Ion optics of laser accelerated protons for therapy applications I. Hofmann, HI -Jena & GSI Darmstadt

Coulomb'11, Bologna, Italy

November 4-5, 2011

1. Introduction

2. Laser acceleration review

3. “Point Study” on ion spectrum from RPA

4. Collection & Chromatic energy filtering

5. Reference parameters

6. Conclusions

Main focus of this talk:

• discuss how to bridge gap between a laser ion output and therapy dose requirements

• at full energy (200 MeV protons) and for 1 model (RPA)

2

Acknowledgment:

H. Al-Omari, I. Strasik, G. Kraft, GSI

LIGHT-collaboration (TU-Darmstadt / GSI)

J. Meyer-ter-Vehn, X. Yan (MPQ)

3

Much higher gradients in acceleration have a potential to

reduce size (cost?) of accelerators But: Need high peak power and structures supporting very high fields

– Laser-driven dielectric structures

– Beam-driven dielectric structures

– Laser-driven plasmas

– Beam-driven plasmas

~26.000 accelerators worldwide

– ~ 44% are for radiotherapy,

– ~ 41% for ion implantation,

– ~ 9% for industrial processing and research,

– ~ 4% for biomedical and other low-energy research,

– ~ 1% with energies > 1 GeV for discovery science and research

Where are accelerators today?

4

“Future needs” of laser acceleration monitored by

ICFA-ICUIL joint task force >2009

Promote relationship between ICUIL (International Committee on Ultra-

High Intense Lasers) and ICFA (International Committee for Future

Accelerators):

Common interest in laser driven acceleration

Joint Task Force formed (2009)

• Convene international panel of experts on laser technology

• Create a survey of the requirements for laser based light and

particle sources

• Emphasis on sources that can advance light and particle science

AND require lasers beyond the current state of the art

• Identify future laser system requirements

– Identify key technological bottlenecks

– Prepare technical report “White paper”

5

1st Meeting: GSI Darmstadt, April 7-9, 2010:

participants from China (1), France (4), Germany (18), Japan (4), Switzerland (2), the UK (4) and US (14)...

relevant topics – emphasis on technology needs Colliders

X-ray sources

Medical applications

…….

plasma wakefield, direct laser acceleration, dieelectric laser acceleration, Compton sources, fiber optics, disk and slab ...

2nd Meeting: LBNL Berkeley, Sept. 20-22, 2011

Comprehensive WHITE PAPER planned to come out soon (12/2011)

ICFA-ICUIL joint task force

6

“Most challenging” example: Linear TeV e+ e- collider

7

Highly critical "review" of laser-proton therapy by U. Linz & J. Alonso PRST-AB 10, 094801 (2007):

Conventional Laser Accelerator

(Cyclotron, Linac+Synchrotron)

1. Beam Energy (p) 200 – 250 MeV in theory possible

2. Energy variability "+" in synchrotron ? demanding

3. DE/E ~ 0.1% ? demanding

4. Intensity 1010 /sec 109/108 at 10/100 Hz

5. Precision for scanning "+" in synchrotrons ? large Dp/p

• Since 2007 good progress was achieved

• Experimental facilities for 5…20 MeV (PRMC, FZ Dresden, …) and

designs for various higher MeV protons (overview by P. Bolton, Erice 2009)

• Research efforts towards higher energies in many labs ...

• Laser ions require very different beam manipulations than conventional

accelerator ions!

8

Target Normal Sheath Acceleration (TNSA)

(source: Tajima, Habs, Yan, Rev. Accel. Sci. Tech., 2009)

9

PHELIX@GSI results ~ Isothermal Scaling (J. Fuchs, 2007)

Maximum p energies increase with laser W/cm2

PHELIX group & Markus Roth et al, 2009

1011 protons in DE/E

= 10% window

Simulation only

Ion beam from UNILAC testing)

Interaction chamber

Short pulse

compressor

(nsfs)

100 TW laser beamline

Courtesy: K. Witte, GSI 2009

Very broad spectrum though small phase space

10

Currently discussed mechanisms for therapy applications

Experiments Status Theory Relevance

to Therapy

TNSA > 1999 >1013 ions,

robust,

reproducible

Analytical

+ 2D/3D

simulation

s

+

TNSA/BOA

(Break-out-

afterburner)

> 2011 120 MeV ?

