THE v IG1., c0R..T..UC’£IOH, MID CALIBHAIIG · 2021. 1. 6. · THE v" IG1., c0R..T..UC’£IOH,...
Transcript of THE v IG1., c0R..T..UC’£IOH, MID CALIBHAIIG · 2021. 1. 6. · THE v" IG1., c0R..T..UC’£IOH,...
THE v" IG1., c0R..T..UC’£IOH, MID CALIBHAIIG
OF A G1.1«auATI1«G VOLIMEIEB
FOR A WO MILLIUN VOLT ELLCIRCMTATIC .Z’TGEI„ RAIOR
V
“v
Robert 1.. Bow/Ian, Jr.
Thesis su\·m1tt•d to the Graduate Faculty ot the
Virginia Polyteohnic Inatitut• V
-2,
TADLD OF uoßranfs
Page
List of Figures .................„.„„...••„.......„•...„..3
Introduction ............•.„„....„„•..•„.„••.•..„........„k
Review of Literature ...............„....•••...........,..6
Design...•.„„•„„•„...••.••••„„„•„•,.„„„..„..„•••........11
rrinciple of Opcratiom .............................11
Rotor und Jtator Assembly ...............„..........15
Rotor Drivc and iressure Housing ....,............,.18
Hectificr and Vacuum Tube Voltmctcr ...,..........,.19
Construction........„.•.„„•„•„„.••..„...„•.„„•.•........25
Rotor and Atator Assenbly..„.„„„.•••.•.••••.„„••...25
Rotor Drive und nrcssure Housing ..•.„.•„..•...„....25
Aectifier ana Vacuum Tube Voltnctor ................28
Assembly ....„..„.....••••„......•......„...........31
Calibration .„•......„„..„...................•••....•....32
Operation of Accc1c·ator .....„„.„.•.„....„.........32
Counting A;>pa.ratus .„............„„„„............33
Calibrating Fxpc·ircnt ....•„„•.•••.•.........„„•...3k
Results .„.......„„.•.„.....••„•„••„„.....„•........36
summary .•....„•„...........................•............NO
Acknowledgcscnta ...............................•..•„....k1
Bibliography......„.„.•„•„••-„•..•„„•••.•••••••„•••„„...h2
Vito
LIST Oi;' FI GUHES
Figure Page
1. Jitlplified Generating Voltmeter •.•••••••••••••••.••.• 14
2. Rotor and Jtator Design ···········•••••••·•••••••••·~16
3. Gim·.:lified Generating Voltmeter of Present Design •••• 17
4. Vol t:r:1eter Asset1bly Design ••••.••••.•••.•••••....•..•• 22
5. nectifier Design ····••••••••••······~~·····•••·•·····23 6. Vacuum 1ilbe Voltnetcr Design .••••..•.•.....••••.•.... 24
7, Rotor and Btator in Tank Reca!;s •.••..•.••.•••. , .•. ! •• 26
8. Helat1ve Position of I~otor and ;3tator with Terminal . . 27
9. Generating Voltmeter Bolted to Tank •••••••..•.••••••. 29
10. Generating Voltoeter Panel ..••..•..•.•..•...•...•.... 30
11 . Gamma Yield from Fluorine ....••••••••••.••••••.••... "3e
12. Calibration of Voltmeter .••••.••••••.••••••.••••••••. 39
-1+..
LHTRODUCTIOH
Becent ccmpletion ot the Virginia Polyteehnlc Institute
alectroatatlc accelerator makes possible the production of
a been ot protens with a maximum energy ot two million elec-
tron volts. It ls of particular convenienee to he able to
read directly the voltage with which the protons are accel-
erated. This ot course is also an indicatlon ct the energy
ot the baum. Iieasurasant ot electrostatic potentlals can be
accomplished with a gancratlug voltmeter. The purpose ot
this thesls is to deeeribc the design, construction, and
calihration ot a genereting voltneter used with the alco-
trostatic generator. The final value ot energy ie deter-
mlned by a nagnetic analyser.
