SPS Longitudinal Impedance Simulations & Measurements Update
e - cloud simulations (update)
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Transcript of e - cloud simulations (update)
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e- cloud simulations(update)
C.Octavio Domínguez, Giovanni Rumolo, Frank Zimmermann
11h February 2011 - e- cloud simulations
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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
11h February 2011 - e- cloud simulations
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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
11h February 2011 - e- cloud simulations
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SPS simulations (2003)
Goal: to reproduce this plot
R?emax?
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SPS simulations (2003)
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
11h February 2011 - e- cloud simulations
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SPS simulations (2003)
11h February 2011 - e- cloud simulations
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SPS simulations (2003)
11h February 2011 - e- cloud simulations
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SPS simulations (2003)
11h February 2011 - e- cloud simulations
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SPS simulations (2003)
Neither with 4 batches
It seems there were several sensitive changes in the code
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SPS simulations (2003)
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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SPS simulations (2003)
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SPS simulations (2003)
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”? …
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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
11h February 2011 - e- cloud simulations
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1411h February 2011 - e- cloud simulations
LCH arcs - Nb scan
From 17/1/2011: P=1 nTorr; nisteps=400
No stripes!!!
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1511h February 2011 - e- cloud simulations
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
- P=320 nTorr; 90% created e- in the beam volume
- P=32 nTorr; 100% created e- in the beam volume
- P=32 nTorr; 100% 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
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1611h February 2011 - e- cloud simulations
LCH arcs - Nb scan
For 100% of the e- generated in the beam volume no stripes at all!!!!
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1711h February 2011 - e- cloud simulations
LCH arcs - Nb scan
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1811h February 2011 - e- cloud simulations
LCH arcs - Nb scan
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1911h February 2011 - e- cloud simulations
LCH arcs - Nb scan
The pressure definitely has an impact on the stripes
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2011h February 2011 - e- cloud simulations
LCH arcs - Nb scan
Nb = 1.5·1011 ppb
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2111h February 2011 - e- cloud simulations
LCH arcs - Nb scan
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2211h February 2011 - e- cloud simulations
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
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2311h February 2011 - e- cloud simulations
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
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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
11h February 2011 - e- cloud simulations
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2511h February 2011 - e- cloud 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)
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2611h February 2011 - e- cloud simulations
LCH IR3 – Method alla D.Schulte
1 or 2 batches 2 different batch spacings Absolute flux
Total # of e- # of with e- E>10eV
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2711h February 2011 - e- cloud simulations
LCH IR3
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2811h February 2011 - e- cloud simulations
LCH IR3
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2911h February 2011 - e- cloud simulations
LCH IR3
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3011h February 2011 - e- cloud simulations
LCH IR3
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3111h February 2011 - e- cloud simulations
LCH IR3
571.01
35.1 s
s
P
P
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3211h February 2011 - e- cloud simulations
LCH IR3
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3311h February 2011 - e- cloud simulations
LCH IR3
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3411h February 2011 - e- cloud simulations
LCH IR3
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3511h February 2011 - e- cloud simulations
LCH IR3
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3611h February 2011 - e- cloud simulations
LCH IR3
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3711h February 2011 - e- cloud simulations
LCH IR3
524.01
85.1 s
s
P
P
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3811h February 2011 - e- cloud simulations
LCH IR3
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3911h February 2011 - e- cloud simulations
LCH IR3
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4011h February 2011 - e- cloud simulations
LCH IR3
114.01
85.8 s
s
P
P
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4111h February 2011 - e- cloud simulations
LCH IR3
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4211h February 2011 - e- cloud simulations
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