Development and Applications of High Intensity Ion Beams using Cyclotrons
UHM Physics Department Colloquium
Daniel Winklehner, MITHonolulu, HI, Feb 27th, 2020
Introduction Physics &Technology Applications
Intro
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ctionSometimes we see the accelerator like this…
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Image adapted from Cartoon by David L. Judd and Ron MacKenzie
Intro
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ctionSometimes we see the accelerator like this…
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Energy Intensity
Quality
Intro
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ctionSometimes we see the accelerator like this…
• IsoDAR:• High Intensity
• Pure source
• Well-understood Energy
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Energy Intensity
Quality
Intro
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ction
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Outline
• Motivation: IsoDAR neutrino physics→ In a few years this will yield very exciting particle physics!
• Cyclotrons “101”
• The challenges of high intensity beams→ How we are changing the game!
• More Applications:• Medical Isotopes• Taking it to the next level →Multi-Megawatt!
Intro
du
ction
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Outline
• Motivation: IsoDAR neutrino physics→ In a few years this will yield very exciting particle physics!
• Cyclotrons “101”
• The challenges of high intensity beams→ How we are changing the game!
• More Applications:• Medical Isotopes• Taking it to the next level →Multi-Megawatt!
Intro
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ction
Three massless neutrinos in the Standard Model
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• Three ‘known’ neutrino flavors
• Part of the lepton weak doublets
• Only interact via weak force
• Example: Beta-Decay:
Source: wikipedia.org
Intro
du
ction• First confirmed in SuperK in 1998,
Have been since been observed in many experiments
• Mass and Flavor Eigenstates are not aligned →Mixing
• U is a unitary matrix with 3 free parameters plus extra parameter eiδ
But we know neutrinos have mass and mix
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KamLAND 2003
Intro
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LSND Anomaly
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• Several Experiments have seen anomalies in oscillation probability
• “Sterile Neutrino” could explain it
• Heavier neutrino that does not interact weakly
We need a definitive experiment!And distinguish between 3+1 and 3+2, 3+3, decay, … many models!
LSND Anomaly
Intro
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IsoDAR – Isotope Decay At Rest @ KamLAND
1016.5 m
Isotropic source of through decay at rest
60 MeV
kton scale detector (e.g. KamLAND) Search for sterile neutrinos through oscillations
at short distances andlow energy
Intro
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IsoDAR – Isotope Decay At Rest @ KamLAND
1116.5 m
Isotropic source of through decay at rest
Search for sterile neutrinos through oscillations at short distances andlow energy
60 MeV
kton scale detector (e.g. KamLAND)
Intro
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IsoDAR – If we see a signal…
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Global Fit
Reactor Anomaly
Intro
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All of this is great, but…
• Where do the protons come from?
• High intensity neutrino sources require high intensity proton sources10 mA = 10x more than commercial machines!
• Even more, this one has to be built underground at a reasonable cost
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60 MeV
Intro
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All of this is great, but…
• Where do the protons come from?
• High intensity neutrino sources require high intensity proton sources10 mA = 10x more than commercial machines!
• Even more, this one has to be built underground at a reasonable cost
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BUILDA
CYCLOTRON
60 MeV
Intro
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Cyclotrons are the best suited accelerators
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ҧ𝜈𝑒ҧ𝜈𝑒
ҧ𝜈𝑒
ҧ𝜈𝑒
ҧ𝜈𝑒
ҧ𝜈𝑒
• Cost-effective
• Compact
• Alternatives:• Linac (Linear Accelerator):
Long, Expensive• FFAG (Fixed Field Alternating Gradient):
Larger Ring, Pre-accelerate, Not as well-established
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ysics & Tech
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Outline
• Motivation: IsoDAR neutrino physics→ In a few years this will yield very exciting particle physics!
• Cyclotrons “101”
• The challenges of high intensity beams→ How we are changing the game!
• More Applications:• Medical Isotopes• Taking it to the next level →Multi-Megawatt!
