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High Current Density and High Brightness H - Sources for Accelerators. Vadim Dudnikov Brookhaven Technology Group, Inc. FNAL, December 2005. ACKNOWLEDGMENTS .

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High Current Density and High Brightness H- Sources for Accelerators

Vadim Dudnikov

Brookhaven Technology Group, Inc.

FNAL, December 2005


I am very grateful to the ISIS Team for choosing Charge Exchange Injection and Penning SPS for ISIS operation and for successful demonstration of it’s high performance in real accelerator operation.

Penning SPS in the ISIS RFQ


  • Operation Experience of Compact Surface-Plasma Sources (CSPS) under operation in different laboratories around the world, will be considered.

  • Features of CSPS are small volume, small gaps between electrodes, high plasma density and high emission current density and high brightness, high pulsed gas efficiency and low electron current.

  • In many versions of CSPS were reached very long operation time.

  • Features of CSPS important for long time operation will be considered.


  • Introduction.

  • Historical remarks.

  • Negative ion production in surface- plasma interaction.

  • Cesium catalysis.

  • Surface Plasma Sources- SPS.

  • Charge-exchange cooling. Electron suppression.

  • Beam extraction, formation, transportation.

  • Space charge neutralization. Instability damping.

  • SPS design. Gas pulser, cesium control, cooling.

  • SPS life time. SPS in accelerators.

  • Further development.

  • Summary.

  • Acknowledgment.

Horst Klein (20 ICFA Workshop summary).

“The ion sources, and especially the H- sources, are still somewhat a black magic. Therefore intense theoretical and experimental work has to be performed in different labs to achieve the new requirements. In Europe the Negative Ion Source network, supported by the European Union, with its 8 partners will help to reach the goal. But also such a meeting as we have had in Femilab is very helpful and intensifies the worldwide collaboration. Concerning the different types of ion sources, I think the most promising candidates for H- are the Penning ion source and the volume source (Large Volume SPS). The ECR source may be a hope for the future”.

Intuition and hand experience are important components for H- sources development.

H- beam brightness in different SPS ( R.Welton, SNS).

Beam brightness and pulse current of operational ion sources (points) and new facility requirements (rectangles)Magnetron sources: 1-DESY, 2-BNL, 3-ANL, 4-FNAL. Multicusp RF sources: 5-DESY, 6-SSC; Penning sources: 7-RAL and 8-INR;. Multicusp surface conversion sources: 9-KEK and 10 –LANL Multicusp filament sources: 11-TRIUMF and 12-Jyvaskyla.

Ion Source requirements for new accelerators projects ( from R. Scrivens review)

Ion Source parameters required for selected high power project. 1rms, normalized, in mm mrad

HUASHUNG ZHANG, ION SOURCES,Springer, 1999. p.326

  • Based on the achievements of positive ion sources, H- ion sources have

    been developed in two ways:

  • 1) Negative ions are extracted from the plasma of positive ion sources. Before the 1970's, the H- current was limited to less than 5 mA. This is because in a general high temperature plasma (Te ~> 10 eV) the H- formation cross section(~10-18 cm2 ) is 3 to 4 orders less than the H- destruction cross sections (~2 to 7x10-14 cm2).

  • In 1962, Krohn [7] discovered that the yield of sputtered negative ions increased by one order while Cs+ ions impacted the metal target.

  • Unfortunately, this result was not immediately used to develop a NIS up to 1970. An H- surface plasma source (SPS) was invented by introducing cesium into the hydrogen discharge plasma at 1971.

  • It quickly led to increasing the H- current to several Amperes. Also the cesium sputter NISs were rapidly developed.

  • Since discovering, at the end of the 1970’s, that the dissociative attachment cross section of highly vibrationally excited H2-molecules in a low-temperature plasma is higher by 104-105 than the groundstate[8,9], high-intensity volume H- ion sources have been developed.

  • At the end of the 1980's, H- volume ion sources combined with cesium has evolved with domination of surface- plasma generation of negative ions.

