Multi-Cusp Plasma Device


Basic aim: To confine contact ionized (tungsten surface) cesium ions in a multi-line cusp magnetic field and do its characterization.

Expected Result : A 'text book' like ideal plasma, with Te~Ti, really quiescent, with only 'natural' fluctuations.

Then ? :

(i) Identify the real thermo-dynamic fluctuations and its sources.

(ii) Now perturb the plasma with energy and particles and study the linear/non-linear evolving phenomena


Old Classical Q-Machine



Problem ..

'Drift' waves -low frequency electrostatic waves – propagates perp. B and dn


Solution

  Could it be B ~ 0 in the centre...

  Cusp fields … 



Major Sub-systems



Vacuum chamber

  - Chamber which can withstand the high temperature and with safety features for Caesium handling

Magnet Assembly

  - Electromagnets with Vacoflux-50 core material and copper pipes as winding for water cooling option – being wound through outside      vendor

Hot-Cathode Ionizer

  - Tungsten hot plate with indirect heating from filaments behind – an old    design from Chen

Caesium Vapour Oven

  - Caesium capsules kept inside a heater – will deliver caesium vapour   through small bore heated pipes

Probe Diagnostics

  - Indirectly heated probe tips are necessary to avoid caesium   condensation – also requires linear feed-throughs to work in hot             environment


Major Sub-systems – Vacuum Chamber



 Vacuum Chamber

      Basic Vacuum Testing Done;

      Integration of sub-systems started


Major Sub-systems – Magnet Assembly




Requirement :

Electromagnet with high curie temperature soft-core material.


Status :

  • Special soft core material has been procured with required shape and size;
  • Prototype winding is being tested. Field value has been achieved, but long duration operation needs active cooling. That is being explored with new designs. Expected final delivery of magnets in Dec 2013.

Major Sub-systems – Hot Cathode Ionizer



Requirement :

Indirectly heated Tungsten plate (with uniform heating)


Status :

  • All the materials needed have been procured and machined;
  • Interfacing flanges have also been fabricated;
  • Major Hindrance - Tungsten wires for indirect heating to be spot-welded & tested in the vacuum;
  • Expected delivery of floating power supply –Dec 2013

Major Sub-systems – Caesium vapour oven

  • Caesium capsules have been procured
  • Oven has been redesigned according to the cesium ampoules received and fabricated and is being assembled
  • Interfacing flanges have been fabricated.
  • Delivery pipes (molybdenum material being imported) and lines are being fabricated.
  • Expected completion – September 2013

Major Sub-systems – Probe Diagnostics


Status :

  • Optical emissions do not occur from contact ionized Caesium plasma
  • So only probe diagnostics need to be done.
  • Indirectly heated (Langmuir) probes are needed to avoid caesium ions condensing on the probe tip
  • Expected density and temperature are 109 – 1010 cm -3 and 0.2 eV
  • Fluctuations to be measured first (bandwidth not known, though the drift based fluctuations in classical q-machines are in kHz range).

Experiments planned


  • Firstly measuring fluctuations in a steady state – compare with theoretical fluctuations in a thermodynamic equilibrium

  • Noise measurement – compare with normal Q-machine and identification sources for these noises

  • Excite waves by grids and study its properties

  • Weak beam excitation -sending a weak electron beam – study the excitations – Stochastic wave growth, to see amplification of wave amplitudes, wave trapping etc.

  • Pass a current through the two plates and observe what happens to the original fluctuations

  • Now slightly heat the ion or electron then see how the extra energy get distributed

  • Introduce an inert gas and see how the waves get damped