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The cyclotron as seen by the…inventor
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• B-field forces particles on circular orbit:
• Oscillating “Dee”voltage accelerates
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The cyclotron as seen by the…inventor
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• B-field forces particles on circular orbit:
• Oscillating “Dee”voltage accelerates
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Most modern cyclotrons are isochronous
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• Increase B-Field with radius to counter relativistic effects
• Use Azimuthally Varying Field (AVF) for vertical focusing
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• Dee doesn’t have to be “D”-shaped:
• In general: , RF frequency can be any integer multiple of particle frequency.
• Dees can be made into double gap cavities with angle = 180/h
Higher energy gain per turn with harmonics
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-VRF +VRF 0 V +2VRF 0 V
+2VRF
⨂
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Acceleration (harmonic 6)
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VDee = -70 kV VDee = -70 kV
Vdee (t) =
⨂
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Acceleration (harmonic 6)
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VDee = 70 kV VDee = 70 kV
Vdee (t) =
⨂
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Acceleration (harmonic 6)
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VDee = -70 kV VDee = -70 kV
Vdee (t) =
⨂
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Only a narrow phase window can be populated
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VDee = 70 kV VDee = 70 kV
Vdee (t) =
⨂
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Injection through a spiral inflector
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• Cyclotron Main B-Field
• Electrostatic Field from Spiral Electrodes
• Combination guides particles
• Difficult to simulateprecisely
Incoming Beam
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Extraction from a compact cyclotron
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Grounded septum
-VExtraction Channel
(N+1)th turnDENth turn
⨂
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State of the art in high intensity cyclotrons
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• PSI Injector II:• 2.7 mA of protons
• 72 MeV
• Separated Sector Cyclotron
• Very large! Radius= 5 m
• Commercial Cyclotrons:• Isotope Production
• ~1 mA of H-
• Compact! Radius < 1 m
• We need:• Compact, and
• with more beam (10 mA!)
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ysics & Tech
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Outline
• Motivation: IsoDAR neutrino physics→ In a few years this will yield very exciting particle physics!
• Cyclotrons “101”
• The challenges of high intensity beams→ How we are changing the game!
• More Applications:• Medical Isotopes• Taking it to the next level →Multi-Megawatt!
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ysics & Tech
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What is the basic limitation?
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• “Space charge” and the associated problems
• But also controlled and uncontrolled beam loss!
10 mA of protons do not want to be crowded together in a bunch!
This is a dynamic problem, the shape of the beam is constantly changing as you accelerate.
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ysics & Tech
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What is the basic limitation?
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• “Space charge” and the associated problems
• But also controlled and uncontrolled beam loss!
10 mA of protons do not want to be crowded together in a bunch!
This is a dynamic problem, the shape of the beam is constantly changing as you accelerate.
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What building blocks can we improve?
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• Ion Source
• Low Energy Beam Transport (LEBT)
• Accelerator (Cyclotron)• Injection
• Acceleration
• Extraction
We must consider space charge at every step!
Ion Source
Cyclotron
TargetLEBT Transfer Line
Improve this… …to provide 10 mA here
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Trajectory equations with linear space-charge
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Trajectory Equations: Generalized Perveance:
Envelope equations:
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There are “particle knobs” to turn
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Generalized Perveance:
a measure for space-charge
If we want to increase I, we can change m and E to keep
The perveance as low as possible
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Space-charge makes injection difficult
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• This becomes most problematic in the spiral inflector
• And Low Energy Beam Transport
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Space-charge makes injection difficult
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• This becomes most problematic in the spiral inflector
• And Low Energy Beam Transport
• Let’s Increase Energy
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Space-charge makes injection difficult
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• This becomes most problematic in the spiral inflector
• And Low Energy Beam Transport
• Let’s Increase Energy … and change the ion?
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Innovation #1: H2+ instead of protons
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• Two units of charge for one!
• Remove electron by stripping → get two protons
• Helps with Injection
• Helps with Low Energy Beam Transport
• And there are additional exciting ways to exploit this!
