1. NLC - The Next Linear Collider Project Three Important Questions Studied for a Linear Collider & Putting in Exergue the Importance of NEG xxx – xxx November, 2003 Frédéric Le Pimpec

2. NLC - The Next Linear Collider Project FLP 2 Outlook 1.Vibrations caused by Near Field Sources inside the LINAC Components  Deteriorate the Luminosity 2.Acoustic Localization of RF-Breakdown and Autopsies of RF Structures  Length of the LINAC (Energy of particles) 3.Measures of the Secondary Electron Coefficient of Technical Surfaces (TiN, TiZrV) – Electron Cloud  Deteriorate the Luminosity 4.Molecular Desorption Induced by Electronic Transitions in Technical Surfaces – NEG St707  Background noise inside detectors

3. NLC - The Next Linear Collider Project FLP 3 Next Linear Collider Final focus : beam size of the beam spot ~  x/  y :250nm* 3nm Vibrations must be minimalized over the 30km – Beam size ~  m Dissipated Heat by the RF power (4kW/m): => Need of large water cooling flow (1 l/s at 70 MV/m) Tolerances on vibrating structures is rather loose (  m) More Troublesome: The coupling, even small, between structures and the quadrupole (14 nm tolerance)

4. NLC - The Next Linear Collider Project FLP 4 Sensors Girder Structure vibration tests at NLCTA 1.8m Long RF structure DDS1 (~100 Kg) Installed on Hollow Aluminum girder Girder is connected to concrete block The block is installed on rubber balls (~14Hz resonance) to isolate from noisy NLCTA floor Nominal total flow is 16GPM (~1 liter/s) Sensors: four piezo-accelerometers; one piezo-transducer to measure water pressure fluctuations (not shown)

5. NLC - The Next Linear Collider Project FLP 5 Vibration setup test in SLD Water vessel SLD pit. Gravity fed experiment Study vibration of the Structure - girder due to internal turbulence using gravity-fed water Study vibration transmission to quadrupole in a structure-quad assembly

6. NLC - The Next Linear Collider Project FLP 6 Amplitude of vibration in function of the water flow inside a structure nominal Result with a Gravity fed system Conventional cooling System : Result

7. NLC - The Next Linear Collider Project FLP 7 FNAL geoph & piezo SLAC piezo Vibration at FNAL : Primary vacuum Structure (60cm)-support SLAC Piezo FNAL Geophone FNAL STS-2 Strongback Water IN

8. NLC - The Next Linear Collider Project FLP 8 In Summary (1/2): Vibration of RF structure-girder with NLCTA water supply –And found that external turbulence is important Vibration of RF structure-girder cooled with gravity fed water –And found that internal turbulence gives only 1/3 of the total effect Vibration coupling from RF structure to Linac quadrupoles –And found that coupling is small – on a percent level (~2%) Primary vacuum in the system –Does not affect the vibration level

9. NLC - The Next Linear Collider Project FLP 9 In Summary (2/2): Vibration of a structure-support set in Aluminium and SS, water cooled by FermiLab water system –Al support is noisier than a Stainless Steel support Made ANSYS simulations –Further optimization of girder likely possible Klystrons RF Generated pulse in X-band (11.424 GHz) accelerating structure and coupling to the floor –Effect due to RF pulses is negligible compared to induced vibrations by cooling water –Vibration transfer, by the floor, between a Klystron gallery (8 pack type) and the LINAC is negligible (noise)

10. NLC - The Next Linear Collider Project FLP 10 Acoustic Localization of RF Breakdown

11. NLC - The Next Linear Collider Project FLP 11 1 mm H90VG5R : Historic of RF arcing and localization + e-e- Al

12. NLC - The Next Linear Collider Project FLP 12 1 2 3 4 Input Couplers - “pulse heating” local Horn at the base of the waveguide side. Cracks observed solely on RA; Stress? voids inside the lattice? 50  m Typical for edges on the cavity side: T53VG3R & RA Sharp edges can be back bombarded by ions ?

