Midterm Accelerator Test Facility development goals and new experimental possibilities

Vitaly Yakimenko

April 5, 2007

ATF development plan (Experimental program support)

Support for current exponential program:– Efficient staff allocation

• 2.5 FTE to support accelerator operations, development• 4 FTE to support laser systems operations, high voltage

experimental systems and optical diagnostics, limited laser development and upgrades.

• 4 FTE facility support and maintenance (electrical, mechanical, computer control)

• 1.5 FTE administrative, safety• Additional R&D (laser cavity, OSC) will be covered by

temporary people and additional funding (LDRD, ILC, …)– Spare, interchangeable components– Reliability upgrades/fault proved components – Training/safety, simplified/standardized Experimental Safety

Reviews– Scheduling based on goals instead of the fixed time– Remote experiments…

ATF development plan (Diagnostics)

• Beam quality– Photocathode laser beam shaping– Beam based alignment (Gun- Faraday cup)

• Beams diagnostics– Routine daily emittance/pulse length characterization– Each shot CO2 energy and pulse structure characterization

• Beam structures – ~100 bunches, 24 ns spacing train was operated in the past– IFEL micro bunching at 10 micron was used in many

experiments: (STELA, HGHG, PASER, …)– 3-4 bunches spaced by 360-720 picoseconds were used for

dielectric Wakefield experiments– Beam break up during compression was used for two beam

PWFA– We will place additional effort to ease multibunch operation and

its diagnostics

ATF development plan (program)

• X-band technology– Linac

• Compensated energy spread after compression• Increase in top beam energy• Detailed longitudinal tomography

– Possibility for high gradient/high brightness beam experiments• X-band waveguide-wiggler• Deflection cavity

• Laser only experiments (EUV, Ion beam generation, …)– New experimental area, transport line

• Facility research complimentary to the main program– ILC positron source (High rep. rate CO2 cavity)– OSC test

• Electron beam energy upgrade

ATF development plan (laser) (Goals in this presentation, techniques in next)

• New photoinjector/CO2 slicing laser– Reliable technology– Shorter CO2 beams– 3 dimensional profile control on the cathode

• Single pulse CO2 power increase – Study of the short pulse CO2 limit (1 ps @ 10 atm, 100 fs

with isotopes)– Higher energy extraction 30J– Higher repetition rate, improved stability/predictability

• Laser cavity operations– ~100KW average power laser beam optimized for

Compton interaction (100-1000 times better than alternatives)

– Sustained circulation of the 1J, 5ps laser pulse for few microseconds

X-bend installation timeline

• Modulator construction (03/2007)• Low level RF (4/2007)• Klystron repair and delivery (4/2007)• Klystron test (5/2007)• Linac section installation (8/2007)

• Plasma Wakefield Acceleration experiments and VISA would be the main beneficiary of this upgrade

X-bend installation

Summary of beam parameters with and without x-bend section in the H line.

S bend only With X bend

Maximum beam Energy 75 MeV 100 MeV

Beam length (RMS) 0.25 – 2.5 ps 0.15 – 2.5 ps

Energy spread (RMS) 1 – 0.05 % 0.25 – 0.1 %

• Energy chirp compensation in compressed beam

• Increase in beam energy available to experiments

• New capability for measurement and manipulation of longitudinal phase space

ATF Energy upgrade

• Energy upgrade to 1.5 GeV can be realized by adding recirculation loops

• Benefits are:– Multiple energies would be available– New experimental floor– No interference with existing

operations– Relatively inexpensive…

• Space is available • User input is being investigated… • Cost of the upgrade was estimated at $3M

• Considerable man-power is needed to study and generate scientific case for AARD

Single pulse CO2 power increase

• Two directions: Pulse length and energy• 30-50 J can be extracted from current amplifier with new windows• ~1 picosecond should be achievable with new slicing laser• Isotope mixtures can allow for 100fs beam amplification• Combination of multiple effects needs careful studies:

– Power broadening of the amplification bands – Pulse shortening due to media saturation – Nonlinear dispersion in windows– …

• “Dream beam” or “bubble” accelerator with 10 micron laser– High charge– Compton based X-ray source could have 1027 (s mm2 mrad2 0.1%)-

1

• High gradients for acceleration based on nonlinear effects• High energy/extreme brightness of ion beams • 30J x 100fs : 0.3 Petawatt laser beam at 10 micron is stronger that

any today laser for experiments based on pondormotive potential.

