Pulses from #50 to #210. Searching for correct magnetic surfaces    

  

 

Abstract :  Details about the conditions and gradual improvements of pulses from #50. The vacuum system has been improved and one new e-gun of only 6mm diametre is assembled. The results, deficiencies or absence of the expected outcomes from each pulse is summarized.

 

 

 

  List of pulses and main parameters

 

See "List of pulses and results in UST_1" in this web for more pulses, some photos and details.

 

Meaning of columns:

# = number of order of the pulse

t = pulse length in seconds

B= approximate value of the magnetic field at axis 

It  = kAmpere-turns in each coil

P = Pressure in the vacuum vessel in milli-Pascals

G.V. : grid voltage for acceleration of electrons in e-beam

Is  = current of electrons in e-beam source (not the current in the beam which is less than "Is" but unknown)

Fil. Volt = voltage at the tungsten filament

 

Contractions:

Simul = The pulse was simulated later to compare with experimental points

p. = point or points

dif = diffused ;  int  = intense ; cl = clear, well defined ; 

1 =  1st   ;  2  = 2nd  ; 3 = 3rd

 

# Date t B It P G.V. Is Fil. Volt Result
    s mT kA-turn mPa V mA V  
207-210 23-9 2 ~40 2.1 ~6

51

57

69

74

- 12.2 Pulses during visit. Big e-gun. No relevant
-
205-206 Tests
-
204 24-8 2.5 ~34 1.76 3 94.6 ~1 12.2  e-gun failed (filament or conections)
203 24-8 2.5 ~34 1.76 3 94.6 ~1 12.2  several p.

h=115.4

-
202 23-8 2.5 ~34 1.76 3 94.6 ~1 12.2  5 separate correct clear 115.4 Simul
201 23-8 2.5 ~34 1.76 3 94.6 ~1 12.2  5 separate clear p.

h=115.4

200 23-8 2.5 ~34 1.76 3 84.2 ~1 12.2  5 separate clear p.

h=115.4

199 23-8 2.5 ~34 1.76 4 84.2 ~1 12.2  ~7 separate weak p.

h=115.4

198 23-8 2.5 ~34 1.76 4 84.2 ~1 12.2  5 separate weak p.

h=115.4. Simul

197 23-8 2.5 ~34 1.76 5 84.2 ~1 12.2  Two separate p.

h=115.4

196 23-8 2.5 ~34 1.76 4 84.2 - 12.2  Seems more than 4 turns

h=115.4

195 23-8 2.5 ~34 1.76 4 84.2 - 12.2  Visual. More than 3 p. seen

h=115.4

194 23-8 2.5 ~34 1.76 4 84.2 - 12.2  Weak p. h=115.4
193 23-8 2.5 ~34 1.76 4 84.2 - 12.2  Seems more than 4 turns

h=115.4

192 23-8 2.5 ~34 1.76 4 84.2 - 12.2 3 cl weak p. 

h=114.7

191 23-8 2.5 ~34 1.76 5 84.2 - 12.2  1 saturated,  2  3 int cl

h=114.7

190 23-8 2.5 ~34 1.76 5 84.2 - 12.2  3 cl p. 

h=113.4

189 23-8 2.5 ~34 1.76 5 84.2 - 12.2  More intense p. 

h=113.4

188 23-8 2.5 ~34 1.76 6 61.3 - 12.2  Weak p. 

h=113.4

183-187 23-8 2.5 ~34 1.76 6 61.3 - 12.2  No ground. Nothing 

h=113.3

-
179-182 11-8 (Soon)
173-178 11-8 (Soon)
-
172 10-8 2.5 ~34 1.76 7 61.7 - 12.2 Visual. More weak p. seen

h=111.1

170-171 10-8 2.5 ~34 1.76 7 61.7 -
12.2
12.6
no 
load 
1 weak,  2 dif weak 3 int

#170 h=111.9

#171 h=111.1

169 10-8 2.5 ~34 1.76 7 61.7 - 12.2 1 weak,  2 3 weak

h=112.5

168 10-8 2.5 ~34 1.76 8 55.0 - 12.2 3 weak cl p. 

