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Progresses of Microwave Discharge Ion Sources for
the production of high intensity protons and light
ions beams at INFN LNSions beams at INFN-LNS
S Gammino L Celona L Neri G Castro D Mascali G Torrisi O LeonardiS. Gammino, L. Celona, L. Neri, G. Castro, D. Mascali, G. Torrisi, O. Leonardi
I
Santo Gammino IPAB, 14/3/2016, Legnaro, Italy
Microwave discharge ion sources scheme
High currents of 1+ ions (mA- level)High efficiency ionisation of 1+ ions:
• high electron densit (o erdense plasmas)Plasma
Microwaves,Gas
• high electron density (overdense plasmas)• low plasma confinement time• 2.45 GHz frequency• low magnetic field• low magnetic field
••
l l
Solenoid Coils • Ion Beam
Santo Gammino IPAB, 14/3/2016, Legnaro, Italy
CNR-IFP, Milano,April 3rd, 2008
Overcoming the current limits
Current ~ 100 mA (or larger) for protons and other monocharged species are required for the next years.
I /< q >~ ne τi
I ~ ne /τi
Larger density is requiredg y q
Santo Gammino IPAB, 14/3/2016, Legnaro, Italy
p/H- mA ms Hz DutyF t
π mm.dFactor mad
LEDA p 100 CW CW 100% 0.25IPHI p 100 CW CW 100% 0.25IPHI p 100 CW CW 100% 0.25TRASCO p 30 CW CW 100% 0.2FAIR p 100 1 4 0.4% 0.28PS-ESS p 74 6 14 8% 0.2IFMIF D 125 CW CW 100 0.2
High reliability and high parameters’ reproducibility is
Santo Gammino IPAB, 14/3/2016, Legnaro, Italy4
g y g p p yrequested (i.e. operator-indipendent)
PLASMAS in quasi-constant field traps: MDIS
1. Quasi straight magnetic field lines are obtained by means of two solenoids or a permanent magnet.
2 i fi ( h i fi ld h l h i i i b i i h2. No magnetic confinement (the magnetic field helps the ionization by increasing the electron path inside the chamber)
3. Spontaneous turbulences are possible especially in case of overdense plasmas
Santo Gammino IPAB, 14/3/2016, Legnaro, Italy
p p p y p
Plasma production at B>BECR
The theory of plasma heating in off resonance discharges takes into accountresonance discharges takes into account the so called “plasma effervescence”.
In the case of dense and turbulent plasmasIn the case of dense and turbulent plasmas the strong effervescence leads to a collective scattering
In order to recover the synchronization withIn order to recover the synchronization withthe rotating wave electric field, a magneticfield higher than BECR is needed and theacceleration restart (ECR theory extension to
Santo Gammino IPAB, 14/3/2016, Legnaro, Italy
( ythe collisional case).
Chalk River
Taylor &Wills
Beginning of’90s90s
Breakthroughsimple designsimple design
All successfulsources are
Santo Gammino IPAB, 14/3/2016, Legnaro, Italy
sources are based on it
Great result! 75 mA out of the RFQLos Alamos source for LEDA
Santo Gammino IPAB, 14/3/2016, Legnaro, Italy9
SILHI source and LEBT
SILHI operates at 2.45 or 3 GHz1 ECR zone at RF entrance
Bat 706
Since 1996, SILHI produces H+ beams with good characteristics:
1400
1900
110
130
150
I1=63,I2=84,z1=80,z2=166Bz = 875 GaussI1=57,I2=83.4,z1=82,z2=176
beams with good characteristics:
H+ Intensity > 100 mA at 95 keVH+ fraction > 80 %
400
900
Gau
ss
30
50
70
90I1=61, I2=84, z1=82, z2=176Objet1Objet2ElectrodesSérie7
Beam noise < 2%95 % < Reliability < 99.9 %Emittance < 0 2 π mm mrad
Santo Gammino IPAB, 14/3/2016, Legnaro, Italy
-600
-100-200 -150 -100 -50 0 50 100 150 200
m-10
10
Emittance < 0.2 π mm.mradCW or pulsed mode
140 100%
RF (command) (Watt)
237.2 369.3 501.5 765.7 897.9633.6 1030.0 1162.2
100
110
120
130
0
ent (
mA)
80%
85%
90%
95%
00%
ion
(%)In CW mode, the source
routinely produces
70
80
90
100
DCC
T C
urre
65%
70%
75%
80%
Prot
on fr
acti
Courant DCCT (mA)H+
130 mA total (> 80% H+)
at 95keV
50
60
200 300 400 500 600 700 800 900
RF power (Watt)
55%
60%
(direct - reflected)
Santo Gammino IPAB, 14/3/2016, Legnaro, Italy
TRIPS (TRasco Intense Proton Source)( )
b
A layout of the whole set-up at INFN-LNS: 1- Demineralizer; 2- 120 kV insulating transformer; 3-
Proton beam current:35 mA dc
Beam Energy:80 keV
i
19” Rack for the power supplies and for the remote control system; 4- Magnetron and circulator; 5-Directional coupler; 6 – Automatic Tuning Unit; 7- Gas Box; 8- DCCT 1; 9- Solenoid; 10 – Four sector ring; 11-
Beam emittance: εRMS ≤ 0.2 π mm mrad
Reliability: close to 100%
Turbomolecular pump; 12- DCCT 2; 13- EMU ; 14-Beam stop.