Electron interacting with a strong EM wave acquires energy

where - dimensionless

laser strength parameter.

Thus, CO2 laser (=10 m) produces 100 times higher particle

yield per 1 Joule to compare with presently used solid state

lasers (1 m) provided that a threshold condition

is reached.

222amcW cmeEa

22 100 mTWPL

New prospects for laser-driven ion sources

Non scaling FFAG test with ion or/and electron beams(Thanks to S. Berg)

• FFAGs are useful when rapid acceleration is needed• The have advantages over cyclotrons because

– They can have smaller apertures– They can more easily reach relativistic energies

• Beam resonances prevent ordinary accelerators from having large energy spreads

• FFAGs have several methods for dealing with the fact that circulation time of the beam depends on energy

Conditions for Bubble formation(Thanks to A. Pukhov)

Laser power threshold:

Bubble can be formed in a finite window

of plasma densities: 3

2rel e laser laser

laser c rel laser

P n P

P n P c

2[fs]

30 GW[μm]bubble critP P

lasertrapped e-

cavity

Accelerated charge scales as:

lasere laser

rel

PN

P

Final energy : max 0.65 laser laser

laser rel

c P

P

10 micron laser unlikely to offer record gradient in this application, but might solve problems for practical applications: higher charge, more stable, better controlled final energy.

Compton back scattering – compact sub 100 fs x ray sourse

0.5 ps 50J

5ps 50J

“Dream beam” accelerator

In the proposal • Polarized -ray beam is generated in Compton backscattering inside

optical cavity of CO2 laser beam and 6 GeV e-beam produced by linac.

• The required intensities of polarized positrons are obtained due to 10 times increase of the “drive” e-beam charge (compared to non polarized case) and 5 to 10 consecutive IPs.

• Laser system relies on commercially available lasers but need R&D on a new mode of operation.

• 5ps, 10J CO2 laser is operated at BNL/ATF.

Conventional Non-Polarized Positrons:

6GeV 1A e- beam 60MeV beam

30MeV e+ beam

to e+ conv. target

~2 m

5-ps, 1-JCO2 laser

Polarized Positrons Source (PPS for ILC)

Laser cavity system

am

plifi

er

24ns ring cavities (8 pulses x 3ns spacing) 1J / pulse sustained for 8.5 ms

IP#1 IP#10

CO2 oscillator

8 pulses, 5ps, 10mJ(YAG laser)

8 x 200ps Kerr generator

8 x 5ps1J

Regenerative amplifier

amplifier

8x5ps10mJ

8x300mJ

BS

TFPTFPPC

PC

8x 30mJ 5ps

8 x 1J 5ps

8x30mJ

8 x 1J

1x150ns

Ge optical switch

ampl

ifier

ampl

ifier

ampl

ifier

LDRD – cavity tests

• Has a potential to increase average intra-cavity power ~100 times at 10.6 microns.

Purpose of the test:• Demonstration of 100-pulse

train inside regenerative amplifier that incorporates Compton interaction point.

• Demonstration of linear-to-circular polarization inversion inside the laser cavity.

• Test of the high power injection scheme

4-atm CO2 amplifier

/4-waveplates

parabolic mirrors

YAG (14 ps)

200

ps

Ge

3% over 1 s

“~100 times increase of the average intra-cavity power at 10 m”

• The required laser train format / repetition rate /average acting power at each IP: 100 pulses x 150Hz x 1J = 15 kW.

• Efficient interaction with electron beam requires short (~5ps) and powerful (~1-2J) laser beam.

• Such high-pressure laser does not exist. Non-destructive feature of Compton scattering allows putting interaction point inside laser cavity.

