# Presentation: 618562

## Studying and Applying Channeling at Extremely High Bunch Charges

**Studying and Applying Channeling at Extremely High Bunch Charges**

- Dick **Carrigan**
- Fermilab
**Advanced Photon Sources and their Application**
**Nor Hamberd,** Armenia
**August 31, 2004**** **

**Notes:**
Need to think out master, portrait vs landscape, etc. Use animation, avoid textually dense slides, etc.

## Visionary possibilities for acceleration

- Lasers
- R. Palmer, Particle Accelerators V11, 81 (1980). Recent progress  Kimura et al. PRL **92**, 054801 (2004). See also LEAP at Stanford (Colby)

**Would like much higher accelerating gradients**
**Two thoughts:**

- Plasmas
- Tajima and Dawson PRL **43**, 267 (1979)
- E. Esarey, et al., IEEE Trans. On Plasma Sci, **24**, 252 (1996).
- J. Dawson, Scientific American March, 1989 (p. 54)

## Lasers

- basic laser challenge
- 	good news: can get very high fields
- 	bad news: vectors transverse to particle direction
- ways to defeat
- 	gratings, maybe boundary conditions, special modes
- 	R. Palmer, Particle Accelerators 11, 81 (80)
- Inverse free electron laser IFEL-next transparency

**Notes:**
Watch out – IFEL next transparency

## Cascading laser stages

- [from W. Kimura et al, PRL 86, 4041 (2001)]

- Require fs micro bunches, very good timing
-        24 MW first stage, 300 MW second
- This demonstrated rephasing, not acceleration

- Inverse free electron laser (IFEL)
-    electrons oscillate in undulator and absorb energy from laser
- Gradients not on a scale with plasma accelerators

**Notes:**
My want to update in view of recent BNL resultsThe basic STELLA concept can be applied to many different laser acceleration schemes.  For experimental convenience, inverse free electron lasers (IFEL) were chosen as the laser acceleration mechanism.  An IFEL is a free electron laser operating in reverse.  The laser beam co-propagates with the e-beam within the gap between a pair of parallel-facing magnet arrays called an undulator.  Depending on the sign of the laser field seen by an electron, it will be accelerated or decelerated.

Figure 1 shows a schematic layout of the experiment.  It consists of two IFELs driven by a single laser beam from the ATF CO2 laser.  The first IFEL (IFEL1) is called the buncher and causes the sinusoidal energy modulation.  The second IFEL (IFEL2) is referred to as the accelerator.  This IFEL traps and accelerates the microbunches.  A bunch compressor or chicane is located between IFEL1 and IFEL2.  The chicane has both a fixed magnetic field (i.e., permanent magnets) and a variable magnetic field (i.e., electromagnets).  The fixed field forces the electrons to travel through a “V-shaped” trajectory in which the faster electrons generated by IFEL1 traverse a shorter path than the slower ones, thereby causing the electrons to bunch at the entrance to IFEL2.  (See Principle of Electron Microbunch Formation for more details.)  This creates a train of microbunches separated by 10.6 m with individual bunch lengths of 1 m (equivalent to 3 fs).  Control of the phase delay between the microbunches and the laser field in IFEL2 is achieved by adjusting the variable field of the chicane.  This enables resynchronizing the microbunches with the accelerating portion of the laser field by slightly delaying when the electrons exit the chicane.  Usage of the chicane also makes the entire system more compact with a total length of 1.2 m from the entrance of IFEL1 to the exit of IFEL2.  At the end of the experiment is an energy spectrometer for measuring the electron energy spectrum. See Photographic Tour of STELLA Experiment for more details of the experimental hardware.

## Plasma wake field acceleration

- G= 0.96(n0)1⁄2     (V/cm) 	n0 is electron density
- RF cavity			0.0005 GV/cm
- gaseous plasma		1 GV/cm

- Photo S. Carrigan

**Notes:**
Figure fixed

## Plasma model

- (from Lawson, Scientific American-1989)

- Pendulum cluster moves to the right

- Plasma snapshot: red plasma electrons cluster
- and make field. Electrons in red ball are trapped.

