Magnets, installation andorbit control
KEKB magnet group
K.Egawa,T.Kawamoto,T.Kubo,
M.Masuzawa,Y.Ohsawa, N.Ohuchi
T.Ozaki,R.Sugahara,N.Tokuda,M.Yoshida
KEKB Review Feb21-23, 2005

Contents
1.
2.

Power supply to-do list
Magnet installation & realignment
to-do list
·In order to accommodate the crab optics.

3.

Orbit control· In order to maintain the horizontal orbit at crab
cavities.

KEKB Review Feb21-23, 2005

1. Power Supply to-do list
Power Supplies for Quadrupole Magnets-M.Yoshida, et.al◆

Six new power supplies are needed (HER).
⇒By the end of March◆Two power supplies need to be modified(HER).
Cabling work
Polarity change (D⇔F)⇒During the summer shutdown 2005◆
◆KEKB Review Feb21-23, 2005

2. Magnet installation & realignment
to-do list-R.Sugahara, et al.
◆

Installation of 4 new magnets in LER⇒“Weak bend” magnets: BSWNLP.1&2
BSWNRP.1&2⇒Cabling work from the PS building to the tunnel has been
completed.

◆Exchange the positions of 4 steering
magnets
ZHQS1NP.1⇔ZVQS1NP.1
ZHQS1NP.2⇔ZVQS1NP.2
KEKB Review Feb21-23, 2005

◆Realignment of the chicane magnets

4 sets of chicane magnets, each consisting of 4 bending magnets,
at both sides of the NIKKO and OHO straight sections in the LER.
Originally used tocompensate for thecircumference difference
between the LER and theHER.
They have also beenused to keep the LER
circumference constantsince June 2001.

NIKKO section: 21.208 mrad → 0 mrad
Straighten out the beam path upstream(and downstream) of the crab cavity
OHO section: 21.208 mrad → 30.307 mrad
KEKB Review Feb21-23, 2005

3. Orbit Control-Y.Funakoshi & M.Masuzawa

Goal: To maintain the horizonal beam orbit
at the crab cavities.
From the KEKB Review 2004,“The horizontal position of the beam in the crab
cavity must be controlled to approximately+/1mm to avoid loss of control of the crabbing
mode field due to beam loading. In the HER with
βx=200 m this corresponds to 0.5 beam sigma.
A reliable feedback system will be needed tominimize beam aborts from exceeding this limit.”
KEKB Review Feb21-23, 2005

3. Orbit Control
Similar to the collision feedback systemcalled “iBump.”⇒Orbital feedback system at the IP, used tomaintain good collision conditions.
-12 steering magnets (8 vertical and 4horizontal) in HER.
- Use QCS BPM readings (every 3-4 seconds)
to calculate the beam-beam kick at the IP
and monitor the collision.

This iBump feedback system has beenworking well.
KEKB Review Feb21-23, 2005

3. Orbit Control
For crab orbit feedback:◆ Use 4 horizontal steering magnets to make aoffset bump for each ring.
⇒Need 8 magnets
Only horizontal orbit feedback is
considered at this point.
◆ Use BPM readings to monitor the offset at thecrab cavity.
⇒2 upstream (entrance) BPMs and 2
downstream (exit) BPMs around the crabcavity. 1 Hz read-out speed◆ (Or/andRF beam loading for monitoring.)
KEKB Review Feb21-23, 2005

Bump Orbit (HER)

3.Orbit Control

4 new horizontal
steering magnets
will be installed here.

If Δx at crab cavity is measured to be +1 mm,create a -1 mm bump using these 4 steering magnets.
(5 mm offset bump with 0.2 mrad kick angle possible)⇒The idea is to make a bump which cancels theunwanted offset at the crab cavity.
KEKB Review Feb21-23, 2005

Bump Orbit (LER)
FFD

3.Orbit Control

4 new horizontal
steering magnets
will be installed here.

A 4mm/6mm (tilted) offset possible with 0.52 mradkick angle.
KEKB Review Feb21-23, 2005

Bump Orbit (LER)
FDF
A parallel offset bumpwill create a larger
COD at the neighboring
QF magnet.

KEKB Review Feb21-23, 2005

3.Orbit Control

3.Orbit Control

Orbit feedback magnets &power supplies◆ Use spare magnets and magnets not

being heavily used (horizontal steering
magnets at defocusing quadrupole
magnets, for example).
⇒New fabrication not needed.
◆ Same type of power supplies as theiBump (collision feedback) system.
We have not had any serious problems with the above
components since the start of the beam commissioning and
we are comfortable with them.
KEKB Review Feb21-23, 2005

3.Orbit Control

Orbit feedback : Control system◆ Epics based control system will be used.
◆ System design (VME? PLC? etc) is underway, with the help of the KEKB control
group (T.Nakamura, et.al).
◆ System will be tested before the summer
shutdown.

KEKB Review Feb21-23, 2005

3.Orbit Control

Check list
◆ Can the feedback system suppress suddenchanges in the horizontal orbit?
◆ What kind of sudden orbital changes need tobe taken care of by this system alone?
◆ A big/sudden orbit change has occurred
during injection from 0 mA, for example.
◆ Speed: BPM read-out time, magnet responsetime…
◆ Size of the orbit bump: Max. kick angle big
enough or too much?
KEKB Review Feb21-23, 2005

3.Orbit Control

Example of COD after aborts
1100mA/300sec• CCC, global orbit
correction, corrects theCOD every 10-20
seconds.
• We have seen rather large
COD after the aborts.
• Crab orbit feedback isexpected to correct thelocal orbit much fasterthan CCC.

IP

Horizontal COD 180µm
in the arc section where
βx ~20m.
With βx ~200m @ crab
Sqrt[200/20]*180µm~ 600 µm
KEKB Review Feb21-23, 2005

3.Orbit Control

Orbit Feedback: Schedule◆ Test of the control system planned inspring.
◆ Installation of the magnets will be done
during summer 2005.
◆ The feedback system will be debugged andtested from the fall beam operation.
◆ No crab cavities in the beam line yet in thefall, however we will be running the machinewith “crab optics”.
⇒Good opportunity for testing the feedbacksystem.
⇒Feedforward into design modifications.
KEKB Review Feb21-23, 2005