NLC Main Linac Vacuum System
e-mail: J. Weinberg
11/3/98
The NLC main Linac vacuum will be all metal (no elastomers) with the exception of some ceramic materials. The system will operate in the ultra high vacuum pressure range, with all components needing to be baked and/or glow discharged cleaned.
The system is broken into areas divided by sector boundaries. It encompasses the region from the Klystron window to the beamline accelerator structure.
For the purposes of the pressure profiles, to determine the locations and spacing of pumps, the following pressure requirements were used:
1. Adjacent to the Klystron window the pressure will be ,£ 5 x10-9 Torr.
2. Delay line pressure will be £ 1 x 10-8 Torr.
All pressure calculations assume an outgassing rate of 2.5 x 10-12 Torr l/s cm2 for the copper and stainless steel materials. The copper outgassing rate was taken from measurements made on the PEP II Cu chambers. The stainless steel outgassing rate is a conservative average number arrived at by experiments done at SLAC by Earl Hoyt. This number is well within the range measured by many other sources sited in vacuum literature. There is a wide variation of outgassing rates as a result of there being a wide variation of handling, cleaning and processing methods. The outgassing numbers I used are routinely achieved with our current processes.
Pressure profile calculations were performed using VacCalc written by Michael Sullivan. Each of the major areas was analyzed and the pressure profile was plotted. The following is the pump count per nonet needed to achieve the required pressures. The assumed conductance from the pump to the component can be found in the detailed calculations.
| Location | Number of Pumps per 8-pac |
Pump Size (l/s) |
Number of Pumps per Sector |
Pump Connection Type |
Klystron dublet three port combiner magic tee manifold. |
4 |
25 |
36 |
manifold TBD |
Round to Rect. Trans. before waveguide valve. |
4 |
25 |
36 |
rt. angle round to WR90 |
After waveguide valve |
4 |
25 |
36 |
3" tee |
Turret Roughing Line Pump (Hi-C manifold) |
1 |
75 |
9 |
3" tee/roughing manifold |
Bottom of penetration |
4 |
75 |
36 |
5" tee |
First run of delay line (52 meters) |
2 |
75 |
18 |
5" tee |
Second run of delay line (104 meters) |
4 |
75 |
36 |
5" tee |
Third run of delay line (156 meters) |
6 |
75 |
54 |
5" tee |
(RF Feed and RF Loads Pumped by Manifold) |
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Accelerator Structure Pumps |
12 |
25 |
108 |
RF Feed 3 port |
Total Number of Pumps per Sector |
369 |
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Each Sector will be roughed down (to 10-4 Torr, at the turbo pump) by a combination of turbo and diaphragm pumps. These roughing stations will be located at each four pack where a large vacuum manifold will be joined to the four descending RF lines. The rough down time from atmospheric pressure to turning on the ion pumps (10-3 Torr) should take about one shift (8 hours).
Each Klystron pair will be able to be isolated from the vacuum system by a waveguide valve. A beamline gate valve will isolate each sector. Gauges will be placed on both sides of every valve to ensure that it is safe to open the valves.
The Linac Drift sectors, where there is no RF, will be a .5 inch diameter Cu tube. In order to satisfy a maximum pressure requirement of 1 x 10-8 Torr, 6 l/s pumping needs to be provided every 3 meters. A parallel 6-inch diameter stainless steel manifold with pumping ports every 3 meters will provide the necessary pumping. The manifold will have a 300 l/s pump every 38 meters. Each sector will have a roughing manifold from the tunnel to the gallery for rough pumping and leak checking. There will be vacuum isolation valves and gauges every sector as in the RF sectors.
Pressure profile plots and detailed calculations are available for review by contacting Julia Weinberg at extension 3814.