• We can keep and repetitively utilize a circulating laser pulse inside a cavity until nominal laser power is spent into mirror/windows losses.

• Assuming available 0.5 kW CO2 laser and 3% round-trip loss, 1-J pulse is maintained over 15,000 round trips/interactions (100 pulses x 150 Hz). Thus, 0.5 kW laser effectively acts as a 15 kW laser.

• Equivalent solid state ( 1m) laser producing the same number of gamma photons should be 150 kW average power with ~10J, 5ps beam.

• Applications: – Compact femtoseconds x-ray source– X-ray source for RIA– Gamma collider laser– …

Compact femtoseconds x-ray source

• 50-100 MeV photo injector/LINAC combination producing train of 500 bunches (0.8 nC, 100fs, ~2 m) at 150Hz.

• CO2 laser cavity / few cavities (2J, 5ps, 500 turns)

• Head on Compton interaction• X-ray energies 6-24 keV• Peak brightness: 5x1024

(s mm2 mrad2 0.1%)-1

• Average brightness: 108 (s mm2 mrad2 0.1%)-1

• ~10M$, 100 m2 / 5 beam lines

E_ 4 2

El

1 4 2

El

Ee

2

2

0 1 2 30

5

10

15

20

E_ ( )

keV

.

1.2 Energy spectrum:

d E if E Emax 0 d E

0 5 10 15 200

8 1015

1.6 1014

2.4 1014

3.2 1014

d E( )

E

keV

.

Real CCD imagesNonlinear and linear x-rays

Potential for generating exotic beams of nuclei

(Thanks to V. Litvinenko)

• Idea came from SPIRAL II Project (electron option) to use 45 MeV electron beam to generated 10-20 MeV Bremmstrahlung -rays and use Giant Dipole Resonance (GDR) for photofission of 238U into rare (neutron reach) nuclei http://ganinfo.in2p3.fr/research/developments/ spiral2/index.html

• Because of the hard-edge in the energy spectrum, an ERL-based Compton -ray beam with high average power average is a better choice for such source

• BNL is developing both high-current high-energy ERLs and high power C02

lasers - the key ingredients of such source

• 3 GeV, 20 mA ERL (20 nC/bunch, 1 MHz rep-rate) in combination with four CO2

lasers (2J/pulse, Rayleigh range of 0.2 cm, 500 Hz rep-rate x 500 reflections) will provide 90 kW (i.e. 4x1016/sec) of -rays within the 10-20 MeV range of GDR

• This -ray beam has very small divergence ~ 150 rad, and can be used to for photofission of 238U to generate ~1016/sec nuclei, including exotic

CO2 lasers-ray beam

OSC test at NSLS (VUV ring) (Thanks to S. Kramer, A. Zholents)

• 1st stage: lattice control (time of flight) test–studies of mirror less FEL

• 2nd stage: cooling rate measurement …

• Busy ring but Wigglers are already installed!• Linear optics are very appropriate• Hardware needed:

–~6 Power supplies–Vacuum port, 2-3 windows–Additional nonlinear correction? –Optical parametric amplifier at ~1.5 micron

Practical Layout

Electron Beam Path Le = 51/2 = 25.5 M

Jogged Optical Path (25 M)

Electrical Cabinets

Conclusion

• Staff problems will be addressed in 2008 to improve user support.

• Quality of the beam will be improved with beam based alignment, better diagnostics, shaped laser and possibly new gun.

• X-band power should become available for experiments in 2007. High gradient, new beam diagnostic will studied.

• High brightness, short beam structure with bunch spacing from femtosecons to nanoseconds is important part of program at ATF.

• CO2 laser development will be directed towards tens of terawatt, sub-picosecond, stable and well diagnosed system.

• Additional sources of funding would be needed to investigate high rep. rate and cavity mode of operations.

Studies for TeV-LC

• Photoinjector• CO2 laser/Compton based positron source• Diagnostics (cavity based BPM, Tomography, …)• Beam handling (IFEL “heating” before compression)• Laser converter for Photon collider• Many studies for high gradient …