Dynamic vacuum zeroorder Dynamic vacuum requirement H 2

Dynamic vacuum zero-order Dynamic vacuum requirement H 2 and CO 2 partial pressures < 1 n. Torr (G. Rumolo and D. Schulte) BD meeting Sergio Calatroni - 24. 3. 2010 1

From Cedric Based on outgassing (H 2 O): 10 -10 mbar. l. sec-1 cm-2 for 100 h pumping (Paolo’s vacuum course: 2*10 -11 for 100 h) !!!! BD meeting Sergio Calatroni - 24. 3. 2010 2

Structure test layout e- on faraday cup BD meeting Sergio Calatroni - 24. 3. 2010 3

Model • Only one cell is modelled • Electrons are field-emitted, then accelerated and distributed uniformly in the cell • Dynamic vacuum by ESD: desorbed molecules fill the whole cell volume, or only the “beam channel” - are uniformly e • No pumping distributed inside the cell e- on faraday cup Cell [mm] Ext diam Iris diam Length BD meeting dimensions e- on faraday cup outer area beam area copper area volume [mm 3] beam channel [mm 3] 20 1086. 99 28. 27 1030. 44 2293. 36 206. 40 6 volume [liters] beam channel [liters] 7. 3 2. 29 E-03 2. 06 E-04 Sergio Calatroni - 24. 3. 2010 4

Farady cups cuurrent [µA] Faraday cup measurements - T 18_VG 24_Disk_2 - KEK Eacc [MV/m] BD meeting Sergio Calatroni - 24. 3. 2010 5

ESD data • No much data on unbaked copper (N. Hilleret, CAS Vacuum School 2006 - G. Vorlaufer CERN-Thesis (2002) ) BD meeting Sergio Calatroni - 24. 3. 2010 6

Data Total e- current [A] Pulse duration [ns] 1. 00 E-04 Total charge [C] 200 ESD coefficient for H 2 Total H 2 molecules (unbaked copper) per RF pulse 2. 00 E-01 2. 00 E-11 1. 12 E-08 ESD coefficient for CO 2 Total CO 2 molecules (unbaked copper) per RF pulse 2. 73 E+08 ESD coefficient for H 2 Total H 2 molecules (copper baked 250 C) per RF pulse 1. 30 E-02 ESD coefficient for H 2 Total H 2 molecules (copper baked 300 C) per RF pulse 3. 00 E-03 7. 29 E-10 BD meeting 7. 29 E+06 G. Vorlaufer CERN-Thesis (2002) 3 -30 times maximum allowed 250 C / 24 h Benvenuti et al LEP 2 94 -21 3. 74 E-09 1. 68 E-10 ESD coefficient for CO 2 Total CO 2 molecules (copper baked 300 C) per RF pulse 1. 60 E-03 107 pulses to start conditioning 8. 11 E-09 3. 37 E-10 1. 37 E+07 4. 42 E+08 3. 74 E-08 2. 73 E+07 4. 56 E+09 10 -100 times maximum allowed ESD coefficient for CO 2 Total CO 2 molecules (copper baked 250 C) per RF pulse 0. 027439024 1. 25 E-07 3. 37 E-09 5. 92 E+07 6. 00 E-03 1. 25 E+08 Equivalent pressure at RT (total volume) at RT (beam channel) 9. 11 E+08 6. 00 E-02 Solid angle (one Total electrons Number of electrons cell, one side) on copper Dose per pulse (e- /cm 2) Mathewson-JVSTA 15(1997)3093. pdf 1. 87 E-09 8. 98 E-11 9. 98 E-10 Sergio Calatroni - 24. 3. 2010 7

Molecule speed H 2 Atomic mass Mass [kg] Molecule speed @ 300 K displacement in [m/s] RF pulse [m] 2 3. 32 E-27 1579. 232695 3. 16 E-04 H 2 O 18 2. 988 E-26 526. 4108982 1. 05 E-04 CO 28 4. 648 E-26 422. 0676912 8. 44 E-05 CO 2 44 7. 304 E-26 336. 6935418 6. 73 E-05 BD meeting Sergio Calatroni - 24. 3. 2010 8

Mauro’s vacuum course BD meeting Sergio Calatroni - 24. 3. 2010 9

Water desorption due to pulsed heating • • RF pulse duration = 10 -7 s >> =1/ 0 = 10 -13 s Desorption depends on the sojourn time as a function of temperature Pulse heating: 300 K 350 K ( T ≈ 50 K) Sojourn time: 6 s 0. 06 s Dynamic desorption : 10 -11 mbar. l. sec-1 cm-2 10 -9 mbar. l. sec-1 cm-2 Desorbed flux [mbar. l. sec-1 cm-2] 1. 00 E-09 BD meeting Pulse duration [s] 2. 00 E-07 Specific amount Total amount [mbar. l. cm-2] [mbar. l] 2. 00 E-16 Sergio Calatroni - 24. 3. 2010 2. 06 E-15 Equivalent pressure cell [mbar] 8. 99 E-13 Equivalent pressure beam [mbar] 9. 98 E-12 10