[email protected] Beam-Wall Interaction in the LHC Liner: a former PhD student experience...
15
[email protected] Beam-Wall Interaction in the LHC Liner: a former PhD student experience A. Mostacci La Sapienza, University of Rome Francesco Ruggiero Memorial Symposium, 3 October 2007
-
Upload
percival-morris -
Category
Documents
-
view
212 -
download
0
Transcript of [email protected] Beam-Wall Interaction in the LHC Liner: a former PhD student experience...
Beam-Wall Interaction in the LHC Liner:
a former PhD student experience
A. MostacciLa Sapienza, University of Rome
Francesco Ruggiero Memorial Symposium, 3 October 2007
Francesco believed in the need of the SL-AP group of preserving and transmitting AP know-how. When he became group leader, training of students was explicitly declared in the SL-AP group mandate.
I had the honor to be one of Francesco’s students.
Francesco as my PhD thesis supervisorFrancesco as my PhD thesis supervisor
… I learnt from him a method.
He was always looking for the physical insight of results, first condition for them to be correct.
The first step to assess a result was to always look for a counter-example.
The need (and the pleasure) to understand in depth the issues that we were dealing with.
Constant in-depth discussions during all my thesis work.
Ability of highlighting the critical points in my work and recommending clever following steps.
Warm atmosphere for young people in the group.
LHC beam pipeLHC beam pipe
Pumping holes.
Artificial (saw-tooth) roughness.
Weldings.
Interaction between the beam and a surface (synchronous) wave in a (rectangular) beam pipe with “small” periodic corrugations.
Currents distribution in a (metallic) beam pipe whose conductivity varies with the azimuth (ultrarelativistic beam).
EM coupling, through holes, between a cylindrical and a coaxial waveguide.
LS
kQcP
b
2
bS bunch spacing
L device length
• Ohmic losses in the coaxial region:
• Holes and equivalent dipoles (Modified Bethe
Theory).
• Polarizability including also the wall thickness.
• Coupling impedance (beam stability).
• Loss Factor k() (energy losses).
• Power lost per unit length: P.
b internal radius d external radius
r.m.s bunch length
2 d
2 b
resistivity
Pumping holes in a coaxial beam pipePumping holes in a coaxial beam pipe
.
• Randomising the position of the holes does not affect the loss factor.
• Ohmic losses in the coaxial region:
• Limit of negligible ohmic losses (N equispaced holes, at distance D) :
magnetic polarizability
electricpolarizability
Pumping holes: loss factorPumping holes: loss factor
.
.
100 300 500 700
0.2
0.6
1
Plin
P
PmW/m
Length (m)
Plin no attenuation
LHC parameters
P limit value
P “exact” formula
A. Mostacci, L. Palumbo and F. Ruggiero, Physical Rev. ST-AB (December ‘99).
Pumping holes: power lost per unit lengthPumping holes: power lost per unit length
2
1.5
10.6 0.8 1
1
5
1015
W (mm)
T (mm)
Curves of constant power per unit length (mW/m)
A. Mostacci and F. Ruggiero, LHC Project Note 195 (August ‘99).
Around LHC nominal values ():
WTExpPP 75.1 0
4
0 5.1 / 42
mm
WmmWP
W slot width (rectangular)
T wall thickness
.
,
Pumping holes: impact on the liner designPumping holes: impact on the liner design
Power loss per unit length is negligible for holes of the nominal dimensions.
0 p€€€€€2
p 3 p€€€€€€€€€€2
2 p
123456
Beam pipe with azimuthally varying conductivityBeam pipe with azimuthally varying conductivity
• Cylindrical geometry (circular cross section).
• Leontovich conditions (SIBCs):S/m107
n=1
)(
b
,
.
.
.
/2 /2following an approach proposed in
F. Ruggiero, Phys. Rev. E, Vol. 53, 3, 1996
0 p€€€€€2
p 3 p€€€€€€€€€€2
2 p
0.20.40.60.8
1
0 p€€€€€2
p 3 p€€€€€€€€€€2
2 p
0.20.40.60.8
1
Stainless steel / “cold” copper
1 GHz
1 MHz
20 kHzn=1 n=1
• Ultrarelativistic limit.
• From B.C, we get a system for the coefficients (truncation).
• Semi-analytic solution.
• A posteriori check of B.C.
mm FF~
,
Stainless steel / “warm” copper
Azimuthally varying conductivity: solution (I)Azimuthally varying conductivity: solution (I)
/2 /2/2 /2
100
105
1010
1015
0
0.2
0.4
0.6
0.8
1
FrequencyBoundary conditions validity limits (no anomalous skin effect).
Room TemperatureCryogenic Temperature
Azimuthally varying conductivity: solution (II)Azimuthally varying conductivity: solution (II)
Surface currents are constant over the azimuth (at all the relevant frequencies). The losses in the welding is 5 % of the ones in the copper at room temperature (50% at cryogenic temperatures).
0 0.5 1 1.5 2-0.6
-0.4
-0.2
0
0.2
0.4
0.6
H zH
A/m
z/
• Wire method.
• f = 1 GHz, P = 1 W.
• No solution inside the conductor.
Azimuthally varying conductivity: simulation (HFSS)Azimuthally varying conductivity: simulation (HFSS)
Azimuth. varying conductivity: Q measurements (I)Azimuth. varying conductivity: Q measurements (I)
Coaxial resonator:
Q measurements in
various configurations.
F. Caspers, A. Mostacci, L. Palumbo and F. Ruggiero, LHC Project Note 493 (August ‘01).
Francesco’s legacyFrancesco’s legacy
Respect and promote young people’s work.
Intellectual honesty and rigour.
Many small and practical tips which I still pass on to our students.
Ability to give meaningful comments or suggestions on many technical aspects of several accelerator physics problems.
Francesco’s legacyFrancesco’s legacy
I am proud to have been one of Francesco’s students. I am proud to have been one of Francesco’s students.
Respect and promote young people’s work.
Intellectual honesty, rigour and attention to details.
Many small and practical tips which I still pass on to our students.
Ability to give meaningful comments or suggestions on many technical aspects of several accelerator physics problems.
![Cavity impedance measurement with PNAarpg-serv.ing2.uniroma1.it/mostacci/didattica/lab... · Copia formato diapos tiva C] Sezione. Appunti Diapositlve ITALIANO (ITALIA Power Leve](https://static.fdocuments.us/doc/165x107/5ffb9fc14aade97c9c183ec1/cavity-impedance-measurement-with-pnaarpg-serving2-copia-formato-diapos-tiva-c.jpg)
