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High Power Proton
Accelerators: Capabilities and
Challenges
John Galambos
Spallation Neutron Source
Oak Ridge National Laboratory
University of Tennessee Colloquium
10/7/2013
“Rough” Outline
• Why high power proton accelerators?
• Brief introduction to accelerators
• The Spallation Neuron Source Accelerator
• Future high power proton accelerators and challenges
2
Managed by UT-Battelle
for the U.S. Department of Energy
The world of particle accelerators
Traditional accelerators aim
towards higher and higher beam
energy to probe for smaller and
smaller particles.
The SNS is part of class of
accelerators called “proton drivers”
which operate at lower energies,
and instead push the beam
intensity limit.
Proton drivers are useful for a variety of
applications:
 neutron spallation
 transmutation of nuclear waste
 secondary particle sources...
Its a whole different ball game!
Getting Neutrons – Two Ways
Fission
chain reaction
continuous flow
1 neutron/fission
180 MeV/neutron
Higher average
neutron density.
Spallation
no chain reaction
pulsed operation
30 neutrons/proton
30 Mev/neutron
Higher peak
neutron density.
Properties of neutrons for measurements
Charge neutral
deeply penetrating
S=1/2 spin
probe directly magnetism
Li motion in fuel cells
Solve the puzzle of High-Tc
superconductivity
Nuclear scattering
sensitive to light elements
and isotopes
Actives sites in proteins
Help build electric cars
Efficient high speed trains
Better drugs
Why Neutron Scattering?
H
Li
C
O
S
Mn
Zr
X-rays
neutrons
• Neutrons have higher scattering cross –
section on light nuclei
• Compliment light sources (x-rays)
Cs
Engineering materials
Non-destructive analysis of a steel armed concrete block with neutron imaging and X-ray tomography.
09/10/2013
Source: PSI, CEMNET workshop 2007
7
Why Neutron Scattering ?
• Neutrons are penetrating – can image high Z dense
materials
• Can produce moderated neutrons with wavelengths of
interest for material studies (atomic spacing)
– 0.1 – 10 Å
8
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for the U.S. Department of Energy
Neutron sources:
How far have we come?
SNS
Thermal Neutron Flux (n/cm2-sec)
1018
SNS
MTR
1015
NRX
X-10
1012
109
106
10
3
NRU
HFIR ILL
HFBR
KENS
ZING-P
Tohoku Linac
ISIS
LANSCE
IPNS
SINQ
ESS
SINQ-II
ZING-P
Berkeley
37-inch
cyclotron
CP-2
CP-1
0.35-mCi Ra-Be source
Next-generation sources
Fission reactors
Particle driven (steady-state)
Particle driven (pulsed)
trendline reactors
trendline pulsed sources
Chadwick
ORNL 97-3924f/djr
100
1920 1930 1940 1950 1960 1970 1980 1990 2000 2010 2020
(Updated from Neutron Scattering, K. Skold and D. L. Price: eds., Academic Press, 1986)
High Power Proton Sources are
Needed for Rare Event Searches in
HEP
• Stopped pion decay at rest neutrino source
– Well understood energy spectra
– Study neutrino /nuclei scattering cross-sections, supernove
nucleo systhesis, dark matter detectors
– Sterile neutrino searches
10
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for the U.S. Department of Energy
Rare kaon decays provide important
tests of the flavor structure of the
Standard Model
Need MW proton beams with high duty factor, 3 GeV,
100 kW – 1 MW
ORKA test at the FNAL Main Injector
11
4 th Generation K     Experiment
Managed by UT-Battelle
for the U.S. Department of Energy
Ultra Cold Neutron Source for
Fundamental Physics
NUCLEAR PHYSICS
ann & apn scattering
lengths
PARTICLE PHYSICS
nucleon-nucleon
weak interactions
Electric charge
scattering lengths
in matter
gravity
beta-decay
static EDM
N-N oscillations
• < 100 n-eV neutrons
nucleon
structure**
neutron crosssections*
ASTROPHYSICS
/COSMOLOGY
• Proton beam
12
– 1-3 GeV, 1 MW, near CW
Managed by UT-Battelle
for the U.S. Department of Energy
A. Young , NC-State
Muon Beams
• Charged lepton flavor violation (muons changing into
electrons without neutrino emission)
– 1 MW, 1 GeV, CW proton beam
13
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for the U.S. Department of Energy
What is ADS?
