WO2000042633A1

WO2000042633A1 - A method and apparatus of continuously monitoring and recording parameters associated with pulsed ion beam surface treatment processes

Info

Publication number: WO2000042633A1
Application number: PCT/US2000/000810
Authority: WO
Inventors: Forest E. White
Original assignee: Quantum Manufacturing Technologies, Inc.
Priority date: 1999-01-14
Filing date: 2000-01-14
Publication date: 2000-07-20
Also published as: AU2725300A

Abstract

A method and apparatus for continuously monitoring and recording parameters associated with pulse ion beam surface treatment (IBEST) processes or with other repetitively pulsed beam systems. The method includes measuring characteristics of an IBEST treatment process as pulsed waveforms, gating and integrating the measured pulsed waveforms over a predetermined period of time to produce a single value, converting the single value into an absolute digital value, and then using digital single value to calculate parameters indicative of the IBEST treatment process. The apparatus may include a gated integrator which receives and integrates the measured pulsed waveforms and a microprocessor which calculates the parameters indicative of the IBEST treatment process or of the performance of a general pulsed beam system. Alternatively, the apparatus may include a hard wired circuit which has a plurality of integrators and a series of circuit components for calculating the parameters indicative of the IBEST treatment process.

Description

A METHOD AND APPARATUS OF CONTINUOUSLY MONITORING AND RECORDING PARAMETERS ASSOCIATED WITH PULSED ION BEAM SURFACE TREATMENT PROCESSES

FIELD OF THE INVENTION

The present invention pertains to a method and apparatus for continuously

monitoring and recording parameters associated with pulsed ion beam surface

treatment (IBEST) processes or other similar beam treatment processes and systems.

More particularly, the present invention pertains to a method and apparatus which uses

a single value quantity for measured characteristics of an IBEST or other pulsed beam

process.

BACKGROUND OF THE INVENTION

Pulsed ion beam energy surface treatment (IBEST) processes are known to

improve the corrosion, wear, hardness and other characteristics of a material. The IBEST process uses intense, high energy (typically 50J - 10KJ), repetitively pulsed

annular ion beams to rapidly deliver energy into the upper layer of a material.

Typically, the repetitive pulses have a frequency of less than 40Hz and a pulse width of

approximately 150 ns FWHM (full width half maximum). The pulsed annular ion beam

is focused, i.e. it converges toward a focal spot, on an object, and rapidly deposits

energy into a upper surface layer (approximately 0.1 μm - 20 μm in thickness) of an

object. The rapid infusion of energy into the upper surface layer of the material causes

near instantaneous melting of the thin upper layer of the material. After the ion beam has melted the thin upper layer, the ion beam is turned off, causing rapid cooling of the

melted layer by virtue of thermal conduction into the bulk of the material. The melted

layer rapidly cools, typically at a rate on the order of 10⁹ degrees per second. The

rapid cooling causes re-solidification of the melted layer into a homogeneous, fine-

grained structure on the surface of the material. The homogeneous, fine-grained

surface layer has superior corrosion, wear, hardness and other characteristics as

compared to the upper surface layer of the original material.

A schematic block diagram of a typical IBEST treatment apparatus is illustrated

in Figure 1. As shown in Figure 1 , an AC power supply 1 provides AC current to a

pulse compression system 2 which compresses the AC current into a very short pulse,

i.e. on the order of 1 μs in width. The structure of the pulse compression system 2 is

known in the art, and it may include a series of serially connected capacitors and

magnetic inductive switches or SCRs (silicon controlled rectifiers). A typical pulse

compression system may be found in U.S. Patent No. 5,532,495 to Bloomquist et al. or

U.S. Patent No. 5,525,805 to Greenly. In Fig. 1 , the pulse compression system 2

provides the compressed pulses to a linear induction voltage adding (LIVA) system 3,

which stores at least two compressed pulses and adds the at least two compressed

pulses together by simultaneously discharging the at least two compressed pulses to

the ion diode unit 4. In this manner, a very short pulse (0.05 μs - 10μs FWHM) of ions

with up to 20KJ total ion energy at ion velocities corresponding to several MEV can be

delivered by the ion diode unit 4. The structure of the LIVA 3 is known in the art, and a

typical LIVA structure can be found in U.S. Patent No.s 5,532,495 or 5,525,805. As is apparent to those of ordinary skill in the art, the power applied to the ion diode unit 4

may be increased by adding stages to the LIVA 3.

