# Presentation: 681742

## High Current Density and High Brightness H-  Sources for Accelerators

**Vadim Dudnikov**
**Brookhaven Technology Group, Inc.**

- FNAL, December 2005

## ACKNOWLEDGMENTS 

-    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

## Abstract

-      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.

## Contents

-     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 Physicswww.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 

- INP Novosibirsk, 1965, bunched beam

**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

- _Other __**INP PSR 1967**_:
**coasting**
**beam instability**** **
**suppressed by**
**increasing beam**
**current****;**
- fast accumulation of
- secondary plasma
- is essential for
- stabilization;
- 1.8x1012 in 6 m

- V. Dudnikov, PAC2001,
- PAC2005

## Cs PATENTV. 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 BacalFourth 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

**Schematic Diagrams of Surface Plasma Sources**

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

## Schematic of negative ion formation on the surface Michail 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 sourcesR.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, 

**First version of Planotron (Plain Magnetron) SPS, INP, 1972, **
**Beam current up to 230 mA, 1.5x10 mm****2 ****, J=1.5 A/cm****2****  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  *Figure**** ***illustrated 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)

**Cross sections of Planotron (Magnetron) SPS of second generation: 3.7 A/cm****2**** with Cs (0.75 A/cm****2**** 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 ofSPS 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. 1157-1160 Investigation 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 cathodesK.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)_x000b_P.W. Allison (LAML)_x000b_

-     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/cm****2** 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

**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

**H****-**** Beam Intensity of SPS**

- Beam intensity vs discharge current
- for first version of semiplanotron 1976

- Evolution of H- beam intensity in ISIS

- Years

## Emittance, Brightness, Ion Temperature 

- Emittance

- 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:

**Emittance, Brightness, Ion Temperature**

- l

- δ

- Δα

- Δx

- y

- x

## Discharge Stability and Noise

**Discharge Stability and Noise**

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

- The effective transverse electron
-  mobility μ  vs effective scattering
-  frequency ν and cyclotron frequency ω

- B, kG

- n,1016 cm-3

- noisy

- noiseless

- n*

- Bmin

- no discharge

- μ

- ν / ω

- noiseless

- μ = eν/m (ν2 + ω2)

## Noise of discharge voltage

- Dependence of discharge noise of magnetic field

## Discharge Noise Suppression by Admixture of Nitrogen

**no N****2**

**Q****N****2**** = 0.46 sccm**

**Discharge Noise Suppression by Admixture of Nitrogen**

- P.Allison, V. Smith,
- et. al. LANL

## Design of SPS with Penning Discharge 

**Design of SPS with Penning Discharge **

## Fast, compact gas valve, 0.1ms, 0.8 kHz

- 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.

## Photograph  of a fast, compact gas valve

## CSPS with Penning discharge

## 100 Hz

- Discharge voltage

- Discharge current

- Extraction voltage

- Extraction current

- H-  current after
- magnetic analyzer

- Noiseless operation

- Tested for 300 hs of
- continuous operation with H-
- Current>100mA

## Beam Formation and Diagnostics of SPS

**Beam Formation and Diagnostics of SPS**
**with Penning Discharge**

## Emittance measurement, Direct Brightness determination

- Ion beam
- Collector 1 with collimator for J.
- Collector 2 with collimator s1 for B
- Beamlet
- 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 diagramms

***H- beam current 80 mA,  Energy 23 keV,  ***

- 0.5X10 mm mm
- εxn 90% =0.06 π mm mrad
- εyn 90% =0.2   π mm mrad
- Tx~ 16 eV, Ty~2 eV

## 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 SPS for UMD

- 1- cathode;
- 2-anode;
- 3-extractor;
- 4- ground ext.;
- 5-magnet;
- 6-insularors;
- 7-cooler.
- 1 ms, 10 Hz, 1 A/cm2
- Teff ~1 eV

## Design of Fermilab Magnetron with a Slit Extraction

## Fermilab Magnetron with a Slit Extraction

**Fermilab Magnetron with a Slit Extraction**

## Simulation of H- Ion Beam Extraction from the Slit Magnetron 

**Simulation of H****-**** Ion Beam Extraction from the Slit Magnetron**

- Electrodes trajectories and equipotentials

- Slit 2x10 mm
- I=87 mA
- U=21 kV
- neutral 95%

- 0

- 10

- 5

- 0

- 5

- X, mm

- Y, mm

- 0

- 2

- 2

- Current density

- Emittance  plot

- -2.5

- 2.5

- -250

- 250

- X, mm

- X’, mrad

- J, A/cm2

## Discharge Parameters and Beam Intensity 

**Discharge Parameters and Beam Intensity **
**in Fermilab Magnetron**

- 200

- 100

- 80

- 0

- 0

- time, mks

- Beam current, mA

- time, mks

- 0

## Beam Intensity vs Discharge Current and 

**Beam Intensity vs Discharge Current and **
**Extraction Voltage in Fermilab Magnetron**

## Extraction System of BNL Magnetron

**Extraction System of BNL Magnetron**

## H-  Current vs Extraction Voltage

**H****-****  Current vs Extraction Voltage**
**  ****for Magnetron**

- H- Current, mA

- Extraction voltage, kV

## Design of the first Version of Semiplanotron

**Design of the first Version of Semiplanotron**
**SPS**

- 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 .

- V. Dudnikov, INP, 1976

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

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

## Design of a Semiplanotron SPS for accelerators

**Design of a Semiplanotron SPS for accelerators**

## Semiplanotron SPS with a Slit Extraction

**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

- D-, D+,e, H-

- Plasma Source

- Ionizer, SPS

- solenoid

- extractor

- analyzer

**Polarized Negative Ion Source with a Resonance Ionizer**

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

## DC SPS

**DC SPS**
** ****with a High Emission Current Density**

## Anode of DC SPS

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

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

- Extraction aperture of D=1 mm

- Extraction aperture of  D=0.4 mm

## Compact DC SPS with Hollow Cathode Discharges

**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 

**Assembly of the negative ion source in vacuum chamber**** **

- Brookhaven Technology Group

-  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.
- .

## Typical Assembling of CSPS on

**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.

## Helicon discharge plasma source for SPS

-      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 Surface Plasma Source. 

**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. 

**Antennas of RF plasma generator.**

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

-  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.

## FNAL SPS in preaccelerator, 0.75 MV, 0.1 A

## ANL SPS in preaccelerator, 0.75 MeV, 80 mA

## LEBT with Solenoidal Focusing

**LEBT with Solenoidal Focusing**
** ****( BNL, LANL)**

## 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 .

-  Schematic of upgraded Compact Surface Plasma Source.

## DC CSPS with HC Penning discharge Yu. 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 yield 

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

## 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.