Adsorption of alkaline metals significantly increases the secondary emission of negative ions

  • In 1961, by Ahmet Ayukhanov (Tashkent Electronics Institute) was observed that the adsorption of alkaline metals significantly increases the secondary emission of negative ions. A little later the investigations of this effect were presented by Krohn (Argonne Nat. Lab.). However, even with the presence of cesium on the surface the intensity of beams of negative ions obtained by the secondary emission did not exceed the microampere level.

  • These results became the basis of secondary-emission sputtering negative ion sources with a microampere level intensity for tandem accelerators.

  • A. Ayukhanov, PhD. Thesis, Secondary emission of negative ions with bombardment by alkali positive ions. 1961.

  • U. A. Arifov, and A. Kh. Ayukhanov, Izvestiya AN Uzbek. SSR, Ser.

    Fiz. Mat. Nauk. No. 6, 34 (1961).

  • in book U. A. Arifov, Interactions of Atomic Particles with a Solid (Nauka, Moscow, 1986).

  • V. E. Krohn, J. Appl. Phys. 33, 3523 (1962).

Budker Institute of Nuclear Physicswww.inp.nsk.su

History of

Surface Plasma Sources Development

(J.Peters, RSI, v.71, 2000)

Cesium Catalysis:

“Enhancement of negative ion production by admixture into discharge a substance with a low ionization potential, such as cesium”.

Intensity of Negative Ion Beams: 1971-discovery of Cesium Catalysis.

H-/D- LV SPS for Tokomac Neutral Beam Injectors

~$0A, ~1 MeV, 1000s,…

~1 Billion $

History of Charge Exchange Injection(Rees, ISIS , ICFA Workshop)

1. 1951 Alvarez, LBL (H-) ;

1956 Moon, Birmingham Un. (H+2)

2. 1962-66 Budker, Dimov, Dudnikov, Novosibirsk ;

first achievements;discovery of e-p instability.IPM

3. 1968-70 Ron Martin, ANL ; 50 MeV injection at ZGS

4. 1972 Jim Simpson, ANL ; 50-200 MeV, 30 Hz booster

5. 1975-76 Ron Martin et al, ANL ; 6 1012 ppp

6. 1977 Rauchas et al, ANL ; IPNS 50-500 MeV, 30 Hz

7. 1978 Hojvat et al, FNAL ; 0.2-8 GeV, 15 Hz booster

8. 1982 Barton et al, BNL ; 0.2-29 GeV, AGS

9. 1984 First very high intensity rings ; PSR and ISIS

10. 1980,85,88 IHEP, KEK booster, DESY III (HERA)

11. 1985-90 EHF, AHF and KAON design studies. SSC

12. 1992 AGS 1.2 GeV booster injector

13. 1990's ESS, JHF and SNS 4-5 MW sources

INP Novosibirsk, 1965, bunched beam

Other INP PSR 1967:


beam instability

suppressed by

increasing beam


fast accumulation of

secondary plasma

is essential for


1.8x1012 in 6 m

first observation of an e- driven instability?

coherent betatron oscillations & beam loss

with bunched proton beam; threshold~1-1.5x1010,

circumference 2.5 m, stabilized by feedback

(G. Budker, G. Dimov, V. Dudnikov, 1965).

F. Zimmermann

V. Dudnikov, PAC2001,


Cs PATENTV. Dudnikov, The Method for Negative Ion Production, SU Author Certificate, C1.H013/04, No. 411542, Application filed at 10 March, 1972, granted 21 Sept,1973, published Bul. No 2, 15 Jan.1974.

“Enhancement of negative ion production by admixture into discharge a substance with a low ionization potential, such as cesium”.

SPS was developed in cooperation of BDD, G.Dimov, V.Dudnikov,and Yu.Belchenko

SPS for Accelerators was developed in cooperation with G. Derevyankin

History of Volume Sources Development

(J.Peters, RSI, v.71, 2000)

Blue frame is separate Surface Plasma dominated H- formation

Development of Volume Sources is finished by conversion into Large Volume SPS.

