Commissioning and Early Experiments at the PHELIX Facility

Vincent Bagnoud

GSI - Helmholtzzentrum für Schwerionenforschung GmbHDarmstadt, Germany. V.bagnoud@gsi.de

ICUIL conference, 27-31 October 2008Shanghai TongLi, China

PHELIX is in operation since May 2008.

• PHELIX has been commissioned for use with short pulses (120 J, 700 fs) and nanosecond pulses (300 J - 1kJ)

• The short-pulse beamline uses a 90-degree off-axis parabolic mirror to achieve high on-target intensity, confirmed by the energy spectrum of accelerated protons

• The nanosecond beamline has been used to support the GSI plasma physics program with first encouraging results on ion stopping in laser generated plasma

• A call for proposal for experiments in 2009 is running until 3-11-2008, please see me for details

summary

PHELIX is commissioned and part of the GSI-infrastructure.

UNILAC Experiment hallStorage Ring

PHELIX

The PHELIX laser serves three experimental areas.

Injection box

Mai

n am

plifi

erse

nsor

Faraday Isolator

Switch Yard

Compressor

Target Chamber

fs front endFiber ns front end

Pre-amplifier2 x 19 mm heads1 x 45 mm head

X-ray lab(low energy)

TW compressor

Target chamber

Z6 experimental area

Heavy ions

Laser Bay

Double-pass 31.5 cm amplifier

70 m

The main amplifier delivers the targeted gain of 100 for 17 kV.

0 2 44 6Input Energy (J)

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100

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0 2 44 60

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•504 J

Out

put E

nerg

y (J

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Output Energy before the Faraday Rotator

28 cm

Injection box

Mai

n am

plifi

erse

nsor

Faraday Isolator

Switch Yard

INOUTEntrance

window

T > 90%

We use a single-pass two-grating compressor.

• The advantage is high throughput but at the expense of pulse lengthening

• An elliptical beam is used to better fill the MLD gratings: Horiba-Jobin-Ivongratings 47 x 35 cm2 at 72° incidence require an 12 x 23 cm2 elliptical beam

elliptical beam

The pulse compressor has been successfully commissioned.

We use a birefringent filter* in the front-end to pre-compensate gain narrowing.• The PHELIX two-regenerative-amplifier front-end is particularly suited to the

method,

• Without loss in output energy, a birefringent plate and a polarizer are introduced between the amplifiers to spectrally shape the spectrum and create a hole at the gain peak of the glass amplifier,

1050 1055 10600

0.5

1Shot 525

Wavelength (nm)

Inte

nsity

(nor

mal

ized

)5.9 nm

• Spectra > 5 nm wide are routinely obtained at the end of the main amplifier, capable of supporting < 350 fs (Fourier transform limited) pulses.

* Barty et al.: Optics Letters, Vol. 21 Issue 3, pp.219-221 (1996)

Characterization of the compressed short pulse is under way. • On a sub-aperture, the short pulse compresses well (see below)• Over the full aperture, an increase to 700 fs is visible

– This is a strong effect due to the geometry (single pass) and the ratio between beam size and wavelength spread.

• The data needs to be confirmed at full power

-3 -2 -1 0 1 2 30

0.2

0.4

0.6

0.8

1

time delay (ps)

inte

nsity

(nor

mal

ized

)

autocorrelation trace, fs-front end only

394 fs

A 90-degree low-cost off-axis metallic parabola achieves good focusing capability.

5 10 15 20 250

1

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5

surface roughness (nm)sc

atte

red

ener

gy (%

)

• The 90-degree massive metallic mirror is machined to ~1 micron accuracy(PV),

• The surface roughness and machining precision have to the balanced to get the best trade-off between scattering losses and wavefront error.

Mirror in its Holder

Back View Estimation of scattered energy based on simulated surface roughness

Experimental evidence indicates an on-target intensity > 1019 W.cm-2

• A calculation based on the far-field intensity distribution yields 3.5 1019 W.cm2

• According the accelerated proton spectra obtained by the Technical University Darmstadt (TUD), the intensity is rather ~1020 W.cm2

Prot

on d

ensi

ty (M

eV-1

)

Proton energy spectrum

X, µm

Yµm

,

focus intensity, 100 J, 0.7 ps pulse

-100 -50 0 50 100

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-50

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x 1019

75% in 50 µm

Strehl ratio: 0.3

Currently proton acceleration is being evaluated

• Laser accelerated ions are of interest to GSI as a complementary tool to the existing accelerator

• First experiments are aimed at helping with the commissioning of the system

• So far > 30 MeV protons have been accelerated with PHELIX, indicating that high intensity conditions (~ 1020 W.cm2) are obtained at the focus

More on-target intensity estimates are planned in the near term

Combined ion-laser experiments were conducted twice this year to study the stopping power of plasmas.

• In the context of inertial fusion with heavy ions, we study the energy loss of ions in laser-generated plasma,

• We used PHELIX pulses with 7-15 ns and 50 - 315 J, to compare to measurements done at lower energy using nhelix

– 1-mm focal spot achieved with 4-m lens + phase mask and,

– UNILAC S 15+ and Ar 16+; 0.3 mm diameter

• We measure the ion-energy loss via time-of-flight measurements

• In a plasma, the theory predicts that ion-energy loss is dominated by free electrons but our experiments do not only illustrate this.

Time (ns)

Ener

gylo

ss(%

)

Time evolution of the ion-energy loss100 corresponds to the cold target

Our program requires PHELIX for improving the experimental data • A higher energy allows for a full ionization of thicker foils with higher Z to

improve the measurement accuracy– We have experiment plan to extend the on-target deposited energy to

500J- 1 kJ

• A major limitation to our setup is the non-uniformity of the plasma:– In the best case, the plasma is one dimensional,– This is further reduced by the on-target beam non-uniformities

• We are currently looking into two solutions to this problem– Indirect heating using 2ω light creates uniform conditions – Under critical foams have shown good smoothing capabilities and

volume absorption to create uniform conditions

We applied PHELIX to the investigation of X-ray laser in the sub-10 nm regime.• We are using PHELIX to pump X-ray laser with Ni-like Samarium (6.8 nm)

– We have developed an innovative two pulse scheme* to create transient collisionaly excited (TCE) plasma X-ray laser

* Zimmer et al.: Optics Express, 16, pp.10398-10404 (2008)

13 13.2 13.4 13.6 13.8 14 14.2 14.4 14.62200

3000

3800

wavelength [nm]

inte

nsity

[pix

el v

alue

]

Sm-XRL (2nd order)C-edge (3rd order)

PHELIX is in operation since May 2008.

• PHELIX has been commissioned for use with short pulses (120 J, 700 fs) and nanosecond pulses (300 J - 1kJ)

• The short-pulse beamline uses a 90-degree off-axis parabolic mirror to achieve high on-target intensity, confirmed by the energy spectrum of accelerated protons

• The nanosecond beamline has been used to support the GSI plasma physics program with first encouraging results on ion stopping in laser generated plasma

• A call for proposal for experiments in 2009 is running until 3-11-2008, please see me for details

summary