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Tuning the Beam: A Physics Perspective on Beam Diagnostic InstrumentationSlide 1 Operated by Los Alamos National Security, LLC for the U.S. Department of Energy’s NNSA
U N C L A S S I F I E D
Tuning the Beam: A Physics Perspective on Beam Diagnostic
Instrumentation
Santa Fe, NM
LA-UR-10-02862
Editor's Note: PDF version of slides from Beam Instrumentation Workshop 2010, Santa Fe, NM
Slide 2 Operated by Los Alamos National Security, LLC for the U.S. Department of Energy’s NNSA
Where does the typical accelerator physicist come from?
• Often (?) – experimentalists who go from conducting experiments with accelerators to operating/designing accelerators.
• Mark Gulley – started as an accelerator-based atomic physicist at LAMPF. • Glen Johns– Experimental nuclear physics (gamma-ray spectroscopy). • Rod McCrady – Particle physics. • Chandra Pillai – experimental nuclear physics. • Larry Rybarck – experimental nuclear physics. • Thomas Spickermann – started as a particle physicist at CERN. • Ferdinand Willeke – NSLS-II – studied nuclear solid state physics.
• BUT… There are accelerator physicists who were trained as accelerator physicists
• Jeff Kolski – Started as an accelerator physicist at IU studying the PSR at LANSCE. • Frank Zimmermann – Started as accelerator physicist studying emittance growth at HERA proton
ring at DESY. • Yuri Batygin – Trained in USSR as an accelerator physicist.
• What might the ratio be?
Where does the typical accelerator operator come from?
• Depends on the machine (sorta) • LANSCE – ex-Navy Nuclear operators, some
nuclear reactor operators, some local (Elec/mech tech AAS).
• FermiLab – physics/engineering/CS BA/BS. • NSCL – knowledge from 4-year
physics/engineering program. • SNS – AAS in physics, engineering. • J-Lab – BS in physics, engineers, ex-Navy Nuclear
operators as well.
What does the typical tuner want?
• Reliable Measurements – Equipment works – Results are trustworthy – Timely Measurements
• There is a relationship between the person who knows what the equipment does and how it works and the person who understands the information it generates.
• Do the tuners care about the details of the equipment functionality? Yes (you don’t have confidence in the results if you don’t think you know what is going on to get the data).
Physically, what do we need to know?
• We want the beam to get from Point A (usually a source/injector) to Point B (usually a target) in the right condition.
• So, what is the Right Condition? – Where is the beam in the pipe – steering. – Is the beam focusing the way it should – transverse tuning. – What is the beam energy and bunching – longitudinal
tuning. – What is the intensity of the beam? – What is the transmission of the beam? – …and how are these related?
Transverse Tuning
• This is the “keep it between the ditches” part. • Bending
– Magnets designed to bend correctly. – Correctors/steerers are still needed. – Quad steering, other higher order effects.
• Focusing – Beam size. – Diverging/converging properly. – higher order effects.
What could possibly go wrong? • The Gulley-Lovato hole in the TR beam pipe
The Transition Region (TR) at LANSCE
Transverse Devices – a partial list
• Wire scanners – beam size (and details like how Gaussian does it look?).
• Harps – same info as wire scanners. • Screens – usually qualitative picture of beam
size/shape/position. • Slit/collectors and other emittance-measuring
devices. • Beam Position Monitors – position of centroid. • Laser Wires – wire scanner “2.0”
Transverse Tune in a Transport - Emittance
• Emittance is needed to be below a certain value or the beam blows up too quickly for reasonable transmission.
• Beam waists need to be in the correct locations (buncher centers, chopper centers, etc.).
• Beam needs to have proper divergence at entry point into next stage of acceleration (matching).
Typical “particle” parameters of various machines
Facility # of Particles per bunch/macropulse
LANSCE 5.9e13 H+ 3.3e13 H-
SNS 1.6e14
ISIS 2.5e13
APS 2.3e12
ALS 4.16e9
LHC 1.1e11
The collection of these particles constitutes the ‘beam’ which will have a transverse as well as an energy
distribution.
• E.g. A Gaussian (‘normal’) distribution
Converting particle distributions to beam envelopes
Beam envelope
X – position X’ – angle wrt x-axis Y – position Y’ – angle wrt y-axis P – momentum φ- phase
In accelerator and beam transport systems, the behavior of an individual particle is often of less concern than the behavior of a bundle of particles (the ‘beam’) of which the individual particle is a member.
In accelerator terminology, a particle in a ‘beam’ is represented by a vector whose coordinates are:
Macroparticles – an example from the LANSCE 750 keV LEBT
Courtesy of Yuri Batygin
The emittance ellipse The entire beam can represented by a phase ellipse whose coordinates are, again, similar to that of the individual particle, but about an assumed central trajectory.
Emittances of Different Machines
Facility Emittance Normalized Emittance
SLC 50/8 µm
SPS-LHC 3 um/3.5 um
LANSCE (750 keV) 5 π mm mrad .2 π mm mrad
LANSCE (800 MeV) .2 π mm mrad .3 π mm mrad
There are various ways of reporting emittances, depending on the type of machine…
There is a sizeable dynamic range of spot sizes
Facility Spot Size
LANSCE ~ 1 mm
LHC 16 µm
Many of these numbers are from Minty and Zimmermann’s “Measurement and Control of Charged Particle Beams”
Twiss parameters – because physicists can’t talk about an accelerator without
mentioning Twiss parameters
Needs formatting work….
