The ESS Proton Source LEBT WP 6 WU
The ESS Proton Source & LEBT WP 6 -WU 2 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) page 1
WU 2 – Proton source & LEBT WU 6 – Prototype & Tests 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. page 2
WU 2 – Proton source & LEBT Large currents (60 -90 m. A) 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) page 3
WU 2 – Proton source & LEBT Loss fluxes + + - - - - + + + The insulators cannot allow to the currents to flow along the chamber walls + Insulator embedded the walls page 4
WU 2&6 – Proton source & Tests VIS (50 m. A - f=7 mm) page 5
WU 2&6 – Proton source & Tests SILHI 90 m. A f=9 mm page 6
BOOSTING OF EBW-heating to overcome density limitations 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. page 7
WU 6 – Tests at higher frequency and observation of overdense plasmas 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. page 8
Experimental apparatus for mode conversion detection H-Ge X-ray detector Set-up for X-ray spectroscopy and CCD imaging Positioning of the CCD for the pass-band filters measurements (plasma imaging). 9 Pressure gauge Hall probe for measurement of the magnetic field Microwave line with insulator page 9
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. 5 E-4 mbar hot electrons are generated for Prf>80 W; 3. In the same RF power domain, a plasma hole appears and it is observable in the visible range. page 10
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 page 11
Trasco Intense Proton Source (TRIPS) Beam energy 80 ke. V Current up to 60 m. A Proton fraction > 80% RF power < 1 k. W @ 2. 45 GHz CW mode Reliability 99. 8% over 142 h (35 m. A) Emittance 0. 07 π mm mrad (32 m. A), 0. 15 to 0. 25 at max current page 12
Optimum magnetic field profile Best operational point: Extraction coil: pos= 22 mm curr=128 A Injection coil: pos= 26 mm curr=127 A ECR zones page 13
Versatile Ion Source (2008) page 14
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. page 15
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 page 16
SCC via Residual Gas (RG) injection or Space Charge Lens (SCL) RG SCL RG in the beamline improves the emittance. Problems may be connceted to an eventual energy degradation of the incoming ion beam SPACE CHARGE LENS MAY BE THE SOLUTION Problems of currently employed SCL are basically connected with non-linearities and aberrations due to electron cloud non homogeneity. page 17
SCC test @SILHI (75 m. A) In conclusion, using 84 Kr or Ar, a factor three beam emittance decrease has been achieved, losing only about 5% of the beam current. page 18
SCC test @SILHI (75 m. A) with N 2 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 N 2 in the beam line: p 1=4. 5· 10 -5 T, p 2= 4. 5· 10 -5 T RMS=0. 13 mm mrad page 19
SCC test @SILHI (75 m. A) with 84 Kr 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 page 20
SCC test @SILHI (75 m. A) with FGA Cross- over in the diagnostic-box Cross- over in front the FGA page 21
Electron Accumulation inside the SCL via CNT based electro guns 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 m. A), electron beam is focused and directionality ensured by the gun design Twin guns placed on the injection waveguide: field emission effect at electric field E>23 V/mm For an emission surface of 0. 12 cm 2. j drastically grows with Vbias. page 22
New design of Space Charge Lens (SCL) based on CNT guns The annular displacement automatically increase the electron density in the center of SCL. Longitunal confinement is ensured by the magnetic field Ring for circular array of CNT guns Annular displacement of CNT guns Transversal profile of electron density Magnets for longitudinal trapping page 23
Open questions Redundancy source needed? Extracted current Beam stop current Availability over 142 h 25’= 99. 8 % START 22/05/2003 19: 32 Parameter Extraction voltage Puller voltage Repeller voltage Discharge power Beam current Mass flow 80 k. V 42 k. V -2. 6 k. V 435 W 35 m. A 0. 5 sccm STOP 28/05/2003 17: 57 page 24
Open questions Redundancy source needed? Availability over 142 h 25’= 99. 8 % Fast chopper behaviour. page 25
Proton source & LEBT ADU_1. 6. 2. 1. 1 Magnetic system design 12/12/2011 ADU_1. 6. 2. 1. 4 RF system design 22/6/2012 ADU_1. 6. 2. 1. 7 HV system design 20/2/2012 ADU_1. 6. 2. 2. 2 LEBT design 9/4/2012 page 26
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