Based on CRNL LANL CEA design
Santo Gammino IPAB, 14/3/2016, Legnaro, Italy
Based on CRNL-LANL-CEA designMANY INNOVATIONS
TRASCO INTENSE PROTON SOURCE (TRIPS)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)
Santo Gammino IPAB, 14/3/2016, Legnaro, Italy
Microwave injection and beam extraction ti i tioptimisation
a2
EMicrowave Injection
2bs2bs2bs2bs Z4Z3Z2Z1 >>>Z0 > Z5>
PLASMAIMPEDANCE
2b1
Es4Es3
Es2Es1E0Use of a step binomialmatching transformer with afield enhancement factor
a1
1234
WR284
(Es4/E0)≈ 1.95 (a2=0.0126 m)
Beam extraction
The extraction process has been deeply studied with the aim toincrease the source reliability and to keep emittance low.The used codes were AXCEL-INP and IGUN.
Santo Gammino IPAB, 14/3/2016, Legnaro, Italy
L.Celona, G. Ciavola, S. Gammino, R. Gobin, R. Ferdinand, Rev.Sci.Instr. 71(2),(2000), 771
TRIPS performance vs. mass flow@450W
60
40
50
A)
IEXTR
IDCCT1
30
am c
urre
nts
(mA IDCCT1
lBS
10
20
Bea
0
10
0 4 0 45 0 5 0 55 0 6
Santo Gammino IPAB, 14/3/2016, Legnaro, Italy
0,4 0,45 0,5 0,55 0,6
Mass flow (sccm)
TRIPS performance vs forward powerTRIPS performance vs. forward power65
Iextr
60(m
A)
IextrIdcct1Ibs
55
curr
ents
50Bea
m
45300 350 400 450 500 550 600
Forward RF Power (W)
Operating voltage = 80 kV Mass flow= 0.6 sccmO ti i d ti fi ld fil E t ti t 6
Santo Gammino IPAB, 14/3/2016, Legnaro, Italy
Optimized magnetic field profile Extraction aperture = 6 mmElectron donor= BN disks Current density up to 210 mA/cm2 (near Jchild)
Essential items for the future developments:
- Beam handling
- Beam ripple
- Ability to operate in pulsed modeAbility to operate in pulsed mode
- Reliability
P ibl i t t b b i ht- Possible improvement to beam brightness
- Space charge compensation
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ION EXTRACTION SYSTEMION EXTRACTION SYSTEM
Santo Gammino IPAB, 14/3/2016, Legnaro, Italy
YOU ARE NOT OBLIGED TO DESIGN COMPLEX SYSTEM
ION EXTRACTION SYSTEMION EXTRACTION SYSTEM
TRIPS FiveTRIPS Five--electrodes topologyelectrodes topology VIS FourVIS Four--electrodes topologyelectrodes topology•• onon--line optimisation of the extracted line optimisation of the extracted beambeam•• wide range of operations (10wide range of operations (10--60 mA)60 mA)
optimized for a 40 mA beam (90% optimized for a 40 mA beam (90% proton, 10% Hproton, 10% H22
++))
Santo Gammino IPAB, 14/3/2016, Legnaro, Italy
RmsRms normalizednormalized emittanceemittance calculatedcalculated withwith AxcelAxcel codecode isis 00..0404 ππ mmmm mradmrad..