(Accelerator Driven System)
High-power, highly reliable proton
accelerator
• ~1 GeV beam energy
• ~1 MW of beam power for demonstration
• 10s of MW beam power for Industrial-Scale
System
Subcritical reactor
•
• •m
Chain reaction sustained by
external neutron source
Can use fuel with large minor
actinide content
Spallation neutron target
system
•
Provides external source of
neutrons through spallation
reaction on heavy metal target
Why ADS ?
Transmutation of long lived nuclear wastes
• “Fast reactor” neutronics used in ADS systems
are favorable for actinide burning
– Reduce the burden on long term waste storage
Why ADS ?
Electrical Production
• Many ADS concepts utilize the
Thorium based fuel cycle :
– greater natural abundance than Uranium,
– proliferation resistance, and
– significantly reduced production of longlived transuranics
• An ADS system based on Th fuel would not require incorporation of
fissile material into fresh fuel
• Expanded use of Th-based fuels is actively pursued in several countries
Why ADS?
Safety
• ADS systems operate far from “prompt criticality”
– Important advantage for actinide burning
Standard light water reactor
Fast reactor breeder
Fast reactor burners
safer
ADS Applications
Why Proton Accelerators
What about other external neutron “seeds”?
Process
Example
Yield
Neutron
energy cost
(MeV/n)
D-T fusion
400 keV
4x10-5 n/D
10,000
Photo-nuclear
20 MeV e- on 238U
~10-2 n/e
2000
Spallation
800 MeV p on 238U
~ 30 n/p
27
• ~ 1 GeV protons are an efficient way to produce external
neutrons
– High energy physics, nuclear physics, neutron scattering have a rich
experience with accelerators in this energy range
• Accelerator power is easily “throttled”
– Greater flexibility for fuel consumption and safety
The First Particle Accelerators - DC
• These accelerators use at static, DC, potential difference
between two conductors to impart a kinetic energy
• Highest voltage achieved is 10’s of MV
MIT Van de Graaff ~1930
ORNL Tandem
Cockroft-Walton
RF Accelerating Cavities
• An RF Cavity has a characteristic “resonant frequency”, just
like a bell has a resonant frequency (a note that rings)
• When RF waves with the correct frequency are introduced into
the cavity, the cavity resonates (the bell rings)
• The electric field that accelerates particles
oscillates (changes direction!) in time
Electric Force
in Cavity
Time
Sinusoidal Nature of RF Fields
The beam must be timed right to pass through the field only during acceleration,
and be shielded from the field during deceleration.
accelerated
Electric Force
in Cavity
accelerated
Time
decelerated
The SNS linear accelerator RF runs at a frequency of 402.5 MHz (over
4 hundred million sign changes of the field per second). This accommodates the
real-time pulse structure of the beam.
Two types of RF Accelerators
• Two approaches for accelerating with time-varying
fields
v
E
v
E
E
E
Circular Accelerators
Linear Accelerators
Use one or a small number of Radiofrequency accelerating cavities and make
use of repeated passage through them.
This approach is realized in circular
accelerators: Cyclotrons, synchrotrons and
their variants
Use many accelerating cavities
through which the particle
beam passes once:
These are linear accelerators
The Magnetic Lattice
The accumulator ring:
- No acceleration, only RF bunching
- Accumulates 1×1014 protons, 1060 beam pulses from linear accelerator
- Has over 200 magnets for bending the bending and focusing.
N
Dipole magnets
used for bending
the beam.
+
Quadrupole magnets
used for transverse
focusing the beam.
Keeps the beam from
expanding due to
mutual repulsion of
protons.
248 meter
circumference
S
injection
point
S
N
N
S
extraction
point
Focusing the Beam
• The ring and transport lines use many different types of
electromagnets to bend and focus the beam.
• The linac also uses many magnets to focus the beam, some
electromagnetic, some permanent magnets.
• A beam without focusing wouldn’t get very far!
• An accelerator has many quadrupole magnets to keep the
beam focused.
Beam particles
without
focusing
Beam
particles with
focusing
The Concept of a Cyclotron
B
E
E. O. Lawrence: Nobel
Prize, 1939
Accelerators accelerate
particles with electric fields (Efields), and bend particles with
magnetic fields (B-fields).
TRIUMF, the world's largest cyclotron at Canada's National
Laboratory for Particle and Nuclear Physics. (520 MeV). The
machine started in 1974 and is still in operation (now for rare
isotope acceleration).