h=112.5

-
161-167 9-8 2.5 ~34 1.76 15-11 61.3 - 11.6 1 no or weak,  2 weak 3 dif int

#161 h=112.3

#162 h=111.2
#163 h=109.8

#164 h=110.4

#165 h=111.8

#166 h=109.4

#167 h=111.9

-
155-160 8-8 2.5 ~34 1.76 40 53.6 - 11.6

3 weak dif  p.
#155 h=114.0

#156 h=112.8
#157 h=111.1

#158 h=111.8

#159 h=110.0

#160 h=111.1

-
154 6-8 2.5 ~34 1.76 11 53.8 ~2 11.6 1 weak,  2 3 dif weak h=112.8
152 6-8 2.5 ~34 1.76 11 53.8 ~2 11.6 1 weak,  2 3 dif ; h=111.5
151 6-8 2.5 ~34 1.76 11 53.8 ~2 11.6  1 weak small,  2 big cl, 3 dif ; h=113.1
150 6-8 2.5 ~34 1.76 11 43.1 ~2 11.6 1 no,  2 3 big ; 3-twin, h=112.8
149 6-8 2.5 ~34 1.76 11 30.8 ~2 11.6 1 no, 2 3 diffus. h=112.8
148 6-8 2.5 ~34 1.76 11 30.8 ~2 11.6 1 3-twin clear , 2 no, h=113.5
147 6-8 2.5 ~34 1.76 11 39.5 ~2 11.6 1 3-twin clear , 2 no, h=114.0
146 6-8 2.5 ~34 1.76 11 39.5 ~2 11.6 Magnets off. Nothing
145 6-8 2.5 ~34 1.76 15 28.7 ~2 11.6 Nothing, h=114.0
143-144 6-8 2.5 ~34 1.76 15 53.0 ~2 11.6 1 3 clear , 2 weak, h=114.3
-
142 4-8 2.5 ~34 1.76 14 51.8 ~2 11.6 Change camera focus. h=113.5
141 4-8 2.5 ~34 1.76 15 51.8 ~2 11.6 Visual inspection
140 4-8 2.5 ~34 1.76 15 51.8 ~2 11.6 1 clear, 2 big clear 3 dif  h=113.5 ;Simul
139 4-8 2.5 ~34 1.76 15 51.8 ~2 11.6 1 clear, 2 big clear 3 dif  h=113.5
138 4-8 2.5 ~34 1.76 15 51.8 ~2 11.6 1 clear, 2 big clear 3 dif  h=110.8
137 4-8 2.5 ~34 1.76 15 51.8 ~2 11.6 1 weak, 2 3 big dif int h=111.5
136 4-8 2.5 ~34 1.76 15 51.8 ~2 11.6 1 cl int ; 2 big cl ; 3 dif ; h=112.0
135 4-8 2.5 ~34 1.76 15 51.8 ~2 11.6 1 3 cl small, 2 weak  h=114.6 ;Simul
134 4-8 2.5 ~34 1.76 18 51.8 ~2 11.6 h =114.6(neutral
-
130-133 3-8 2.5 ~34 1.76 7 51.8 2.75 11.6 h=113.5 , 111 118, rotated. Nothng
-
129 1-8 2.5 ~34 1.76 6 53.1 ~4 11.6 h=110.0  One in new place
128 1-8 2.5 ~34 1.76 6 53.1 ~4 11.6 h=112.0 ,  3 points  OK
127 1-8 2.5 ~34 1.76 6 53.1 ~4 11.6 h=114.0 ,  3 points OK
126 1-8 2.5 ~34 1.76 7 53.1 ~4 11.6 h=119.2 , 3  points OK
125 1-8 2.5 ~34 1.76 8 43.8 ~4 11.6 h=119.2  Three points
-
124 1-8 2.5 ~34 1.76 8 29.9 - 11.6 h=109.0  One in new place
123 1-8 2.5 ~34 1.76 8 29.9 - 11.6 h=109.0  One in new  place
122 1-8 2.5 ~34 1.76 8 26.2 - 11.6 h=109.0  No current