The generatlng voltacter is a rotating grounded shutter
type developed tor electrostatlc gencrntora operating under
pressure. It essentially conslste ot two sectored vanes
located ln the electrostatic field. One ot the vancs is
grounded. It is rotated, alternately shieldlng the other
vane, generating an alternating charging current which is
proporticnal to the potential ot the high voltage source
creating the electric field. This current passes through
a rectitler clrcuit and the voltage developed across a re-
sistance is neasurcd hy a vacuua tube voltmeter. The netcr
was callhrated ln place utilislug encrgies ot knmn nuclear
-5-
ruunaucsa obtaimd by ganra-ray yiclris from bombardmant
ot tluorino with protonm
-6-
MEVILH UF LITKnAlU.m
Many generating voltneters have been described in the
literature. The original generatlng voltmeter was developed
independently by Gunnö and by Kirkpatrick and H1yake.15,16
It was developed in order to have a rugged portable instru-
ment for measurizg eloctrostatic fields. This type of in-
strunent proved very valuable in measuring electrostatic po-
t ntlals which were too high or where meusurcnent by other
m<ans was irpractical.
Uith the advent of thc high Voltage elrctrostatic acoel-
erators the probler of obtainirg a convcnicnt and reliable
mezsurenent of this high potential received considerable
attentl¤.2h•25 several methods co ld have possibly been
used. Axong these arc the methods of high resistance, at-
tr cted disk, proton range, generating voltmcter, and mag-
netic end electrostatic defleetion of ions. The high resis-
tanoe method reeulres a resistence difficult to construct and
ehield fror corona, ant probably results in non-linear rea-
ponse because of the size of the apparatus and the magnitude
of the Voltage involved. An attracted disk is subject to large
calibrati g errors because of the squared scale and the rela-
tivcly low available calibrating voltages. The nagnctic and
eloctrostatic deflection and proton range were felt to be more
conplicated than at first thought to be necessary,
-7-
Because it had been used with good results for a variety
of purposes6*9*15 ant becnuse of the advantxges offered by
its relative sirplicity and its independence of the ion beam,
the nethod utilizing a generating voltmeter was tried with
good Censequently, voltmeters of linear scales
and aecuracies ranging from 5 percent to 0.2 pereent have•-
volved for use xdth oloctrostatic gcnerators. The generating
voltneter has remained the primary means of measuring the
voltage on many ef the renerators for several years. With
the addition of concentric electrodes on the electrostatie
generators some other means of obtainlng the absolute voltage
have ha= to be devised siner the generating voltmeter would
only neasure the potential of the outer electrode. Also, the
desire for more accurate energy measurcments dictated the use
of other methods. Accur te measuroments are made today by
electrostatic analyzers er calibreted magnetic analyzers.
The geaeratlng voltmeter remains a verk useful tool with the
electrestatic generators, especially during initial focusing,
u
because of its continuous scale reading.
Because of its usefulness, it is well to review the
type of generating voltneter devcle~ed with respect to choice
cf parameters, d1ffie·lties found, methods ef calibrntien,
and the advant·ges found from the use of this type of meter.
The review is by no means cenplete, but contains references
to some typical voltmeters.
-8-
The parameters lnvolved in generating voltmeters es will
be shown in the next section include the size und shape of
the vanes and the speed of rotation of the grounding vane.
An early attuzpt by Van Atta, Northrup, Van Atta, and Van de
Graaffzs vas to shape the vanes es to generate a sine wave
current. However, the most expedient shaped vanes have been
sector shaped. The University of Kentuclqm and The Call-
fornla Institute of Technologyw electrostatio sccelerator
groups built voltmeters consisting of sem circular pole piece!.
Herb, Parkingson, and Ke:-et$•“•‘9 ef Wisconsin and Williams,
Hubevsh, um 1·at•2'I er Minnesota mut voltmeters er wo
pole sectored vanes. The c rrent from these voltmetcrs was
ccmrrutated by a sjmchronous meehanlcal rectifier and displayed
on a sensitive gelvanometer. Trump, Safford, and Van de
Gmaf!22 reported s four pole voltmeter the output of which
was reetified by s full-wave-bridge vacuum tube rectifler
and displayed on a mleroammeter. An in ovation of the shut-
ter type voltncter is the cue developed by Haxby, Shoupp,
Stephens, and Wel1s8•26 using the DTL ciple of compeasating
voltages described by Harnwell and Van Voorhis.7 In this
voltmeter, the generatlng voltmeter itself is used onl;· to
detect the absrnce of lnhonogencitles in the field behind a
voltege plate. Voltage is apwliod to this plate until it co-
incidcs with an equipotential surface of the field frnn the
high potential elec‘rode. This condition is detected b· the
•9-
abscaoa ot plokpup in tha ganarating voltnatar part. Tha
high voltaga la than proportional to thn voltaga on thn
voltagn plata and is mcaaurad by nnans of prnoislon r•a1s•
tore and a mllliannntar. Tha alu ot thn vanas of th•s• vas~•
loua voltuatnrs rangns h·¤¤ about twnlvn lnahas to thran
inchns depandlng on thn sinn of thn generator. In nost
••s•s thn rotating wann ia npnn hy althar an 1800 r.p.a. or
a 3600 r.p.¤• synohronous motor.
