LARP AC Dipole Task

1
LARP AC Dipole Task

• M. Bai,1 R. Calaga,1 W. Fischer,1 A. Jansson,2
• S. Kopp,3 R. Miyamoto,3 P. Oddo,1 M. Syphers2
• 1Brookhaven National Laboratory
• 2Fermi National Accelerator Laboratory
• 3University of Texas at Austin

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Test of the Nonlinear Optics Measurements Using
an AC Dipole in the Tevatron

• At the injection energy (150 GeV), a (skew)
  sextupoloe and an
• octupole family are set to various values.
• Large amplitude oscillations are produced by a
  vertical AC dipole
• and the turn-by-turn data and its Fourier
  spectrum are observed.

• TBT data of a BPM
• in the arc
• s 1.3 mm
• ß 100 m

3
An Example of Nonlinear System
Equation of Motion
HO with a Cubic Potential

• Consider 1st order of k
• Expansion x x0 x1
• Leading order

1st order
A sextupole 1. shifts the central orbit. 2.
produces a higher order mode (2?).
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Shifts of the Closed Orbit by a Sextupole

• A skew sextupole is changed
• from 0 A to -30 A.
• The closed orbit changes
• more for a larger kick.

The phase of the orbit flips if the sign of the
sextupole current is flipped.
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Higher Order Modes

• Higher frequency modes appear for a larger
  oscillation.
• The frequencies of the higher order modes change
• with the driving frequency.

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Detuning
?d lt ?
Amplitude of the driven motion when the tune
depends on the action
?d gt ?
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What do we measure?
The closed orbit formula
Behavior of w or W
s
If we know ß and ?, from information of two BPMs
1 and 2,we can construct
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Generating Function of the 1st Order Mode

• A fixed sextupole current, different AC dipole
  current.
• The strength of the sextupole is determined from
  the step size.
• The kick strength depends on the action.
• The action is not factored out, here.
• The BPM nonlinearity will be considered in
  future analyses.

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Generating Function of the 3rd Order Mode

• A similar analysis is possible for the 3rd order
  mode (Two same condition).
• Two generating functions for resonances of 2?d-?
  and 2?d?.

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Summary

• AC dipole based nonlinear optics measurements are
  tested with intentional sources in the Tevatron.
• Sextupole driving terms are measured by observing
  the change of the closed orbit and the 3rd order
  mode (Accuracy 510? BPM effect should be
  considered.).
• The detuning effect caused by octupole elements
  is also measured.

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LARP Accelerator Instrumentation AC Dipole Task
Status

• Achieved deliverables
• LHC ac dipole constructed based on FNAL model.
  Resonate a kicker magnet
• BNLs binary weighted cap bank tuning circuit
  developed for the LHC ac dipole circuit.
• The dynamic tuning technique development at
• BNL. This will allow one to stay with the
  high Q
• ac dipole design
• Beam optics measurement at BNL and FNAL

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Current Status of LHC AC Dipole

• the FNAL solution of audio amps(Lab-Gruppen
  Class-H amp) driving pinger(MKQs)
• Spec 1800 A in MKQ for 7s _at_ 7 TeV.

• Two Lab.Gruppen FP13000 amps and 41 transformers
• 2000Apk magnet current achieved
• The 7s (1800Apk) goal is reached with
  comfortable margin
• plan to upgrade the current copper claps of the
  capacitor banks to MOSFET switches

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Current LHC AC-Dipole Tunning Schemedesigned by
P. Oddo (BNL)

• 5-bit binary-weighted capacitor-bank
• 0.255-0.345 (15) tune range
• 2.867-3.880kHz
• 0.002-0.005 tune steps
• 22-54 Hz
• Static MOSFET switching
• Can be replaced with mechanical switches or
  straps
• Conservative design
• Can withstand CW operation
• Peter have been working with Javier Serrano to
  implement this solution

Bit2
Bit3
Bit4
Capacitor
Bit1
Bit0
GND Plate
MOSFET Module
Coil/Drive Plate
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Effect of secondary driving terma thin
quadrupole error
Phase Space _at_ an IP

• sensitive to the work point
• For work point close to half integer
• like Tevatron, this effect can be as
• big as 12
• For RHIC and LHC working points,
• the effect is about 6
• R. Miyamoto et al, Submitted to
• PRST-AB (also arXiv0709.4192)

?d - ?
ßd m
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Dynamic Tuning Development P. Oddo(BNL)

• A dynamic tuning technique using single switched
  capacitor with MOSFT was proposed by P. Oddo at
  BNL
• Simulations shows a tuning range of D? 0.01,
  should be achievable
• A test setup using a half meter RHIC type ac
  dipole is under construction.

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Dynamic Tuning Development P. Oddo(BNL)
Low-power Switched-capacitor Results

• 7.33-9.04kHz (10) range
• Basic Topology, 0.56W, Q15-19
• Coil current fairly constant 2.2Apk
• 3rd harmonic 33dBc
• Consistent with simulation

7.33kHz
9.04kHz
8.67kHz
Always on
Always off
Switching
Coil current
Drive current
Coil voltage
Switch voltage
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1kW Dynamic Tuning Test

• Test RHIC prototype magnet over Spin-
• Flipper frequency range
• 39kHz 800Hz (0.01 tune)
• Magnet current 145Apk
• Magnet field 92Gm
• Magnet Q155, System Q135-153
• Estimated MOSFET losses 86W

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AC dipole task plan in FY09

• A new task under the Accelerator Physics
• Focusing on commissioning
• LHC ac dipole system to achieve the design goal
  of delivering 1800 Amps_at_3kHz, control software
• Linear optics measurement
• A lot of data have been taken in RHIC and
  Tevatron
• Help the development of LHC on-line optics
  measurement/gradient error correction application
• explore various techniques for gradient error
  correction using ac dipole
• dynamic aperture measurement
• non-linear resonance driving term measurement

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What is needed to enhance AC dipole task in FY09

• To have an experienced person for this task
• need experience with the FNAL type ac dipole
• system to help the ac dipole system
• commissioning
• need experience with ac dipole based optics
• measurement
• Hence we propose to have a joint post doc
• between LARP AC dipole task and BNL

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Summary

• AC dipole task has achieved its goal as an
  accelerator instrumentation task
• A new task under the Accelerator Physics to focus
  on commissioning
• To have an experienced person for this task is
  very critical

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Backup slides
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A Method to Detect Sources
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Phase Measurement
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FNAL AC dipole Status

• Successfully share the FNAL musical ac dipole
  technique with LHC ac dipole system
• transform a kicker to an ac dipole
• take advantage of commercially available audio
  power amplifier
• impedance matching between ac dipole and its
  power amplifier
• Measured linear optics using its musical ac
  dipole
• confirmed the effect of the secondary driving
  term on the measured optics

A. Jansson
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Parameters of RHIC, TeV, and LHC
Seranos talk _at_ LTC gives bm258m at location
of MKQ kicker