121 1-8 2.5 ~34 1.76 9 21.5 - 11.6 h=118.5  weak point
119-120 1-8 2.5 ~34 1.76 9 28.2 - 11.6 h=118.5  3 points
117-118 1-8 2.5 ~34 1.76 11 28.2 - 11.6 h=117.0   3 points
-
116 31-7 2.5 ~34 1.76 14 47.2 ~2 11.6 h=118.0  points
115 31-7 2.5 ~34 1.76 16 47.2 ~2 11.6 h=117.5  points
113-114 31-7 2.5 ~34 1.76 16 47.2 ~2 11.6 Points h=111.9
111-112 31-7 2.5 ~34 1.76 16 47.2 ~2 11.6 More correct points. h=114.7
110 31-7 2.5 ~34 1.76 16 47.2 ~2 11.6 h=116.5 Good repetitiveness
109 31-7 2.5 ~34 1.76 18 47.2 ~2 11.6 No current h=116.5
108 31-7 2.5 ~34 1.76 25 47.2 ~2 11.6 First 3 p. of magnetic surface h=116.5
-
107 31-7 2 34.68 4 batteries. Pressed splices
105-106 31-7 2 34.27 4 batteries Definitive coils
103-104 31-7 2 26.81 3 batteries Definitive coils
101-102 31-7 2 18.87 2 batteries Definitive coils
99-100 31-7 1.5 10.26 One battery. Definitive coils
-
96-97 23-7 2.5 ~14 - 5.3 43 5.7 11.6 h=114 One weak point
95 23-7 2.5 ~14 - 6 54 7 11.6 h=114 Two  points
92-94 23-7 2.5 ~14 - 11-6 28.1 3.9 11.6 h=116 Nothing
-
90-91 22-7 2.5 ~14 - 7.5 65 ~5 11.6 h=112  Two points
88-89 22-7 2.5 ~14 - 8 65 ~5 11.6 h=112  No current
87 22-7 2.5 ~14 - 8 65 ~5 11.6 h=114.5  Two points
86 22-7 2.5 ~14 - 9 65 ~5 11.6 No points
85 22-7 2.5 ~14 - 9 65 ~5 11.6 h=114.5  Two points
84 22-7 2 ~14 - 9 65 ~5 11.6 h=114.5  One point
83 22-7 2 ~14 - 11 65 ~5 11.6 h=114.5 No current
82 22-7 2 ~14 - 15 65 ~5 11.6 h=116 One point
-
71-81 22-7 2 ~14 - - 69 - 11.6 No fluorescence
68-70 22-7 2 ~14 - 11 69 - 11.6 Visble e-beam in different locations
64-67 22-7 2 ~14 - - 69 - 11.6 movable e-gun
-
62-63 20-7 2 ~14 - 9 62 5 11.6 e-gun not positioned
61 20-7 2 ~14 - ~200 62 5 11.6 Visible e-beam
58-60 20-7 2 ~14 - 9 62 5 11.6 Visual. Nothing
56-57 20-7 2 ~14 - 11 62 5 11.6  Recorded. Nothing
-
50 19-7 2 ~14 - 11 62 1.1 11.6 No visible e-beam
51-52 19-7 2 ~14 - 9 80 3.5 11.6 No visible e-beam
53 19-7 2 ~14 - ~500 80 3.5 11.6 Visible e-beam
54 19-7 2 ~14 - ~500 80 3.5 11.6 Recorded with camera
                   

 

 

 

 Results and improvements

 

 

 

Pulses #196 to #202

 

Conditions of the experiences:

* The same as in Pulses #188 to #196 

* Acceleration voltage is further increased in the last two pulses.