Dltticnltlns arislng with thosa voltaatars ars those
usually assoolatad with location. Ditticulty has bnan notad
man thn voltmatar ams looatad so that it night"s••"
a
chargod lnsulatad anrtaoa or mara thn tlald ie large enough
to panit •park¤v•¤·.25 Sonn ooamaxats hava han aadn on thn
nttnot ot oorona ouzrant. Tramp, Sattord, and Van dn Graatfzz
ahownd that thn artnet ot corona onrrnnt ln thalr dnslgn us
nagllgihla tor thn prassurn lnenlatad generator. Herb, Park-
lngson, and I•rst“ toamd that tha suaaltlvity o! thn ult-
aator changad radloally it the vanas warn ohangad alightly
with rnspaot to thn tank wall.
Tha most axpadisnt way ot calibrating thn voltmntar la
to apply to thn high voltagn alactroda a potential mich aan
ha maaaurad hy soma othor aaana. 81nc• thn voltmntar in
linaar a ralatlvnly small voltags can ba appliad and nau-
urnd by a proviously oallhratnd high rnsistanon. From this
-10-
a voltage sensitivity car bc est·blished. This is the method
used by Trump, Jnfford, and Van de Graaff•22 Another standard
method is to cvmpare the veltmeter reading with the value of
the terminal voltare at known nuclear rosonxnces. This method
has ben used by a nunbwr of grou;e.?•11•17•27 The linearity
has also been checked by utilizing the double and triplc
energies needed for diatomic and triatomlc ions to undergo
the sans reaetions as monatcmic lens.I
The rain advantage: of thc renerating voltveter have been
found te be as follows. The voltnetar is inve endent of the
ion beaa. The voltretrr Lrains no current from the source of
high voltage. It has a contlnuous scale reading. It is rela-
tively ruggcd. The indicating meter is at or near ground
potential and can be located at a aistanee from the generator.
•11•
DESIGN
The generatlng veltueter coneiste easentially ot an
lneulated atatcr member mounted in the ground plane ot the
tank racing the high Voltage terminal fron mich it 1:
periodlcally ahielded by the rotation et conetent speed ot
a grmmded sectored disk. The stator-to-terminal capaci-
tance 1: thus caused to Vary periedically and the induced
etator current, mich 1: a aeasure of the terminal voltage,
paesea through a rectlfler giving rise to a Voltage acroee
a resletance B. The d.o. potential developed across thia
reelstance ie measured by a special vacuu tube voltneter.
A einplified circuit tor a generating vcltneter ls given
In Figure 1. In this figure and in the analyele below V
ie the ccnetant potential to be meaeuredg G is the period-
ically varying cepacitance between the high Voltage terminal
end the stationary etatcr, the naximun Variation ct which 1:
G'.
The cycle ct operation 1: aa followe. A: G increase:
Iron its nininum value, the etetor ie charged through the
rectirler T, by the influence of the potential V until G
reachee lt: naximun Value. Then ae G decreaees, the etatcr
dicahargea through the reetitier T2 and ma p•e1,;zg¤¤• 3
until G again reaches ite ninlnun value, whcreupon the cycle
-13-
is ropeatcd„ It is evident that the current ln R le uui-
directlonel and is independent of the polarity cf V. It
is of interest to note that the total charge transferred
over one cycle is zero. Theretore, the voltmoter draws no
current frca the high voltage source, but rather the power
used for the cyclic transfer of charge is supplied by the
nechenical force varying the capacitance G.
