter-measure Mechanical support of the magnets
 Solution of spatial confilicts among components
 Design of IR special beam monitor system Detector beam background and design of IP beam pipe

(under study) Etc.