Marthe BacalFourth IAEA Technical Meeting on “Negative Ion Based Neutral Beam Injectors”9 May 2005

  • “What ion source for volume production ??

  • New ion sources were proposed for making use of the volume production mechanism. The magnetic multipole, used in 1976 in our first experiments (Nicolopoulou et al, J. Phys. 1977) was modified by the addition of a magnetic filter. This seemed to solve the problem of H- destruction by fast electrons, since they were eliminated from the extraction chamber.

  • However, this solution was only partial, for two reasons :

  • * the negative ions may not be formed in the extraction chamber, but in the driver, near the filaments ;

  • * the magnetic multipole is very efficient to dissociate molecules, but H atoms destroy H- and H2(v) !

  • When cesium was introduced in the magnetically filtered multipole , it appeared as a suitable source for producing atoms and positive ions for surface production. Obviously, this device is not suitable for volume production !! It is really a good Large Volume Surface Plasma Source, not a Volume Source.”

General Diagram of the Surface-Plasma Mechanism

for Production of Negative Ions in a Gas Discharge

Surface plasma generation of H- on anode often is a dominant process of H- formation in discharges without Cs, as well with Cs

Schematic Diagrams of Surface Plasma Sources

(a) planotron (magnetron) flat cathode

(b) planotron geometrical focusing (cylindrical and spherical)

(c) Penning discharge SPS (Dudnikov type SPS)

(d) semiplanotron

(e) hollow cathode discharge SPS with independent emitter

(f) large volume SPS with filament discharge and based emitter

(g) large volume SPS with anode negative ion production

(h) large volume SPS with RF plasma production and emitter

1- anode 6- hollow cathode

2- cold cathode emitter 7- filaments

3- extractor with 8- multicusp magnetic

magnetic system wall

4- ion beam 9- RF coil

5- biased emitter 10- magnetic filter

Probability of H- emission as function of work function (cesium coverage)

Schematic of negative ion formation on the surfaceMichail Kishinevsky, Sov. Phys. Tech. Phys, 45 (1975)

Coefficient of negative ionization as function of work function and particle speed

Enhancing surface ionization and beam formation in volume-type H- ion sourcesR.F.Welton, M.P.Stockli, M.Forrette, C.Williams, R.Keller, R.W.Thomae, EPAC 2002, Paris.

  • “Cleary, once again Cs must reside on the surface for the vast majority of its lifetime in the source and therefore surface ionization must account for the observed enhancement of H- yield.

  • In these cases, the term ‘volume ion source’ is misleading since, most of the H- results from surface, rather than volume ionization processes. Therefore, ion source design, careful consideration should be granted the interior surfaces of the source”.

  • Correct classification of ion sources is important, because it should determine a direction of devices optimization: to optimize a volume production, or surface-plasma production. Incorrect speculation of main mechanism of negative ion generation was reason of long time delay in improving of beam parameters.

First version of Planotron (Plain Magnetron) SPS, INP, 1972,

Beam current up to 230 mA, 1.5x10 mm2 , J=1.5 A/cm2 with Cs

H- energy spectra from planotron

The ion spectra from a planotron usually have two peaks separated by a valley. The location of the first peak coincides with the energy eUex imparted to the negative ions by the extraction voltage. The ion energy of the second peak is higher than that of the first peak by an amount close to eUd. The oscillograms in the upper part of illustrate the change in the spectra, as a result of increasing the discharge voltage Ud from 120 V ( l ) to 210 V (4) by reducing the cesium supply. The oscillograms (1-4) in the lower part of Figureillustrated how the spectra vary as a result of increasing the hydrogen supply to the discharge chamber

Cross sections of Planotron (Magnetron) SPS of second generation: 3.7 A/cm2 with Cs (0.75 A/cm2 without Cs)

H- current density from planotron with Cs (3.7A/cm2) and without Cs (0.75 A/cm2), INP, Novosibirsk, 1972

Schematic of semiplanotron SPS

1- emission aperture;

2- anode;

3- cathode;

4- cathode insulator;

5- discharge channal;

6- extractor;

7- magnet with magnetic insertions.