Perfect beams – what is going on in each case?
And for more realistic-looking beams…
Funny shapes of emittance ellipses
From “Emittances, Straight and Simple: their Usefulness and their Limitations”, Feb. 28, 2008, Martin Stockli, SNS
Schematic of how a slit/collector emittance measurement
A typical emittance scan at LANSCE Editor's Note: PDF version of slides from Beam Instrumentation Workshop 2010, Santa Fe, NM
TRACE calculation of the transport Editor's Note: PDF version of slides from Beam Instrumentation Workshop 2010, Santa Fe, NM
The area will stay constant, but the emittance ellipse shape and
orientation changes
This is a dynamic process! Editor's Note: PDF version of slides from Beam Instrumentation Workshop 2010, Santa Fe, NM
Click the picture if a movie does not run automatically
Longitudinal Tuning
• This is the getting the energy/acceleration right part (and keeping it together until the finish line…).
Energy Parameters Machine Beam Energy Particle type
APS 7 GeV e-
SNS 1 GeV H-
ALS 1.5-1.9 GeV e-
LHC 7 TeV protons
LANSCE/ISIS 800 MeV Protons (H-)
Choose φs to Produce Stable Motion about Synchronous Particle
Courtesy of Larry Rybarcyk
The other choice for φs will produce Unstable Motion about the Synchronous Particle
Stable Beam Motion in Phase Space
Phase scans for longitudinal tuning
Figures from Dong-o Jeon, Proceedings of PAC05
Measured acceptance plot from SNS
Figure from Jeon, Stovall, Shafer, and Crandall, Proceedings of LINAC02
Delta-T measurement for longitudinal tuning
From K. Crandall, et al., Proceedings of the 1972 proton linear accelerator conference
Most facilities use BPMs; LANSCE uses loops.
The t turn-on procedure is the method by which suitable rf amplitude and phase set points are determined for the first 8 modules (modules 5 – 12) of the LAMPF side-coupled linac. The name is derived from the relative time-of-flight measurements that are required. A method such as this must be used because direct field measurements are not sufficiently accurate to determine the rf amplitudes and phases within the required tolerances.
module 5 module 6 module 7
Loop/BPM Loop/BPM
Phase measurement
Phase measurement
Indirect Tuning – minimizing spill
• Sometimes used when other diagnostics are unavailable.
• Operators become very well-versed in this. • At LANSCE, it has been successful in linac. • In areas with insufficient coverage, this
technique may “hide spill”.
Example of spill detection in the LANSCE Linac
Transmission
• Poor transmission means something is not right with the phase distribution of the particles.
• Reasons to care – Whole point is to get the beam to Point B – Beam spill heats stuff up. – 1 W/m rule of thumb.
Software Tools … an incomplete list
• Trace 2-D, 3-D • TRANSPORT • Turtle • Parmilla • Beampath
Physics Tune vs. Production Tune
• Are the same tools needed for both? (read “same diagnostics?”).
• Skills of the physicist vs. skills of the operator. • Having a feel for how the machine should be
running (or how the beam line should be)
The Human-Machine Interface – The Control Room
Rose McFarland, Ken Moody, and Glenn T. Seaborg in control room of 88-inch cyclotron on October 1, 1981.
Bevalac produces first beams, control room
Control Rooms II
ALS
LANSCE
Control Rooms III
APS
J-Lab
Control Rooms IV
SNS
LHC
Control Rooms – The Future? Editor's Note: PDF version of slides from Beam Instrumentation Workshop 2010, Santa Fe, NM
Concluding Remarks
• Physicists care about the phase distribution of the particles, both transversely and longitudinally. This is what we want the instrumentation to tell us about.
• Where should we go from here?
• “Computers are incredibly fast, accurate and stupid. Human beings are incredibly slow, inaccurate and brilliant. Together they are powerful beyond imagination.”
(often attributed to Albert Einstein, but unlikely…)
Tuning the Beam: A Physics Perspective on Beam Diagnostic Instrumentation
Where does the typical accelerator physicist come from?
Where does the typical accelerator operator come from?
What does the typical tuner want?
Physically, what do we need to know?
Transverse Tuning
The Transition Region (TR) at LANSCE
Transverse Devices – a partial list
Transverse Tune in a Transport - Emittance
Typical “particle” parameters of various machines
The collection of these particles constitutes the ‘beam’ which will have a transverse as well as an energy distribution.
Converting particle distributions to beam envelopes
Macroparticles – an example from the LANSCE 750 keV LEBT
The emittance ellipse
There is a sizeable dynamic range of spot sizes
Twiss parameters – because physicists can’t talk about an accelerator without mentioning Twiss parameters
Perfect beams – what is going on in each case?
Funny shapes of emittance ellipses
Schematic of how a slit/collector emittance measurement
A typical emittance scan at LANSCE
TRACE calculation of the transport
The area will stay constant, but the emittance ellipse shape and orientation changes
This is a dynamic process!
Longitudinal Tuning
Energy Parameters
Choose fs to Produce Stable Motion about Synchronous Particle
The other choice for fs will produce Unstable Motion about the Synchronous Particle
Stable Beam Motion in Phase Space
Phase scans for longitudinal tuning
Measured acceptance plot from SNS
Delta-T measurement for longitudinal tuning
Indirect Tuning – minimizing spill
Transmission
The Human-Machine Interface – The Control Room
Control Rooms II
Control Rooms III
Control Rooms IV

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