* The e-gun is slowly moved towards outer magnetic surfaces.

* The sequency of pulse is now the same as the old pulses. It allows 2 seconds to start the filament. It seemed that the beam current increased at the end of the pulses what might imply a lack of temperature of the filament.

* The rod is moved ~1second before the TF current is ON. It is not easy but the background of the rod might be substracted.

* Optical filter is reinstalled

 

Results :

 

* Magnetic surfaces as simulated are recorded.

 

* The correction of the magnetic surfaces support the correction and accuracy of all the design and building process of UST_1. Only the external surfaces can be recorded here but it seems, like in W7-X theory, that the internal ones are univocally defined by only one external surface or the LCFS.

* The maximum number of points is limited by vacuum quality but the number of points is enough to compare with the simulated results.

* Only the left part of the surfaces is well visualised because the right part of the image is saturated on the rod (only 8 bits pixel depth)

* After ~12 turns (the value depend on the exact position of the e-gun) the e-beam again collide with the rear of the e-gun but up to now 12 turns are not achieved due to vacuum limitations.

* The images confirm that the e-beam collides with the rear of the big e-gun because the distance between consecutive points is like in the simulations (less than 7mm)

*  Image 2 shows the pulse #202 and the theoretical simulation.

 

 

 

Pulses #188 to #196

 

Conditions of the experiences:

* AIMS gauge is moved far from the torus and the influence is reduced 25 times. The loop created by the leads, at 50cm from the torus is eliminated. Now the improve in the quality of vacuum is only apparent because the gauge is not on the VV.

* The e-beam has been rebuit and improved. (moreover a new bulb is used because the old filament was very brittle and it broke when improving the e-gun). The distance from filament to accelerator is now ~0.5mm.

* The acceleration voltage is increased up to 84.2. It increases drifts but it seems that the improve in emission power compensate the drawback.

* Neutral position is  h=113.3

* The vacuum vessel was opened during one day before the pulses.

*  The e-gun is the small  model, 6mm diam.

* The e-gun is situated 3mm higher and 2mm deeper according to more accurate simulations to try to obtain more points.

 

Results :

* Two promising points separated ~3mm and situated in the theoretical position are seen in two pulses. It is important because the points could separate when extracting the e-beam (outer surfaces) and it will prove that it is not a fake image (for example due to a big point divided in two points due to shutter effect).

 

Ideas for the next experiences

* Move vertically the e-gun to obtain outer magnetic surfaces. The external surfaces are the only ones that can allow the 4th turn to pass near and do not collide with the rear of the e-gun. (Iota is very near to 1/3 at this high drifts). However excessive extraction gives an orbit out of the LCFS. So high accuracy and care is necessary.

 

 

 

 

Pulses #183 to #187

 

Conditions of the experiences:

* AIMS gauge is moved far from the torus and the influence is reduced 25 times. The loop created by the leads, at 50cm from the torus is eliminated.

* The e-beam has been rebuit and improved. (moreover a new bulb is cut because the old filament was very brittle and broken when improving the e-gun). The distance from filament to accelerator is now ~0.5mm.

 

Results :

* The ground at the rod was disconnected and nothing was seen or recorded.

 

 

 

 

Pulses #179 to #182

 

Conditions of the experiences:

* No ferromagnetic elements remain near the torus, but one loop forming the leads and the AIMS gauge is not yet removed.

* No optical filter

*  YUV  4:2:2 and different combinations of shutter and saturation are tested.

* Some visual inspections are done.

* Shutter at 12ms and gain at maximum. Speed 30 f/s

* Only points at  h=110.3 are taken.

*  The e-gun is the small  model, 6mm diam.

* The vessel was not opened from the last session.