The circultal relation during the last half of the
cycle ie
V ¤ E•
LB,G
wheree q ¤ the charge at any time on G,
1 ¤ the instantaneoua current,
V•
the high voltage potential,
C ¤ the etator•to-terminal capacitance, and
R ¤ the voltage dropping reeistanoe,
aeeumlng negligible rectitier voltage drope„ This eqnatlon
ie difficult to eolve ainoe G is a function of tue. If,
however, it is noted that LB is very srall in comparison with
V (a departare of about two parts in one million for the
present voltneter) the relation may be written with good
approxlnatlon ae
V e ,
-13•
D1rferent1at1ng with renpect to t1ne,
2. g 5- V,
dt dt
°’•
1 dt ¤ GC V.
1ntegret1¤g ever cne halt period, 1/2, the •quat1o¤ becceen
‘!0
31 dt • jd!} V.
1/2 a,
the left eide cf thin equation 1n einply the total charge,
Q, wh1ch flcwn through the r•n1ntence K dur1ng thin helf
cycle. Therefore,
Q ¤ •¤,V.
hat beceune the c1r·cu1t 1n ennentielly e he1f•weve rect1f1er,
thin 1e eleo the tctel charge through I d¤r1ng e ccuplete
cycle cf cpereticm Then d1v1d1ng by 1,
Q ¤vV
'{ '°T‘
Since Q/1 1n the current, I, in B during ue eycle end
I/T ¤ fc, the verietion frequency of the cepecitence ¢, the
voltege ecrosn the ren1stnnce B 1n
IH•
•l£°6'V„
‘!h1n reletion nhcvee that the vcltege ecronn l 1e propcrticnal
to fo end tor ccnetent frequency in proport1enal tc the potte-
@
-15..
tial V. By reading this Voltage dlrectly with an appropriate
Veen: tnhe Voltaeter, the high Voltage potential V can be
read directly.
Hotor and Stator Alseahl!
A
ASuce the lnduced statcr current ls proportional tc the
frequency cf the variatlon ct C, lt is desirahle to dlvlde
the atator menher into several peles so se to lncreaee the
nagnitude cf the lnduced current: tor a fixed speed ef the
roter. The period of Variation ot the capacitance should of
course hc large in comparison with the relaxatlen tue cf
the circult. he stator cf the present Voltaeter ls dlvided
inte light
‘•5°
secters. Alternate stator sectcrs are elec-
trically connected to fern two statcr groups cf four polel
180 electrical dogrees cut of phase with each other. The
tour pole roter ls e conplenent to each of these state!
groups. Figure 2 shows a detail drawing cf the roter and
etator. It may he noted that the induced stator corrnt
will he eseerntlally a perlodlc roctangular wave of 180•1•••
trlcal degrees. With each etator gro-ap provided with an in-
dependent rectlfier systen as ahown in Figure 3, e s¤hstan•
tially constant rectitied current flows in the reslstanoe B.
. since the frequency ot Variation of the cepaeitance ls ese•n•
tially twice that ct the previous analysis the current output
ls doohled.
@
~
'
'
HIGH VOLTAGE ELECTRODE
STATOR NO. 2
I R STATOR NO. I
SIMPLIFIED GENERATING VOLTMETER OF PRESENT DESIGN FIG. 3
•18•
It is also desirable to make the etator•to-terminal
capaaurnee as large as possible to increase the magnitmde
of the. current generated. The capacitance 1:: determined
prinarily by the size (area) ot the stator and its dlstance
from the hlgh Voltage terminal. These two paraneters, how-
ever, were fixed by the geometry of the pres ure tank and
high veltage terminal. The distance tc the stator from the
high voltage terminal was determined by the relative die-
tance between the accelerator electrode am the ground plane
of the apex of the tank. The size of the stator was 11: ited
by the *+.9 inch elameter recese aporture in which the stator
is located.It
has been noted that the generating voltneter output
ls proportional to the high voltage potential only if the
frequency ef the periedic st¤to1·•to-terminal capaeitance ia
constant. This is accomplished by spinning the roter with
a synchronous motor. For thc present voltmeter a Bodine,
1/20 h.p. 1800 r.p.m. synchronous motor is used. Slnce a
motor cf this capacity will not fit into a three inch wald-
ing well opening to the pressure tank, it was necessary tc
design a rotor drive in which the motor is located outside
ef this well. In order to oomgletely pressurize thc entire
geaerating voltmeter, the motor is located in a flange and
•19•
plpe pressure chanber which bolts onto the {lange of the
weldlng well. he rotor ls atfixcd to the end of e double
ballbearlng shett arrangement which is located down the
length ot the well. The shaft ls driven by the synchronuue
motor, being coupled by a flexible coupling. A cross-see-
tional detail drawlng of the voltmeter is shown in Figure B.