Synchrotrons – Common Ring Accelerator
Technique
• Ramp magnetic field and RF frequency to keep beam on constant
orbit during acceleration
– Separated function bending and focusing magnet systems critical element
27
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CERN accelerator complex for protons
 The CERN accelerator complex is presently fed by LINAC2
(proton source) that pulses at a rate of 0.83Hz, i.e. cycles
which are multiple of 1.2s, known as basic period
 The accelerator complex uses time-sharing to provide beam to
the different fixed target experiments and to fill the LHC
LINAC 2
50
MeV
1.4 GeV
25 GeV
450 GeV
PSB
PS
SPS
3.5 TeV
LHC
LHC (CERN) is the “Mother” of all
particle accelerators, energy wise
27 km circumference
• 3.5 TeV on 3.5 TeV proton collisions
– To be doubled !
• Beam stored energy ~ 360 MJ
29
– But when only replenished 2/day, ~ 8 kW average power
Managed by UT-Battelle
for the U.S. Department of Energy
Linear Cavity Structures
•Linear accelerator operates with RF fields of 402.5 MHz.\
•Since we are keeping the RF fields at a fixed frequency in time,
we must space the cavities farther and farther apart to account for the
increasing particle velocity.
accelerating
cavity
time= 0 seconds
E
shielded area
E
E
E
time= 0 + 1/402,500,000 seconds
E
E
E
E
An accelerating tank of the first, Alvarez, linac built
just after WWII.
Father of all spallation sources:
Lawrence’s Materials Testing Accelerator
• Deuteron accelerator
for production
of plutonium and tritium
• NaK-cooled Be target
• 500 MeV
• 320 mA
• 160 MW
The Materials Testing Accelerator (MTA), built, in the early
1950s, at a site that would later become the Lawrence
Livermore Laboratory. The purpose of the machine was to
produce nuclear material, but it never produced any (due to
uncontrollable sparking).
SNS Accelerator Complex
Accumulator
Ring
Collimators
Front-End:
Produce a 1-msec
long, chopped,
H- beam
1 GeV
LINAC
Accumulator
Ring: Compress 1
Extraction
Injection
msec long pulse to
700 nsec
RF
1000 MeV
RTBT
2.5 MeV
HEBT
LINAC
Chopper system
makes gaps
mini-pulse
Current
945 ns
Liquid
Hg
Target
Current
Front-End
1 ms macropulse
1ms
Neutron scattering users want beam power and reliability
The Drift Tube Linac Structure
RFQ
DTL
2.5 MeV
Ion
Source (7% speed
of light)
CCL
Super Conduct 1
87 MeV
(40% speed
of light)
• 6 Drift tube tanks, 210 unique drift tubes
Super Conduct 2
To
Ring
Drift Tube Linac Installed
DTL in the tunnel, ~ 37 m
Coupled Cavity Linac Installed
CCL in the tunnel, ~ 55 m
SNS Superconducting Multicell Cavities
RFQ
DTL
CCL
Super Conduct 1
186 MeV
86.8 MeV
Ion
2.5 MeV
Source (7% speed (40% speed (55% speed
of light)
of light)
of light)
Two types of
superconducting
cavities:
•
Medium Beta: designed
for v = 61% speed of
light
–
•
Gives 10-20 MV/m
High Beta: designed for
v = 81% speed of light
–
Gives 10-20 MV/m
Super Conduct 2
387 MeV
(70% speed
of light)
To
Ring
1000 MeV
(88% speed
of light)
Cryomodules Technology demonstrators
Helium tank
5-cell elliptical cavity
Cold tuning
System
Power coupler
Space frame
 Cavities Cryomodule Technology Demonstrator results by the end of 2015
SCL Cryomodules in the Tunnel
• 11 medium beta cryomodules 12 high beta cryomodules
Ring and Transport Lines
HEBT Arc
Ring Arc
Injection
RTBT/Target
Beam Charge Accumulates Throughout the
Pulse
Ring Beam Current Monitor
1 ms
End of
accumulation
700 ns
Final Extracted Beam
SNS Power History
Cost
savings
• SNS has run at ~ 1 MW for the past 3-4 years
43
– Not accelerator limited
–by UT-Battelle
Recently operated up to 1.4 MW
Managed
for the U.S. Department of Energy
Target
concerns
1.4 MW
R&D Areas for Multi-MW Applications
• Beam loss mitigation
– Simulation not good enough to predict losses at this level
– Smart scraping
• Reliability
– For user facility support and ADS applications
• Target survivability / robustness
– Uncertainty in material properties
• Charge exchange injection
– Laser stripping
• Accelerator technology
– High power RF generation
– Beam chopping
– …
Beam Loss in the Superconducting Linac
Average SCL Residual Activation
60
Activation (mRem/hr)
Activation
50
700
Reduced Magne c Field
Charge
600
40
500
30
400
300
20
200
10
100
3/
11
12
/2
4/
11
9/
1
6/
11
6/
6/
11
2/
2
/1
0
/1
0
11
/1
8
8/
10
/1
0
5/
2
/1
0
1/
22
/0
9
/0
9
10
/1
4
7/
6
/0
9
3/
28
/0
8
/0
8
12
/1
8
9/
9
/0
8
6/
1
/0
8
2/
22
/0
7
11
/1
4
/0
7
0
8/
6
4/
28
/0
7
0
Run
• High power proton beam operational loss limit: 1 W/m
– 1 part per million at full energy!
