Synchrotron Radiation (SR) in Super-KEKB / Belle

Osamu Tajima

( Tohoku univ )

Contents

• Introduction (Soft/Hard-SR, simulation tools)

• Experience at Belle

- Troubles in 1999

- Efforts for SR reduction

- Current Status

• Ideas for SR reduction in Super-B

Dose is given only for 1st layer of SVD

Synchrotron Radiation (SR)

Scattered at downstream photon-stop (OC2RE chamber)

Soft-SR

High energy SRis generated inOCS magnet

Hard-SR (backscattering)

Several keV

keV ~ 150 keV

Belle

Beam orbit in Soft-SR simulation• We can estimate real orbit from BPM• Real orbit is calculated by 2 fitting with IP constraint (<1mm)• Design orbit is adopted for Super-KEKB

Simulation Tools in Detector etc.

• Simulate down to 1 keV or less• Photoelectric-effect is important in keV range ex. Au L-edges (14keV…), Cu K-edge (8keV) etc.

Requirements

EGS4 / Geant4

#### Experience at Belle ####

Belle had miserable experience

Understanding & Reduction are Important !

Soft-SR killed readout chipCurrent limited, 100mAby high rate Hard-SR

Simulation reproduce Gain-drop

azimuthal distributionactual orbit

byT.Abe (KEK)

Solved by limiting steering magnets operation No more troubles

Reduction of Hard-SR

Put photon-stop far place : 6 9.5 m ~ 0.4 Chamber material : Al Cu ~ 1/3

Energy spectra of Hard-SR (simulation)

~1/10

Higher current 100 1100mA achieved !!

More Reduction Efforts

Au-coating !

crescent shapeSR-mask

SVD 2.0

More Reduction Efforts

Au-coating !

crescent shapeSR-mask

Au coating absorbs low energy photon less than 8 keV

SVD 2.0

More Reduction Efforts

Au-coating !

crescent shapeSR-mask

Saw-tooth surface shape in Ta blind Soft-SR reflected on Ta

SVD 2.0

More Reduction Efforts

Au-coating !

crescent shapeSR-mask

Crescent shape SR-mask blind Be section from Soft-SR

SVD 2.0

More Reduction Efforts

Au-coating !

crescent shapeSR-mask

SVD 2.0

Hard-SR isshielded byTa-chamber

Dose expectation SVD2 (r=1.5cm)

Scattered at downstream photon-stop (OC2RE chamber)

Soft-SR

High energy SRis generated inOCS magnet

Hard-SR (backscattering)

Several keV

keV ~ 150 keV

few kRad/yr

29 kRad/yr

Azimuthal Distribution of SR

33 kRad/yrat HER 1.1A

21 kRad/yrat HER 1.1A

Single-Bunch 15 mA (trigger-timing is adjusted)Total 0.8 A w/ 1284 bunch (random timing)

Only above threshold 10 keVSimulation complements below thereshold

simulation

29 kRad/yr

Hard-SR simulation

Current Status of SR at Belle

• Simulation reproduced experience• Current beampipe (r =1.5 cm) at Belle is

designed based on BG simulations• Hard-SR is dominated (~30 kRad/yr)• Data is consistent with simulation

• Success of beampipe design rbp=1.5cm

Strong support for - Design Concept in Super-B - Reliability of BG Simulation

#### Study for Super-B ####

Super-KEKB Machine Parameters

KEKB SuperKEKB

Horizontal emittance 24 nm 33 nm

x-y coupling ~ 3 % 6.4 %

x* / y* (cm) 63 / 0.7 30 / 0.3

Beam current 1.1 A 4.1 A

Crossing angle 22 mrad 30 mrad

HER-beampipe tilt 11 mrad 15 mrad

HER FunctionsBased on IR_HER6.sad

Beampipe in Super-Belle

Can we also scale SR-mask height ?

