1. Proton driven plasma accelertion
G. Xia
Max-Planck-Institute for Physics
July 15, 2011
LC Forum meeting, July, Munich

2. LC Forum meeting, 14-15 July, Munich
Outline
Energy frontier machines
Plasma wakefield acceleration-PWFA
Proton-driven PWFA
Summary
LC Forum meeting, July, Munich

3. Energy frontier machines
Energy frontier machines (terascale or 1012 eV in beam energy) will help us unlock many
secrets of our Universe, however,
the machine size reach our limit (tens of kilometers), price tag is extremely high (billion dollars)
How to make the life easier?
LC Forum meeting, July, Munich

4. LC Forum meeting, 14-15 July, Munich
Motivation
With an increase of beam energy, the size and cost of modern high energy particle accelerators reach the limit
Plasma can sustain very large electric fields, a few orders of magnitude higher than the fields in metallic structures
The plasma accelerators (laser driven-LWFA or beam driven-PWFA) developed rapidly in last decade, GV/m accelerating gradients have been demonstrated in labs
The novel plasma accelerators can potentially minimize the size and cost of future machines
LC Forum meeting, July, Munich

5. The New Livingston Plot
LC Forum meeting, July, Munich
Joshi & Katsouleas Physics Today 2003

6. Plasma Wakefield Acceleration (PWFA)
I) Generate homogeneous plasma channel
Ionization of gas via:
Laser
Beam RF
Gas
Plasma
II) Send dense electron beam towards plasma
= ion = electron
Beam density nb
Gas density n0
LC Forum meeting, July, Munich

7. LC Forum meeting, 14-15 July, Munich
PWFA
III) Excite plasma wakefields
Electrons are expelled r z
Ion channel
Space charge force of beam ejects all plasma electrons promptly along radial trajectories
Pure ion channel is left: Ion-focused regime, underdense plasma
LC Forum meeting, July, Munich

8. PWFA Space charge of drive beam displaces plasma electrons.
Electron motion solved with ...
Space charge of drive beam displaces plasma electrons.
driving force:
Space charge
oscillations
(Harmonic
oscillator)
Plasma ions exert restoring force
restoring force:
Longitudinal fields can accelerate and decelerate!
Plasma “structures” are also super-strong “quadrupoles”!
(many thousands to Mega Tesla/m)
Approximately mm-wave length!
LC Forum meeting, July, Munich

9. LC Forum meeting, 14-15 July, Munich
Proton-driven PWFA p+ e-
Drive beam: p+
E=1 TeV, Np=1011
σr=0.43 mm, σθ=0.03 mrad,
σz=100 μm, ΔE/E=10%
600 GeV e- beam
Witness beam: e-
E0=10 GeV, Ne=1.5x1010
≤1% ΔE/E
in ~500 plasma
Plasma: Li+
np=6x1014cm-3
External magnetic field:
Field gradient: 1000 T/m
Magnet length: 0.7 m
LC Forum meeting, July, Munich
A. Caldwell et al, Nature Physics 5, 363 (2009).

10. LC Forum meeting, 14-15 July, Munich
Simulation results
Energy gain
energy change
energy spread
LC Forum meeting, July, Munich
A. Caldwell et al., Nature Physics 5, 363 (2009).

11. LC Forum meeting, 14-15 July, Munich
PWFA vs. PDPWA
Pros. of PWFA
Plasma electrons are expelled by space charge of beam, a nice bubble will be formed for beam acceleration and focusing.
The short electron beam is relatively easy to have (bunch compression).
Wakefield phase slippage is not a problem.
Cons. of PWFA
One stage energy gain is limited by transformer ratio, therefore maximum electron energy is about 100 GeV using SLC beam.
Easy to be subject to the head erosion due to small mass of electrons
Pros. of PDPWA
Very high energy proton beam are available today, the energy stored at SPS, LHC, Tevatron
SPS (450 GeV, 1.3e11 p/bunch) ~ 10 kJ
LHC (1 TeV, 1.15e11 p/bunch) ~ 20 kJ
LHC (7 TeV, 1.15e11 p/bunch) ~ 140 kJ
SLC (50 GeV, 2e10 e-/bunch) ~ 0.1 kJ
Cons. of PDPWA
Flow-in regime responds a relatively low field vs. blow-out regime.
Long proton bunches (tens centimeters), bunch compression is difficult.
Wave phase slippage for heavy mass proton beam (small γ factor), especially for a very long plasma channel
blow-out
(p+)
flow-in
linear response
nonlinear response
LC Forum meeting, July, Munich
G. Xia, Talk given at PAC11 meeting in New York