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• Filament-Driven Multicusp Ion Source
• Based on: Ehlers and Leung (LBNL)
• Currently commissioning at MIT (highest current density: 40 mA/cm2)
Innovation #2: Dedicated H2+ion source
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Faraday Cup
Axani, DW et al. RSI (2016) https://aip.scitation.org/doi/10.1063/1.4932395DW et al., AIP Conf. Proc. (2017) https://arxiv.org/abs/1811.01868
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Ion Source
Cyclotron
TargetLEBT Transfer Line
Improve this… …to provide 10 mA here
What building blocks can we improve?
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Multicusp Ion Source Technology
Inn
ova
tio
ns
#1&
2
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Ion Source
Cyclotron
TargetLEBT Transfer Line
Improve this… …to provide 10 mA here
What building blocks can we improve?
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Multicusp Ion Source Technology
Inn
ova
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#1&
2
Now let’s jump to here: Understanding Extraction
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Extraction from a compact cyclotron
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Grounded septum
-VExtraction Channel
(N+1)th turnDENth turn
⨂
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Reality is more complicated…
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Reality is more complicated…
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E
3 m
3 m
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Reality is more complicated…
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Radial Probe
• Septum can only tolerate 200 W of beam losses. That’s very little!
• Here is where H2+ is very useful
again:→We can protect the septum with a foil
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A carbon stripper foil can protect the septum
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~.02% intercepted
on foil
Grounded septum
-VExtraction Channel
(N+1)th turn
stripping foil
Protons
H2+
⨂
Nth turn
Nth turn (N+1)th turn
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ysics & Tech
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Ion Source
Cyclotron
TargetLEBT Transfer Line
Improve this… …to provide 10 mA here
What building blocks can we improve?
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Multicusp Ion Source Technology
Inn
ova
tio
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#1&
2
Inn
ova
tio
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3 Protect w/ foils
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Ion Source
Cyclotron
TargetLEBT Transfer Line
Improve this… …to provide 10 mA here
What building blocks can we improve?
47
Multicusp Ion Source Technology
Inn
ova
tio
ns
#1&
2
Inn
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3
Protect w/ foils
Now let’s jump to here: Beam Dynamics
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Two ways to maximize the turn separation
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• Maximize Energy Gain/turn 250 kV Vdee, 4 Dees (8 gaps) → 2 MeV/turn
• Beam Dynamics: Vortex Motion• Vortex-like curling up of the beam into a
circle in longitudinal-transverse space
• Only happens in isochronous cyclotrons
• Beam needs to be well matched
Local Frame
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Vortex Motion - The “Intuitive” Picture
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Lorentz force: Cyclotron radius:
Courtesy of Wiel Kleeven, IBA
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Vortex motion – OPAL Simulations for PSI Injector II
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Turn 0 Turn 5 Turn 10
Turn 20 Turn 30 Turn 40
“Local Frame”
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Comparison of 0 mA and 6.65 mA for IsoDAR
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Start After 7 Turns
DW, IsoDAR 60 MeV/amu simulations, http://arxiv.org/abs/2002.11264 (2020)
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Optimize phase, RF voltage, cavity shape, collimator placement
• Phase: -5°, V = 70-240kV
• Collimate Halo → 25% loss
• 98 W on septum
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Turns 1-6
Turns 92-104
DW, IsoDAR 60 MeV/amu simulations, http://arxiv.org/abs/2002.11264 (2020)
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But do we trust the simulations?
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• Three important benchmark studies: • LEBT
• Spiral Inflector
• Cyclotron ✓
In order to have the highest realism, PICcodes are necessary!→ OPAL and WARP
Ion Source
Cyclotron
TargetLEBT Transfer Line
Improve this… …to provide 10 mA here
Adelman, DW et al. The OPAL Code https://arxiv.org/abs/1905.06654
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Versatile Ion Source (VIS) loaned from INFNCyclotron + Teststand provided by Best Cyclotron Systems, Inc. (BCS)
Injection tests at BCS, Inc.
54DW et al. JINST (2015), arXiv:1508.03850
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Inside the cyclotron
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WARP Code: LEBT simulations agree well
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• Using WARP
• Need to include careful treatment of space charge compensation!
• Good agreement.