* The ultimate vacuum is tested. Several days outgassing

 

Results :

* The best vaccum in the chamber is obtained 5.5 x 10-3 Pa.

* Some points are seen by visual inspection but the rod moves fast and it is not clear i they form any kind of magnetic surface.

*  (more soon)

 

Possible improvements

 *  Implement more improvements cited in Pulses #168 to #172. .

 * Create a new very small e-beam of higher quality of modify the present one.

*  For the present e-beam : - Create two small (0.5mm) windows on the e-beam to see the distance between the filament and the accelerator. Try to achieve the less distance. - Create means to move and grasp the accelerator metal cyllinder. - Repaint in black.

 

 

 

 

Pulses #173 to #178

 

Conditions of the experiences:

* No ferromagnetic elements remain near the torus, but the loop from the leads and the AIMS gauge is not yet removed.

* The optical filter is removed supposing that the pass frequency is not totally correct.

*  Different combinations of shutter, image format (RGB YUV 4:4:4  YUV  4:2:2 and gain are tested to improve the sensibility of the camera and quality of the images.

* Shutter at 12ms and gain at maximum. Speed 30 f/s

* Only points at  h=112.9 are taken.

*  The e-gun is the small  model, 6mm diam.

* The vessel was not opened from the last session.

 

Results :

* RGB is not possible at 30frames/seg with this camera. The best recording format seems YUV 4:2:2 that have the max. colour definition and 30 frames/second.

*  (more soon)

 

 

 

 

Pulses #168 to #172

 

Conditions of the experiences:

* The same as in pulses #161 to #167 to have redundant information.  

*  The filament voltage has been increased up to 12.2V with load.

* Shutter at 12ms and gain at maximum. Speed 30 f/s

* Only points around h=112 are taken.

*  The e-gun is the small  model, 6mm diam.

* The vessel was not opened from the last session.

* One visual inspection has been done.

 

Results : The points remain diffused and weak. No significant improvement.

 

Possible improvements

 *  Remove the optical filter.

 * Work in RGB mode even if the frame speed is reduced to 15 frames/s.

*  Remove the magnetic weighty elements outside the camera to move the e-beam. It can be a brass or stainless steel bolts or weight.

*  Reduce the magnetic loop after the contactor. It is far from the VV but could have influence.

* Increase the visual inspections. Sight is much more sensitive than the present camera.

* Centre again the camera to the whole to avoid intensity losses.

 

* Only one brand of low cost camera having 10 or 12 bits pixel depth has been found. The present is 8 bit pixel dept and sensitive is mediocre.

* Try to cool the CCD chip to reduce noise at low iluminance.

* Return the e-gun to one old position (the inferior part of the magnetic surfaces).

* Try to built an e-gun using Barium Oxides.

* Increase the oscillating time of the fluorescent rod to allow the use of high sensitivity low cost astronomical cameras.

 

 

 

Pulses #161 to #167

 

  Conditions of the experiences:

*  The internal e-gun is painted in black (like the 14mm model)

*  The filament is nearer the accelerator. The distance is about 1mm but in this model the regulation and accuracy is far more difficult than in the 14mm model,

* Visualisation of a whole magnetic surface or at least 4 or 5 points is the objective.

* Sequence : the same as #155 to #160

* The acceleration voltage has been increased moderately up to 62V

* h=114.0 = position without applying force to the e-gun

* The e-gun is the small  model, 6mm diam.

* The vessel was not opened from the last session.

Results :  

* The points using this very small e-beam remain diffused and weak. No significant improvement.

 

 

 

Pulses #155 to #160

 

    Conditions of the experiences:

*  The visualisation of a whole magnetic surface or at least 4 or 5 points is the objective.

* A smaller but less precise e-beam has been built and it is installed. Diameter =  6mm.

* The position of the e-gun is very similar to the one in pulses #134 to #142.

* The camera is focused to cover well all the right side area.

