Tandem - Revision history

RichardLefferts at 14:13, 22 March 2011

2011-03-22T14:13:52Z

RichardLefferts at 13:02, 5 October 2010

2010-10-05T13:02:34Z

RichardLefferts: Added brief theory of operation

2010-10-05T13:02:19Z

Added brief theory of operation

RichardLefferts: operation instructions

2010-10-05T12:33:32Z

operation instructions

RichardLefferts: make parallel to Ion source

2010-10-05T12:20:30Z

make parallel to Ion source

RichardLefferts: Adding some background info

2010-10-05T12:18:26Z

Adding some background info

RichardLefferts at 09:16, 27 August 2010

2010-08-27T09:16:41Z

RichardLefferts at 09:28, 26 August 2010

2010-08-26T09:28:21Z

RichardLefferts: New page: Herein should be a general intro to Van de Graaffs, some history of High Voltage Engineering and some specifics about ours. sources, negative ion sources and our source. A set of links sho...

2010-08-12T14:40:32Z

New page: Herein should be a general intro to Van de Graaffs, some history of High Voltage Engineering and some specifics about ours. sources, negative ion sources and our source. A set of links sho...

New page

Herein should be a general intro to Van de Graaffs, some history of High Voltage Engineering and some specifics about ours. sources, negative ion sources and our source. A set of links should include one to National Electrostatic Corporations page on their [http://www.pelletron.com/charging.htm Pelletron].

===Operation===

This section has been written. We'll find it ....

Return to [[Lab Manuals]]

@@ Line 11: / Line 11: @@
 In short, a Van de Graaff produces a high, dc voltage via having a constant current source deliver charge into an enormous resistance.
-The constant current source is the charging belt, which mechanically transports charge from ground against the potential and delivers it to the high voltage ''terminal''.  In our FN-8, this belt is a chain of aluminum, stainless steel and plastic called a Laddertron. It is ~12 meters long, revolves at 12 meters per second and can deliver a total charge of 250 microAmps. Charge is induced on the links of the belt by exposure to a high voltage (up to 50 kV) power supply while the links are in contact with a grounded, conductive pulley. Each charged link is then moved away from the pulley and is now isolated, except for a very high resistance path back down the chain through the plastic insulators. The charged link is moved to the terminal where another conductive pulley receives the charge. This is an excellent demonstration of Faraday's Law: the charge transfer takes place within a conductor and so is driven by only the induced voltage (less than 50 kV) on each link.
+The constant current source is the charging belt, which mechanically transports charge from ground against the potential and delivers it to the high voltage ''terminal''.  In our FN-8, this belt is a chain of aluminum, stainless steel and plastic called a Laddertron. It is ~12 meters long, revolves at 12 meters per second and can deliver a total charge of 250 microAmps. Charge is induced on the links of the belt by exposure to a high voltage (up to 50 kV) power supply while the links are in contact with a grounded, conductive pulley. Each charged link is then moved away from the pulley and is now isolated, except for a very high resistance path back down the chain through the plastic insulators. The charged link is moved to the terminal where another conductive pulley receives the charge.
 There are three paths for this charge to return to ground: with the beam, into the corona circuit (used for control, see below) and down the VdG support columns. These columns (locally referred to as High Energy and Low Energy) are split electrically into 200 planes. These planes are connected by 800 MegOhm resistor assemblies, creating a total column resistance of ~80 GigaOhms. If the total beam current is small (less than 1 microAmp) and the control circuit takes 20 microAmps, then 70 microAmps of Laddretron current will result in 80 x 10<sup>9</sup> x 50 x 10<sup>-6</sup> = 4 Million Volts.

@@ Line 42: / Line 42: @@
 * The desired voltage can be found through calculation from the desired energy. An online utility can be found at [http://casensl4.physics.sunysb.edu CASE Experiment Manager]
-====Troubleshooting====
+===Troubleshooting===
 * Seek expert assistance!
 Return to [[Lab Manuals]]