(LANL)

2 D / 3D

simulation

s

++(+)

RPA >2008 experimental

evidence not

conclusive

2 D / 3D

simulation

s >GeV

++(+)

Coulomb

explosion

- - 2 D

simulation

+

Gas Jet -

RPA

> 2009 2 MeV

observed

2D ++

from: ICFA-ICUIL white paper 2011 – to be published

11

source: Tajima et al., RAST 2, 2009

Experiment at MBI, 30 TW Ti:Sa 5 1019 W/cm2

Henig et al, PRL 2009 might be indicative to RPA:

CAIL (Coherent Acceleration of Ions by Laser)

• Radiation Pressure Regime proposed by Esirkepov et al., 2004

• Laser acts like a piston that accelerates foil as a whole

• Promises several hundred MeV protons (or carbon) “mono-energetic”

• needs experimental confirmation

Radiation Pressure Acceleration RPA/ CAIL

is basis of our study

12

Options for ion optics

Relatively large angular and energy spread is an issue

no collector – angle selection by aperture + dipole energy filter + exit aperture:

- simple, preferred option in current experiments

- reduced transmission (~10 mrad "usable")

collection by solenoid lens:

- higher transmission (~ 50 mrad „usable“ more efficient use of p)

- combined collection and energy filter due to chromatic focusing effect

quadrupole triplet may be another option

< ~10 mrad: "nearly parallel" beam

no collector: solenoid collector:

dipole

angle aperture

exit aperture

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Example: Fox Chase Cancer Center, Philadelphia, 2006

20 cm

100 cm

• Aperture collimation (no focusing)

• Energy selection (bends + apertures) 250 MeV

• Passive elements to form dose

Source: C.M. Ma et al., 2006

14

We use simulation spectra from Coherent Acceleration of Ions (CAIL or RPA, 2009)

by X. Yan et al. - "one of several models"

• claims ~ 1012 p for energies up to GeV

with laser intensity 1022 W/cm2

• "narrow" peaked energy spectrum

("clump")

• a "theoretical model" – not the only one! Scaling of MeV with laser intensity (protons)

Radiation Pressure Acceleration

from nm thick C foils

• > 3 1021 W/cm2 / 45 fs / 10 mm spot radius

• results from 2D numerical simulation assuming

circular polarized light

15

GeVdE

EdN 1,(

spectral density E, (rad)

total high energy

proton yield per shot:

~1011 ~ 3 J

I.H., J. Meyer-ter-Vehn, X. Yan et al., PRST-AB 14, 031304 (2011)

Spectral proton yield

combined with chromatic emittance scaling

typical window

DE/E=+/- 10%

=+/- 50 mrad

4 1010 p

„fitted“ energy distribution to

start of simulation beamline

RPA simulation predicts more

“monoenergetic” p spectrum

16

Chromatic effect on focusing:

5/

/

EE

ff

change of focal length

effective emittance increase

-E

-f

17

Final beam quality map

echromatic =c DE/E 2source [m rad]

• defines curves of constant emittance

• "usable" fraction of yield for given final emittance

Solenoid collected beam

on ~1 cm2 spot:

• yield: 2-3x1010

• need: 7x108 for 2 Gy

• large intensity margin!

aperture collimation:

• ~ yield: 109

• no intensity margin!

+

18

Simulation with TRACEWIN*) accelerator code (CEA)

using fitted spectrum from RPA model as input

Initial phase space space centered around 200 MeV

*) D. Uriot et al. CEA, 2010

19

Chromatic effect We replace dispersive (dipole) energy selection by seelction due to chromatic

effect of solenoid focusing – combined with transverse collection

Behind solenoid:

Averaging over bunch length

effective emittance increase head

tail

Selection of initial angle (50 mrad)

Selection of energy

selected DE/E

20

Energie selection proportional to aperture radius

erms,n= 7 mm mr

e = 40 mm mr

24% transmission in DE/E=±8%

3.5 1010 protons

3/

/.

