Vacuum Simulations for ELENA’s LNR-01 R. Kersevan IIC Meeting 9/6/2015

Recent measurements in VSC premises have shown that the ELENA kicker tank and magnet is far from the specified pressure value, due to an extremely high outgassing (possibly virtual leaks in trapped volumes of the magnet), and also to the fact that the purpose-built NEG-coated plates inserted on the two bulging flanges become saturated during the long bake-out/activation phase; This short and necessarily preliminary presentation aims at showing how an improved pumping on the kicker tank may help attaining a lower pressure along the LNR-01 ring section; The values presented here should NOT be taken at face value: they should be used as an inter-comparison for different configurations… baseline pumping vs upgraded pumping, with and without NEG coating on the neighbouring chambers;

The critical section LNR-01, with the “Y” septum chamber, BTV, kicker tank, BPM, and connecting bellows, as been modelled and analysed with Molflow+; The figure on the left shows the geometry; the pulses kicker magnet is highlighted in red; An outgassing rate of 2E-12 mbar*l/s/cm2 has been assumed for the chambers’ walls; 4E-12 for the surfaces representing bellows; 2E-11 for the surfaces representing the magnet; The kicker chamber shown here represents the updated version with 2000 and 2100 l/s NEG pumps

Distributed pumping (NEG-coating): Vacuum Gauge (CCG) Lumped pumps: 1x 500 l/s NEXTorr at BTV; 2000 l/s CapaciTorr at bottom kicker flange (was 500 l/s StarCell ion-pump); 2100 l/s ZAO pump at kicker side port; Pumping at boundaries (LNI, left side of LNR-01, and right of the BPM: either 300 l/s or 500 l/s; ---*-- Distributed pumping (NEG-coating): On “Y” chamber, BTV body, BPM; No coating on bellows; No coating on kicker tank (coated panels are assumed to be saturated);

Distributed pumping (NEG-coating): Baseline case: NEXTorr D1000 on side port of kicker; 500 l/s StarCell ion-pump at bottom flange of kicker; 3x 300 l/s at boundaries; ---*-- Distributed pumping (NEG-coating): On “Y” chamber, BTV body, BPM; No coating on bellows; No coating on kicker tank (coated panels are assumed to be saturated);

NO Distributed pumping (NEG-coating): Baseline case: NEXTorr D1000 on side port of kicker; 500 l/s StarCell ion-pump at bottom flange of kicker; 3x 300 l/s at boundaries; ---*-- NO Distributed pumping (NEG-coating):

WITH Distributed pumping (NEG-coating): Baseline case: NEXTorr D1000 on side port of kicker; 500 l/s StarCell ion-pump at bottom flange of kicker; 3x 300 l/s at boundaries; ---*-- WITH Distributed pumping (NEG-coating):

NO Distributed pumping (NEG-coating): Upgraded Pumping: CapaciTorr 2000 l/s; ZAO 2100 l/s; ---*-- NO Distributed pumping (NEG-coating):

Upgrade pumping and NEG-coating on “Y”, BTV body, BPM ---*-- WITH Distributed pumping (NEG-coating):

Conclusions An improvement of the installed pumping speed from 500+1000 l/s (nominal, for H2) to 2000+2100 l/s on the kicker tank does not bring a proportional improvement on the average pressure calculated along the antiproton beam trajectory; The main reason for this seems to be the reduction of the corresponding effective pumping speed caused by the geometry of the magnet and the tank, which creates rather narrow passages for the H2 desorbed in large part by the magnet; The pressure bump is localised inside the kicker tank; The pressure measured by the gauge placed on top of the tank should be a bit higher than the average pressure along the magnet; Work to do: try to match precisely the pressures recorded during the lab tests;

SOLID surfaces at the flanges of the kicker tank; “SEPARATED CHAMBERS” ---*-- SOLID surfaces at the flanges of the kicker tank; Outgassing and pumping as per slide 9;