A typical ion diode assembly is illustrated in Figure 2. As shown in Figure 2, a

cathode current is provided on the cathode 10 by an inductive field generated by the

anode 12 from the LIVA 3. The cathode current drives an ion diode assembly 14 to

produce an annular ion beam. The ion diode assembly may be a magnetically-confined

anode plasma (MAP) diode or any other suitable type of ion diode. The structure of the

MAP diode is known in the art, and it may form ions by charging a gaseous medium or

by surface arcing between a cathode and an anode. An example of a gaseous ion

forming MAP diode may be found in U.S. Patent No.s 5,532,495 or 5,525,805. The

ions are formed into a ring between an inner anode flux excluder 30 and an outer

anode flux excluder 32. When the voltage pulse from the LIVA is applied between the

cathode 10 and anode 11, ions are projected from between the inner and outer flux

excluders 30 and 32 toward the object to be treated 22. The annular ion beam passes

through an opening 16 in an outer wall 28 of the treatment chamber.

In connection with such an ion diode assembly, the annular ion beam current

may be characterized, for example, by measuring the beam current using outer and

inner B-dot Rogowski coil monitor located in the outer and inner anode flux excluders

30 and 32 respectively. The ion beam current density is preferably measured in

several locations, for example by a fixed Faraday cup 26 located on an outer surface of

a vacuum treatment chamber 18. A table 20 is located in the vacuum treatment

chamber 18 for holding the object to be treated 22. The ion beam current density may also be measured by a set of Faraday cups 24 placed at the plane of treatment

adjacent to the object being treated 22.

In order for the IBEST process to be most effective, the surface of a particular

material should be treated in a prescribed manner. Proper and adequate surface treatment of the workpiece depends upon providing an ion beam to the surface having

the proper characteristics, namely, the ion accelerating voltage, ion beam energy and

energy density should be within a desired range. The beam energy is a measure of the

amount of total energy transported by the ion beam. The energy density is a measure

of the amount of energy transported by the ion beam per unit area. Energy densities

measured at various locations in the footprint of the ion beam indicate the uniformity of

the ion beam profile. Beam uniformity is an important parameter in ensuring adequate

and uniform treatment across the surface of the workpiece. Accordingly, it is

advantageous to control the energy density of the ion beam which is incident on the

surface being treated. In addition, it is often useful to ensure that a particular surface

has been treated in the manner which has been prescribed by the operating system.

Therefore, continuous monitoring of beam parameters, especially those which are

indicative of the energy density of the ion beam, is desirable.

The IBEST treatment process may be characterized by three basic parameters:

1 ) the ion diode voltage; 2) the ion beam current; and 3) the spatial map of the energy

density of the ion beam in the vicinity where it is incident on the surface which is being

treated. The ion diode voltage is indicative of the kinetic energy of each ion in the

beam. The beam current is indicative of the number of ions which comprise the total beam. Using these parameters, the ion beam energy (the energy delivered by the ion beam) as well as the energy density of the ion beam can be ascertained. Additionally,

current density measurements at various locations near the item which is being treated

indicates the uniformity of the ion beam profile.

The parameters which may be monitored to yield the characteristics of the ion

beam and performance of the ion diode system, as indicated in Figure 3, include 1 ) the

cathode current, 2) the linear induction adder voltage, 3) the outer ion beam current,

and 4) the inner ion beam current. These measured parameters are detailed as

follows:

Cathode current (ik(t)): the total electrical current which flows into the ion diode

assembly from the modulator system.

Linear induction adder voltage (V_ak(t)): the voltage delivered by the modulator

system which appears across the anode-cathode gap of the ion diode

assembly.

Outer ion beam current (i₀(t)): the ion current which flows through an outer Rogowski coil located in the anode outer flux excluder of the ion diode

assembly.

Inner ion beam current (ij(t)): the ion current which flows through an inner Rogowski coil located in the anode inner flux excluder of the ion diode

assembly. These four parameters may subsequently be used to calculate: 1 ) the average

cathode current delivered to the ion diode assembly, 2) the average diode voltage

impressed across the ion diode assembly, 3) the impedance of the ion diode, and 4) the efficiency of the ion diode. In equation form, each of these parameters can be

written as follows:

t_P Equation 1 : Average cathode current: Iκ(avg) = 1_ J IK(t)dt t_p 0

t_P Equation 2: Average diode voltage: V_ak(avg) = 1_ J Vak(t)dt

Equation 3: Diode impedance: Z_diode (avg) = V_a (avq) lκ (avg)

Equation 4: Ion diode efficiency: η_diode = In (avg) - lι (avg) ^" l_k(t) ^"

In these equations, t_p is the pulsewidth of the ion beam. These calculated

parameters of the ion beam may subsequently be used to calculate the total energy in

the ion beam.

The energy density of the ion beam may be ascertained by measuring the

current density of the ion beam using the Faraday cups 26 and 24 located in the path of

the ion beam, as shown in Figure 2. Each Faraday cup samples a small potion of the

ion beam and produces a voltage output which is proportional to the current density of

the beam at the location where the ion beam is intercepted by the Faraday cup. Faraday cups are typically placed at several locations throughout the beam path.

