Preliminary calculations for the vacuum system of ELENA

R. Kersevan TE/VSC-IVM – 21/6/2012

The vacuum sectors, the position of vacuum pumps, flanges, and bellows have been tentatively outlined based on the lattice information available (P. Belochitski, e-mail 21/2/2012).

The following assumptions have been made:• vacuum chamber: 80 mm ID (84 mm OD) in the 6 straight

sections; 140x80mm2 rectangular cross section at BMs; • Flanges: ConFlat flanges, ~ 30 mm long. width (incl. space

for bolts/nuts)• Bellows: hydroformed bellows, 70 mm long (if welded); add

~ 30 mm for any additional flange• Minimum 250 °C bake-out capability of ALL components

Preliminary calculations for the vacuum system of ELENA - R. Kersevan TE/VSC – 21/6/2012

Symbols: flange; bellows; vacuum pump; VVS: ~ 80 mm flange-to-flange;

Preliminary calculations for the vacuum system of ELENA - R. Kersevan TE/VSC – 21/6/2012

Pump “Tees”: vertical tube same ID/OD as for the beam pipe. Height 100 mm from beam axis; Supports for beam pipe and pumps: to be decided. Each dipole has one 1000 l/s NEG/Ion-pump (SAES) and two line-of-sight extensions for the two dipoles on the e-cooling section; All gauges to be installed on pumps’ necks and Tees. The two sections on this page have limited/insufficient space for bellows, and no space for pumping on the e-cooling one.

Preliminary calculations for the vacuum system of ELENA - R. Kersevan TE/VSC – 21/6/2012

Preliminary calculations for the vacuum system of ELENA - R. Kersevan TE/VSC – 21/6/2012

First integration essays (S. Maridor, L. Faisandel, march 2012):

Preliminary calculations for the vacuum system of ELENA - R. Kersevan TE/VSC – 21/6/2012

“NEXTorr D300” integrated NEG/Ion-pump (SAES Getters, Milan)

Preliminary calculations for the vacuum system of ELENA - R. Kersevan TE/VSC – 21/6/2012

Stray Magnetic Field of ion-pump on NEXTorr D100 (SAES Getters, Milan)

Preliminary calculations for the vacuum system of ELENA - R. Kersevan TE/VSC – 21/6/2012

First calculations of pressure profiles (work in in progress…):Uniform H2 outgassing, at rate giving <P>=3.0E-12 Torr (baseline pressure)

Installed Pumping Speed: 1000 l/s at each Dipole Chamber + 290 l/s at each straight section (NEG/ion-pump combination) + NEG-coating on 100% of internal surfaces (sticking coeff H2 = 8.0E-3 34,000 l/s at 9.66 m2)

Preliminary calculations for the vacuum system of ELENA - R. Kersevan TE/VSC – 21/6/2012

H2 outgassing at rate giving <P>H2=3.0E-12 Torr (baseline), 1.162E-7 Torr·l/s, i.e. 1.203E-012 Torr·l/s/cm2 , reasonable for a baked-out stainless steel chamber.

Installed Pumping Speed: 1000 l/s at each Dipole Chamber + 290 l/s at each straight section (NEG/ion-pump combination) + NEG-coating on 100% of internal surfaces (sticking coeff H2 = 8.0E-3 34,000 l/s at 9.66 m2)

Preliminary calculations for the vacuum system of ELENA - R. Kersevan TE/VSC – 21/6/2012

How much does the NEG coating contribute, even at a relatively low value of 8.0E-3?

The NEG-coating lowers the average pressure by > 80%! It pumps >85% of the H2 gas load.

Without it we would need a ~ 10x lower total outgassing load, which could be problematic to achieve with localized components such as un-coated inj/extr

kickers, diagnostics, etc…

Preliminary calculations for the vacuum system of ELENA - R. Kersevan TE/VSC – 21/6/2012

Zero Pumping Speed on Sect.1 Straight Section Pump: 5% increase of <P> at Sect.1

Switch-off or malfunction of SS1 NEG/Ion-Pump means ~ 5% pressure rise DPH2 at Sect.1, i.e. DPH2< 1% over complete ring.

Preliminary calculations for the vacuum system of ELENA - R. Kersevan TE/VSC – 21/6/2012

What if we have a localised increase of outgassing at one location, 10% of total thermal load?

Pressure bump distributed along dipole 1 chamber and preceding SS6. Total average pressure rise, DPH2 ~ 45%, still manageable?

Preliminary calculations for the vacuum system of ELENA - R. Kersevan TE/VSC – 21/6/2012

Next: effect of non-getterable gases (CH4) on pressure profile. No pumping from NEG coating or pump, only 12x 10 l/s from integrated ion-pumps

Flat pressure profile (blue line), equilibrium pressure ~ 3.9E-12 Torr

Preliminary calculations for the vacuum system of ELENA - R. Kersevan TE/VSC – 21/6/2012

Conclusions

• An initial draft of the vacuum chamber geometry compatible with the magnetic lattice has been made by the integration team

• The corresponding 3D model for running the vacuum code Molflow+ has been made, with 6-fold symmetry (2-fold symmetry with longer/shorter straight-sections will be implemented soon)

• An 80 mm ID round pipe geometry for the 6 straight sections, and a 140x80 mm2 (HxV) rectangular cross-section for the 60° dipole magnet chambers has been chosen

• No injection/extraction elements have been modeled yet, waiting for them to be drafted• Pumping of the ring is mainly accomplished by 100% NEG-coating, with additional help

from NEG/Ion-Pump combination pumps (NEXTorr technology, SAES Getters, Milan)• The pressure profiles obtained by Test-Particle Montecarlo simulations seem to give

results compatible with the baseline average pressure of 3.0E-12 Torr, provided:• the totality of the internal surface of the chamber (9.7 m2) be NEG-coated• localized leaks or increased outgassing be limited to 10-20% of total thermal baseline

outgassing • no multiple failure of pumps take place simultaneously

• No contribution to the gas load within the ring due to back-streaming of gases from experimental lines has been considered yet, pending decision by experimental line management on window or windowless set-up (likely requiring full bakeability as well)

• Detailed 3D models will be created for the ring geometry and the experimental beamlines as soon as all related components are drafted. Pumping philosophy for the experimental beamlines will then be chosen.

More to come soon… and thank you all for your attention!