Beam Current vs an Arc Current for Different Slit Geometry in the Semiplanotron

Dependences of the Н- ion beam current on the discharge current have the N-shaped form with three sections: linear growth at small discharge currents, saturation or a falling section at medium currents, and linear, but slow growth at the high currents.

Cross section through LANL version ofSPS WITH Penning Discharge.

Beamlet images at pepper-pot scinti1lator (noiseless discharge). Emission slit 0.5x10 mm2.

Vertical: Y Plane

Horizontal: X Plane

Schematic of ISIS version of Penning discharge SPS

Cathode and Plasma Plate of ISIS Penning SPS after long time operation

H- Energy Spectra from Penning SPS

Review of Scientifi Instruments, March 2002, Volume 73, Issue 3, pp. 1157-1160Investigation of the mechanism of current density increase in volume sources of hydrogen negative ions at cesium adding

  • V.P. Goretsky, A.V.Ryabtsev, I.A. Soloshenko, A.F. Tarasenko, A.I. Shchedrin

    Institute of Physics of National Academy of Sciences of Ukraine, 46 prospect Nauki, Kiev 03650, Ukraine

  • In the present article the influence of adding cesium into the volume and on the surface of an ion source on its emission characteristics is studied both theoretically and experimentally. It is shown that cesium in the volume at conditions of a real ion source brings in a significant contribution to kinetic processes, but weakly influences the current of H– ions extracted from the source. It is shown both theoretically and experimentally that an observed increase of the current of H– ions with cesium added is due to the conversion of fast particles at the anode surface.

  • Thus, on the basis of experimental results and calculations it can be stated that cesium in a volume of the source under study can not lead to the increase of current H- ions. Observed growth of this current with cesium introduction is due to conversion of hydrogen atom at discharge anode surface, covered by cesium. In other words, cesium adding results in the transformation of the source of H- ions of volume type to the source of surface-plasma type.

  • Yu.Belchenko,G.Dimov, V.Dudnikov, Nucl.Fusion, 14, 113 (1974)

Operation of Dudnikov type Penning source with LaB6 cathodesK.N. Leung, G.J. DeVries, K.W. Ehlers, L.T. Jackson, J.W.Stearns, and M.D. Williams (LBL)M.G. McHarg, D.P. Ball, and W.T. Lewis (AFWL)P.W. Allison (LAML)

The Dudnikov type Penning source has been operated successfully with low work function LaB6 cathodes in a cesium-free discharge. It is found that the extracted H– current density is comparable to that of the cesium-mode operation and H– current density of 350 mA/cm2 have been obtained for an arc current of 55 A. Discharge current as high as 100 A has also been achieved for short pulse durations. The H– yield is closely related to the source geometry and the applied magnetic field. Experimental results demonstrate that the majority of the H– ions extracted are formed by volume processes in this type of source operation.

Review of Scientific Instruments -- February 1987 -- Volume 58, Issue 2, pp. 235-239

H- Detachment by Collisions with Various Particles

and Resonance Charge-Exchange Cooling

Resonance charge -exchange cooling

Cesium escaping from a pulsed discharge in SPS

there is a strong suppression of the gas and cesium flow from the emission slit by the high density plasma of the discharge.