Specifically, the Faraday cup 26 samples a small portion of the ion beam as it enters

the treatment chamber. Up to three other Faraday cups 26 may be placed in the

vicinity of the surface which is to be treated. The purpose of the Faraday cups 26 is to

measure the current density of the ion beam in the vicinity of the surface where a

treatment is to take place. Conventionally, the IBEST process uses a pulsed ion beam having a pulsewidth

of approximately 50 ns up to several μs FWHM. Since the IBEST process is a pulsed

process, each of the above noted parameters; voltage, currents and Faraday cup output waveforms, are also pulsed. Typically, the pulse waveforms are recorded and analyzed using high bandwidth digital oscilloscopes or other high speed digitization

instrumentation, as shown in Figure 3. Particularly, a high speed digitizer 36 receives

measured pulse waveforms of the cathode current from a measurement device 35a,

measured pulse waveform of the LIVA voltage from a measurement device 35b,

measured pulse waveforms of the outer ion beam current from a measurement device

35c, measured pulse waveforms of the inner ion beam current from a measurement

device 35d, and measured pulse waveforms from the Faraday cups 24 and 26. Each of

the measured pulse waveforms are digitized by the high speed digitizer 36 and

converted to relatively large arrays which contain both time and amplitude information.

The arrays are stored in a memory 38, which may be any type of commonly known

memory device. The waveforms are subsequently analyzed in a microprocessor 40 by

performing mathematical operations on the arrays using spreadsheets or other known

computer programs.

While such a technique is effective and offers a high level of accuracy, there are some disadvantages associated with it. First, the instrumentation required to digitize the measured signals is relatively expensive and adds to the cost of the IBEST system. Second, the digitized measured signals (data) become relatively large data files which require a large memory capacity to be stored and managed, further adding to the expense of the IBEST system. Third, the creation of large data files, the storage of such files, and the analysis of such large files to calculate the above parameters

requires a significant amount of time, which greatly limits the rate at which an IBEST

treatment process can be performed when data is being continuously collected and

analyzed. Accordingly, in an IBEST process or other repetitively pulsed beam process

in which it is necessary to monitor and record every treatment pulse, implementation of

this technique may significantly limit the repetition rate of the process itself, thus

increasing the time it takes to treat the material. Therefore, an economical method is

required to continuously monitor, characterize and record the above parameters.

SUMMARY AND OBJECTS OF THE INVENTION

It is an object of the invention to provide a cost effective method for monitoring IBEST or other repetitive pulsed beam process treatment parameters.

It is another object of the invention to allow continuous monitoring of IBEST or

other repetitive pulsed beam process treatment parameters without disrupting the

treatment process.

It is yet another object of the invention to allow feedback control of an IBEST or

other repetitive pulsed beam process treatment process.

To achieve the foregoing and other objects and in accordance with the purpose

of the present invention, as embodied and broadly described herein, the apparatus of

this invention may comprise a measurement device which measures a characteristic of

at least one of the pulsed beam apparatus and a beam as a waveform; a gated

integrator which integrates the waveform over a period of time to produce a single

value indicative of the waveform; and a microprocessor which calculates a parameter indicative of an operation of at least one of the pulsed beam apparatus and the beam

based on the single value.

The gated integrator preferably comprises a gated integrator circuit which

receives the waveform; and a gate interval timer which provides a pulse signal to the

gated integrator circuit which defines the period over which the received waveform is

integrated.

The gated integrator preferably further comprises a gain control circuit which

adjusts the gain of the single value according to an attenuation factor of the

measurement device.

The pulsed beam apparatus preferably comprises an ion diode for generating an

ion beam including a generally conical annular ion beam having inner and outer

peripheral regions and an apex approximately at an object to be irradiated, the ion

diode including a cathode, wherein the characteristic which is measured by the

measurement device includes at least one of the following: a current to the cathode, a

voltage across the diode, an ion beam current at the outer peripheral region, an inner

ion beam current at the inner peripheral region, and at least one ion density

measurement of the ion beam in the vicinity of the locations of the object to be

irradiated.

The pulsed beam apparatus preferably comprises an ion diode for generating an

ion beam including a generally conical annular ion beam having inner and outer

peripheral regions and an apex approximately at an object to be irradiated, the diode

including a cathode, and wherein the calculated parameter includes at least one of the

following: average cathode current, impedance of the diode, average diode voltage, fixed energy density of the ion beam, efficiency of the ion diode, and energy density

calculations of at least one location of an ion beam.

The measurement device preferably measures a plurality of characteristics of at

least one of the pulsed beam apparatus and the beam, and provides a plurality of

waveforms respectively, the gated integrator preferably further comprises a plurality of

gated integrator circuits, each of which receives a single waveform; a gate interval

timer which provides a pulse signal to each gated integrator circuit which defines the

period over which the received waveform is integrated.

