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Introduction Since the end of 1950-s Neutral Particle Diagnostics with the use of Neutral Particle Analyzers (NPA) is being intensively developed in the Ioffe Institute. For this purpose several types of Neutral Particle Analyzers were designed in Ioffe Institute in order to measure the energy distributions and the absolute intensity of hydrogen and helium (and their isotope) atom fluxes, emitted by a high temperature plasma due to charge exchange process.

Operating principle The NPA is an energy and mass spectrometer. Its operating principle is based on the ionisation of neutral particles emitted by plasma with the following analysis of resulting secondary ions in electric and magnetic fields. The ionisation occurs due to stripping in a gas cell or due to passing through a thin Diamond Carbon Like (DLC) foil. The electric and magnetic fields provide mass-resolved energy spectra of particles. The traditional scheme of NPA uses parallel electric and magnetic field (E||B), which leads to mass and energy separation of particles in the detector plane.

Detectors The following types of detectors are employed in analyzers:

  • Channel electron multipliers (channeltron).

  • Microchannel plates (MCP).

  • Photomultiplier tubes (PMT) with thin layer of scintillator.

NPA parameters The following types of NPAs have been recently developed in Ioffe Institute.

 

These NPAs are available from Ioffe Institute

NPA Set NPA Type Detected Atom Species Energy Range

keV

Number of Energy Channels Stripping method Bstray*)

mT

Fn**)

cm-2s-1

Overall dimensions

cm

Weight

kg

I. ACORD

ACORD-12

H0

0.25 - 100

6

N2 gas

2

1×107
 

71 x 51 x 36

50

D0

0.4 - 50

6

ACORD-24

H0

0.25 - 100

12

D0

0.4 - 70

12

II. ISEP

ISEP

H0

5 - 740

14

DLC foil

5

1×109

110 x 96 x 29

1200

D0

5 - 370

10

T0

5 - 250

 8

III.GEMMA

GEMMA-2M

3He0,4He0

400 - 4000

6

DLC foil

2

1×109

139 x 115 x 52

950

H0,D0,T0

200 - 2000

6

GEMMA-3

3He0,4He0

400 - 4000

8

H0,D0,T0

100 - 4000

16

IV.Compact

NPA

CNPA-L

H0

0.064 - 0.968

25

He gas

5

1×107

17 x 30 x 33

42.5

D0

0.032 - 0.484

25

CNPA-M

H0

0.8 - 80

14***)

DLC foil

D0

0.66 - 36

14***)

CNPA-H

H0

0.82 - 168

40

D0

0.41 - 84

40

*) Bstray - maximum allowed magnetic field at NPA location
**) Fn - maximum allowed neutron flux at NPA location
***) up to 40 detectors in one row

NPA energy ranges and detection efficiencies