## Characteristic field strengths

- highly relativistic laser driven plasma. Laser pulse length is .03 cm, pulse moves to right, fast oscillations are laser freq. Density (n0) is 1016/cm3. Moderate case would be more sinusoidal.)

- (cm)

- Laser
- pulse

- (from Sprangle, et al.)

## A wakefield accelerator - E157 at SLAC

- Head of beam generates plasma wakefield,
- tail is accelerated by 80 MeV. Also do e+ - E162.

- (E-164 later version , ne O(3*1015), 100 micron bunches
-  - see 2003 Particle Acc. Conf, p. 1530)

- M. Hogan  Phys. Plasmas 7, 2241 (2000)

## Results from SLAC E-157

- Barov and Rosenzweig (UCLA) see similar results at Fermilab.
- 100 MeV/m using A0 14 MeV photoinjector. 6-8 nC, ne ~ 1014/cc.

- Acceleration

- M. Hogan  Phys. Plasmas 7, 2241 (2000). See also Muggli, et al. PRL **93**, 014802-1 (2004)

**Notes:**
Note that I have a transparency from Piot. See fig 7 in Phys. Plasmas 7, 2241 (2000)

## Bob Hofstadter "The Atomic Accelerator" HEPL 560 (1968)

*"**To anyone who has carried out experiments with a large modern accelerator there always comes a moment when he wishes that a powerful spatial compression of his equipment could take place.  If only the very large and massive pieces could fit in a small room!”*

## Hofstadter wanted a crystal accelerator!

- A table top accelerator ("miniac")
- The first solid state accelerator
- use channeling for focus
- maybe an after-burner scheme
- excite atoms coherently with 1 keV-xray

- Problem-transit time

- Get out 1 keV/Å
- in 1 cm would get 100 GeV

- Need an **x-ray laser** (1968)

## Plasma wake field acceleration – solid state

- G= 0.96(n0)1⁄2     (V/cm) 	n0 is electron density
- RF cavity			0.0005 GV/cm
- gaseous plasma		1 GV/cm
- solid state plasma		100 GV/cm

- Photo S. Carrigan

**Notes:**
Figure fixed

## At least four groups see high energy ions, electrons from intense lasers hitting foils
Livermore PRL 85, 2945 (2000)
Michigan APL 78, 595 (2001)
Rutherford PRL 90, 064801 (2003) – discussion of mechanisms, target evolution
LULI  PRL 85 1654 (2002)

- Livermore PRL _85_, 2945 (2000)
- Michigan APL _78_, 595 (2001)
- Rutherford PRL _90_, 064801 (2003) – discussion of mechanisms, target evolution
- LULI  PRL **85** 1654 (2002)

- Pseudo solid state accelerators

- 3*1020 W/cm2, 1000 TW, 1013 proton beams with E to 58 MeV, electrons
-    protons can be focused by curving target
- process: electrostatic fields produced by ponderomotively accelerated hot
-    electrons act on protons from absorbed hydrocarbons rear side (downstream)

**Notes:**
Fig fixed-there are additional mechanisms. Note two purple spots from ion beams normal to foils

## Basic Crystal Accelerator Concept

- Big problems!
- blow away material
- dechanneling

- excite plasma wake field in solid with density a thousand times gas
**use ****channeling**** to reduce energy loss, focus, and maybe even cool**
**Chen-Noble Tahoe (1996), p. 441**

- Positives
- very high power, femtosec lasers
- radiative damping (Huang, Ruth, Chen)

## The Fermilab A0 photoinjector

**So what did the Fermilab A0 photoinjector do?**
-   studied channeling nearer extreme conditions needed for
-        a channeling accelerator
-   Could we make a crystal accelerator or do