Gas trapping by discharge in CSPS

  • qo-gas flux without discharge

  • qp- gas flux with discharge

  • Id- discharge current

H- Beam Intensity of SPS


Beam intensity vs discharge current

for first version of semiplanotron 1976

Evolution of H- beam intensity in ISIS

Emittance, Brightness, Ion Temperature



Emission slit



Normalized emittance



Normalized brightness


Half spreads of energy of the

transverse motion of ions

Reduced to the plasma emission slit

Characteristics of quality of the beam formation:

Discharge Stability and Noise

n,1016 cm-3


Diagram of discharge stability in coordinates of magnetic field B and gas density n

no discharge




B, kG

μ = eν/m (ν2 + ω2)



The effective transverse electron

mobility μ vs effective scattering

frequency ν and cyclotron frequency ω

ν / ω

Noise of discharge voltage

Dependence of discharge noise of magnetic field

Discharge Noise Suppression by Admixture of Nitrogen

P.Allison, V. Smith,

et. al. LANL

no N2

QN2 = 0.46 sccm

Design of SPS with Penning Discharge

1 -current feedthrough;

2- housing; 3-clamping

screw; 4-coil; 5- magnet

core; 6-shield; 7-screw;

8-copper insert; 9-yoke;

10-rubber washer-

returning springs;

11-ferromagnetic plate-

armature; 12-viton stop;

13-viton seal; 14-sealing

ring; 15-aperture;

16-base; 17-nut.

Fast, compact gas valve, 0.1ms, 0.8 kHz

Photograph of a fast, compact gas valve

CSPS with Penning discharge

Discharge voltage

Noiseless operation

Discharge current

100 Hz

Extraction voltage

Tested for 300 hs of

continuous operation with H-


Extraction current

H- current after

magnetic analyzer

Beam Formation and Diagnostics of SPS

with Penning Discharge

Ion beam

Collector 1 with collimator for J.

Collector 2 with collimator s1 for B


Deflector Horizontal

Deflector Vertical

Screen with collimator s2 for B detection

Collector 3 for B detection.

B= I L2/s1 s2, s1=s2=0.1x0.1 mm2, L=250mm,

I~10-6 A.

Emittance measurement, Direct Brightness determination

Emittance diagramms

0.5X10 mm mm

εxn 90% =0.06 π mm mrad

εyn 90% =0.2 π mm mrad

Tx~ 16 eV, Ty~2 eV

H- beam current 80 mA, Energy 23 keV,

Beam instability with a secondary electron emission

Beam instability with current density fluctuation

Beam current density distribution for different currents/extraction voltages

Dependence of current and pick current density for different extraction voltages on discharge current

BINP version Penning DT SPSfor UMD

1- cathode;



4- ground ext.;




1 ms, 10 Hz, 1 A/cm2

Teff ~1 eV

Design of Fermilab Magnetron with a Slit Extraction

Fermilab Magnetron with a Slit Extraction

Simulation of H- Ion Beam Extraction from the Slit Magnetron

Current density


Electrodes trajectories and equipotentials


J, A/cm2

Y, mm


Y, mm



Emittance plot





X, mm

Slit 2x10 mm

I=87 mA

U=21 kV

neutral 95%

X’, mrad



X, mm


Discharge Parameters and Beam Intensity

in Fermilab Magnetron


time, mks



Beam current, mA



time, mks


Beam Intensity vs Discharge Current and

Extraction Voltage in Fermilab Magnetron

Extraction System of BNL Magnetron

H- Current vs Extraction Voltage

for Magnetron

H- Current, mA

Extraction voltage, kV

Design of the first Version of Semiplanotron


V. Dudnikov, INP, 1976

1- Cathode 5cm long;

2- Anode -discharge chamber;

3- Magnetic insert;

4- Magnetic poles;

5-emission slit, d=0.5 mm;

6- Extractor;

7- cylindrical grove for plasma confinement;

8- plasma trap for discharge triggering.

H- Beam up to 0.9 A, 1 ms, 10 Hz, slit 0.7x45 mm2 ; 0.22 A, slit 1x10 mm2 .

NI Beam intensity as function of discharge current in the Semiplanotron SPS

Design of a Semiplanotron SPS for accelerators

Semiplanotron SPS with a Slit Extraction

Beam Current vs an Arc Current for Different Slit Geometry in the Semiplanotron

Dependences of the Н- ion beam current on the discharge current have the N-shaped form with three sections: linear growth at small discharge currents, saturation or a falling section at medium currents, and linear, but slow growth at the high currents.