* Sequence :  At t=0  filament ON ; t=0.5s accel. ON ; t=1s coils ON ;  t=3.5s coils and filament OFF ; t=4s  accel OFF.

* h=114.0 = position without applying force to the e-gun

* The e-gun is the small  model, 6mm diam.

* The vessel was opened and closed at the beginning of the session

 

Results :  

   *  The e-beam generates more background light and less e-beam power than the 14mm e-gun, so the points are weaker.

  * No image of more than 3 points. Three weak and diffused points are observed.

 

Necessary improvements

 Reduce background and improve the e-gun.

 

 

 

Pulses #143 to #154

 

    Conditions of the experiences:

* The same as in pulses #134 to #142 to have redundant information.  

* All pulses up to now whose length is 2.5 seg  run with the next sequence :  At t=0  filament ON ; t=1s accel. ON ; t=2s coils ON ;  t=4.5s coils OFF ; t=5s filament and accel OFF.

* h=114.5 = position without applying force to the e-gun

* The e-gun is the big model, 14mm diam.

* The vessel was not opened from the last session.

 

Results :  

* Some interesting coincidences with the past repeated experiences.

* Some of the phenomena have no explanation and happened again so they should be analysed.

 

Necessary improvements

* A smaller e-gun is necessary.

* Simulate possible shadows of e-beam. For example to explain why the 2nd points is usually weak.

 

 

 

Pulses #134 to #142

 

    Conditions of the experiences:

* The e-gun is located near the equatorial plane and outwards to try to obtain more than 3 points. The 4th turn pass at 10mm from the centre of the e-gun. The  external radius of the present e-gun is 7mm so the 4th orbit should pass very near the e-gun, but do not collide.  * The e-gun is the big model, 14mm diam.

 

 

Results :  

* Some interesting points forming surfaces are obtained. The results are commented in a next page. There is a small deviation from the simulated results. It is unknown by now.

 

 

Necessary improvements

A smaller e-gun is necessary.

 

 

 

 

Pulses #130 to #133

 

    Conditions of the experiences:

* The  e-gun was rotated from the exterior to try to obtain new positions but the rotation was excessive and no points were obtained.

 

 

 

 

Pulses #125 to #129

 

    Conditions of the experiences:

* The objetive is to find magnetic surfaces.

* The e-gun is moved in vertical direction (really an arc of circle)  and the results are recorded.

* Acceleration voltage  = 53V to obtain luminous points

 

Results :  

   * After the comparation with the theoretical orbits and the measure of the exact position of the e-beam some very important provisional conclusions could be extrated : 

* SimPIMF code works at some degree of accuracy even to simulte drifts.

* The coils were mechanised as designed by the mechanising device. So the hard work to construct the mechanising device was useful.

* The winding of the coils have a relatively (for a very low cost stellarator) high accuracy and the general phylosofy of the coils and plaster grooves was correct.

UST_1 is really a stellarator

* Common visualisation of the magnetic surfaces is impossible becasue the e-beam, at this high drifts, collide with the rear of the e-gun at the fourth turn (known by SimPIMF simulation). The Poincare orbits (no drifts) and drift orbits at low energy (~5 eV) have the correct Iota~1/3 and lower, but adding high (~50eV) drifts converts Iota a in nearly flat profile in the whole plasma, so the beam collide with the rear of the e-gun.

 

This results are further explained in a next page.

 

 

 

 

Pulses #118 to #124

 

    Conditions of the experiences:

* The objetive is to know the inferior limite of e-beam acceleration voltage. It was tested before. Now is to re-test the results. Low voltage is necessary to have less drift. The ideal value would be 2eV or 5eV, the max. energy of the electrons in the device, but it is impossible with P24 phosphor and a regular cammera.

 

Results :  

   * In pulse #121 a very weak point is obtained at ~21V . but the intensity is maybe unable to turn several times.