Space charge compensation with 84Krp g p
E i l (99%) i h i j i i h b liEmittance plot (99%) without injecting gas in the beam line:
p=1.8·10-5 T εRMS=0.335 π mm mrad
Emittance plot (99%) injecting 84Kr in the beam line:
p=3.0·10-5 T εRMS=0.116 π mm mrad
Santo Gammino IPAB, 14/3/2016, Legnaro, Italy
R. Gobin, R. Ferdinand, L.Celona, G. Ciavola, S. Gammino, Rev.Sci.Instr. 70(6),(1999), 2652
Space charge compensation with H2, N2, Ar, Krp g p 2 2
0.4
0.45
H2N2
0.25
0.3
0.35
m. e
mitt
ance
N2Ar84 Kr
0.1
0.15
0.2
r-r'
rms
norm
Vacuumduring standardoperation
0
0.05
1.00E-05 2.00E-05 3.00E-05 4.00E-05 5.00E-05
P (Torr)( )
• In all the cases considered, a decrease of beam emittance has been observedwith the increase of beam line pressure.• Using 84Kr gas addition a decrease of a factor three in beam emittance hasbeen achieved losing less than 5% of the beam current with a small increase ofpressure (from 1.8E-5 Torr to 2.4E-5 Torr).
Santo Gammino IPAB, 14/3/2016, Legnaro, Italy
p f
R. Gobin, R. Ferdinand, L.Celona, G. Ciavola, S. Gammino, Rev.Sci.Instr. 70(6),(1999), 2652
Emittance measurementsEmittance measurements
0 25
0.30
m m
rad)
0 15
0.20
0.25
ance
(π
mm
with Argon
without Argon
0.05
0.10
0.15
Nor
m. E
mitt
a
0.00
0.05
30 35 40 45 50 55B t ( A)
RM
S N
Beam current (mA)
Santo Gammino IPAB, 14/3/2016, Legnaro, Italy
FGA measurements
95%96%97%98%99%
pens
atio
n
90%
95%
100%
tion
(%)
91%92%93%94%95%
Cha
rge
Com
(%) Argon injection
thou
t Ar
70%
75%
80%
85%
m c
ompe
nsat
88%89%90%
%
5 6 7 8 9 10 11
Spac
e C
Wit
60%
65%
70%
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
Bea
m
Pressure [mPa] RMS beam size (mm)
Santo Gammino IPAB, 14/3/2016, Legnaro, Italy
P. Y. Beauvais, R. Gobin, R. Ferdinand, L.Celona, G. Ciavola, S. Gammino,J. Sherman, Rev.Sci.Instr. 71(3),(2000), 1413
Space charge compensation analysis (SILHI)
Pressure (mPa) (, )
98%
99%
100%
ompe
nsat
ion 7 7.5 8 8.5 9 9.5 10 10.5 11
Upstream the 1st solenoid (source exit)Low variation whatever :
- beam size
96%
97%
98%
ce-c
harg
e co
rms beam size95 keV75 keV
beam size, - added gas,- energy settings
95%10 11 12 13 14 15 16 17 18
RMS beam size (mm) (•)
Spac
Downstream the 1st solenoid,Large variation vs electron flux (gas injection, beam stop, beam losses)
and beam size
%
Santo Gammino IPAB, 14/3/2016, Legnaro, Italy
Between 70 and 98%
IFMIF Beam Line Layoutea e ayout
Total Beam Line Length : 2.050 m
Santo Gammino IPAB, 14/3/2016, Legnaro, Italy
Shorter LEBT: solenoids with H+V steerers inside
A 3D simulation has been studied to verify the possible field integral achievable and the compatibility with the beam dynamics requirements.