• SNS observed a low level of beam loss / machine activation
– Unexpected – not predicted in design stage!
– OK for 1 MW – trouble for 10 MW
Fluence (MW-hrs)
800
Predicting Beam Profiles / Beam Loss:
Space Charge Effects in the Ring
Low intensity
High intensity
• Effects are as expected, at least to “first order” - profile
measurements vs. models
– Not ready for predicting absolute beam loss levels or
locations
Measuring Beam Distributions at 10-5 Levels
• Large dynamic range measurements are difficult
• Typically expert based systems, measuring beam distributions in
a limited number of 6-D cross sections
• What should we use as initial distributions for the models????
40 deg tail
Transverse beam
profiles.
Longitudinal bunch length
How Reliable are High Power Proton
Facilities?
6000.0
Trip Frequency
100
90
MW‐hrs, hours
1000
5000.0
80
70
100
4000.0
3000.0
10
Produc on hours
2000.0
1
PSI
60
ISIS
50
Lujan
40
SNS
30
Total Availability
1000.0
20
Accelerator Availability
0.1
0.0 Trips/day > 1 Trips/day > 1 Trips/day > 1 Trips/day > 3
2007
2008 min. 2009
2010
2011 hrs 2012
sec
hr
10
0
2013
FY
• Turns out high power facilities have similar trip rates
• Good enough for HEP applications
– Need improvement for neutron scattering / ADS applications
High Reliability
• The ADS applications have the most stringent
requirements
– 3 trips/month > 10 seconds
Buy your way out of the problem for the low energy part
– have a hot spare
49
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for the U.S. Department of Energy
Superconducting RF linac layout (ESS
Example)
• Lots of the same thing, over and over
again
• Implications for robustness and
reliability
Superconducting RF Linacs are
Flexible
Sept. 2008
Sept.
2010
Ring Commissioning
Run
First
Run
Cavity
Design
35
35
35
30
30
30
25
25
25
25
20
20
2020
15
15
1515
10
10
10
10
5
5
5
00
81
81
73
73
77
77
65
65
69
69
57
57
61
61
53
53
49
49
45
45
41
41
37
37
33
33
29
29
25
21
17
9
13
1
5
0
1
E0 (MV/m)
E0 (MV/m)
E0
(MV/m)
30
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47 49 51 53 55 57 59 61 63 65 67 69 71 73 75 77 79 81
3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47 49 51 53 55 57 59 61 63 65 67 69 71 73 75 77 79 81
Cavity
Cavity
cavity
cavity
cavity
• SCL can run with a wide range of cavity performance
• But they are flexible, and can accommodate different “gradient profiles”
Operating Gradients
(MV/m)
Medium Beta
High Beta
Design
10.2
15.6
Production (now)
11.9
12.8
Superconducting RF Linac Retuning
Retuning a proton
SCL
3) Calculate the change in beam arrival time downstream, and
apply corrections to RF setup
2) If a cavity gradient
must be reduced….