**unique channeling studies**?

-    built as Tesla injector prototype in the late 1990s by Helen Edwards’ group
-    essentially a gigantic phototube powered by a laser
-      followed by a so-called 3.5 MeV warm RF gun
-      and second stage of a Tesla superconducting nine-cell RF cavity
-    beam energy 14.4 MeV.
-    very large picosecond electron pulses of 10 nanocoulombs or 106 A/cm2

## Crystal survivability?

- _excite electronic plasma_
- tunnel ionization
- partial or total lattice ionization

- Process

**Notes:**
The disordering process proceeds through several levels.  When the laser beam strikes a crystal surface it frees electrons by field ionization.  Schematically, these surface electrons are in atomic potentials that are a combination of a normal atomic state in a metal or semiconductor with an overlay potential due to the laser electric field that is linear with position.  This is similar to the centrifugal potential that appears in bent crystal channeling.  Typical ionization potentials are 10 eV.  H. Milchberg[i] states that LiF is among the best materials to stand up against a laser pulse because it has a high band gap.

The electrons in the Fermi sea move very quickly, in a time comparable to one optical oscillation, on the order of femtoseconds.  The core nuclei and electrons will react more slowly.  These ionic cores will heat from repeated collisions with the electrons elevated from the Fermi sea.  This will generate phonons or lattice vibrations. Typically this will take longer for heavier cores like tungsten because of momentum conservation.  Even these times to create phonons are short.  Observation evidence[ii] shows that silicon exhibits liquid behavior after only 100 fs for typical conditions.  This would seem to be the terminus of channeling behavior but one should be careful to understand the nature of the process in detail.  For example, the laser pulse will also be attenuated by the developing surface plasma so that the process will have some spatial dependence and the surface reflectivity will change.

The time scales of the disordering must also be compared to the coherence times for plasma oscillations.   As noted in Appendix I the plasma oscillation frequency is ?p = (4pn0e2/me)2 so that it increases as the square root of the plasma electron density.  The typical coherence time is 10-100 cycles so that for a plasma density of 1020/cm3 the plasma oscillation frequency might be 0.1-0.2*1015 Hz giving rise to coherence times of O(100 fs).  Chen and Noble[iii] observe that a plasma decays through interband transition processes that produce free electrons.  These electrons can diffuse energy loss out over a 1 mm region.  They estimate that the plasma might take 100 ps to decay.

[i] H. Milchberg, private communication.
[ii] M. Downer, private communication.  See, for example, Stampfli and Benjamin, Phys. Rev B (1992-1996).
[iii] P. Chen and R. J. Noble, p. 517 in Relativistic Channeling, eds. R. A. Carrigan, Jr. and J. A. Ellison (Plenum, 1987).

## Intense beam through crystal could blow away electrons in much less than a picosecond
Acts like a larger screening length

- Acts like a larger screening length

- Dynamic channeling

**Notes:**
Point is that as the temperature increases the critical angle drops and channeling is throttled. But, it happens relatively slowly. r0 is some channel radius, u2 is rms 2 dim lattice vibration amplitude 0.006sqrt(T) at high temp for u2 in A and T in K, aTF is screening length. Slide is from z:\a\docs\santa fe\graphs\

## Crystal destruction

**ACCELERATION**
- G (gradient) proportional to (n0)1/2, P (power) prop to n0
- for G = 1 GeV/cm     P = 105 J/cm3
- 1019 W/cm3
-         for O(10 fs) @ 1 GeV/cm

**LASER**
- 1011 W/gm
-        Belotshitkii & Kumakhov (1979)
-        or 106 a/cm2 for particle beam
- 1012 W/cm3	ns long pulses
- 1013 W/cm3	Chen-Noble (1987)
-        fracture threshold
-        O(0.1 ns) ref 16
- Skin depth < 0.1 mm

**PARTICLE BEAM**
- 1011 A/cm2	Chen & Noble (1987) (crystal OK for 10 fs)

**LATTICE IONIZED**
- 1015-1016 W/cm2	Chen & Noble (1996)/laser

**Notes:**
Laser power for 1 GV/cm – see p. 8 Chen and Noble SLA 7402, FNAL 96/441.
	take 100 GV/cm case at bottom, mult by 4pi, t = 10 fs, then divide by 10^4 for the 1Gv case.
Laser destruction at 10^13 W/cm^3  Carrigan and Ellison p. 519 2/3 way down
Lattice ionization p. 8 Chen and Noble SLA 7402, FNAL 96/441. About half way down.
Particle beam – see Carrigan and Ellison p. 520 half way down.