Polarized Negative Ion Source with a Resonance Ionizer

A.Belov,V. Dudnikov, et. al.




Plasma Source

Ionizer, SPS

D-, D+,e, H-


with a High Emission Current Density

Anode of DC SPS

Collector current Ic vs. discharge current Id and extraction voltage Vex

Extraction aperture of D=0.4 mm

Extraction aperture of D=1 mm

Compact DC SPS with Hollow Cathode Discharges

1- cylindrical cathode body;

2- channel for cesium delivery;

3- channel for working gas;

4- insulator (ring);

5- anode chamber;

6- hollow cathode channel;

7- drifted plasma;

8- extraction aperture;

9- spherical emitter;

10- magnetic pole;

11- extractor;

12- ion beam.

Assembly of the negative ion source in vacuum chamber

1- gas tube;

2- electric vacuum feedthroughs;

3- high voltage flange;

4- high voltage insulator;

5- high voltage feedthrough;

6- base flange;

7- cooling rods;

8- Cs catalyst supply;

9- cathode-emitter;

10- cathode insulator;

11- gas discharge chamber anode;

12- magnet poles;

13- suppression electrode;

14- extraction electrode;

15- permanent magnet;

16- high voltage insulators;

17- base plate-magnetic yoke;

18- ion beam;

19- vacuum chamber;

20- high voltage insulator.


Brookhaven Technology Group

Typical Assembling of CSPS on

the Vacuum Flange

Emittance of DC SPS, 25 keV, 1.5 mA

(DuoSPS) Possible adaptation of NIE in the real Duoplasmatron

SPS with Helicon Plasma Generation and Ion/Atom Converter

Ion flux conversion to fast atoms in converter.

Laser diagnostics and control cesium distribution. Cesium trapping by full ionization with laser excitation in discharge chamber.

Laser beam attenuation for control cesium density without discharge.

A discharge in Hydrogen gas with helicon type antenna in longitudinal magnetic field was developed and tested as plasma generator for H- source with Jim Alessi at the BNL in 1993.

A quartz cylinder 34 mm ID, helicon antenna, solenoid and flanges are shown left. Ion current density of 0.1 A/ cm2 was extracted with a discharge power of 0.4 kW, RF frequency of 40 MHz. The same efficiency was produced before in RF ion source in the Budker Institute of Nuclear Physics (BINP), Novosibirsk, Russia in DC mode of operation with optimized resonance magnetic field.

Helicon discharge plasma source for SPS

Helicon Discharge Surface Plasma Source.

1- gas valve; 2- discharge volume; 3- discharge vessel; 4- helicon saddle like antenna; 5- magnetic coil; 6- ion/atom converter; 7- electron flux; 8- emission aperture (slit); 9- extraction electrode; 10-suppression /steering electrode; 11- ion beam.

Antennas of RF plasma generator.

With replacing of the ordinary helix antenna shown in (a) by saddle type (b) a plasma flux density was increased up to 5 times from 140 mA/cm2 to 700 mA/cm2 with 14 MHz RF frequency and power of 2.5 kW and magnetic field of B=86 Gauss. The plasma flux to the wall was reduced significantly. This big difference is determined by plasma generation near the wall with ordinary helix antenna and a much picked plasma generation with the saddle type antenna.

a- ordinary helix antenna; b- saddle type antenna.

FNAL SPS in preaccelerator, 0.75 MV, 0.1 A

ANL SPS in preaccelerator, 0.75 MeV, 80 mA

LEBT with Solenoidal Focusing


Semiplanatron SPS on the flange

Schematic of semiplanotron SPS (cross section parallel to the magnetic field). 1-ion source flange; 2- insulator flange; 3-vacuum insulator; 4- gas discharge chamber-anode (st.st.) 5- cathode (molybdenum); 6- anode insert; 7-cathode insulator (ceramic); 8-discharge channel; 9- emission slit; 10- source holders; 11- high voltage insulators; 12- magnetic yoke; 13- base plate; 14- gas valve; 15- cathode nuts; 16 cesium oven; 17- ion beam; 18- extractor; 19- permanent magnets (NdBFe, 10x25x50 mm3); 20- magnetic inserts; 21- gas tube; 22-cathode cooling.