Santo Gammino IPAB, 14/3/2016, Legnaro, Italy
IFMIF extraction system
100 KeV, 175 mA total beam current, 1560 A/m² (Φ 12mm)
e- screeningelectrode
Plasma
Φ12mm-9.8 kV
Grounded Plasma
electrodeΦ12mm45° angle
electrode
Φ14mm0 kV45 angle
100 kV
Intermediate electrodeelectrode
Φ12mmAdjustable
57 kV57 kV
Child-Langmuir law space charge limited beam current :IFMIF: rs=6 10-3m, d=25mm, V0=100000 V,
Santo Gammino IPAB, 14/3/2016, Legnaro, Italy29
q/m(D+)=4.79 107, 4pe0/9=1/81*10-9
I=3.8212*(rs/d)²=0.220 A
Reliability
Reliability is affected by
y
-Sparks in the extraction system
-External sparks
M h i l t i-Mechanical components aging
-Electronics faults in the control units
-Power supplies failure
-The use of EMI resistant electronics and the implementation of auto-reset procedures has permitted a remarkable increase of reliabilityprocedures has permitted a remarkable increase of reliability.
-Different campaigns have been made at LANL, CEA, INFN-LNS, sometimes exceeding 99.8 % availability
-The use of sources with permanent magnets is a convenient step forward, as it permits to avoid solenoids/power supply faults and to limit the plasma parameters drifts.
Santo Gammino IPAB, 14/3/2016, Legnaro, Italy
TRIPS RELIABILITY TESTTRIPS RELIABILITY TEST
40Extracted current
TRIPS TRIPS ExtractedExtracted CurrentCurrent: : Availability over 142 h 25 min = 99.8 %Availability over 142 h 25 min = 99.8 %
30
35Beam stop
current
25
30
(mA
)
15
20
Bea
m c
urre
nt
10
15B
Parameter
Extraction voltage 80 kVPuller voltage 42 kVRepeller oltage 2 6 kV
0
5 START 22/05/2003
19:32
STOP 28/05/2003
17:57
Repeller voltage -2.6 kVDischarge power 435 WBeam current 35 mAMass flow ≈0.5 sccm
Santo Gammino IPAB, 14/3/2016, Legnaro, Italy
022/05/2003
16.4823/05/2003
16.4824/05/2003
16.4825/05/2003
16.4826/05/2003
16.4827/05/2003
16.4828/05/2003
16.48Time
Possible improvements
- Current (electron donors Al2O3 inside the chamber e-gun)Current (electron donors, Al2O3 inside the chamber, e gun)
- Larger dimension to improve the plasma uniformity close to the iextraction
- Larger frequency ? Emittance? Energy spread?g q y gy p
- 2.45 GHz + second frequency? To be tested, but
- Brightness improvement (extraction studies, compact LEBT, space charge compensation to be optimized (atomic physics may help?), plasma formation process
- Reliability (Permanent magnets Controls)
Santo Gammino IPAB, 14/3/2016, Legnaro, Italy
Reliability (Permanent magnets, Controls)
But additional improvements will originate by plasma But add t onal mprovements w ll or g nate by plasmastudies with improved diagnostics
Mi i t f t- Microwave interferometry
- Optical metods
X d i- X-ray detection
PS-ESS will be commissioned during 2016 and it will permit to study all issues above along with the “sister” testbench FPT
Santo Gammino IPAB, 14/3/2016, Legnaro, Italy
study all issues above, along with the sister testbench FPT that for some cases will be the ideal setup.
Main plasma diagnostics @LNS
Reference legg
Conical Horn
Plasma reactor Plasma leg Frequency sweep microwaveFrequency sweep microwave interferometer
Santo Gammino IPAB, 14/3/2016, Legnaro, Italy
X-ray pin-hole camera
The ESS Proton Source prototypep yp
• From R&D activities on plasma based compact• From R&D activities on plasma based compact sources to the PS-ESS design;
• Searching a balance between innovative solutions and robust design;
• Flexibility required for the magnetic field and RF system;system;
Santo Gammino IPAB, 14/3/2016, Legnaro, Italy
Body Source
Coils
Water coolingWater cooling
BN disk
Matching transformerCopper chamber
Matching transformer
Santo Gammino IPAB, 14/3/2016, Legnaro, Italy
Flexible magnetic system
Low magnetic field in the injection
Low magnetic field in the i i
in the injection regionto prevent ECR and plasma formation inside wave guide
extraction regionto prevent emittance growth
g
Classical MDIS flat profile (B-flat)
Simple-mirror (B-min) for the prolongation of H2+ molecule lifetime, thus
increasing ionization efficiency and proton fraction
M ti b h (B t i ) ki ibl B t i W (BW )
Santo Gammino IPAB, 14/3/2016, Legnaro, Italy
Magnetic beach (B-asymmetric) making possible Bernstein Waves (BWs)formation through inner-plasma conversion of the input electromagnetic waves.