Preferably the gated integrator further comprises a plurality of gain control

circuits, each gain control circuit of the plurality of gain control circuits corresponding to

each gated integrator circuit, each gain control circuit adjusting the gain of the single

value produced by a corresponding gated integrator circuit according to an attenuation

factor of the measurement device.

In yet another aspect of the invention, a method is provided for monitoring

parameters in a pulsed beam apparatus comprising the steps of: measuring a

characteristic of at least one of the pulsed beam apparatus and the beam as a

waveform; integrating the waveform over a period of time to produce a single value

indicative of the waveform; and calculating a parameter indicative of an operation of at least one of the pulsed beam apparatus and the beam based on the single value.

Preferably the pulsed beam apparatus comprises an ion diode for generating a

generally conical, annular ion beam having inner and outer peripheral regions and an

apex approximately at an object to be irradiated, the ion diode including a cathode, and

the step of measuring a characteristic preferably measures at least one of the following; a current to the cathode, a voltage across the diode, an ion beam current at the outer

peripheral region, an inner ion beam current at the inner peripheral region, and at least

one ion density measurement of the ion beam in the vicinity of the locations of the

object to be irradiated.

Preferably the pulsed beam apparatus comprises an ion diode for generating a

apex approximately at an object to be irradiated, the diode including a cathode, and the

step of calculating a parameter preferably calculates at least one of the following;

average cathode current, impedance of the diode, average diode voltage, fixed energy

density of the ion beam, efficiency of the ion diode, and energy density calculations of

at least one location of an ion beam.

Preferably the step of measuring a characteristic measures a plurality of

characteristic values as a plurality of waveforms respectively, the step of integrating

integrates the plurality of waveforms, and the step of calculating calculates a plurality of

parameters.

In yet another aspect of the present invention a monitoring apparatus for

monitoring parameters in a pulsed beam treatment apparatus is provided, the

monitoring apparatus comprising: a measurement device which measures a characteristic of at least one of the pulsed beam apparatus and the beam as a

waveform; a gated integrator circuit which integrates the waveform over a period of time

to produce a single value indicative of the waveform; and a logic circuit which

calculates a parameter indicative of an operation of at least one of the pulsed beam

apparatus and the beam based on the single value. Preferably the monitoring apparatus further comprises a gate interval timer

which provides a pulse signal to the gated integrator circuit which defines the period

over which the received waveform is integrated.

The monitoring apparatus preferably further comprises a gain control circuit

5 which adjusts the gain of the single value according to an attenuation factor of the

measurement device.

Preferably the monitoring apparatus further comprises a plurality of

measurement devices which measure a plurality of characteristics of at least one of the

pulsed beam apparatus and the beam, and provides a plurality of waveforms

o respectively; a plurality of gated integrator circuits which produce a plurality of single

values, wherein each gated integrator receives a single waveform and produces a

single value based on the received waveform; and a gate interval timer which provides

a pulse signal to each gated integrator circuit which defines the period over which the

received waveform is integrated.

5 The monitoring apparatus preferably further comprises a plurality of gain control

factor of the measurement device; and a plurality of logic circuits which calculate a o plurality of parameters indicative of an operation of at least one of the pulsed beam

apparatus and the beam based on the plurality of single values.

The invention is advantageous over the technique of digitizing measured pulse

waveforms and placing the digitized values into a large array because it provides a single average value for each measured characteristic. This single value quantity can

be subsequently used to calculate the above parameters on an average basis, which

reflects the operation of the treatment system and the overall effectiveness of the

treatment process. In this manner the gated integrator circuits of the present invention

eliminate the need for the high speed digitization instrumentation and a large memory

capacity for storing and managing large data arrays. More particularly, the

advantages of the present invention include: 1 ) the instrumentation required to

implement the present invention is relatively inexpensive compared to high-speed

digitization instrumentation; 2) the single value quantities produced by the present

invention significantly reduces the memory requirements for the data acquisition system

compared to the memory requirements for storing large arrays; and 3) the method

described in this disclosure is relatively fast because it does not require generating and managing an array. As a result, the overall treatment rate is not significantly limited by

the rate at which data can be collected by the data acquisition system.

Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those

skilled in the art upon examination of the following or may be learned by practice of the

invention. The objects and advantages of the invention may be realized and attained

by means of the instrumentalities and combinations particularly pointed out in the

appended claims. BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and form a part of the

specification, illustrate several embodiments of the present invention and, together with

the description, serve to explain the principles of the invention. In the drawings:

Figure 1 illustrates a schematic diagram of a typical IBEST treatment apparatus.

Figure 2 illustrates an IBEST surface treatment process. Figure 3 illustrates the prior art technique of determining IBEST parameters.

Figure 4 illustrates a first embodiment of determining IBEST parameters

according to the present invention.

Figure 5 illustrates the operation of a gated integrator circuit according to first

embodiment of the present invention.

Figure 6 illustrates a schematic diagram for determining IBEST parameters

according to a second embodiment of the present invention.

