Fuji Test Beam Line (FTBL)

K. Egawa

The KEKB Fuji Test Beam Line (FTBL), which was being built in theFuji experimental hall of the KEKB accelerator, was completed inSeptember 2007. Soon after the KEKB operation started in October, thefirst beam was observed to pass through the FTBL successfully.

outlineAfter the KEK 12 GeV PS shutdown, no GeV class test beam line wasavailable in Japan. A new GeV class test beam is strongly desired.
 The feasibility study to construct a test beam line in Fuji experimental
hall of the KEKB accelerator started in 2006.
 The idea is to use bremsstrahlung photons coming from HER 8 GeVelectron vs. residual gas scattering in Fuji straight section. They areconverted to e-/e+ pairs. The obtained electrons have a sharp forward
peak and are sufficient as a test beam at a few GeV/c range.
 The project team was organized and the construction started up.
KEKB Fuji crossing
by Tajima
inside8GeV e-3.5GeV e+outsideBremsstrahlung photons are coming fromHER 8 GeV e- beam vs. residual-gas scattering.
1.6x105 photons/sec (3x10-8Pa is assumed)

Straight section(100m)“Turtle” simulation for Bremsstrahlung photon by T. Higuchi

by Tajima

Brem. photons are converted toe- / e+ pairs

Straight section(100m)

by tungsten converter : 5mm ( 3mm  ~1X0 )Sufficient electrons at a few GeV/cwith a sharp forward peak are obtained.
Generated electron
Based on Geant4 simulation+/- 3.5mrad
Energy(GeV)

profile : px/pz (rad)by T. Higuchi

KEKB Fuji Test Beam Line ( FTBL)

by Tajima

Converted electrons are extracted
to outside of KEKB tunnelsimulation
More than 100 electrons/sec (continuously)
Floor forexperiment(7m x 4m)p = 0.5 ~ 3.4 GeV/c, σp/p ~ 0.4%, spot size +/−1cm

Momentum0.5 ~ 3.4 GeV/c+/−1cm

σp/p = 0.4 %Specification of magnet

BX1.2

Straight section(100m)

Fuji Test Beam Line : magnet parameter
The lattice was designed to make the most use of the recycled magnets andpower converters to save the construction cost.
••••

Aperture– Bendaperture width 80mm (including sagitta 40mm)/ height 40mm
– Q[1,2]
φ50 mmtr BT Q
– Q[3,4]
φ166 mmkekB LER_Q.rf– hole dia. of the concrete shield
φ100
Beam Line Parameters...
– Bendtype
Max B(T) Max I(A) L(m)_eff PSW (kg)
– B1L
tr wiggler L 1.2300
1.00
A3400 * with support– B1S
tr wiggler S 1.2
300
0.513
A
1800 *– B2
new
1.25001.64
B2800 ** w/o support– B3
new
1.2500
1.64
B
2800
– B4
new
1.2500
1.64
B
2800
– B5L
tr wiggler L 1.2300
1.00
A3400
– B6L
tr wiggler L 1.2300
1.00
A3400
– B7Ltr wiggler L 1.2300
1.00
A3400
– Quad type
Max B’Max I(A) L[m]_eff Bore[m] PSW– Q1
tr BT Q
16 T/m
50 A
0.525
0.052
C390 kg– Q2
tr BT Q
1650
0.525
0.052
C390
– Q3
kekB Ler
3.79
300
0.584
0.166
A2070
– Q4
kekB Ler
6.32
500
0.584
0.166
B2070
PC (Power Converter)– Type A: 12 GeV PS Beam channel 300A_55V、(WL: 29.6V、WS : 20.06V @ 300A )– Type B: 12 GeV PS Beam channel 500A_33V、 (new：30V @ 500A)– Type C: KEKB Vac. Group 60A_35VWall power 400V_300A (Fuji A-side)The FTBL is like a “roller coaster” !
Some magnets are tilted at more than 30° to the horizontal plane.
magnet rotation : θrot @ Gxyz = Rotate + Chi3
Beam Line Parameters...
• BendRotate
Angle Edge1• B1L-30.246 -6.050 0.000• B1S-30.246 -3.048 0.000• B2-0.315-9.706 0.000• B3-1.087-9.706 0.000• B4-1.847-9.706 0.000• B5L-2.597 -6.471 0.000• B6L-3.091 -6.471 0.000• B7L
38.173 -6.471 0.000•••••

QuadQ1Q2
Q3Q4Rotate-59.511-54.202-59.712-31.486

Edge2
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000

K1[m^-1]
L[m] Bore[m]-0.515 0.525 0.050
0.365 0.525 0.050-0.194 0.584 0.166
0.222 0.584 0.166

Chi3
0.
0.139080.31471.0865
1.84732.59703.09103.58180.31470.31472.59703.5818before reform
Fuji from upstream

BX1.2

BX1.2
γ extracted here

QX4.2

QX3.2
⇨ slitslit

rearrange cables

QX2.2⇨ cablebefore reformconverter

Q1^Q2

B1L^S

B1L^S

B2,3^4

vw_3dThe first job was to make a 3Ddrawing both of the FTBL andthe KEKB two rings.
As KEKB is always running, the3D drawing is absolutely needed
to proceed the FTBL works.

Hardware Preparation
Vacuum DuctThe new vacuum duct was fabricated for the extraction.

Magnets
•
•
•
•





The lattice was designed to make the most use of the retired
Tristan magnets and KEKB spairs to save the construction cost.
The FTBL design, like a “roller coaster”, was fixed.
Design and fabricate the new 3 dipoles ( B2, 3 and 4 )Reform the TRISTAN magnets and the KEKB spares– TR Wiggler（ WL : ４、 WS : １）
– TR BT Q : Q1, Q2– KEKB LER Q.rf
: Q3, Q4
– reduce the gap of the TR wigglers 64mm → 40mm
– add new surveying bases for the laser tracker– design and fabricate a tilted and sloped support for eachmagnet– put the surveying bases on the supports
Power converter : reuse the old power converters used at 12 GeV
PS beam channel.
Power cabling, cooling watermodify the recycled TR wigglers

On the new supports

new dipoles & LER Q.rf

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The old power converters were fixed and returned to work.

Installation & Alignment

laser tracker• 3D drawing of the FTBL with theKEKB two rings• 3D alignment is absolutely needed.
•→ Laser tracker is used.
• coordinate system– KEKB coordinate– laser tracker coordinate– magnet coordinate• process– mark off the FTBL beam line on the tunnel floor– pre-alignment

3D measure of the newly added surveying bases
confirm each magnet can be adjusted as the FTBL lattice specification– installation– survey several KEKB ring magnets to configure the coordinate system– survey the FTBL magnets

installation

after reform

On the stage

The FTBL overall view

Commissioning•••

Soon after the KEKB operation started in October 2007, the first test
beam was observed to pass through the FTBL successfully on
October 12th.
The FTBL magnet leakage field affects the KEKB operation. → The shields
against the leakage field have been improved.
The test use of FTBL has started. Further FTBL commissioning will becontinued.

2 GeV/c

3 GeV/cbeam profile @ the target完