12. LC Forum meeting, 14-15 July, Munich
Short proton driver
A magnetic chicane for bunch compression
4 km bunch compressor is required for 1 TeV p+ beam!
LC Forum meeting, July, Munich
G. Xia, A. Caldwell et al., Proceedings of PAC09 (FR5RFP011)
F.Zimmermann, G. Xia et al., Proceedings of PAC09, (FR5RFP004)

13. LC Forum meeting, 14-15 July, Munich
Short bunch driver
Self-modulation via plasma wakefield (the transverse instability modulates the long bunch into many ultra short beamlets at plasma wakelength.
density modulation effect
SPS beam at 5m
1e14 cm-3
on-axis (X = 0) beam density profile
after 5 m propagation in plasma
G. Xia, et al., AIP Proceedings of Advanced Accelerators Concepts 2010,
LC Forum meeting, July, Munich
A. Caldwell, K. Lotov, A. Pukhov, G. Xia, Plasma Phys. Control. Fusion 53, (2011)

14. Demonstration experiment at CERN
PDPWA has the potential to accelerate electron beam to the TeV scale in a single stage. As a first step, we would like to demonstrate the scaling laws of PDPWA in an experiment with an existing beam
kick-off meeting-PPA09 held at CERN in December 2009
A spare SPS tunnel is available for demonstration experiment
With no bunch compression in the beginning
old beam lines
Kick-off meeting 2009
beam dump
beam line layout
LC Forum meeting, July, Munich
G. Xia et al, Proceedings of PAC11 (TUOBN5), New York, 2011

15. Demonstration experiment at CERN
Scientific Goal of Experiments:
Initial goal is to observe the energy gain of 1 GeV in 5 m plasma.
A plan for reaching 100 GeV within 100 m plasma will be developed based on the initial round of experiments
Experimental Setup:
Expected Results:
A long SPS beam (uncompression) will be used in the first experiment. a self-modulation of the beam due to the transverse instability will produce many ultrashort beam slices at plasma wavelength.
The modulation could resonantly drives wakefield in hundreds MeV/m with CERN SPS beam.
Simulation shows that at optimum beam and plasma parameters, ≥ 1 GV/m field can be achieved.
LC Forum meeting, July, Munich
G. Xia et al, Proceedings of PAC11 (TUOBN5), New York, 2011

16. Electron acceleration
Plasma density in
use: 7x1014 cm-3
SPS-LHC
SPS-Opt.
Beam energy [GeV]
450
Bunch population [1011]
1.15
3.0
Beam radius [μm]
200
Angular spread [mrad]
0.04
Normalized emittance [μm]
3.5
Bunch length [cm] 12
12.4
Energy spread [%]
0.03
LC Forum meeting, July, Munich
G. Xia et al, Proceedings of PAC11 (TUOBN5), New York, 2011

17. Plasma density variation
6 TeV electron beam can be achieved based on LHC beam,
the wakefield gradient approaching 1 GV/m !
Increasing the plasma density properly at the moment of developed instability, the wave shift with respect to the main body of the beam will be stopped and one can obtain a stable bunch train that propagates in plasma for a long distance
LC Forum meeting, July, Munich
A. Caldwell, K. Lotov, arXiv: v1 (2011)

18. LC Forum meeting, 14-15 July, Munich
CERN’s interest
PDPWA collaboration:
Several workshops, biweekly phone meeting, and site visit at CERN
Sumbitted the LoI two weeks ago to CERN
Proposal defense at 102 SPSC meeting on June 28, 2011
Steve Myers
CERN Director of Accelerators & Technology
"CERN is very interested in following and participating in novel acceleration techniques, and has as a first step agreed to make protons available for the study of proton-driven plasma wakefield acceleration."
LC Forum meeting, July, Munich

19. LC Forum meeting, 14-15 July, Munich
Summary
Simulation shows that proton-driven plasma wakefield acceleration holds promise to accelerate the electron bunch to energy frontier in a single passage of plasma cell.
Short and high energy proton bunch could be produced via conventional magnetic bunch compression or combined other compression schemes.
Demonstration experiment on PDPWA is planning as a future project
Further investigations are ongoing on the key issues such as accelerating positron beam, high repetition rate for high luminosity, beam instabilities, mobile ions, etc.
LC Forum meeting, July, Munich

20. Thanks for your attention !
LC Forum meeting, July, Munich