Figure 7 illustrates flow diagram describing the operation of the first and second

embodiments of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made in detail to the present preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings.

Figure 4 illustrates a first embodiment of the monitoring system 46 of the present

invention. In this embodiment a gated integrator unit 42 receives measured pulsed

waveforms from the IBEST apparatus 5. The gated integrator unit 42 preferably receives measured pulse waveforms of the cathode current from the measurement

device 35a, measured pulse waveforms of the LIVA voltage from the measurement

device 35b, measured pulse waveforms of the outer ion beam current from the

measurement device 35c, measured pulse waveforms of the inner ion beam current

from the measurement device 35d, and measured pulse waveforms from the Faraday

cups 24 and 26. Other measured values may be included according to the particular

demands of the operator of the IBEST apparatus 5 (Fig. 1 ).

The cathode current i_k(t) and the LIVA voltage V_ak(t) may be determined by

techniques known to those of skill in the art. For example, the outer ion beam current i₀(t) may be determined, e.g. using an outer Rogowski coil located in the anode outer

flux excluder 30 (Fig. 2) of the ion diode assembly, and the inner ion beam current ij(t)

may be determined, e.g. using an inner Rogowski coil located in the anode inner flux

excluder 32 (Fig. 2) or by other techniques known to those of skill in the art. The

Faraday cups 26 and 24 are known to those of skill in the art and may be used to

provide measurements of the current density of the ion beam, which in turn are used to

determine the energy density of the ion beam.

The gated integrator unit 42 may be a hard wired circuit, a programmable logic

array such as an EPROM, or it may be a software programmable apparatus. The gated

integrator unit 42 operates on each of the input signals and provides a plurality of

outputs to a microprocessor 44. The plurality of outputs may then be used to determine

the IBEST monitoring parameters, such as average cathode current, the impedance of

the ion diode assembly, the average diode voltage (LVIA voltage), the fixed energy

density of the ion beam, the efficiency of the ion diode assembly, and the energy density at the locations of each of the plurality of Faraday cups represented by number

24 in Figure 2. Other outputs may be included according to the particular demands of

the operator of the IBEST apparatus 5.

Preferably, the gated integrator unit 42 comprises of a plurality of gated

integrator circuits, i.e. one gated integrator circuit for each measured value. Each gated integrator circuit provides a single value quantity which represents the integral of

the measured pulsed waveform over a specified gate interval. These single value

quantities, which are associated with each measured pulsed waveform, may subsequently be processed to yield the above monitoring parameters, which in turn

provide an indication of the operation of the facility and the effectiveness of the

treatment process. In this embodiment, all of the integrator circuits are triggered

simultaneously from a common trigger signal.

An example of a gated integrator circuit according to the present embodiment of

the invention is illustrated in Figure 5. As shown in Figure 5, an input signal V(t) is

delivered to the input of a gated integrator 50. The gated integrator 50 provides at its

output an integrated measurement which is the integral of the input signal defined over

the time interval of the gate signal (t₂-tι). The pulsewidth of the gate signal is

determined by a gate interval timer 56. A trigger input signal, which may be delayed by

an appropriate period by a trigger delay 54 according to the delay of the system relative

to the trigger, is used to initiate the start of the gate interval. The width of the gate

pulse is preferably adjusted to an appropriate value, which may be determined empirically by digitizing the waveforms and calculating at least one of the above

monitoring parameters, and optimizing the gate width which correlates best with the calculated data . The integrated measurement output from the gated integrator 50 is

sampled and held by a sample and hold circuit 52, which is triggered by a trigger signal

from the gate interval timer 56. After the integrated measurement is released from the

sample and hold circuit 52, according to the appropriate trigger pulse, the integrated

signal passes through an amplifier 58 which adjusts the gain of the integrated

measurement appropriately. Finally, the integrated measurement is provided to an A/D

converter 59 where the integrated measured signal is converted into an absolute digital

value.

Output signals, derived from each gated integrator circuit are used as inputs to

the microprocessor 44, shown in Figure 4. The microprocessor 44 preferably contains

software which implements all of the mathematical operations necessary to generate the above IBEST parameters. At this point, it should be apparent that single value

quantities are associated with a period of time for each measured pulsed waveform. These single value quantities are further processed to yield the desired operating and

treatment parameters of the particular IBEST apparatus. It should be noted that the

A/D converter 59 (Fig. 5) may also be included in the microprocessor 44.

In the microprocessor 44, the absolute digital value is multiplied by an

appropriate gauge factor to correct for the inherent attenuation of the measurement

devices. The gauge factors will vary for each measurement device, as is known to those of skill in the art. Then, various mathematical operations are performed to

calculate the above IBEST (or other repetitive pulsed beam process) parameters.