Simulated (face on)
Looking through windowFrom side, took photos
Only two examples. Many plots and images available in arXiv:1508.03850
Beam
CopperSlits
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Innovation #4: OPAL code upgrade
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An aside: Experimental Result was 8 mA before, 7.5 mA inside → 94% transmission - Large Inflector Works!
• Load 3D electromagnetic fields into OPAL• Include boundaries for particle termination and field solver• Benchmarked against theory and experiment with very good agreement
DW et al. Phys. Rev. AB (2017) https://arxiv.org/abs/1612.09018
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But do we trust the simulations? Yes!
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• Three important benchmark studies: • LEBT ✓
• Spiral Inflector ✓
• Cyclotron ✓
Ion Source
Cyclotron
TargetLEBT Transfer Line
Improve this… …to provide 10 mA here
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Ion Source
Cyclotron
TargetLEBT Transfer Line
Improve this… …to provide 10 mA here
What building blocks can we improve?
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Multicusp Ion Source Technology
Inn
ova
tio
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#1&
2
Inn
ova
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3 Protect w/ foils
Inn
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tio
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4
Exploit smart beam dynamics
w/ PIC Simulations
Ph
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Ion Source
Cyclotron
TargetLEBT Transfer Line
Improve this… …to provide 10 mA here
What building blocks can we improve?
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Multicusp Ion Source Technology
Inn
ova
tio
ns
#1&
2
Inn
ova
tio
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3 Protect w/ foils
Inn
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tio
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4
Exploit smart beam dynamics
w/ PIC Simulations
Now let’s jump to here: Better Bunching
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Only a narrow phase window can be populated
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VDee = 70 kV VDee = 70 kV
Vdee (t) =
⨂
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Innovation #5: RFQ-DIP
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• Radio Frequency Quadrupole – Direct Injection Project
DW et al. RSI 87.2 (2016): 02B929. https://aip.scitation.org/doi/abs/10.1063/1.4935753DW et al. NIMA (2018) https://arxiv.org/abs/1807.03759
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RFQ General Principle
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+
+
Front View
Beam
––
Side View
• Continuous focusing like in a series of alternating F/D Electrostatic quadrupoles
• Wiggles lead to acceleration and bunching (RF bunching similar to cyclotron)
• Same frequency as cyclotron
Ez
Er Z
RFQ General Principle
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+
+
Front View
Beam
––
Side View
Ez
Er Z
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Radiofrequency Quadrupole – Direct Injection Project
• Ion Source (MIST-1)
• RFQ
• 1 MeV/amu test cyclotron
• Diagnostics
Funded by NSF MRI ~$1M
RFQ-DIP Prototype
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Split-Coaxial RFQ Design
67Good emittances: εx = 0.34 mm-mrad, εy = 0.34 mm-mrad, εz = 40.24 keV-deg
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ysics & Tech
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Ion Source
Cyclotron
TargetLEBT Transfer Line
Improve this… …to provide 10 mA here
What building blocks can we improve?
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Multicusp Ion Source Technology
Inn
ova
tio
ns
#1&
2
Inn
ova
tio
n #
3
Inn
ova
tio
n #
4
Exploit smart beam dynamics
w/ PIC Simulations
Inn
ova
tio
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5We have designed the
IsoDAR Cyclotron!
Protect w/ foils
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Articles on challenges and solutions in one place
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DW et al., The IsoDAR high intensity H2+ transport and injection tests, JINST vol. 10, 2015
https://arxiv.org/abs/1508.03850
IsoDAR@KamLAND: A Conceptual Design Report for the Technical Facility, arXiv:1511.05130
Axani, DW et al. A high intensity H2+ multicusp ion source for the isotope decay-at-rest experiment,
IsoDAR. RSI 87.2 (2016): 02B704. https://aip.scitation.org/doi/10.1063/1.4932395
DW et al. Preliminary design of a RFQ direct injection scheme for the IsoDAR high intensity H2
+ cyclotron. RSI 87.2 (2016): 02B929. https://aip.scitation.org/doi/abs/10.1063/1.4935753
DW et al., Realistic simulations of a cyclotron spiral inflector within a particle-in-cell framework, Phys. Rev. AB (2017) https://arxiv.org/abs/1612.09018
DW et al., First Commissioning Results of the Multicusp Ion Source at MIT (MIST-1) for H2+, AIP Conf.
