DE2139530A1 - Device for generating intense ion bundles - Google Patents

Description

Our sign ; T 1 060_

THOMSON-CSS ¹

101, vol

75 Paris 1 Gerne, France

Device for generating intense

Ion bundle η (addendum to patent application P 19 17 845.9)

The subject of the main name P 19 17 843.9 is a Device for generating intense ion bundles by charge exchange between a plasma and a given chemical substance, which forms a reaction chamber in which the charge exchange processes take place- said reaction chamber having a first opening for introducing a bundle of said plasma, means : sur Introduction of the chemical substance in gas phase into the cervix and a second opening for the outlet of the products produced in the reaction chamber.

This device also has a primary ionization chamber in which the plasma is generated, which then is introduced into the reaction chamber serving as a secondary ionization chamber. This secondary ionization chamber is preferably designed so that it acts as an expansion chamber works.

209811/1123

In the embodiment described in the main application becomes hydrogen to form the prairie plasma is used, thereby allowing the device to operate without damage to the cathode. -But that The ionization potential of hydrogen is low, the performance of the device is low.

The aim of the invention is a further development of the subject matter of the main patent, which makes it possible to increase the ionization efficiency considerably.

According to the invention this is achieved in that the The primary plasma obtained in the primary ionization chamber is formed from an inert gas whose Molecules have a small effective ionization cross section and a large effective recombination cross section exhibit.

An analysis of the various ionization reactions and experience show that, for example, helium, thus an inert gas, considerable advantages over other gases and in particular over that in the Ionon sources commonly used hydrogen results.

First of all, it should be emphasized that the high ionization potential of helium (24 eV instead of 6 eV for hydrogen) one. considerable increase in the ionization efficiency of the Device enables; in other words, this means that the exiting from the reaction chamber (expansion chamber) Plasma bundle contains very few G ^ ions. As a result, the efficiency is:

IGT + IG *

after 1, if the .ToaeDstrom IG · "} is very small compared to ISp.

2 0 9811/1123

The elementary ionization mechanism, which in this device is created by the interaction of the primary ionization chamber in the secondary ionization chamber and into which a gas G _? containing the secondary ionization chamber introduced plasma of the gas G ₁ can be described by a sequence of reactions that can be separated into three families:

a) Impact ionization reactions, which are summarized as follows can be: -

In the primary chamber:

e "+ G ° -». G + + 2o ~ (1)

Gt + G? - 2Gt + e ~ (2)

'Λ T VT. - CBj

are in it

e negative electrons,

G ° the neutral gas of the primary ionization chamber,

(J ₁ the ionized gas G ^. /
In the secondary ionization chamber (expansion chamber):

e "+ G ° --- G + + 2e ~ (3)

^G t ^{+ G} 2 ~~ ^ ~ ^& t ^{+ G} 2 ^{+ e} " ⁽⁴⁾

In it are:

G ^ the neutral gas introduced into the secondary chamber; ^the ionized gas Gg.

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b) Charge exchange reactions:

^G 1 ^{+ G} 2 ** ^G 1 ^{+ G} 2

• 2 ⁺ 1 "" * 2 ⁺ 1

c) recombination reactions:

G ₁ + e - G ₁ .a;

G + + β "- * - G ° (8)

The best conditions for the generation of Gg ions are obtained when the impact ionization reactions of type (1) and (2) have a low probability i.e. if the effective ionization cross-section of the primary gas is small, which is exactly the pail of Is helium.

Furthermore, the use of helium favors the charge exchange reaction (5) t while the reaction (6), which is ineffective in the device, occurs only with a very low probability.

It should also be noted that the use of helium in the primary chamber also reduces the recombination reaction (7) favored, since the "effective recombination cross section" is greater, the smaller the "effective ionization cross section" is.

The use of helium as the gas G ₁ thus greatly favors the generation and maintenance of the G ^ ions and enables an ion population that is very poor in Gt ions to be extracted.

209811/1123

It should also be emphasized that the use of helium ensures a high level of operational reliability of the device, regardless of the choice of gas Gg (which is not the case is if, for example, hydrogen is chosen for the gas G .. will).

However, other gases such as nitrogen or ' Argon with a less high conversion efficiency ala helium with advantage in the device according to the invention be used.

Pate nt ans pr üche

2098Ί 1/1123

Claims (4)

Claims 1.y Device for generating intense ion bundles by charge exchange between a plasma and a given chemical substance, with a reaction chamber, in which the charge exchange takes place and a first opening for introducing a bundle of the Plasmas, a device for introducing the chemical in the grass phase into the bundle and a second opening for the escape of the generated in the reaction caramer Produlcte, and with a primary ionization chamber, in which the plasma is generated, characterized in that in the primary ionization chamber obtained primary plasma is formed from an inert gas, the molecules of which have a small effective ionization cross section and a large effective recoiling cross section exhibit. 2. Apparatus according to claim 1, characterized in that the primary plasma is helium. 3. Apparatus according to claim 1, characterized in that dag primary plasma is nitrogen. 4. Apparatus according to claim 1, characterized in that the primary plasma is argon. 209811/1123