Mode Matching and Particle Studio * Comparison (with a little digression on the Wire Method)

Mode Matching and Particle Studio* Comparison

(with a little digression on the Wire Method)

Marco Panniello, Vittorio Giorgio Vaccaro, Naples. Carlo Zannini, CERN.

* Particle Studio with the new filtering tool1

Particle StudioThe results from Particle Studio seem almost insensitive to the conductivity and going up in frequency, the reliability is clearly bad.We need a shorter bunch (and then a very thin mesh)to investigate the red frequency region.

Not reliable region, dependent by bunch length

Gaussian bunch adopted as excitation signal

σ=1mmWake-length (WL)=3m

2

Particle Studio & Mode MatchingWithout take care of the bunch and the wakefield length there is an acceptable agreement only from 2.4 to 6.0 nwn.

To reach better results, a shorter bunch (σ) and longer “wake” (WL) are needed.

The bunch length and the WL must be chosen accurately during the simulation setup, to obtain reliable results by PS.

Bad agreement region, dependent by bunch

length in PS simulations.


3

Particle Studio & Mode Matching

Below cutoff, there is agreement on the resonant frequency values, but not on the peaks height. The WL determines a upper limit for the Quality Factor.

c

WLffQ

00max

min

00max f

ffQ


4


Changing the geometrical parameters, the remarks on the comparison between the behaviour of the two codes are the same.In the next slide it is shown the first resonance magnification for two different values of the conductivity.


Bad agreement region, dependent by bunch length

in PS simulations.

5


c

WLffQ

*0

0max

527103

3107528

9

0

.

.fQmax

b

nwnf c

2

00

mWL

GHz.f

3

7520

Wake-length (WL)=3m

6


The peak of the impedance from PS seems be constant to 2.9 kΩ, while the MM results scale according to the square root of the conductance ratio.

7


Conductance

[S/m]Re(Zc) [kΩ] Q QSF Re(Zc/Q) [Ω] f 0 [GHz]

fSF [GHz]

(PEC)

6∙105 MM 62 1808 1427 68.6 2.761 2.760

103 MM 2.6 72 58 70.3 2.798 2.760

6∙105 PS 2.9 56 1427 103 2.754 2.760

103 PS 2.9 60 58 96.7 2.754 2.760

Pillbox:b = 15 mm; c = 43 mm; 2L = 30 mm;βγ > 1000;

Remark: the values of the impedance peaks calculated by MM are proportional to the square root of the conductance ( ) ;The impedance calculated by means of PS without opportune trick, seems to be constant.

600

8

A reliable Q factor by Particle Studio

Increasing the WL, the accuracy in the frequency domain results improved.

The accuracy is fundamental if we are interested to determine the Q and the impedance peak. Otherwise, to determine only the modes resonant frequency, it is sufficient a very short wake because it is important only to excite the modes .

9

c

WLffQ

*0

0max

b

nwnf c

2

00

10

WL [m] Time [s]Memory [Mb]

Qsim Qmax

12 120 46 107 110

30 480 88 253 275

60 1440 157 461 550

120 4680 296 761 1100

300 25920 711 1149 2750

1000 ? >1400 ? 9167

A reliable Q factor by Particle StudioTime and memory needed to simulate a lossy pillbox(b = 15 mm; c = 43 mm; 2L = 30 mm;), by a standard PC.

It is worth of note, the large amount of memory needed to reach a relatively little Q value.

0 100 200 300 400 500 60020

25

30

35

40

45

50

55

60

=1000

Qsi

m

QMax

PS SF

0 500 1000 1500 2000 2500 3000

0

200

400

600

800

1000

1200

1400

1600

=6*105

Qsi

m

QMax

PS SF

Qsim versus Qmax of the first resonance peak, for different conductivity values.The PS simulations tend to the SF results as the Qmax increases.For very high conductivity, PS need an unacceptable amount of time and computer memory, to allow a practical employment.

11



0 500 1000 1500 2000 2500 3000-200

0

200

400

600

800

1000

1200

1400

1600

1800

2000

2200

2400

2600

2800

3000

PEC

Qsi

m

QMax

PS

0.0000 0.0002 0.0004 0.0006 0.0008 0.0010-200

0

200

400

600

800

1000

1200

1400

1600

1800

2000

2200

2400

2600

2800

3000

Qsi

m

[*m]

WL3 WL6 WL12 WL30 WL60 WL120 WL300

SX. Qsim versus Qmax of the first resonance peak, for a PEC pillbox.

DX. Qsim versus resistivity, on changing the WL value.

12

Conclusions

• Particle Studio is able to effectively operate in frequency domain.

• In the case of resistive wall structures (e.g. steel or Copper), it is necessary to simulate very long wakes in time domain to obtain reliable results for the Q factor.

• It means to perform simulations that need a large amount of computer memory and excessive time to be accomplished.

• These characteristics are more evident if compared to Mode Matching Technique performances.

13

Real model & Virtual Measurements

b=10;c=30;2L=20

Steel pillbox--------------- exact evaluation--------------- Virtual measurement

14


15


For this peak we performed simulations varying the wire radius. The results are reported in the next slide

16

Real model & Virtual Measurements(Approaching the Real Model)

Reducing the wire radius the results tend to the resonance of the real model. In order to converge, the radius becomes unfeasible.

17

Documents

Mode Matching and Particle Studio * Comparison (with a little digression on the Wire Method)