PS-ESS refinement
C it f d i t dCavity frequency domain studywith real dimensions an real materials:
Copper chamber cylinder
Optimization of all geometricalparameters of the matching t f Copper chamber cylinder
Two Boron Nitride insulators disksAluminum waveguideExtraction hole
transformer:Step width, height, length, number
Santo Gammino IPAB, 14/3/2016, Legnaro, Italy
Extraction hole
PLASMA CHAMBER PLASMA CHAMBER OPTIMIZATIONOPTIMIZATIONPARAMETRICAL ANALYSIS RESULTSPARAMETRICAL ANALYSIS RESULTS--TETE111111 MODEMODE
ll =101.2 mm=101.2 mml l 101.2 mm101.2 mma a =45 mm=45 mm
Santo Gammino IPAB, 14/3/2016, Legnaro, Italy
TETE111111 ELECTRIC FIELD DISTIBUTION ELECTRIC FIELD DISTIBUTION INSIDE THE CYLINDRICAL RESONANCE CAVITYINSIDE THE CYLINDRICAL RESONANCE CAVITY
REQUIREMENTS FOR ESSREQUIREMENTS FOR ESSREQUIREMENTS FOR ESSREQUIREMENTS FOR ESS
•• LargeLarge currentcurrent (74(74 mAmA protonproton aboutabout 9090 mAmA totaltotal))•• Large Large currentcurrent (74 (74 mAmA protonproton, , aboutabout 90 90 mAmA totaltotal))
•• Low emittancesLow emittances (0.25π mm (0.25π mm mrad)mrad)
•• Long Long lifetimelifetimegg
•• High reliability High reliability ((>99%)>99%)
•• PulsedPulsed operationoperation (2.86 (2.86 msms--14 14 Hz)Hz)
•• Short Short pulsepulse rise time rise time ((100 ns)100 ns)
Santo Gammino IPAB, 14/3/2016, Legnaro, Italy
Upgrade of VIS extraction system
Improvements introduced:
Improved ground shielding- Improved ground shielding
- Single alumina
- All electrodes are cooled, also
repeller by using AlN insulator
- New triple point design
(metal-vacuum-alumina)
Thermal study
Santo Gammino IPAB, 14/3/2016, Legnaro, Italy
PS-ESS#1 + LEBT
Picture to update with the new length:Picture to update with the new length:• 270 mm : extraction system (starting from the plasma electrode)• 100 mm : cable from extraction system ; beam-current-transformer • 400 mm : first solenoid ; bellow• 60 mm : gate valve• 60 mm : gate-valve• 300 mm : iris• 350 mm : chopper• 400 mm : diagnostic box• 400 mm : second solenoid ; bellow
Santo Gammino IPAB, 14/3/2016, Legnaro, Italy
• 400 mm : second solenoid ; bellow• 320 mm : gate-valve ; beam-current-transformer ; collimator ; repeller electrode with cable ;
Simulation of extraction3D b di t ib ti fA multi-parametric
optimization of the geometry was done using AXCEL
2D axial symmetric simulation
3D beam distribution for TraceWin calculation
Own code for the conversion to a 3D beam distribution that take carebeam distribution that take care
about the representativeness and the axial symmetry
Santo Gammino IPAB, 14/3/2016, Legnaro, Italy
Beam transport optimizationThe total beam current used in the simulation was 92.5 mA: the proton fraction considered was 80%, 20% wasH2
+. Optimization of solenoids field lead to 0.22 π mm mrad of beam emittance (required<0.25) close to RFQ.
… not only for the full beam, but also when the iris is used:same twiss parameters can be obtained from 100 % to 10 % of selected beam.