1) Measure the beam arrival
time at each cavity (in RF
phase units)
• Superconducting linac acceleration uses many cavities, each
providing a relatively small fraction of the total energy gain
• Potential exists to “retune” on-the-fly, around an RF equipment
problem
– Design spare cavities in reserve
Handling 1 MW of proton Power is
Challenging
• Pulsed load on the target is especially tough for SNS
• Use a liquid target design (Hg)
- 17 kJ in 700 ns @ 60 Hz
- Induces cavitation damage
53
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for the U.S. Department of Energy
Target Post Irradiation Examination:
key to understanding lifetime
• Target vessel is multi-walled (4 layers)
• Cut-out circular pieces from used targets to examine damage
Focus on innermost wall pieces
54
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for the U.S. Department of Energy
“Gizmo” to cut out
pieces
Target Post Irradiation Examination:
key to understanding lifetime
• Clear indication of cavitation damage
Complete “cut-through along centerline
Damage is much “sharper” than beam deposition
Repeatable
Target 1 – Inner window
Target 2 – Inner Window
center cut
-
Target 4 – Inner Window
55
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for the U.S. Department of Energy
Target Maintenance / Replacement is
with Remote Handling
Target control
room
Manipulator Gallery
• Not hands on maintenance
• “Improvising capability” is limited
High Power Operational Proton Accelerators
Facility
TRIUMF
LANSCE area A
57
Power
(kW)
100 80‐120
Energy
(GeV)
Time Structure
Accelerator Type
0.52
CW, 23 MHz
cyclotron
0.8
120 Hz
linac
70 MeV H– linac + RCS
ISIS Present
200
0.8
J‐PARC MR (FX)
240 30
40 Hz to TS‐1
10 Hz to TS‐2
0.4 Hz x 5 us
J‐PARC RCS
300 3
25 Hz x 1 us 181 MeV linac + RCS
FNAL MI
400 120
9.4 us every 2.2 s
Linac + RCS
CERN SPS
470
400
4.4 s cycle length
linac + 2 stage RCS
SNS 1,000
0.94
60 Hz PSI
1,300
0.59
CW, 50MHz
• Two operational MW facilities
• 7 facilities with order of 100’s kW
• Wide variety of accelerator types
Managed by UT-Battelle
for the U.S. Department of Energy
3 GeV into RCS
linac + accumulator
2 stage cyclotron
Planned Power Increases - Existing Machines
> 500 kW, development effort ongoing
Facility
FNAL MI + ANU
Power
(kW)
700
Energy
(GeV)
120
Time Structure
Accelerator Type
9.4 us every 1.33 s
Linac + RCS
J‐PARC MR (FX)
750
30
0.4 Hz x 5 us
3 GeV into RCS
CERN SPS
750
400
4.4 s cycle length
linac + 2 stage RCS
LANSCE area A
800
0.8
120 Hz x 625 us
linac
J‐PARC RCS
1000 3
25 Hz x 1 us 181 MeV linac + RCS
SNS 2500
1.3
60 Hz linac + accumulator
• In the 5-10 year time scale: several MW class
accelerators expected
58
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for the U.S. Department of Energy
Future High Power Proton Machines
> 1 MW, development or design effort ongoing
Facility
ESS
CERN with SPL
Project‐X (stage 1+2)
Project‐X
(stage 3)
MYRRHHA
Daealus
Power
(MW)
5
Energy
(GeV)
2.0
4
5
3
3
Time Structure
Accelerator Type
50 Hz x 2.5 ms
SRF linac + accumulator
50 Hz x 6 bunches SRF linac + RCS
2.3
60‐120
CW linac
/accumulator
10‐5 duty factor
CW SRF linac + accumulator
+ pulsed 8 GeV SRF linac + RCS
2.4
0.6
CW
SRF linac
3
0.8
60 Hz 2 stage cyclotron
• Superconducting RF linacs play a prominent role
• SRF = superconducting RF
59
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High Power Accelerator History
1000
Average
BeamCurrent
Current(mA)
(mA)
Average Beam
1000
100
100
IFMIF
LEDA
IPHI
Pulsed
CW
ExistingPulsed
+ planned
CW Planned
LEDA
IPHI
10
MYRHHA
10
FRIB
11
PSI PSI
SPL
LANSCE
LANSCE
TRIUMF
TRIUMF
0.1
0.1
SNS
SNS
MMF
MMF
ISIS
ISIS
PSR
PSR
former
ESS
Pulsed
Superconducting
Linacs
CW
Project X
JPARC
JPARC
RCSRCS
JPARC
MR MR
JPARC
0.01
0.01
AGS
AGS
0.001
0.001
0.001
0.001
0.01
0.01
0.1
0.1
11
10 10
Beam
BeamEnergy
Energy(GeV)
(GeV)
• Relevant accelerators with ~ MW beam experience
– PSI: 600 MeV cyclotron, 1.3 MW
– SNS 925 MeV superconducting linac , 1 MW
– LANSCE: 800 MeV copper linac, 800 kW
FNALFNAL
MI MI
100100
10001000
The Accelerator: Different Perspectives
…the operator
Summary
• There is a demand for high power proton accelerators
• These are large expensive machines
• We have reached the mega-Watt beam operational level
• Several Multi-mega-Watt machines are planned for
62
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