Typical mathematical operations, which may be performed are illustrated in equation

form as follows: tgate

Equation 5: Average cathode current: l_k(avg) = J_ J i_k(t)dt tgate 0

tgate

Equation 6: Average diode voltage: V_ak(avg) = J_ J V_ak(t)dt tgate 0

Equation 7: Diode impedance: Z_diode (avg) = V_ak (avg) lκ (avg)

tgate tgate

J i₀(t)dt - J i,(t)dt Equation 8: Average ion current: lι(avg) = __0 0 tπate

Equation 9: Ion diode efficiency: η_diode = 100 x lι(avg)

I_k(avg)

tgate

Equation 10: Energy density: E(ion beam) = V_ak (avg) jV_Fc..p (t)dt

0

A second embodiment of the present invention is illustrated in Figure 6. The

embodiment in Figure 6 differs from the first embodiment in that a gated integrator unit

60 shown in Figure 6 includes hard wired circuitry to calculate the IBEST parameters

directly, and thus does not require an additional microprocessor for such calculation.

As shown in Figure 6, a series of eight measured pulsed waveforms are

monitored by a data acquisition system 60. Particularly, each of a plurality of gated

integrator circuits 62 receives a different input, e.g. a measured pulse waveform from

the cathode current from measurement device 35a, a measured pulse waveform from

the LIVA voltage from measurement device 35b, a measured pulse waveform from the

outer ion beam current from measurement device 35c, a measured pulse waveform

from the inner ion beam current from measurement device 35d, and a measured pulse waveform from the Faraday cups 24 and 26. Other measured values may be included

according to the particular demands of the operator of the IBEST apparatus 5.

The cathode current i_k(t) and the LIVA voltage V_ak(t) may be determined by common techniques known to the of skill in the art. The outer ion beam current i₀(t)

may be determined, e.g at the outer Rogowski coil located in the anode outer flux

excluder 30 (Fig. 2) of the ion diode assembly, and the inner ion beam current ij(t) may

be determined at the inner Rogowski coil located in the anode inner flux excluder 32

(Fig. 2), by again, using techniques known to those of skill in the art. The gated

integrator circuit operates on each of the input signals and generates a plurality of

parameters indicative of the operation of the IBEST treatment process. The plurality of

parameters preferably include average cathode current, the impedance of the ion diode assembly, the average voltage (LIVA voltage), the fixed energy density of the ion beam,

the efficiency of the ion diode assembly, and the energy density at the locations of

each of the plurality of Faraday cups represented by number 24 in Figure 2. Other

outputs may be included according to the particular demands of the operator of the

particular IBEST apparatus or other repetitive pulsed beam process.

As shown in the example of Figure 6, a series of integrator circuits 62 are

arranged to receive the series of measured pulse waveforms from the particular IBEST

apparatus, each integrator circuit preferably receives a single input. The gate interval

of each integrator circuit is defined by an internal timer circuit which, when triggered by an external trigger, provides a specified gate window. This gate window is

subsequently used to activate the integration of the input signal to the integrator circuit

62. In this embodiment, all of the integrator circuits are triggered simultaneously from a common trigger signal. Alternatively, the trigger of the integrator circuits do not need to

be simultaneous by using a fixed delay time for the A/D converters from the associated gated integrator channel trigger.

The integrator circuits 62 provide their respective outputs to a corresponding

A/D converter 64, which receives the trigger signal from a delay 66, where the

integrated measured signals are converted into an absolute digital value. The absolute

digital value is provided to a corresponding amplifier 68 where it is multiplied by an

appropriate gauge factor 69 to compensate for any attenuation attendant to the

measurement devices 61. In Fig. 6, the gauge factors have been collectively labeled

as 69 although the particular factors will typically vary from one another. At this point,

single value quantities are associated with each measured parameter. These single value quantities are further processed to yield the desired operating and treatment parameters of the typical IBEST apparatus.

Specifically, the integrated pulsed waveforms associated with the cathode

current and the diode voltage are divided by the gate interval received from a timer 96

(is this a timer?) at dividers 70 and 72 respectively, then preferably scaled down, e.g.

by 1000, at dividers 82 and 84 respectively, to yield the average cathode current and

diode voltage. The average cathode current and the average diode voltage are used to

calculate the average impedance of the ion diode by dividing the average diode voltage

by the average cathode current in a divider 80. The average ion current may for

example be calculated by subtracting the integral of the inner ion current from the

integral of the outer ion current by a subtractor 74, and then dividing the obtained

difference by the gate interval at a divider 76. Using the average ion current determined at the divider 76, the diode efficiency may be determined by dividing the

average ion current by the average cathode current at a divider 78, and then preferably

multiplying by a scale factor of 100 to determine a percentage of efficiency at a

multiplier 88. Finally, each of the integrated signals from the Faraday cups 24 and 26

may be multiplied by the average ion diode voltage to yield the energy density of the

ion beam at multipliers 86, 88, 90, 92 and 94. It is should be apparent that in the

illustrated embodiment, all of the calculations are done in the preferable manner using

single value quantities.