It is obvious that the emittance decrease a lot proportionally to the cut
Santo Gammino IPAB, 14/3/2016, Legnaro, Italy
It is obvious that the emittance decrease a lot proportionally to the cut.Experimental check is needed to measure the effect of a not ideal iris geometry.
Defocusing chopper
E EEx Ey
≠0
Experimental test done at CEA with our prototype
Chopped and defocused
Chopped beam
beam
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Chopper and collimator test at CEA-Saclay
HV chopper electronics
Chopper Collimator
BETSI
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Beam pulse rise time
CH4: beam stop after the LEBT collimatorCH2: beam at LEBT collimatorCH1: chopper HV probe
Santo Gammino IPAB, 14/3/2016, Legnaro, Italy
Beam pulse fall time
Ch4: Beam Stop (Rτ = 5,5 ohm; C = 183 pf ; Rτ * C = 1 ns)Ch2: Collimatore (Rτ = 5,5 ohm; C = 534 pf ; Rτ * C = 2,9 ns)
Santo Gammino IPAB, 14/3/2016, Legnaro, Italy
Movable iris: 0 to 40 mm radius, 600 W, 300 mm length100 % of beam => 30 mm radius
To increase the axial symmetry of the selected beam
100 % of beam > 30 mm radius10 % of beam => 5 mm radius
the shape of the six blades was chosen merging the minimum circumference of 5 mm radius and a
dodecagonal shape
Santo Gammino IPAB, 14/3/2016, Legnaro, Italy
ESS site preparation at INFN-LNS
Catania
ESS-ABLund
(Sweden)
Santo Gammino IPAB, 14/3/2016, Legnaro, Italy
Iris, Solenoid, Steerer and pipe with gas injection and bellow
Santo Gammino IPAB, 14/3/2016, Legnaro, Italy
New chopper and LEBT collimator with ppintegrated ACCT and repeller electrode
Santo Gammino IPAB, 14/3/2016, Legnaro, Italy
Microwave Discharge Ion Source performances optimization
How to increase the electron density ?o o c ease e e ec o de s y
I. “Passive" methods, like the use of electron donors.
At INFN-LNS the insertion of a thick Al2O3 tube inside the TRIPS plasma chamber increased current and stability.
II. “Active" solutions include alternative plasma heating mechanisms, with particular attention to Bernstein Waves generation.
1. The case of a high frequency microwave discharge source has been considered, at 5 GHz instead of the usual 2.45 GHz.
1 El t t ti h ti t 2 45 GH b d b i i th BW ti ffi i ith1. Electrostatic heating at 2.45 GHz may be done by increasing the BW creation efficiency with a proper microwave injection angle single cut antennas (waveguides) launching O waves in a proper direction with respect to the magnetic field lines.
Santo Gammino IPAB, 14/3/2016, Legnaro, Italy
Generation of High intensity He+ beamPressure: 6.10-5 mbarExtraction hole: 10 mm Alumina and BN nested in plasma
Magnetic field slight modifiction
Z 30
50
pchamber Z=0
mmZ=30 mm
40
50
t [m
A]
20
30
He+ c
urre
nt
z=0 mmz=2 mmz=4 mm
900
1000
ECR
200 400 600 800 1000 1200 14000
10
z=6mm
700
800
Bz [G
]
Δ z=0 mm 200 400 600 800 1000 1200 1400Microwave power [W]
-15 -10 -5 0 5500
600
Δ z=2 mmΔ z=4 mmΔ z=6 mm
More than 50 mA He+
h b bt i d t
Santo Gammino IPAB, 14/3/2016, Legnaro, Italy57
Magnets shift Δ z [mm] have been obtained at z=0 position
The influence of the magnetic field on the proton fraction
20
25
30
]
Magnetic field slight modifiction
Z 30
10
15
20
H2+ fr
actio
n [%
]
Δ z= 0 mmΔ z= 2 mm
Z=0 mm
Z=30 mm
200 400 600 800 1000 1200 14000
5
Mi [W]
Δ z= 2 mmΔ z= 4 mmΔ z= 6 mmSeveral keV x-
rays are Microwave power [W]
106
900
1000
ECR
ygenerated atZ=0,2 magnetsposition: Connection
104
y co
unts
700
800
Bz [G
]
Δ z=0 mm
Connection betweenmagnetic fieldand EEDF!