13. NLC - The Next Linear Collider Project FLP 13 Examples of particles distribution inside cavities 60% of particles < 1  m of diameter

14. NLC - The Next Linear Collider Project FLP 14 In summary No proven link between particles contamination and breakdowns. - Results are different for superconducting RF, DC breakdown at room temperature cf. Cornell & Windowtron experiment(SLAC). However particles are still players ! H90VG5R & H90VG3N : contamination by a foreign element is responsible of quasi-systematic breakdown. - Areas of low E field (7 MV/m – 65MV/m) but high H (0.6MA/m – 0.03MA/m). Arcing depends : RF Pulse length ? Energy level ? E or H field ?… Combination ? New design for the input couplers; rounded edges design

15. NLC - The Next Linear Collider Project FLP 15 Thin film TiN – TiZrV (NEG)Thin film TiN – TiZrV (NEG) measure SEY, reproducible results. Test of different surface treatment : Ionic conditioning, electronic, bakeout, air baking (CERN), Free radical exposure Freon11 (CERN), O, H, N … Measure of the energy spectrum of the SEY at low energy < 40eV Results will be used to improve electron clouds simulation models NEG SEY results after 43 days of vacuum exposure does not seem to be in agreement with CERN ones (  =1.35) Secondary electron yield (SEY):

16. NLC - The Next Linear Collider Project FLP 16 My Three most Important Questions for a Linear Collider : Conclusions - Support design for RF structures or quadrupoles is important, but also the design of the cooling system and its components. RF generating components are not problematic (vibration wise) as long as they are installed on an adequate anti-vibratory structure. An independent Klystron gallery does not guarantee sufficient vibrations attenuation. - The technique of acoustic localization for breakdown is complementary, and could be supplementary, of the RF technique. - Autopsies have revealed that the level of vacuum cleanliness for the structures must be comparable to the one in superconducting RF, even perhaps at the level of semi-conductor industry. Surprising ? - Surface treatment to deal with the electron cloud issue, LHC, NLC, KEK B, PEP II… Not New ! But new ways, NEG films. As we talked of NEG…

17. NLC - The Next Linear Collider Project FLP 17 NEG : Advantages – Drawbacks non-exhaustive List for an accelerator Distributed Pumping (S(l/s) increase with the Roughness) Low activation Temperature, TiZrV - 180°C Low initial ESD / PSD compared to standard technical surfaces– ISD it depends (Light or heavy ions and their energies) Low  (SEY)– Electron cloud solution Life Cycle : Number of possible activation Pumping Capacity : depends of the thickness Film stability in time on the substrate Require activation Does not pump CH 4, unless hot 110°C - St707 or ionized Inserted “linear” pump Inserted “total” pump (TiZrV) Surface pump / diffusion barrier Lump pumping Cf. Benvenutti Future Sputtering - flaking Wakefield

18. NLC - The Next Linear Collider Project FLP 18 Dynamic Vacuum (300K) Desorption Coefficient  Photodésorption Ionodesorption Molecular density coming From the sides Electrodesorption Linear Pumping NEG Molecular density Thermal Outgassing Multipacting Fct (SEY…)

19. NLC - The Next Linear Collider Project FLP 19 Photodesorption at EPA (1997-1999)  c = 45 eV and 194 eV E e - = 308 MeV  = 3.7 10 16 photons.s -1. E e - = 500 MeV  = 1.08 10 17 photons.s -1 Roughness NEG St 707 [Zr (70%) V (24.6%) Fe (5.4%)] ~ 60 x R SS Exposed Surface 119 cm 2 ; directly irradiated ~5 cm 2.. NEG St 707 ???? No access to TiZr (1998)

20. NLC - The Next Linear Collider Project FLP 20 PSD and/or ESD Measurement Limitation Photodesorption coefficient are corrected by a Monte Carlo which take care of the system geometry (from the target to the conductance). Coefficient  under-estimated Correction for an activated NEG Coefficient  over-estimated, OK for ESD Activation  Target is pumping  Need to correct the measured  Outgassing flux of a baked RGA (80% H 2 ) Q ~ 10 -9 Torr.l.s -1 Parasitic molecular desorption - RGA resolution limit Molecular desorption induced by reflected photons from the target - Important for an activated NEG Q paras ~ 0.5 Q NEG100% Electronic Target Current Limitation, Thermal outgassing H 2

