KEKB ACCELERATOR REVIEW COMMITTEEFEB 22 2005

IR 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

ξy0.052

0.052

0.14

0.14

L

1 x 1034[/cm2/sec]

σl [mm]52.5 x 1035
533

IR basic parameters
KEKB (design)

SuperKEKB

LER

HER

LER

HER

βy*[mm]

101033βx*[cm]

33332020

εx [nm]18182424

φ [mrad]1115

βy* : basic assumption of SuperKEKB design
βx*, εx : from beam-beam simulations
φ : assumption for IR designCrossing angle (φ)

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

tightlower

higherlower

higher

Not yet studied

Talk by Tawada

IssuesIssues of IR Design
Issues

CausesMeasuresDynamic aperture

Lower beta’s at IP.

Place QCS magnets.
closer to IP.
Damping ring.

Physical aperture

Lower beta’s at IP.
Energy switch.

Damping ring.
Larger crossing angle.

Heating and mechanicalbreakdown of IRcomponents

Higher beam currents.
Higher power of SR from QCSmagnets.
Shorter bunch length (HOM).

Under study.

Detector beam background

Higher power and critical energy of Under study by BelleSR from QCS magnets.
Group.
Higher beam currents.
QCS closer to the IP.
Higher ξy and shorter bunch length.

Design Work
Overview

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

works until we find a consistent set of solutions.
Choice of machine parameters Beam-beam simulations (Talk by Tawada)
 IR Magnet design (Talks by Ohuchi) Optics and dynamic aperture (Talk by Ohnishi)
 IR Vacuum design (Talk by Kanazawa) Detector beam background (Talk by Tajima)QCS Magnets Design (Ohuchi) Design principles
Move QCS’s closer to the IP.
 Higher field gradient.
 Detector solenoid field is cancelled in each side of the IP.
Parameters

SuperKEKB

KEKB

Units

Distance from IP to QCSL

0.969

1.60

m

Distance from IP to QCSR

1.163

1.92

m

Effective length of QCSL

0.39820.483m

Effective length of QCSR0.333

0.385

m

Field Gradient of QCSL

35.4

21.66

T/m

Field Gradient of QCSR

37.2

21.73

T/m

Place QCS magnets closer to IP
SuperKEKBKEKBThe boundary between KEKB and Belle is the same as that of present KEKB.
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).

IR magnet layout

QC2RE
QC2LP
QC1RE

HER
beam
QC1LE
QC2LE

QCSL

QCSR
QC2RP

LERbeamRequired information for further
IR magnet designs
 Required ring acceptanceDetermined by the beam injection requirement.
 Every magnet should keep the required acceptance.
 Required ring acceptance is also needed from theviewpoints of estimation of dynamic aperture.
 Fan of SR from the QCS magnets
Every IR magnet should be designed to avoid irradiationby the SR.
 SR fan is also needed for the vacuum chamber design andthe estimation of the detector background.
Required Ring Acceptance
LER

HER

e-/e+e-e+

Energy [GeV]

3.5

8.0

Damping RingNoYesAx [µm]

2.6

1.5

Ay [µm]0.180.025

Energy switch is assumed from the beginning of SuperKEKB operation.
A damping ring will be needed for the e+ beam.

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Dynamic Aperture for Injected Beam
Injected beam Jy/Jx = 7 %νx = 45.510
νy = 43.545

Ohnishi

Injected beam Jy/Jx = 4 %νx = 45.510
νy = 43.570

required
acceptancefor injected beamrequired
acceptancefor injected beam

red: no machine error
blue: machine error + optics correction(12 lines indicate different seed numbers.)

Estimated dynamic aperture of HER is marginal. Do we need a local chromaticity
correction also In HER?

Synchro-betatron Resonance
Another reason of need for HER Local correction
Resonance line2νH + νs = integer
10/29/2002
4/2/2003
5/9/2003
12/18/2003
1/21/2004νs = -0.0249@8MV

Beam-Beam simulation (Tawada)νs = -0.0209@13MV(May 09 2003)
νs = -0.0225@15MV(Dec 18 2003)
νs = -0.0217@14MV(Jan 21 2004)

Problem HER local chromaticity correction scheme is notcompatible with installation of crab cavities inTsukuba section.
 If we want to install crab cavities in Tsukuba, wecan not adopt the local correction scheme in HER.
 We need to wait for the results of the experimentwith the crab cavities in Nikko section next year.

Fan of SR
 Consideration of the particle distribution in thephase space Effects of dynamic-β and dynamic-emittance These effects are very large with the horizontal

tune very close to the half integer.

 We took 9εx (3 σx, 3σx’) into consideration.

Enlargement of SR fan due to dynamic effects
without dynamic effects

with dynamic effects

Source point

QCSRE(Arc side)
HER

QCSLE(Arc side)
LER

QCSRE(Arc side)
HER

QCSLE(Arc side)
LER

Observation point

Exit of QC1RE

Exit of QC1LE

Exit of QC1RE

Exit of QC1LE

εx[nm]2458

γx* (1/βx*) [/m]522.5

Distance from asource point [m]Δx[mm]COD
Δx[mm]
3 σx, 3σx’
Δx[mm]
Total

2.87

1.94

2.87

1.94

5.2

5.5

5.2

5.5

5.1

5.4

17.7

18.3

10.3

10.9

22.9

23.8
ξx = 0.1, νx = .510

Fan of SROhuchiPower of SR from QCS Magnets
QCSR

QCSL

Magnet length [m]0.330.42

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

Vacuum system design issues(Kanazawa) SR from QCS’s
How to handle the high power?
 How to suppress the SR background to Belle?
 HOM power
A few * (100kW) will be turned into heat in IR (Kanazawa).
 How to deal with its power?
 More durable vacuum components?
 Denser vacuum pumps from reducing particle beambackground?

Detector beam backgroundissues (Tajima)
Mechanism

Reason of severenessRadiative Bhabha

High Luminosity, QCS’s closer
to IP

Collision withParticle loss residual gas

SRHigh currents

Touschek effect

Short bunch length, high ξy,smaller dynamic aperture

Emitted at QCS’s

High current, larger φc, Higher
field of QCS’s

M. Sullivan
HL Workshop Nov. 13 2004

Tajima

Rad. Bhabha BG sim. for Super-KEKB
BarrelBWD
EndCap

FWD
EndCapRealistic design
based on discussion
with QCS group

Expected BG
from othersources

L=25x1034/cm2/s

with heavy metal
total ~ 1.5 ton

L=1034 /cm2/s
Radiative Bhabha process is important at SuperKEKB.
However, its effects are effectively suppressed by using
heavy metal shields.

~4 % oftotal BG

Spare Slides

Other works to be done Other engineering issue Mechanical support of the magnets
 Solution of spatial conflicts among components

 Design of IR special beam monitor system

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)
 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 be
increased from ±11mrad to ±15mrad.

QC1 magnet design
 Severe physical aperture requirement
 Two options (-> Ohuchi and Tawada’s talk) Normal quadrupole Superconducting Normal quadrupole has higher priority.
 The option of superconducting magnets is a backup.

Geometrical Relationship betweenSuperBelle and SuperKEKB!"./0!1232)
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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.

Critical energy of SR from QCS magnets
QCSR

QCSL

1163.3969.4

Δx [mm]

34.5

29.1

G [T/m]

37.2

35.4

Eb [GeV]

8.0

3.5

uc [keV]54.7(37.4)

8.40(5.95)

Distance from IP tomagnet center [mm]( ): present KEKB