Development and Applications of High Intensity Ion Beams ... · Source: wikipedia.org. tion •First confirmed in SuperK in 1998, Have been since been observed in many experiments

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

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Energy Intensity

Quality

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• IsoDAR:• High Intensity

• Pure source

• Well-understood Energy

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Energy Intensity

Quality

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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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Intro

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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

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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

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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

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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

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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)

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IsoDAR – If we see a signal…

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Global Fit

Reactor Anomaly

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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

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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

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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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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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VDee = 70 kV VDee = 70 kV

Vdee (t) =

⨂

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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 (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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Outline





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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 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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• Let’s Increase Energy

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• 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

https://aip.scitation.org/doi/10.1063/1.4932395

https://arxiv.org/abs/1811.01868

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Ion Source

Cyclotron




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Multicusp Ion Source Technology

Inn

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#1&

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Ion Source

Cyclotron




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Now let’s jump to here: Understanding Extraction

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Extraction from a compact cyclotron

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Grounded septum


(N+1)th turnDENth turn

⨂

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Reality is more complicated…

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E

3 m

3 m

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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


(N+1)th turn

stripping foil

Protons

H2+

⨂

Nth turn

Nth turn (N+1)th turn

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Ion Source

Cyclotron




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Inn

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Ion Source

Cyclotron




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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)

http://arxiv.org/abs/2002.11264

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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



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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



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

http://arxiv.org/abs/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

http://arxiv.org/abs/arXiv:1508.03850

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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



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Ion Source

Cyclotron




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Inn

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Exploit smart beam dynamics

w/ PIC Simulations

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Ion Source

Cyclotron




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Inn

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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 (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

https://aip.scitation.org/doi/abs/10.1063/1.4935753


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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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Ion Source

Cyclotron




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Inn

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w/ PIC Simulations

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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


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 et al. High intensity cyclotrons for neutrino physics, NIMA (2018) https://arxiv.org/abs/1807.03759



https://aip.scitation.org/doi/10.1063/1.4932395

https://aip.scitation.org/doi/abs/10.1063/1.4935753





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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:

https://www.nature.com/articles/s42254-019-0095-6

https://doi.org/10.1186/s41181-020-0090-3

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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

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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?

Documents

Development and Applications of High Intensity Ion Beams ... · Source: wikipedia.org. tion •First confirmed in SuperK in 1998, Have been since been observed in many experiments