• Scaled to 2/3 ( rbp 1.5 1.0 cm)

Discussion for SR-mask (rbp=1cm)

200 kRad/yr

2/3 scale 2 MRad/yr !!

Discussion for SR-mask (rbp=1cm)

Mask height should be same as rbp=1.5 cm case ( ~2.5 mm height)

200 kRad/yr

2/3 scale 2 MRad/yr !!

Acceptable height

Discussion for SR-mask (rbp=1cm)

outside inside

200 kRad/yr

Discussion for SR-mask (rbp=1cm)

outside inside outside inside

If vertical direction is higher ?

200 kRad/yr

Discussion for SR-mask (rbp=1cm)

outside inside outside inside

80 kRad/yr200 kRad/yr

Dose distribution Sym. SR-mask

~20 kRad/yr

~50 kRad/yr

QC1L(-3m) during injection

QC2L(-7m) at stored

~10 kRad/yr

Dose distribution Sym. SR-mask

~50 kRad/yr

QC1L(-3m) at injection

QC2L(-7m) at stored

~10 kRad/yr

!! WARNING !!Soft-SR is localized

~20 kRad/yr

SR AlarmOnline Alarm system based on the SR-sim.1. Real orbit fitting with BPM (=100mm)2. SR simulation into detector Monitor Soft-SR immediately Control BG level (hopefully) Permit challenging accelerator operation

BPM Operator

simulationOrbit fit Alarm

Feed-back

Hard-SR at Super-KEKB / Belle

- No correlation with beampipe radius - Determined by beam current and solid angle HER current: 1.1 A 4.1 A beampipe tilte: 11 mrad 15 mrad 29 kRad/yr(SVD2) x (4.1/1.1) x (15/11) ~ 150 kRad/yr

In case of current configuration

For Hard-SR reduction Reduce scattering on photon-stop Put photon-stop far place

Hard-SR : materials of photon-stop

Cu:150 kRad/yr Ag:100 kRad/yr Ta:140 kRad/yr

• Heavy material reduce compton scattering• K-edge of heavier material is higher Ag looks good for Radiation Dose Wattage w/ Ag (Ta) is 36 (64) % higher than Cu

Idea for Hard-SR reduction

HER-beam

HER-beam

If we can bend beam photon-stop far place

SR

SR

If 2 times far place 1/4 BG

Summary• We had serious troubles by SR, but Solved

simulation reproduces them

• Beampipe for SVD 2.0 (rbp= 1.5 cm) was designed based on the BG simulation Measured dose agrees to expectation

• Basic design for Super-B is same as SVD 2.0, rbp= 1.0 cm scaled to 2/3 SR-mask shape is symmetric w/o 2/3 scale No serious increase for Hard-SR Soft / Hard-SR ~ 80 / 150 kRad/yr only 8 times higher than current SR-BG

No problem for Super-KEKB / Belle !

##### backup #####

QUAD Parameterss (m) k1

SuperKEKB KEKB SuperKEKB KEKB

QCSR (+2m) + 0.72 ~ 1.68 + 1.48 ~ 2.40 - 0.46 - 0.30

QCSL (-1m) - 1.52 ~ -0.52 - 2.08 ~ 1.12 - 0.56 - 0.38

QC1L (-3m) - 3.12 ~ 2.48 - 3.61 ~ 2.99 - 0.37 - 0.32

QC2L (-7m) - 7.70 ~ 5.70 - 8.23 ~ 6.17 + 0.25 + 0.24

Based on IR_HER6.sad

SR Background (1)

Xoffset = 10mm, x = 0.9mm

x = 24nm, y / x = 3%

*x / *y = 63 / 0.7cm

~ 1 kRad/yr in physics runs

~ 1 kRad/yr in injections

Soft SR : radiated at HER upstreamEcrit ~ keV

Orbits : Nov 7(2001), May 15(2002)

SVD1.5 ~ 0.5 KRad/yr