1. page The ESS Proton Source & LEBT WP6-WU2 L. Celona Warm Linac meeting, 06 July 2011, INFN-LNS, Catania WU 1 – Management (S. Gammino) WU 2 – Proton Source & LEBT (L. Celona) WU 3 – RFQ (B. Pottin) WU 4 – MEBT (I. Bustinduy) WU 5 – DTL (A. Pisent) WU 6 – Prototype & Tests (S. Gammino) 1

2. page WU2 – Proton source & LEBT 2 Achieved -Electron enrichment investigations with passive methods with VIS. -Emittance measurements with typical ESS parameters. In preparation/progress - Tests of new plasma heating methods with electrostatic Bernstein waves using a plasma trap. - Preparation of tests with carbon nanotubes to improve the space charge compensation. Delayed -Magnetic system design will start after the tests of EBW heating (TWTA failure! Exp. Sep. 2011), provided that additional manpower may be hired. Achieved -Electron enrichment investigations with passive methods with VIS. -Emittance measurements with typical ESS parameters. In preparation/progress - Tests of new plasma heating methods with electrostatic Bernstein waves using a plasma trap. - Preparation of tests with carbon nanotubes to improve the space charge compensation. Delayed -Magnetic system design will start after the tests of EBW heating (TWTA failure! Exp. Sep. 2011), provided that additional manpower may be hired. WU6 – Prototype & Tests

3. page WU2 – Proton source & LEBT 3 Large currents (60-90 mA) Low emittance (0.2 to 0,3 π mm mrad) Long lifetime (>> 1 mo.) High reliability (> 99%) Pulsed operation (2.86 ms - 14 Hz) Short pulse rise time (100 ns) Robust extraction system LEBT optimization (know-how available)

4. page WU2 – Proton source & LEBT 4 Loss fluxes Insulator embedded the walls - +++ ++ + ++ - - - - - - - The insulators cannot allow to the currents to flow along the chamber walls

5. page WU2&6 – Proton source & Tests 5 VIS (50mA -  =7mm)

6. page WU2&6 – Proton source & Tests 6 SILHI 90mA  =9mm

7. page BOOSTING OF EBW-heating to overcome density limitations 7 Measurements with the Plasma Reactor @ LNS in the framework of HELIOS already showed the formation of an overdense plasma in case of UHR active inside the chamber and EBW absorption in higher harmonics of the cyclotron field The UHR is accessible through the tunneling of the X cutoff. The wave encounters the UHR and it is there converted.

8. page WU6 – Tests at higher frequency and observation of overdense plasmas 8 The electromagnetic wave energy distribution inside the plasma filled chamber, measured at 3.76 GHz, shows that: Increasing of EM energy MW Window The EM forms a standing wave inside the resonator although the presence of an absorbing mean like the high density plasma The EM is partially absorbed at pp=24 cm and no other layers of EM to plasma energy transfer are evident EM-ES conversion takes place at 24 cm.

9. page 9 Experimental apparatus for mode conversion detection 9 H-Ge X-ray detector Hall probe for measurement of the magnetic field Microwave line with insulator Pressure gauge Set-up for X-ray spectroscopy and CCD imaging Positioning of the CCD for the pass-band filters measurements (plasma imaging).

10. page 10 X-ray spectra during EM-ES conversion 1.Boost of X-ray energy for low pressures; 2.The plasma exhibits a threshold-like behavior: at 1.5E-4 mbar hot electrons are generated for P rf >80 W; 3.In the same RF power domain, a plasma hole appears and it is observable in the visible range.