## A0 RF GUN FOR COMPARISON
I/cm2 = 10 nc/1 ps in 1 mm2     or      106 A/cm2  (OK driver @ 1GeV)

A0 LASER FOR COMPARISON
10 W/cm3	slap ruptured (continuous, 1015W/cm3 for 10 fs)
109 W/cm2	damage on lens
1018 W/cm2	1 Joule on 10 μm spot in 1 ps (OK driver)

**A0 RF GUN FOR COMPARISON**
- I/cm2 = 10 nc/1 ps in 1 mm2     or      106 A/cm2  (OK driver @ 1GeV)
**A0 LASER FOR COMPARISON**
- 10 W/cm3	slap ruptured (continuous, 1015W/cm3 for 10 fs)
- 109 W/cm2	damage on lens
- 1018 W/cm2	1 Joule on 10 μm spot in 1 ps (OK driver)

- Situation for Fermilab A0 photoinjector

**Notes:**
First box may not be in right place.

## Fermilab A0 experiment

- ICT

- ICT

- goniometer

- S1

- Detector

- 1 m

- R. Carrigan, et al. Phys. Rev. A68, 062901 (2003)

- Ne = 5*1010 or 10 nC peak,
-     ε typically 10 mm*mrad, 10 ps

**Notes:**
Most recent reference, maybe combine some more info like detector, picture

## Planar and axial scans

- random

**Notes:**
update. X‐ray yields for planar (left panel) and axial (right panel) scans obtained from a Si crystal in the 14.4 MeV electron beam. The quantities Θx and Θy describe the rotation of the crystal around a horizontal and a vertical axis perpendicular to the beam axis, respectively. The yields were measured using the AberX‐Lite detector. The solid line fitted to the axial spectrum results from a double Gaussian fitting function as explained in the text 

## Summary of high charge measurements

-  σb is O(0.5 mm),         length = > 7 ps ()
-   Peak n/cm2 is 1013 electrons/cm2
-   I/cm2 = 105 A/cm2
-    flat is not ruled out

- Fermilab

**Notes:**
Emphasize that this is “flat.” Channeling radiation yield (x‐rays/bunch in a 10% band) over a twelve decade span of bunch charge. The present data are represented for the AberX‐Lite detector by open and filled diamonds obtained for axial channeling from Si with the laser on and with dark current, respectively, and for the AberX detector as indicated by the open triangle for planar channeling. The filled circles [8] result from an earlier measurement of axial channeling in a diamond crystal with electrons of 5.4 MeV and the filled triangle [21] from planar channeling in a Si crystal at 30 MeV. All points have been scaled to T = 5.4 MeV.

## The Future Beyond the Fermilab A0 Experiment

- get into 10 fs regime
- ne 103 to 105 larger (small beam size important)
- higher energy might be better for channeling, beam size
- But new experimental geometry, channeling approaches needed

- Possibilities:
- SLAC E164 geometry for channeling radiation at 30 GeV
- Livermore
- Toronto – studying laser melting with sub picosec electron diffraction

## Using SLAC E164 to study channeling

- Add crystal, goniometer, x-ray det. (integrating). Now at FFTB (final foc TB) for big q.
- Channeling radiation ala N. A. Filatova, Phys. Rev. Lett.  **48**, 488 @ 12 GeV, (1982), K. Kirsebom, et al., NIMB **119**, 79 (96) @ 150 GeV.