   * The voltage will be increased again up to 45-55eV because the drift increase is only several mm and it compensates the weak points at lower voltage.

I

 

 

 

Pulses #108 to #116

 

    Conditions of the experiences:

* The coating of fluorescente powder has been improved. Now the copper colour of the rod is no visible because a relatively thick layer of P24 phosphor is deposited.

* Definitive coils are set-up.

*  4 batteries are installed in series

 

Results :  

   * In pulse #108 a first record of magnetic surface is obtained. It is still of low quality, probably due to the excessive acceleration voltage, 47V.

   *  5 batteries are necesary to achieve 2nd harmonic resonance for ECH heating. 4 batteries were calculated.  Perhaps the splices have excesive resistance. It will be analysed.

 

 

 

 

Pulses #99 to #107

 

    Conditions of the experiences:

* The definitive coils are installed. 6 turns, double pancake, 12 splices. up to 4 batteries are available. The current is gradually increased to test the performace of the system.

* Pulse 107 was taken after revising and press again the splices between conductors.

   

Results :  

   * About 35mT have been achieved at the magnetic axis and toroidal 0.

   *  5 batteries are necesary to achieve 2nd harmonic resonance for ECH heating. 4 batteries were calculated.  Perhaps the splices have excesive resistance. It will be analysed.

   * A small improvement is obtained after re-pressing the splices.

 

 

 

 

Pulses #92 to #97

 

    Conditions of the experiences:

* The acceleration voltage and the position of the e-gun is changed to know at what level the e-beam is  undetectable by the camera.

* Simulations of the drift orbits at 15V  29V and 64V . Amper-turns = 505 (and 1050 in two cases) were carried out some time ago.  The e-beam is launched from the vacuum magnetic axis. The drifts are notable due to the low magnetic field and the relative high energy of the electrons. The radius of the apparent magnetic surfaces generated by the drifts are aprox :

64V ; 505 A-turn ; The beam escapes before completing a turn. Simulated with theoretical coils and with real-like coils and the results are similar. It was the behaviour of the real electrons in the experiences before the use of two batteries and minimum  energy e-beam.

29V ; 505 A-turn ; Radius =10mm

15V ; 505 A-turn ; Radius =6mm

15V ; 1010 A-turn ; Radius =3mm

 

45V ; 2080 A-turn ; Radius =2 mm ;  Bo =  0.041T = 41mT  ; Max Larmour radius electron = 0.67mm  ;  2 x cyclotron frequency (1.15) = 2.3Ghz ~ 2.45GHz. Simulated with perfect theoretical coils. Four batteries are needed.

- There is a displacement with respect the non-drift trajectories around 5mm towards higher major radius. The displacement is very similar for the magnetic axis and for the LCFS. The value is notably high but  8-9 batteries are needed to reach the first harmonic (87mT) and decrease drifts . 8 batteries is considered excessive and the second harmonic will be used at first.

 

 

Results :  

  *  The ray was slightly visible using 34V grid voltage in two old experiences. Here no recorded fluorescence using 28V . Weak fluorescence at 43V and good at 54V.

 * Vacuum is obviously improving with the outgassing time. Almost 5 x 10-3 Pa is reached.   Density = 8 x 1017 m-3  at 25C.

 

Necessary improvements :

*  Because the fluorescence is impossible at 15V, very weak or non at 35-40V and correct at 55V acceleration voltage, the magnetic field necessary to obtain good magnetic surfaces needs to be calculated. Some simulations at 45eV will be done.

* The increase in the magnetic field strength is also necessary to reach resonance of the heating waves. The definitive coils will be installed in the next days.

* To obtain maximum fluorescence even at low energy: a) the filament of the e-beam will be increased to 12V or slightly more.  b) Improve the coating on the movable rod.

 

 

 

 

Pulses #82 to #91

 

    Conditions of the experiences:

* The e-gun is externally movable like in the past series of pulses.