11. page 11 Validation of BW heating for ESS ion source -Preliminary test on VIS environment -Test with a dedicated plasma trap with versatile magnetic field configurations to optimize the BW excitation within the plasma chamber Parallel and perpendicular launching of EM waves

12. page 12 Trasco Intense Proton Source (TRIPS) Beam energy 80 keV Current up to 60 mA Proton fraction > 80% RF power < 1 kW @ 2.45 GHz CW mode Reliability 99.8% over 142 h (35 mA) Emittance 0.07 π mm mrad (32 mA), 0.15 to 0.25 at max current

13. page 13 Best operational point: Extraction coil: pos= 22 mm curr=128 A Injection coil: pos= 26 mm curr=127 A ECR zones Optimum magnetic field profile

14. page 14 Versatile Ion Source (2008)

15. page 15 To summarize: proton source A new design of the magnetic field profile is considered as a possible option (in order to get a denser plasma  HELIOS programme at INFN) and the microwave injection system will be deeply revised according to the recent experience gained with the VIS source. New ideas to enhance the electric field in the plasma chamber will be tested in order to get highest ionization rates. Further studies about brightness optimization are mandatory, which can be carried out either at CEA and at INFN-LNS.

16. page 16 LEBT The LEBT from the source extractor to the RFQ entrance must take into account different and competitive requests as it should be the shortest as possible and it should permit to allocate the necessary diagnostics and the low energy chopper. The ESS LEBT will share some similarities with the IFMIF-LEVEDA LEBT. The chopping scenario has to be simulated: 1.Space charge compensation is not fulfilled in high intensity beams. 2.B introduces non linearities. 3.B must be very strong

17. page 17 SCC via Residual Gas (RG) injection or Space Charge Lens (SCL) Problems of currently employed SCL are basically connected with non-linearities and aberrations due to electron cloud non homogeneity. RG in the beamline improves the emittance. Problems may be connceted to an eventual energy degradation of the incoming ion beam RG SCL SPACE CHARGE LENS MAY BE THE SOLUTION

18. page 18 SCC test @SILHI (75 mA) In conclusion, using 84Kr or Ar, a factor three beam emittance decrease has been achieved, losing only about 5% of the beam current.

19. page 19 SCC test @SILHI (75 mA) with N2 Emittance picture without injecting gas in the beam line: p 1 =1.6·10 -5 T, p 2 = 1.2·10 -5 T   RMS =0.386  mm mrad Emittance picture injecting N2 in the beam line: p 1 =4.5·10 -5 T, p 2 = 4.5·10 -5 T   RMS =0.13  mm mrad

20. page 20 SCC test @SILHI (75 mA) with 84Kr  RMS =0.33  mm mrad, p 1 = 1.8  10 -5 Torr, p 2 = 1.2  10 -5 Torr  RMS =0.11  mm mrad, p 1 = 3.5  10 -5 Torr, p 2 = 2.7  10 -5 Torr

21. page 21 SCC test @SILHI (75 mA) with FGA Cross- over in the diagnostic-box Cross- over in front the FGA

22. page 22 Electron Accumulation inside the SCL via CNT based electro guns Twin guns placed on the injection waveguide: field emission effect at electric field E>2- 3 V/  m For an emission surface of 0.12 cm 2. j drastically grows with V bias. Electron beam CNT based electron guns have been used @ LNS inside the CAESAR source. Emitted electrons were able to modify plasma diffusion, thus increasing the density and damping instabilities. The emitted current is very intense (several mA), electron beam is focused and directionality ensured by the gun design CNT based electron guns have been used @ LNS inside the CAESAR source. Emitted electrons were able to modify plasma diffusion, thus increasing the density and damping instabilities. The emitted current is very intense (several mA), electron beam is focused and directionality ensured by the gun design

23. page 23 New design of Space Charge Lens (SCL) based on CNT guns Magnets for longitudinal trapping Ring for circular array of CNT guns Annular displacement of CNT guns Transversal profile of electron density The annular displacement automatically increase the electron density in the center of SCL. Longitunal confinement is ensured by the magnetic field

24. page 24 Open questions Redundancy source needed? START 22/05/2003 19:32 STOP 28/05/2003 17:57 Extracted current Beam stop current Parameter Extraction voltage 80 kV Puller voltage 42 kV Repeller voltage -2.6 kV Dischargepower 435 W Beam current 35 mA Mass flow  0.5 sccm Availability over 142h 25’= 99.8 %

25. page 25 Open questions Redundancy source needed? Availability over 142h 25’= 99.8 % Fast chopper behaviour.

26. page Proton source & LEBT 26