21. NLC - The Next Linear Collider Project FLP 21  CO at  c = 194 eV CO Sat ( 13 C 18 O) CO Sat ( 13 C 18 O) 13 C 18 O SS NEG 0% NEG 100 % An activated NEG desorbs less H 2 CO CH 4 CO 2 than a baked Stainless Steel. A saturated NEG desorbs more CO than a baked Stainless Steel

22. NLC - The Next Linear Collider Project FLP 22 Electrodesorption E e- = 300 eV Roughness NEG St 707 [Zr (70%) V (24.6%) Fe (5.4%)] ~ 60 x R SS Irradiated NEG Surface ~15 cm 2  = 1.6 10 15 élect.s -1. = 0.25 mA T max = 52 °C NEG St 707 !!!! No Access to TiZr or TiZrV (1998-2000)

23. NLC - The Next Linear Collider Project FLP 23  CO at E e- = 300 eV Cu NEG Saturated by CO NEG Sat ( 13 C 18 O) CO NEG Sat ( 13 C 18 O) 13 C 18 O NEG 100 % CO An activated NEG desorbs less H 2 CO CH 4 CO 2 than a 120 °C baked OFHC Cu surface. A saturated NEG desorbs less *C*O than a 120 °C baked OFHC Cu surface

24. NLC - The Next Linear Collider Project FLP 24 Conclusion : NEG from none to everywhere… NEG St 707 – TiZr and TiZrV activated at 100% photodesorbs and electrodesorbs less gas than a baked standard technical surface. Roughness and porosity of St707 ! Diffusion under photon or electron bombardment of surface atoms ! 2 hypothesis combination – Smooth thin film can be of used to test those hypothesis Molecular desorption in 13 C 18 O or CO is relatively low despite the quantity of gas deposited onto the surface !! (Identical observation with photons) NEG study in the vacuum group – Competition with the Material group  Better NEG  LHC (TiZrV)… Experimental areas With advantages which of today are undeniable … NEG MATERIAL of the FUTUR LHC – NLC – RHIC (60m) – SOLEIL …

25. NLC - The Next Linear Collider Project Extra Transparents

26. NLC - The Next Linear Collider Project FLP 26 Raison pour autopsier les structures RF?! T53VG3R : Autopsie du coupleur d’entrée (IC- horns). Contamination par des particules de MnS (ou métal- soufre) T53VG3RA : Problème accru au niveau de l’IC (horns). Contamination par des particules de MnS H90VG5R : Une cavité RF, sur l’ensemble de la structure montre un niveau de claquage anormal – Débris d’Al H90VG3N : Une cavité RF, sur l’ensemble de la structure montre un niveau de claquage anormal – Particule d’acier

27. NLC - The Next Linear Collider Project FLP 27 An activated NEG desorbs less H 2 CO CH 4 CO 2 than a baked Stainless Steel SS Cu Présentation des résultats Photodesorption at EPA : 11 mrad incidence  c = 194 eV

28. NLC - The Next Linear Collider Project FLP 28 Preliminary evaluation for cooling induced vibration (nominal flow 1l/s) RF structure vibration: –About 110nm if fed with quiet water (Slide 8) –About 350nm mostly due to turbulence in supplying (Slide 4) pipes for water system similar as in NLCTA –About 150nm if fed with SLD water (Slide 8) SLD water system seems similar as NLCTA EM quad receive –About 13nm (18 2 -12 2 ) 0.5 due to coupling to structure if structure fed with SLD water; (2.4nm with quiet water; >30Hz) (Slide 8-9) 24nm > 4Hz Total vibration (if all sources are independent) for EM quad with NLCTA-like water system (cf Nanobeam talk): 8.3nm  all “if”, all simplifications and difference from the real system