0
102X-ra
y-15 -10 -5 0 5
500
600
Δ z=0 mmΔ z=2 mmΔ z=4 mmΔ z=6 mm
Santo Gammino IPAB, 14/3/2016, Legnaro, Italy58
0 1 2 3 4 5 6100
Magnets shift Δ z [mm]
Magnets shift Δ z [mm]
Generation of extremely overdense @3.76 GHz plasmas through EBW heating in flat B field devicesthrough EBW-heating in flat-B-field devices
Plasma hole @ 90 W
BW absorption leads to generation of high energy electrons without multi-crossing of the resonance in multi-
i fi ld
Santo Gammino IPAB, 14/3/2016, Legnaro, Italy
59
mirror fields
Generation of extremely overdense plasmas through EBW-heating in flat-B-field devices
In the 3.76 ± 0.1 GHz, 7 resonant modes exist having r=5, 0< n,<2 (60° < < 80°).
in flat B field devices
Displacement of cutoffs and resonances for these modes is compatible with Budden-type mode
conversion scenario
Plasma densityPlasma density
Magnetic field
Sidebands are the fingerprint of EBW-generation!!
Santo Gammino IPAB, 14/3/2016, Legnaro, Italy
KHz sidebands MHz sidebands
Under-resonance discharge on VIS proton source
injection
Boost of output current at low RF power
ECR
EBW heating produces high energy electrons even at low RF power But EBW also cause IAW generation
No X-rays X-rays
Santo Gammino IPAB, 14/3/2016, Legnaro, Italy
61
EBW heating produces high energy electrons even at low RF power. But EBW also cause IAW generationand following ion heating: the emittance grows when turbulences are activated.
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 passPositioning of the CCD for the pass-band filters measurements (plasma imaging).
Hall probe for measurement of the
magnetic fieldPressure gauge
Santo Gammino IPAB, 14/3/2016, Legnaro, Italy
62
magnetic field Microwave line with insulator
CCD imaging during plasma startup at different PRF
PLASMA HOLE FORMATION
Increasing power20 W 90 W
Santo Gammino IPAB, 14/3/2016, Legnaro, Italy63
Well established itemsWell established items•• Larger current, larger brightness, better reliability seem to be realisticallyLarger current, larger brightness, better reliability seem to be realisticallyLarger current, larger brightness, better reliability seem to be realistically Larger current, larger brightness, better reliability seem to be realistically achievable in few years’ termachievable in few years’ term
•• There are ‘billion $’ projects leading the run (ESS and IFMIF for There are ‘billion $’ projects leading the run (ESS and IFMIF for p,dp,d))
•• Study of pulsed operation (2 msStudy of pulsed operation (2 ms--20 Hz) needs more insights20 Hz) needs more insights
•• Looking for short pulse rise time (100 ns)Looking for short pulse rise time (100 ns)
B d i l i l tiB d i l i l ti•• Beam dynamics vs. plasma simulationsBeam dynamics vs. plasma simulations
•• LEBT optimizationLEBT optimization
•• Plasma chamber dimensions are not free parametersPlasma chamber dimensions are not free parameters•• Plasma chamber dimensions are not free parametersPlasma chamber dimensions are not free parameters
•• Electron donors may helpElectron donors may help
•• Microwave coupling is a useful “knob”Microwave coupling is a useful “knob”p gp g
•• Magnetic field probably less…Magnetic field probably less…
••Space charge will be always a nightmare!Space charge will be always a nightmare!
Santo Gammino IPAB, 14/3/2016, Legnaro, Italy
A special remarkp
•• The time that ion sources people did their job and The time that ion sources people did their job and LEBT/diagnostics people were on their own IS OVER.LEBT/diagnostics people were on their own IS OVER.
••No developments will be possible without a close cooperation No developments will be possible without a close cooperation between these different tasks.between these different tasks.
•• In future, at least for intense current sources, one should In future, at least for intense current sources, one should di t fdi t fdiscuss not ofdiscuss not of
ION SOURCES + a LEBT ION SOURCES + a LEBT
Santo Gammino IPAB, 14/3/2016, Legnaro, Italy
ION SOURCES & their LEBT ION SOURCES & their LEBT