Parameter sensitivity tests for the baseline variant

Konstantin Lotov, Vladimir Minakov, Alexander Sosedkin

Budker Institute of Nuclear Physics SB RAS, Novosibirsk, Russia

Novosibirsk State University, Novosibirsk, Russia

AWAKE Collaboration

presented by K.Lotov at AWAKE collaboration meeting, Geneva 05.12.2013

The baseline variant:

Infinite plasmaHalf-cut beam

discussed here discussed earlierno study or interest

presented by K.Lotov at AWAKE collaboration meeting, Geneva 05.12.2013

Variations of plasma density:It is convenient to characterize the field by the noise-resistant wakefield potential and use max(z) as the integral measure of wakefield quality

max

2e14

3e14

5e14

7e14

1e151.5e15

2e15

3e15

5e15

High density plasmas support stronger fields, but hosing or filamentation may develop

The baseline is at the optimum excitation efficiency

2e14

3e14

5e14 7e14 1e15

1.5e152e15 3e15

5e15

n0*50/7, E0*7, E = const,: 0.1 -> 3/16,Em/E0: 0.37 -> 0.22

limit due to elongation of wave period:

not enough bunches to reach saturation field

presented by K.Lotov at AWAKE collaboration meeting, Geneva 05.12.2013

Variations of ion mass:

1 (H)

6.9 (Li)

24.3 (Mg)

85.5 (Rb)

39.9 (K)

77 94 133 (Cs) 197 (Au)

Rubidium is heavy enough to have no problems with ion motion

presented by K.Lotov at AWAKE collaboration meeting, Geneva 05.12.2013

Variations of driver population:

5e114e11

3.5e11

3e11

2.5e11

2e11

1.5e11

1.15e11

The baseline regime is close to the limit (~40% of wavebreaking field),

further increase of population does not result in proportional field growth

N1/3

The limit due to nonlinear elongation of the wakefield period: K.V.Lotov, Phys. Plasmas 20, 083119 (2013)

presented by K.Lotov at AWAKE collaboration meeting, Geneva 05.12.2013

Variations of driver length and population (constant peak current):

8 cm

6 cm

12 cm

20 cm

Fewer bunches at shorter lengths produce proportionally weaker fields,

but more bunches make no sense, as the limit is reached

presented by K.Lotov at AWAKE collaboration meeting, Geneva 05.12.2013

Variations of driver length (constant population):

z=6 cm

z=12 cm

z=24 cm Weak dependence,

fewer and denser macro-bunches are more efficient

In the linear model, the field is determined by the total driver charge and independent on how many bunches it is distributed over.

presented by K.Lotov at AWAKE collaboration meeting, Geneva 05.12.2013

Variations of driver radius (constant emittance):

0.2 mm

0.25 mm

0.3 mm

0.5 mm

0.15 mm

0.1 mm

0.05 mm

Wide beams are not dense enough to drive the wave to the limiting fieldNarrow beams are quickly diverging due to the transverse emittance

Baseline radius is the optimum one for this emittance

Beam fragments at z=3.6 m:

rb=0.2 mm

rb=0.05 mm

presented by K.Lotov at AWAKE collaboration meeting, Geneva 05.12.2013

Variations of the driver energy:

100

200

400

600 800 1000 2000 GeV

/Wb1/2

Weak dependence:

peak field is near saturation,

Wb1/2 scaling of the length

(at constant normalized emittance)

presented by K.Lotov at AWAKE collaboration meeting, Geneva 05.12.2013

Variations of driver energy spread:

0.17%0.35%0.7%

No dependence

presented by K.Lotov at AWAKE collaboration meeting, Geneva 05.12.2013

Variations of driver emittance (angular spread):

1e-5

2e-53e-5

4.5e-5

4e-5

5e-5

7e-5

1e-4

2e-4

Lower emittance: same fields, slower beam destruction

Higher emittance: lower fields

presented by K.Lotov at AWAKE collaboration meeting, Geneva 05.12.2013

Variations of cut location:

propagation

length fraction remained

20%

25%

35%

50%

65%

95%

80%

Late cut: no beam to excite high fields

Early cut: slow instability growth, beam has time to diverge

Optimum: z ahead of the center

0 12 24-12-24cm from the center

presented by K.Lotov at AWAKE collaboration meeting, Geneva 05.12.2013

Varying plasma radius:

E.Oz, P.Muggli, NIMA paper:

simulations

cone-shaped plasma

infinite plasma (baseline)

fears: detuning of the wave frequency,different wave structure,different trapping conditions

no more

Wakefield phase: regions of stable phase velocity are still there

has small effect on wakefields

Wakefield amplitude: changes are small

presented by K.Lotov at AWAKE collaboration meeting, Geneva 05.12.2013

Summary:

Infinite plasmaCut location

Sensitivity, S

max/max = S X/X

0.7

0 (extremum)

0.40

0.3

0.0700.3

0

150%

The way to higher fields: lower emittance, smaller beam radius, higher plasma density

Of less importance: increase of beam peak current

False target: increase of beam population at the expense of elongation

Thank you