TCTP impedance

Benoit Salvant for the impedance team

Many thanks to Elias, Hugo, Nicolas, Roderik and Stefano

22/04/2013

Foreword

• Very preliminary…

New simulations with a cleaned model• We redid some checks on the TCTP model and found that the

low frequency mode at 100 MHz is quite large.

Real

Hor

izont

al im

peda

nce

for a

disp

lace

men

t of 0

.3 m

m

Frequency (GHz)

Jaw half gap in mmRe(Z(f)) for a displacement of 0.3 mm

Impedance as a function of jaw half gap (not accounting for beta)

1 2 3 4 5 6 7 8 9 10 110.00E+00

5.00E+05

1.00E+06

1.50E+06

2.00E+06

2.50E+06f(x) = 10502898.897128 x^-2.09672127440883

jaw half gap in mm

horiz

onta

l im

peda

nce

in O

hm/m

270 kOhm/m at 5 mm half gap and 80 kOhm/m at 10 mm half gap

What was the prediction in 2011

I used 45 kOhm/m and beta function of 635 m.

I am sorry I used an incorrect formula from frequency domain simulations to get Rs and it is on this value (45 kOhm/m) that we based our recommendation.

(impedance meeting Oct 17th 2011)

Conclusions of the impedance team at that time (Oct 17 2011)

• New design already generates very large intensity effects below 3 mm half gap (due to new taper).

• Open plate gap without ferrite seems unacceptable from power loss point of view.

• Both other choices present risks from impedance point of view:– RF fingers:

• Impedance of fingers seen by the beam?• no damping of longitudinal modes• Contact resistance not known

– ferrite:• Decreasing the gap is not an option• Increase of low frequency transverse impedance (before 100 MHz)• Low frequency transverse modes are damped but present• Problem of knowing exactly the ferrite material and its specs

It will be difficult to guarantee that the new design is at least as good as the old one…

Parameters given by Nicolas and Roderik (B1H)

Nicolas 7TeV 55 cm (B1H)TCTH.4L2.B1 TCTH.4L5 TCTH.4L8 TCTH4L1

beta 78 1569 97 1569avbeta 70 70 70 70

half gap (mm) Z(Ohm/(0.3mm)) Z(Ohm/m)2 637 2.12E+063 350 1.17E+064 192 6.40E+055 112 3.73E+05 4.16E+05 5.17E+056 75 2.50E+057 50 1.67E+058 40 1.33E+059 30 1.00E+05

10 25 8.33E+04 1.87E+06 1.87E+06

Total horizontal real contribution at 100 MHz (B1H): 4.7 MOhm/m (about 20 % of the total real impedance at that frequency)

Parameters given by Nicolas and Roderik (B1V)

Total vertical real contribution at 100 MHz (B1V): 5.5 MOhm/m(about 23 % of the total real impedance at that frequency)

Nicolas 7TeV 55 cm (B1V)TCTVA.4L2.B1 TCTVA.4L5 TCTVA.4L8 TCTVA4L1

beta 89 645 89 645avbeta 70 70 70 70

half gap (mm) Z(Ohm/(0.3mm)) Z(Ohm/m)2 637 2.12E+063 350 1.17E+064 192 6.40E+055 112 3.73E+05 4.75E+05 4.75E+056 75 2.50E+05 2.30E+06 2.30E+067 50 1.67E+058 40 1.33E+059 30 1.00E+05

10 25 8.33E+04

What was the prediction in 2011

I used 45 kOhm/m (from the incorrect formula) and beta function of 635 m.Using the same scaling and with the corrected real impedance from time domain, we see that the first transverse mode would be damped by ~10 A in the octupoles.

To be checked with the codes of Nicolas and Alexey and with Headtail multibunch

(impedance meeting Oct 17th 2011)

roderik beta *=55 cm

roderik beta *=40 cm roderik beta *=30 cm

TCTH TCTVA TCTH TCTVA TCTH TCTVAbeta 1575 639 2167 879 1172 639avbeta 70 70 70 70 70 70

half gap (mm) Z(Ohm/(0.3mm))Z(Ohm/m)

2 637 2.12E+063 350 1.17E+064 192 6.40E+05 5.84E+065 112 3.73E+05 4.69E+066 75 2.50E+05 2.28E+067 50 1.67E+05 3.75E+068 40 1.33E+05 4.13E+069 30 1.00E+05 1.67E+06

10 25 8.33E+04

With these more pesssimistic settings (8 sigma),the impedance at 100 MHz would be multiplied by ~2 to 3

Parameters given by Roderik for more pessimistic gaps

What to do next? • Continue to validate the values obtained for the 100 MHz transverse mode

• Check the impact of this transverse mode at 100 MHz on beam dynamics– Analytical codes of Alexey and Nicolas– Headtail simulations

• Assess the impact of the other higher order modes

• Understand why the frequency domain data are still off by a large factor (new release of CST enables computing the impedance with ferrite)

• reassess heat load with the new models (original topic of this talk), but the error does not affect the computation of power loss.

Wake decay for d=5 mm and 60 m