- C. Barnes et al., Proc. 2003 Particle Acc. Conf. 1530 (03)

- Beam:
- 	charge: 2*1010/bunch   (< A0), size 25 m.
- 	time: 100 mm/c = 300 fs
- 	I/cm2: 50*106 A/cm2  (500 times better than A0)

- This could take channeling measurements nearly to the plasma regime.

**Notes:**
Note OTR for beam size.

## High energy density application channeling with intense  “proton beam”

- “Isochoric Heating...”, P. Patel, et al., PRL **91**, 125004 (03)  [Livermore]

- flat                                focused

- ns

- m

- _Laser_:
- 50 m dia
- 5*1018 W/cm2
- 100 fs

- _Protons_
- 80-250 m dia
- 1012 protons
- 4-12 MeV

- Instrument with streak camera, layers of radiochromic film, interferometer, etc.

- Could one see channeling blocking patterns, RBS off of oriented target film
- and study lattice properties as a function of pump and probe
- or time evolution after hit? World class laser could give 1014 protons.

- _Plasma_
- Temp O(4eV)

**Notes:**
FIG. 1 (color). (a) Experimental setup
for flat and focusing target geometries.
Each target consists of a flat or hemispherical
10 m thick Al target irradiated
by the laser, and a flat 10 m thick
Al foil to be heated by the protons.
(b) Corresponding streak camera images
showing space- and time-resolved
thermal emission at 570 nm from the
rear side of the proton-heated foil. The
streak camera images an 800 m spatial
region with a 1 ns temporal window.

## Toronto - studying laser melting with sub picosec electron diffraction

- See solid to liquid phase transition for electron diffraction in 0.02 m polycrystalline aluminum foil heated with 7*1010 w/cm2 laser over 3.5 ps. Transition is electron – phonon coupling.

- B. Siwick, et al., Science **302**, 1382 (03), D. Von der Linde, Science **302**, 1345 (03)

- fcc lattice

- liquid

**Notes:**
Note that foil is thin. Microchannel plate-phosphor screen detector, 30 keV, 500 fs electron gun. 775 nm laser (near infrared, with 120 fs length. From Fig. 1 of SiwickFemtosecond electron diffraction study of an ultrafast solid-liquid phase transition in polycrystalline Al. (A) Sequence of diffraction patterns (partial images) taken at pump-probe delay intervals (T) through the phase transition. The first four rings in the powder diffraction pattern, associated with the fcc lattice structure, are still clearly visible 500 fs after laser excitation. At T = 3.5 ps, features associated with Bragg reflections are no longer visible, and the diffraction pattern exhibits only a single broad ring, which is characteristic of a liquid. Each diffraction pattern contains the cumulative diffracted intensity of only 150 electron pulses. (B) Radial average of the difference in diffracted intensity, with respect to that of the unperturbed crystalline state (that is, before the phase transition) at each time delay (AU, arbitrary units). The decay time of the diffraction rings has a strong dependence on the scattering vector s, which is characteristic of thermal excitation. The loss of long-range order associated with the phase transition is best seen in the dramatic broadening of the (111) and (200) diffraction ringfeature in the s < 0.4 region, not simply in the reduction in ring intensities, because they are strongly temperature-dependent. 

## The Far Future?

_**C**_**hanneling**
_**R**_**elated**
_**A**_**ccelerator**
_**P**_**roject**

**Notes:**
Change to channeling related accelerator... Where is the original drawing?

## Fermilab A0 Participants

- R. A. Carrigan, Jr., J.-P. Carneiro, P. L. Colestock, H. T. Edwards,
- W. H. Hartung, and K. P. Koepke
*Fermi National Accelerator Laboratory*
- M. J. Fitch
*University of Rochester*
- N. Barov
*University of California at Los Angeles*
- J. Freudenberger, S. Fritzler, H. Genz, A. Richter, and A. Zilges
*Institut für Kernphysik, Technische Universität Darmstadt,*
- J. P. F. Sellschop
*Schonland Centre, University of the Witwatersrand*

## Questions?