Figure 7 is a flow diagram which illustrates the operation of the present

invention. As shown in Figure 7, the desired characteristics of an exemplary IBEST

treatment process are measured in step S1. The measured values are continuously

measured and are in the form of pulsed waveforms. The pulsed waveforms are sampled by a gated integrator circuit and integrated over a predetermined period of

time, as shown in step S2. The predetermined period of time in the gated integrator is

controlled by a timing circuit, as shown in Figure 5. The integration of the waveforms

over the predetermined period of time produces a single value indicative of the area

under the curve of the waveform. This single value is converted to an absolute digital

value in step S3. The gain of the single value may be adjusted to compensate for

attenuation factors in the measurement device. This gain adjustment may be either

before or after the single value is converted to an absolute digital value. As shown in

step S4, the desired IBEST monitoring parameters are calculated based on the

absolute digital values. The calculation of the IBEST monitoring parameters is preferably performed according to equations 5-10 above. It should be noted that above method describes the operation of both the first and second embodiments.

The gated integrator unit 42 in both embodiments of the present invention

provides a single value quantity which is proportional to the area under the input signal

waveform over the gate interval. This single value quantity can be subsequently used to calculate the above parameters on an average basis, which reflects the operation of

the treatment system and the overall effectiveness of the treatment process. In this

manner the gated integrator circuits of the present invention eliminate the need for the

high speed digitization instrumentation and a large memory capacity for storing and managing large data arrays. More particularly, the advantages of the present invention include: 1 ) the instrumentation required to implement the present invention is relatively

inexpensive compared to high-speed digitization instrumentation; 2) the single value quantities produced by the present invention significantly reduces the memory

requirements for the data acquisition system compared to the memory requirements for

storing large arrays; and 3) the present method does not require generating and managing an array and is therefore relatively fast. As a result, the overall treatment

rate is not significantly limited by the rate at which data can be collected by the data

acquisition system.

Since the present invention provides the ability to quickly determine the data required to obtain the above parameters, the invention may be employed to continuously monitor and record parameters associated with an IBEST or other pulsed

beam treatment process during treatment of an item. Particularly, the forgoing

embodiments of the present invention may also be implemented in part of a feedback control loop in an IBEST or other pulsed beam treatment apparatus. In such an implementation, the various treatment parameters would be monitored, recorded and processed to indicate the effectiveness of the treatment process. This information

would then be used to automatically adjust various control parameters of the IBEST or

other pulsed beam treatment apparatus to produce the desired treatment conditions. The foregoing description of the preferred embodiments of the invention have

been presented for purposes of illustration and description. As alluded to throughout the specification, the present invention can also be used to measure, characterize and

control other repetitively pulsed beam systems such as those used to create electron beams, laser beams or ion beams formed by other methods. It is not intended to be exhaustive or to limit the invention to the precise form disclosed, and obviously many modifications and variations are possible in light of the above teaching. It is intended

that the scope of the invention be defined by the claims appended hereto.

Claims

CLAIMSWe claim:

1. A monitoring apparatus for monitoring parameters of a pulsed beam generated by a pulsed beam apparatus, the monitoring apparatus comprising: a measurement device which measures a characteristic of at least one of the pulse beam apparatus and a beam as a waveform;

a gated integrator which integrates the waveform over a period of time to produce a single value indicative of the waveform; and a microprocessor which calculates a parameter indicative of an operation of at

least one of the pulsed beam apparatus and the beam based on the single value.

2. The apparatus according to claim 1 , wherein the gated integrator further

comprises: a gated integrator circuit which receives the waveform; and

a gate interval timer which provides a pulse signal to the gated integrator circuit

which defines the period over which the received waveform is integrated.

3. The apparatus according to claim 2, wherein the gated integrator further

comprises: a gain control circuit which adjusts the gain of the single value according to an

attenuation factor of said measurement device.

1 4. The apparatus according to claim 1 , wherein said pulsed beam apparatus

2 comprises an ion diode for generating an ion beam including a generally conical

3 annular ion beam having inner and outer peripheral regions and an apex approximately

4 at an object to be irradiated, said ion diode including a cathode, wherein the

5 characteristic which is measured by the measurement device includes at least one of β the following: a current to the cathode, a voltage across the diode, an ion beam current

7 at said outer peripheral region, an inner ion beam current at said inner peripheral

8 region, and at least one ion density measurement of the ion beam in the vicinity of the

9 locations of the object to be irradiated.

1 5. The apparatus according to claim 1 , wherein said pulsed beam apparatus

4 at an object to be irradiated, said diode including a cathode, and wherein the calculated

5 parameter includes at least one of the following: average cathode current, impedance

β of the diode, average diode voltage, fixed energy density of the ion beam, efficiency of 7 the ion diode, and energy density calculations of at least one location of an ion beam.