D

=

-solensourceeff

sourceeffA

LEE

ff

E

EmR

Radius RA independent of E • geometrical effect

• Lower E: lower solenoid field

produces same DE/E

21

Solenoid collector focused beam has advantages (or quad triplet lens)

solenoid focusing: proton yield ~ 3x1010 per shot within e ~ 40 mm

mrad chromatic emittance

still factor of 30 intensity margin (2 Gy per shot)

- can be used to optimize target and laser pulse towards factor

5-10 lower yield and expected lower average laser power

(cost issue)

- enough margin to raise physical dosis per shot >> 2 Gy

- margin for uncertainties on acceleration physics

aperture 2

solenoid

target

Laser

aperture 1

aperture 1: angular selection from target

aperture 2: chromatic energy selection

22

Energy filter: obtain "arbitrary" energy distribution by shaping

aperture boundary away from circular (alternative to a ridge filter)

Central energy

23

How to reach depth dose uniformity? Depth scanning (U. Weber et al, 2000)

with few Bragg peaks seems to match best with laser ions

• U. Weber et al. (2000) proposed

ridge absorber to broaden DE from

synchrotron for depth scanning

• laser ions: naturally broad energy

profile depth scanning applicable • quantify # shots and SOBP‘s to

reach dose uniformity

• Transverse spot scanning

Alternative way : passive formation

with large beam and objects

24

Testing spectrum for dose uniformity

25

Energy spectrum – depth dose uniformity using 5-6 SOBP’s

DE~20 MeV fwhm 1 SOBP

26

Spot scanning Passive formation Comments

Protons / laser shot 2x107 2x108 reach 2 Gy by

accumulation

# transverse 10x10

Spots

10

reps for lateral

uniformity

Energy steps 10 10 DE/E=±5%

Reps dose spec.

(~30% intensity jitter)

40 40 10 reps

4 gantry

directions

Total # shots

per fraction

10000 1000 Factor ¼

applied

Duration of fraction

Laser rep rate

5 min

30 Hz

1.5 min

10 Hz

Parameter estimates

for spot scanning or passive formation Recent ICFA/ICUIL workshop (September 2011) recommendations

Assume each laser shot gives a „reproducible“ transverse and energy profile, but not so well

defined intensity adding up small portions to achieve nominal dose for 1 fraction

27

Some estimates of radiation load FLUKA-calculations (I. Strasik,GSI)

assumed:

1. 1.5x1011 p at source

2. 3x1010 p (20 mr) into

solenoid

3. 2x1010 p through

energy filter aperture

4. find 5 mSv per shot

5. few hundred shots

at assumed full power

tolerable

6. need to optimize laser

accel. towards lower

yield for spot scanning

case

Neutron absorber

28

Laser requirements Recent ICFA/ICUIL workshop (September 2011) recommendations

laser proton laser carbon

Rep rate (spot/passive) 30 Hz / 10 Hz

Laser intensity (W/cm2) 1-3 1021 1-3 1022

Pulse duration (fs) 50-150

Rise time (fs) <20

Contrast (5 ps / 500 ps) <10-8 / 10-12 <10-9 / 10-13

Laser energy stability 1-5%

Spot radius (mm) 5

Peak power (PW) 1-3 10-30

Pulse energy (J) 50-150 500-1500

Average power (kW) 10 Hz (30 Hz) 0.5-1.5 (1.5-4.5) 5-15 (15-45)

Laser cost assumption <10 M€ ~15 M€

Laser wavelength (nm) 800-1054

Efficiency 1-10%

Polarization lp/cp

Laser beam quality diffraction limit

Pulse stability 0.01

Laser pointing (mrad) 1-10

Laser availability 12 h/day (50% duty factor)

Failure rate <2%

29

Target chamber

Rebuncher cavity

(DE/E 4% <1%)

Ion beam diagnostic

Solenoid

Post-acceleration

structure (CH-)

Short pulse diagnostics

LIGHT: Test stand at GSI Z6 experimental area 6 D beam diagnostics – energy filter concept

operational since January 2011

Partners:

GSI , TU Darmstadt, HI Jena, U

Frankfurt (IAP), FZ Dresden

• ~ 6 PHD students

• Non-planat targets

• Early deneutralization in B-field

• Solenoid collection & focusing

• Energy selection by aperture

• RF bunch rotation (re-compression)

• Fast diagnostics

30

Some conclusions

Beam quality determined by "collector" chromatic effect (not source!)

"Point Study" based on RPA (Yan et al.) simulation shows

- Can work on rising part of energy spectrum

- Sufficient intensity margin for solenoid collector

Chromatic energy filter: combined function collection + energy selection

- Variation of energy by solenoid strength is an option (constant production)

Depth scanning with ~ 5-6 SOBP‘s to get dose uniformity

10/30 Hz laser system: 1 fraction (2 Gy) in 1 … 5 min possible

Inefficient use of ion production reduce production?

Demonstrate RadPressAcceleration at energies > 100 MeV

Demonstrate longitudinal and transverse quality of a reference beam

…