* The fluorescent rod and vacuum vessel is reconnected to ground.

 

Results :  

  * Poloidal projections are routinely obtained.

  * Only max. two points are obtained by now. Perhaps the provisional coils are too inaccurate or the e-beam energy =65V is too high. Some previous simulations shown that electrons escape after 90 turn at this energy (Bo is only 14mT now).

 

Conditions for the next experiments :  

*  The same pulses will be repeated at grid = 34V . 

 

 

 

 

Pulses #64 to #81

 

    Conditions of the experiences:

* The e-gun is externally movable now. The present feedthrough uses of o-rings that fit on a hermetic flange. The support of the e-gun, at the same time the ground reference for the acceleration grid-hole, now is slightly movable thanks two piled o-rings that act as a flexible coupling (no  rotary or linear feedthrough available). It moves the e-gun +-6mm  in vertical direction. 

* The intention is to work at high vacuum and record the projections of several turns of e-beam around the torus.

 

Results :  

  * The e-gun is easily moved and located although not very accurately. No leak are observed through the movable feedthrough.

   * However the fluorescent projection did not appear. The issue was studied after the end of the session of pulses and it was discovered that the ground was disconnected from the vacuum vessel and so from the fluorescent rod. A curious thing was visually observed during the pulses. The glowing e-beam was visually observed to collide with the rod but the rod did not show fluorescence. It seemed that the beam passed around the rod and really it was happening. The rod was at +65V  with respect the e-beam.

* AIM-S reached 8.76V at some moment after the disconnection of the heater of the diffusion pump. Not clear why.

 

* The session of pulses was quite useless

 

 

 

 

Pulses #56 to #63

 

    Conditions of the experiences:

* The same conditions as in pulses #53 to #54. Here the same experiences are repeated to confirm the absence of e-beam at low vacuum.

 

Results :  

  The e-gun is at near the LCFS. It was the position of the very first pulses and the fluorescent points were obtained with the e-gun in a central position.

 

Necessary improvements :  

*  The e-beam should be externally movable to speed up the field mapping. A NW40 bellows might be used to act from the external part of the vessel.

 

 

 

 

Pulses #53 to #54

 

    Conditions of the experiences:

* The ball valve is closed and the pressure raises slightly. By now it is one of the few methods to regulate the pressure above the ultimate pressure. A NW50 or bigger gate valve is necessary for the new improved vacuum system.

 

Results :  

 The e-beam is seen again. It seems a glowing magnetic surface but it will be checked soon by fluorescent field mapping. The e-beam is strategically positioned, although not very accurately located, at a point were the rear returning beam do not collide with the relatively big diameter of the e-gun after about 10 turns.

* The glowing magnetic surface is recorded but the image is weak and a little off-centre.

 

 

 

 

Pulses #50 to #52

 

    Conditions of the experiences:

* The ultimate vacuum is tested with the improved vacuum system. The system consist of a NW50 bellows, a NW50 Tee  a weld half nipple  and a reducer NW40 to NW50.

 

Results :  

  - The e-beam was too weak to be observed supposedly due to the low pressure. Nitrogen should be the main component in the chamber. The e-beam was later observed under the same conditions and changing only the pressure.

 

 

 

 

 References

None
 

 

 

 

 

 

Expand

Image 2  .  Pulse #202. Finally 9 correct turns of the e-beam are recorded. The simulated drift orbits at 94eV and the experimental points agree notably well.

 

 

 

 

 

Image 1  .  Pulse #126. The implicit simulated magnetic surface is represented. Whole magnetic surfaces cannot be recorded because the e-beam collides with the rear of the e-gun at the 4th turn.

 

 

 

 

 

 

Expand

Figure 1  .  Field line mapping experimental setup. The flexible coupling has been changed into an oscilating rod.

 

 

 

 

 

 

 


 

Date of publication 19-07-2006. Continuous updating