e - cloud simulations (update)

e- cloud simulations(update)

C.Octavio Domínguez, Giovanni Rumolo, Frank Zimmermann

11h February 2011 - e- cloud simulations

2

Contents

1) SPS simulations (2003) reproduction

I. Method

II. Partial conclusions

2) LHC simulations

III. Nb scan with higher seed pressure

IV. Parameter studies at the LHC IR3: State of the art


3

Contents


I. Method


2) LHC simulations




4

SPS simulations (2003)

Goal: to reproduce this plot

R?emax?


5


No agreement at the beginning (especially for 150 G) Let’s try whit those plots:

Parameters: sz=0.225 m;eNx=(1.66Nb + 1)mm1 batch, 72 bunches, 25 nse- cloud monitorP=9 nTorrR=0.3, 0.5, 0.7; emax= 230, 260

No agreement yet


6



7



8



9


Neither with 4 batches

It seems there were several sensitive changes in the code


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Nb (·1011 ppb) 1.4; 90% 1.6; 90% 1.4; 100% 1.6; 100%

0.2 0.0 0.0 0.0 0.0

0.4 0.0 4.56 0.0 4.104

0.6 8.512 8.968 8.56 8.816

0.8 11.552 11.552 11.248 11.552

1.0 13.376 13.528 12.768 13.68

1.2 15.048 15.2 14.896 15.048

1.4 16.872 16.568 16.568 16.56811h February 2011 - e- cloud simulations

Only 100 G simulations(No multipacting at 150 G!)

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12


Conclusions

The code has suffered sensitive changes along these years mainly due to the correction (by G.Belodi) of the bug in the model for the angular dependence of dmax

“100% option” seems to agree slightly better with measurements (?)

We cannot simulate yet the measurements accurately enough

BUT: We see the stripes We can trust our results not enough seed pressure in the Nb scan study at the LHC arcs? Was the inter-bunch time step too “coarsy”? …


13

Contents


I. Method


2) LHC simulations





LCH arcs - Nb scan

From 17/1/2011: P=1 nTorr; nisteps=400

No stripes!!!


LCH arcs - Nb scan

• The Nb scan at the LHC arcs was repeated for 4 different cases:

- P=32 nTorr; 90% created e- in the beam volume




• For all cases: nbstep=200 and nistep=2500 (not so course; nistep(fine)=7462)

•Other parameters used were: dmax=2.6, R=0.5, emax=230 eV


LCH arcs - Nb scan

For 100% of the e- generated in the beam volume no stripes at all!!!!


LCH arcs - Nb scan


LCH arcs - Nb scan

The pressure definitely has an impact on the stripes


LCH arcs - Nb scan

Nb = 1.5·1011 ppb


LCH arcs - Nb scan


LCH arcs - Nb scan

Even if we don’t know the exact energy of the e- at which the effects in the walls start to be important, the scrubbing strategy shouldn’t depend on this parameter


LCH arcs - Nb scan

Conclusions

• The stripes formation depends radically on the assumed amount of e- created in the beam volume

• Pressure shows also an effect in the position as well as in the shape of the stripes

• The scrubbing strategy should not depend on the energy threshold for e- impinging the walls

24

Contents


I. Method


2) LHC simulations





LCH IR3

Spacing [ms] Pressure at VGPB.2.5L3.B [mbar] Pi-P38.85ms [mbar] Pi/P1ms

38.85 4.00E-08 0.00E+00 0.00E+00

28.85 4.80E-08 8.00E-09 3.81E-02

8.85 6.40E-08 2.40E-08 1.14E-01

1.85 1.50E-07 1.10E-07 5.24E-01

1.35 1.60E-07 1.20E-07 5.71E-01

1 2.50E-07 2.10E-07 1.00E+00

b

a

b

aii P

PP

Measurement

ECLOUD (from qlosswh.data)


LCH IR3 – Method alla D.Schulte

1 or 2 batches 2 different batch spacings Absolute flux

Total # of e- # of with e- E>10eV


LCH IR3


LCH IR3

571.01

35.1 s

s

P

P


LCH IR3


LCH IR3

524.01

85.1 s

s

P

P


LCH IR3


LCH IR3

114.01

85.8 s

s

P

P


LCH IR3


LCH IR3

Work to do:

• Identify better the interesting regions for each batch spacing

• Make finer grids

• Try to do simulations setting as seed pressure the value from the measurement for each batch spacing

• Cross the fingers and hope that we get a good agreement, .

Preliminary conclusions (maybe too optimistic?):

• 2.1 < dmax < 2.3

• 0.4 < R < 0.7

e - cloud simulations (update)

Documents

e cloud simulationsonly

e cloud simulations1411h

e cloud simulationsupdate

lhc arcs

nse cloud monitorp

lhc simulationsnb scan

nb scan study

lhc ir3