Beam Collimators
KEKB Review
March 3rd, 2014
Takuya Ishibashi

General❖

We plan to install 10 horizontal and 3 vertical new typecollimators in LER for SuperKEKB.

❖In Phase-I, 2 horizontal collimators are going to be installed
in an arc section of LER.

❖A prototype of the horizontal collimator was manufactured.

❖

In HER, KEKB type collimators are going to be reused at
the same locations as KEKB in the Phase-I stage.

Collimators Location (Phase-I)
IRHER
D12: H1, H2, H3, H4
V1, V2, V3, V4

e5.

HERe+.

D01

D02
TSUKUBA

D12LER
D03

D05

ARES

OHO

D10

WIGGLER

D04
ARES WIGGLERD11
NIKKOSC
SC

WIGGLER

SuperKEKB.Main.Ring

:.Horizontal.Collimator.(KEKB.type).

HER
D09: H1, H2, H3, H4
V1, V2, V3, V4:.VerCcal.Collimator.(KEKB.type).
:.Horizontal.Collimator.(SuperKEKB.type)

D09

FUJI

D08
e5.

D07
e+.

ARES
ARES

D06

LER
D06: H3, H4

Basic Structure❖

SLAC PEP-II collimators as a reference.

❖The chamber and the heads are made from copper.

❖The strokes of the movable heads are d=5-25 mm in horizontal and 2-12 mm in vertical.
(“d” refers to the distance between the central beam axis and the tip of the head.)❖❖Tungsten is jointed at the tip of the head with Hot Isostatic Press(HIP, already succeedin the test).
RF fingers are attached between the heads and chambers.
ramp ~12°tungsten on tip
cooling channel
tapered beam pipe

bellows

Mock-up of Head❖

A mock-up of the movable head was manufactured.

❖Tungsten, copper and stainless steel are jointed with HIP.

Prototype❖❖

A prototype of the SuperKEKB type horizontal collimator wasmanufactured.
We’ve improved supports for the movable heads, RF fingers and so on
through tests.

System Configuration❖2-axis for a collimator❖

5-phase stepping motor with no backlash ball screw
RTD Movable Head
Stroke: 20 mm

Displacement Gauge(Potentiometer or LVDT)
Scale
Stepping Motor
DamperPhysical Stopper

Limit Switch
Physical Stopper

Displacement Measurement with LVDT❖In vacuum❖

positioning accuracy without feedback: ~±25 µm❖

We try to put the motor axis on the same axis of the movable head tominimize the deflection at the support, but there is a limitation to the width.
500

200400050

100

150

300
Displacement,(µm)

Displacement,(µm)

-20200100-40-60-80-100

00-100100200300

Time

300 pulses/step

400

500

600

vent (vacuum to air)-120-140,Time

vent

200

250

300

RF Fingers❖❖

The base material is INCONEL, which is also used for RF fingers of bellows
chambers in KEKB.
A comb-type RF shield would be adopted at the longitudinal side of the head.

Silver plated RF fingers (ver.1)

Silver plated RF fingers (ver.2)

Long-duration Test❖

shuttle the head back and forth for about 100 hours
repeatedly.

❖stroke: 12 mm, velocity: 2 mm/s❖

total distance of the movement in the test: ~720 m

Copper surface

Stainless surface

Long-duration Test❖

We’ve adopted the silver plated INCONEL for the RF fingers andthe stainless steel for the contact surface.

❖It still generates dusts, so we continue to seek a better combination.
\RF Fingers
Contact Surface\INCONEL

Rhodium plated INCONEL

Silver plated INCONEL

CopperNG(soft contact surface)NG(soft contact surface)NG(soft contact surface)

StainlessNG(too much SS dusts)

NG(too much SS dusts)

OK(small Ag dusts)

Control System❖

We would adopt a MECHATROLINK-III system in which a
PLC module controls multi-devices.
-

F3NC07-0N (YOKOGAWA)-Max. 15-axis control with a module-

Communication rate: 100 Mbps

-Communication cycle: 0.25 ms/4-axis, 0.5 ms/8-axis, 1.0 ms/15-axis
MECHATROLINK-III Network

Rack in Control Room

DriverDriverDriverDriverDriverTunnelDriver
・・・

Motor

Motor

Motor

Motor

Motor

Motor

Summary and Future Plans❖

We’ve developed a new type collimator for SuperKEKB.

❖A prototype of the SuperKEKB type horizontal collimator has
been manufactured, and we‘ve improved the structuralproblems through tests.

❖

We’ve adopted a silver plated INCONEL for RF fingers and astainless steel for the contact surface so far.

❖It still has an issue about long-term durability and dustgenerations.

❖We plan to build and install two horizontal collimators in LER
by Phase-I commissioning.

❖We have to study a radiation shield at the collimators.

back-upCollimators Location (Phase-II)
HER
D01: H1, H2, H3, H4, H5
V1HER
D12: H1, H2, H3, H4
V1, V2, V3, V4

D01

LER
D02: H1, H2, H3, H4
V1
LER
D03: H1, H2
V1, V2

D02

D12

D03

D11

D04

D10

D05

HER
D09: H1, H2, H3, H4
V1, V2, V3, V4
D09

D08

D07

D06

LER
D06: H1, H2, H3, H4

TMCI❖

We estimated the threshold of the Transverse Mode Coupling Instability using
actual β value at each collimator with σz = 6 mm.

❖The bunch current of the design value in LER is 1.44 mA/bunch.

❖A kick factor in D02V1 is quite large because of the narrow aperture (±2 mm), andit limits the bunch current.

❖We may need an another structure, such as long heads with gradual slope, for
D02V1.
TMC Threshold (mA/bunch)

All Closed

Actual Apertures

Horizontal

1.41

13.15

Vertical

0.96

1.25

Collimator and Aperture List

C1 fs E/eIthresh = P
i i ?i ( z )