← Older revision		Revision as of 13:02, 5 October 2010
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	== Theory of Operation==		== Theory of Operation==
		+
		+	There are many descriptions of the operation of a Van de Graaff available online, in textbooks and in the literature. An excellent reference recently added to the SBU Math/Physics Library is Electrostatic Accelerators: Fundamentals and Applications, edited by Hellborg.
		+
		+	In short, a Van de Graaff produces a high, dc voltage via having a constant current source deliver charge into an enormous resistance.
		+
		+	The constant current source is the charging belt, which mechanically transports charge from ground against the potential and delivers it to the high voltage ''terminal''. In our FN-8, this belt is a chain of aluminum, stainless steel and plastic called a Laddertron. It is ~12 meters long, revolves at 12 meters per second and can deliver a total charge of 250 microAmps. Charge is induced on the links of the belt by exposure to a high voltage (up to 50 kV) power supply while the links are in contact with a grounded, conductive pulley. Each charged link is then moved away from the pulley and is now isolated, except for a very high resistance path back down the chain through the plastic insulators. The charged link is moved to the terminal where another conductive pulley receives the charge. This is an excellent demonstration of Faraday's Law: the charge transfer takes place within a conductor and so is driven by only the induced voltage (less than 50 kV) on each link.
		+
		+	There are three paths for this charge to return to ground: with the beam, into the corona circuit (used for control, see below) and down the VdG support columns. These columns (locally referred to as High Energy and Low Energy) are split electrically into 200 planes. These planes are connected by 800 MegOhm resistor assemblies, creating a total column resistance of ~80 GigaOhms. If the total beam current is small (less than 1 microAmp) and the control circuit takes 20 microAmps, then 70 microAmps of Laddretron current will result in 80 x 10<sup>9</sup> x 50 x 10<sup>-6</sup> = 4 Million Volts.
		+
		+	Voltage control is achieved with the Corona Circuit. Sharp needles are placed on a motor-driven rod and moved close enough to the terminal to draw ~20 microAmps of current. This current is allowed to flow to ground only through a vacuum triode; control of the grid voltage of that triode regulates the Corona Current and so regulates the terminal voltage. The grid voltage is controlled either by the Generating Voltmeter circuit, which compares the terminal voltage as measured by a GVM to a reference value, or by Beam (sometimes called ''slit'') regulation. In this method the Tandem output beam is bent 90<sup>o</sup> by the Analyzing magnet and allowed to hit a pair of slits. Most of the beam passes through but the tails of the current are intercepted, amplified and compared; a circuit then controls the triode grid to keep the slit currents equal.

	== Operation ==		== Operation ==

@@ Line 9: / Line 9: @@
 == Operation ==
-====Preparation====
+===Preparation===
 The Tandem drive motor is interlocked to several systems to prevent danger to operators and equipment. These are all satisfied under normal conditions; one usually finds a problem when the interlock acts by preventing the Drive Motor from starting. They include
@@ Line 16: / Line 16: @@
 * relays in the Low and High Energy Vacuum gauges; these are set to ~5 x 10<sup>-6</sup> Torr
-====Start-up====
+===Start-up===
 * Go to the High Energy end of the tandem
@@ Line 24: / Line 24: @@
 * If any of the above values are far from nominal, please seek assistance.
-====Taking the Tandem to Voltage====
+===Taking the Tandem to Voltage===
 ====Troubleshooting====
 Return to [[Lab Manuals]]

@@ Line 7: / Line 7: @@
 == Theory of Operation==
+====Preparation====
-====Interlocks====
 The Tandem drive motor is interlocked to several systems to prevent danger to operators and equipment. These are all satisfied under normal conditions; one usually finds a problem when the interlock acts by preventing the Drive Motor from starting. They include
@@ Line 16: / Line 16: @@
 * relays in the Low and High Energy Vacuum gauges; these are set to ~5 x 10<sup>-6</sup> Torr
-====Starting the Drive Motor====
+====Start-up====
 * Go to the High Energy end of the tandem
@@ Line 28: / Line 28: @@
 At present, raising and setting the Tandem voltage involves a mixture of analog controls and the Master Control program in LabView. Proceed to the Control Room and you will learn the latest version.
+====Troubleshooting====
 Return to [[Lab Manuals]]

@@ Line 1: / Line 1: @@
 ==Background==
-Herein should be a general intro to Van de Graaffs, some history of High Voltage Engineering and some specifics about ours. sources, negative ion sources and our source. A set of links should include one to National Electrostatic Corporations page on their [http://www.pelletron.com/charging.htm Pelletron].
+The particle accelerator we will be using is FN-8, the eighth ""King Tandem"" built by the High Voltage Engineering Corporation. High Voltage was founded by Robert Van de Graaff and partners as the first commercial manufacturer of Van de Graaff generators. Our FN was built in 1966 and first brought into operation in 1968. The original specification was for 7.5 Million Volts with beam; our FN attained over 10 MV without beam (or accelerator tubes) and has run for experiments at 9.8 MV. It will still reach the original spec. today but the maintenance staff will limit operation to below 8.5MV out of simple fear.
 ====Interlocks====

@@ Line 12: / Line 12: @@
 * a flow switch on the Cooling Water to the coils inside the High Energy end;
 * switches on each of the 4 access ports;
-* relays in the Low and High Energy Vacuum gauges; these are set to ~5 x 10(-6) Torr
+* relays in the Low and High Energy Vacuum gauges; these are set to ~5 x 10<sup>-6</sup> Torr
 ====Starting the Drive Motor====