Semiplanatron SPS on the Flange

Schematic of semiplanotron SPS (cross section perpendicular to the magnetic field). 1-ion source flange; 2- insulator flange; 3-vacuum insulator; 4- gas discharge chamber-anode (st.st.) 5- cathode (molybdenum); 6- anode insert; 7-cathode insulator (ceramic); 8-discharge channel; 9- emission slit; 10- source holders; 11- high voltage insulators; 12- magnetic yoke; 13- base plate; 14- gas valve; 15- cathode nuts; 16 cesium oven; 17- ion beam; 18- extractor; 19- permanent magnets (NdBFe, 10x25x50 mm3); 20- magnetic inserts; 21- gas tube; 22-cathode cooling

Schematic of upgraded Compact Surface Plasma Source.

Left-cross section along the magnetic field; right- cross section perpendicular to the magnetic field; 1-cooled anode; 2- high thermoconductive insulator AlN; 3- discharge gap; 4- cathode with channel for HCD; 5-plasma plate with emission aperture; 6- cooled high voltage flange; 7- first extractor-electron collector; 8- permanent magnet with magnetic poles and yoke; 9- high voltage insulators; 11- grounded extractor; 12- suppresser of positive ions; 13- ion beam; 14- gas valve; 15- cesium delivery system;16 -cooling chanel;17-magnetic yoke .

DC CSPS with HC Penning dischargeYu. Belchenko, BINP

The source uses a Penning discharge with a hydrogen and cesium feed through the hollows in the cathodes. Discharge voltage is about 60–80 V, current 9 A, hydrogen pressure 4–5 Pa, magnetic field 0.05–0.1 T, and cesium seed ,1 mg/h. Negative ions are mainly produced on the cesiated anode surface due to secondary ion/atom emission. DC H- beam current up to 15 mA.

Sputtering and flakes formation are main reason of failures. Operation below a sputtering threshold is good for a lifetime increase.

Sputtering yield

Average current and source lifetime in hours and in A hr . Circle is anticipated parameters of BTG phase II.

Summary 1

The CSPS have high plasma density, high emission current density. They are very small, simple and effective have a high brightness in noiseless mode of operation, and high pulsed gas efficiency. The CSPS are very good for pulsed operation and continues operation during many months has been achieved. Negative ion formation, charge-exchange cooling of H- below 1 eV, high brightness beam extraction, formation, transportation, space charge neutralization, brightness preservation instability dumping are discussed. Practical aspects of SPS design, simulation and operation, a gas pulsing and cesium admixture control, lifetime enhancement of selected SPS are described and compared.

Summary 2

Features of all discussed CSPS are small volume, small gaps between electrodes, high plasma density and high emission current density. These features have complicated the long time operation of CSPS with high beam parameters, because a sputtering rate, flakes formation, deposition of insulators surface and probability of short circuit of electrodes should be high. But in many versions of CSPS was reached a very long operation time.

Summary 3

The operation time of ion source is limited by cathode erosion in plasma, deposition of conducting films to the insulators and flakes formation with a short circuit of a discharge gap between insulated electrodes. A typical current of DC discharge Id=1-10 A is small enough for long time conducting by these short circuit. It was observed, than during operation of CSPS with a pulsed discharge with low impedance forming line a flake formation is significantly suppressed and short circuit, created by deposition could be recovered. Short circuit created by conductive film deposition to the insulator or flakes can curry a low DC current but can be evaporated by high pulsed current. Evaporated material form a dust accumulated in any pockets in gas discharge chamber without disturbing of discharge.

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