Proc. (2017) https://arxiv.org/abs/1811.01868
DW, IsoDAR 60 MeV/amu simulations, http://arxiv.org/abs/2002.11264 (2020)
DW et al. High intensity cyclotrons for neutrino physics, NIMA (2018) https://arxiv.org/abs/1807.03759
Ap
plicatio
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Outline
• Motivation: IsoDAR neutrino physics→ In a few years this will yield very exciting particle physics!
• Cyclotrons “101”
• The challenges of high intensity beams→ How we are changing the game!
• More Applications:• Medical Isotopes• Taking it to the next level →Multi-Megawatt!
70
Ap
plicatio
ns
My vision: A paradigm shift at the intensity frontierThere are many applications that require high intensity beams, which are out of reach at the moment (cost, size)
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1.0 MW 5.0 MW 10.0 MW
100 MeV 500 MeV 1.0 GeV
Protons 10 mA cw
Power
10-100 MeV: Production of much needed medical isotopes
500 MeV to 1.0 GeV: Demonstrationsfor Accelerator Driven Systems and Accelerator Driven Subcritical Reactors
60 MeV: IsoDARDiscovery level particle physics
800 MeV: DAEδALUSCP-violation in neutrino sector
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Example 1: IsoDAR can produce much needed medical isotopes
72Alonso et al., https://www.nature.com/articles/s42254-019-0095-6Waites et al., https://doi.org/10.1186/s41181-020-0090-3
• Two Examples:• 68Ge/68Ga: PET isotope
• 225Ac: Alpha emitter
• We can increase world production by orders of magnitude!
• Two schemes for beam delivery:
Ap
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Example 2: Accelerator Driven Systems (ADS) and Subcritical Reactors (ADSR)
• Molten Salt Reactors using thorium as fuel
• Low CO2
• Nuclear waste transmutation
• Cyclotrons: Cost-effective choice for demonstrator experiments
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Accelerator
Proton Beam
Heat
nn
n
Generator ElectricityA fraction of electricity produced is used to power the accelerator
nn
Target
Sub-critical amount of fissile
material
Ap
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The proposed path to multi-megawatt proton beams using chained cyclotrons
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Superconducting Ring Cyclotron500-1000 MeV
Compact Cyclotron10-100 MeV/amu
Ion Source10 keV/amu
+RFQ
35 keV/amu
New Challenge: Understand vibrational states
H2+
Measure vibrational states:• Collision-induced dissociation• Photo-dissociation• Lorentz-stripping
Mitigation strategies:• Quenching in ion source• Forced dissociation
• after compact cyclotron• inside superconducting ring
cyclotron
Timeline
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2015 2016 2017 2018 2019 2020 2021 2022 2023 2024
IsoDAR R&D
BCS Tests
MIST-1
RFQ-DIP
Building/Running IsoDAR
Vibrational States
1 GeV Design
Ironfree Cyclotron
Published Papers Planned Papers
NSF MRI
MIST-1/RFQ-DIP Group
• Grad student Spencer Axani (Design, plasma physics)
• Undergrad Aashish Tripathee (Control System)
• Undergrad Frances Hartwell (Electronics)
• Undergrad Jesus Corona (Emittance Scanner)
• PostBac Thomas Wester (Control System)
• Grad students Joseph Smolsky and Loyd Waites (LEBT, Extraction Simulations, final physics results)
• PD Jungbae Bahng, RFQ
• PD Medani Sangroula, RFQ
• Undergrad Philip Weigel, Spiral Inflector
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Conclusion
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• We have overcome many challenges for IsoDAR
• Very interesting accelerator physics has come out and will continue to do so
• Successful run of IsoDAR will be a game-changer• For neutrino physics
• For accelerator physiscs
• For industry: medical isotopes, materials
• Of course that just takes us to the next level→ reach 1 GeV!
• We went from 0 to 60 (MeV) in five years…can we do 60 to 1000 in another five?