1 6. The apparatus according to claim 1 , wherein the measurement device

2 measures a plurality of characteristics of at least one of the pulsed beam apparatus

3 and the beam, and provides a plurality of waveforms respectively, the gated integrator

4 further comprising: a plurality of gated integrator circuits, each of which receives a single waveform; and

a gate interval timer which provides a pulse signal to each gated integrator

circuit which defines the period over which the received waveform is integrated.

7. The apparatus according to claim 6, wherein the gated integrator further comprises:

a plurality of gain control circuits, each gain control circuit of said plurality of

gain control circuits corresponding to each gated integrator circuit, each gain control

circuit adjusting the gain of the single value produced by a corresponding gated

integrator circuit according to an attenuation factor of said measurement device.

8. A method for monitoring parameters in a pulsed beam apparatus, the method comprising the steps of:

measuring a characteristic of at least one of the pulsed beam apparatus and a

beam as a waveform;

integrating the waveform over a period of time to produce a single value

indicative of the waveform; and

calculating a parameter indicative of an operation of at least one of the pulsed

beam apparatus and the beam based on the single value.

9. The method according to claim 8, wherein the pulsed beam apparatus

comprises an ion diode for generating a generally conical, annular ion beam having inner and outer peripheral regions and an apex approximately at an object to be

irradiated, said ion diode including a cathode, wherein the step of measuring a characteristic measures at least one of the following: a current to the cathode, a voltage

across the diode, an ion beam current at said outer peripheral region, an inner ion

beam current at said inner peripheral region, and at least one ion density measurement

of the ion beam in the vicinity of the locations of the object to be irradiated.

10. The apparatus according to claim 8, wherein the pulsed beam apparatus

comprises an ion diode which generates a generally conical, annular ion beam having

inner and outer peripheral regions and an apex approximately at an object to be

irradiated, said ion diode including a cathode, wherein the step of calculating a

parameter calculates at least one of the following: average cathode current, impedance

of the diode, average diode voltage, fixed energy density of the ion beam, efficiency of

the ion diode, and energy density calculations of at least one location of an ion beam.

11. The method according to claim 8, wherein the step of measuring a

characteristic measures a plurality of characteristic values as a plurality of waveforms

respectively, the step of integrating integrates the plurality of waveforms, and the step

of calculating calculates a plurality of parameters.

12. A monitoring apparatus for monitoring parameters in a pulsed beam

treatment apparatus, the monitoring apparatus comprising: a measurement device which measures a characteristic of at least one of the

pulsed beam apparatus and a pulsed beam as a waveform;

a gated integrator circuit which integrates the waveform over a period of time to

produce a single value indicative of the waveform; and

a logic circuit which calculates a parameter indicative of an operation of at least

one of the pulsed beam apparatus and the pulsed beam based on the single value.

13. The apparatus according to claim 12, wherein the gated integrator circuit

receives the waveform, and the monitoring apparatus further comprises;

which defines the period over which the received waveform is integrated.

14. The apparatus according to claim 13, wherein the gated integrator circuit

receives the waveform, and the monitoring apparatus further comprises;

a gain control circuit which adjusts the gain of the single value according to an

attenuation factor of said measurement device.

15. The apparatus according to claim 12, wherein said pulsed beam

apparatus comprises an ion diode for generating a generally conical, annular ion beam

having inner and outer peripheral regions and an apex approximately at an object to be

irradiated, said ion diode including a cathode, wherein the characteristic which is

measured by the measurement device includes at least one of the following: a current

to the cathode, a voltage across the diode, an ion beam current at said outer peripheral region, an inner ion beam current at said inner peripheral region, and at least one ion

density measurement of the ion beam in the vicinity of the locations of the object to be

irradiated.

16. The apparatus according to claim 12, wherein said pulsed beam apparatus comprises an ion diode for generating a generally conical, annular ion beam

irradiated, said ion diode including a cathode, and wherein the calculated parameter

includes at least one of the following: average cathode current, impedance of the

diode, average diode voltage, fixed energy density of the ion beam, efficiency of the ion

diode, and energy density calculations of at least one location of an ion beam.

17. The apparatus according to claim 12, wherein the monitoring apparatus

further comprises:

a plurality of measurement devices which measure a plurality of characteristics

of at least one of the pulsed beam apparatus and the pulsed beam, and provides a

plurality of waveforms respectively; a plurality of gated integrator circuits which produce a plurality of single values,

wherein each gated integrator receives a single waveform and produces a single value

based on the received waveform; and

a gate interval timer which provides a pulse signal to each gated integrator

18. The apparatus according to claim 17, wherein the monitoring apparatus

further comprises:

integrator circuit according to an attenuation factor of said measurement device; and

a plurality of logic circuits which calculate a plurality of parameters indicative of

an operation of at least one of the pulsed beam apparatus and the beam based on the

plurality of single values.