Complete detail drnwings of the generatlng voltmeter are
lnserted in a pocket Ln the beck cover•
Since lt ls deslrable to take advantage of the linear
scale ot a direct current meter, it is necessary to rectify
the generated sigel {rom the voltmeter. Referring again to
Figure 3, it can be seen the rectlfier circuit is sie-
ply a t*¤ll•wave-bridge type. A t*ul1•wave•bridg• reetitier
was designed utilising the high reverse resistance of e
vaeuun tube diode. ho twin 6% diodes were used with the
heater current limited to about one half rated value to in-
hibit the {low ef emission current d··1·1ng the non•conducting
part et the cycle. The filement supply to the rectltier ls
controlled by the Vacuum tube voltmeter power switch. Fig-
ure 5 shows the diagram tor the rectitier.
The vacu m tube voltmetor shown ln Figure 6 is based
on e difference anpllficr circuit. The voltncter power sup-
ply ia a conventiohal full-wave VH tube reg elatod supply.
•20•
The output is read on a meter brtweon the pl tcs of the tue
trlodes ot a 6SH7. The 5000 ohm variable resistaace ln the
plate circult serves to balance the plrte voltage ot the
two tubes so that ne current is indicated by the meter.
The rcctltled output signal from the geaeratlng voltmcter
ls developer across a 3.1k negohm reslstance. Thls resis-
tance is connected to a switching arrangement so that either
all, one half, or one fourth ot the total voltage drop across
the rcslstance ls a plled to the Frid ot one trlode glvlag
relative voltage raages ot one, two, and tour resgectlvoly.
An ldutlcal reslstance switchlxg arrangement ls ln the other
grld clrcuit so that ia swltchlng fror one range to another
the zero dritt ls mlnimlzed. The apgllcutlon of the signal
to the grid causcs an unbalance between the plates and the
dlttereatiel plate current ls given by
ߤi'
1 =———————"”——"“““
1
Hz + rp(2 + Rn/R1)
where: p = gala ot vacuua twbe,
e = voltage ay lied te grld,
Rh = reslstance ot meter,
rp = plate rcslstance of tube, and
R1 = loan reslstance.
This shows that unter preyor operating conditions the output
of the vacuum tube veltreter cerresroats directly te
'c”
and
heace by previous analysis ta the potential of the hlgh volt-
-21•
age el•ot1·ode•
The meter between the two plotes ls e 0•100 nicroas-
neter movement shunted so the output ranges correspond
closely to ne, two, and tour nillicn volts• Further call-
bration is achdeved with the adjustable resistanees marked
"Gal C" and 'Cel I". Since lt is not known which setting
corresponds to one, two, and tour million volts full seele,
the meter clreuit contains a swltching arrangement so that
two different calibratlng resietances nay be pleced in the
cix·cuit„ Iith the 'Scele Selector" switch in the "Ce1" pc-
sltlm, the resistence 'Cal ¢" ls adjustcd until the output
is thought to be such that a full scale reading will corres•
pcnd to one alllian volts. It is in this position that the
voltueter ls ce.l1brated• Atter celibratlon, the 'Scele
Selector" is ewltched to the "lull" position end the resis-
tance "<2el F" is adjusted until mll scale deflection cor-
reepuads to one nillicn vo1ts•
It was noted that the rectitler developed a contact
potential end that e eonstant signal across R was always
present. Ihis seall current ls coupenseted hy with the
nero edjustnent„ However, this makes lt impossible to have
a eonventional nero check bv simply lnterrupting the signal
tree the generatlng voltnetcr. A sero check is provided lv
e switch in the voltage supply to the synehronous motor.
v l/ / l PRESSURE I HOUSING TANK WALL /
STATOR \\
WELDING WELL I cCJVL.
, ' I
\
I
I I
SYNCHRONOUS MOTOR
" ' '\_,
"
ROTOR DRIVE
' 0-RING GASKET r/.' '~ \ I \
BUSHING
VOLTMETER ASSEMBLY DESIGN FIG. 4
0-RING GASKET I
I I\) I\) I
STATOR NO. I
•
VTVM I I
:r=i-11 -=-1 I
.J L Ir. __ Ir ---------11 11---11 11
JONES PLUG
6.3 VAC
RECTIFIER DESIGN FIG. 5
----il
:~IL_ ___ _ 11 , , , ,
f
STATOR NO. 2
I f\)
l,v I
5A (
115 VAC
5V 3A
120MA 350-0-350 V
.3V FIL
6H6 1S
JONES PLU G
2A
TO SYN MOTOR
NORMALLY CLOSED 11ZERO CHECK"
1.57M 1%
.787M 1%
.787M 1%
IOH
160 MA
8}J F 18UF 600V 600V
VR 105 VR 105
5 K
' 18 K-2 "ZERO ADJ°' 18 K-2
37n
IOK 11CAL1 F
IOOµA
' /
" /
' I
GEN VM
I I _c-i I r~ - II --r--
1 I 1
I I I I
1.57M, 1%
\ ----/ \_ , / 6SN7 \ -; / / I "--- / '.._ __/ I
.787M 1%
L ------------------ ___ _J .OlµF .01 µF
(M) 220D. (M) _ .787M ~ 1%
VACUUM TUBE VOLTMETER DESIGN FIG. 6
•
-25-
roter and etater are made er 1/16-lneh elunlmn.
The elght neben of the eteter are fustened te e 1/2-inch
bakelite lnsuleter by two screve each. Theee sorewe serve
also es electrloal contacts vlth every other uenber cen-
nected and tvo leads away from the stator. The bekellte
lneulater ls eeeured te the front bearlng housing ot the
roter drive by four aerews. The roter is eftlxed to the
shatt h a renevable oollar. The roter le adjueted until
tuereterie|ll¢tlybeh1ndthegrexmdpl.aneetthetenk
wall. The spaelng between the etetor and roter ls about
0.1 inch. The vhele roter end stator aseebly la reeessel
lnanepelng ln theapexot the tank. Because et thlsre-
eese the roter and steter nust be meunted Iren inelde the
tank. Figure 7 shoes the roter and stator ln this r•eeu•
Figure 8 shows the relative pesltlon ot the stetor end the
high voltage terminal.
A V
The roter drive end preseure housing ae were all the
other parts ot the voltmeter were naehined in the Virginia
Pelyteehnle Institute Physles Department shop. The rote!
drlvlng ehett and bearlng heusings are nade ef steel. The
bearing heuslngs are eeparatedhy a thin vall bress eyl£n¤•r•
~
ROTOR AND STATOR IN TANK RECESS FIG. 7
I I\) 0\ I
~
I I\) -...J I
RELATIVE POSITION OF ROTOR AND STATOR WITH TERMINAL FIG. 8
•2F-
The synchronous notor is oncloscd by a welded steel pressure
chambcr. The charbcr is fastened to the tank by four 3/N-
inch ca; screws. Pressure seals arc schievcd with *0* ring
pressure gaskets. Figure 9 shows the voltreter assenbled
and holte to thr tank. Four clectrioal connections are
brought out through the front ·late of the pressure chamber.
These bushings were soldered into place after welcing by
preheatiug the complete plate. Access to the bushings is
ma.e by 1/¥·inch pipe plugs.
Rectifier and Vacuum Tube Vsltxeter
The rectifier is nounte= on a senicircular chassis lo-
cated oa the pressure chamber. The signal from the restl-
fier is carrioe to the vacuum tubc voltretcr bv a low loss
coaxial cable. The power supply for the synchronous motor
und filament supplt for the rectifier are brought from the
Vacuum tube voltmeter loc‘te„ on the remote control console.
A view of the rectlficr may bc seen in Figure 9.
The vacuu tube voltneter is located on a control con-
sole so that the meter may F< reae easlli by the operator.
It is of conventional _anel and chassis construction and is
rack nounted. The range selector, scale selector, zero avjumt,
and zero check are located on the front of the panel for eas
use. Figure 10 shous a view of the console panel of the gen-
erating voltneter. The calibrating rzsixters are located on
the chassis and can be adjusted from the top of the rack.
GENERATING VOLTMETER BOLTED TO TANK FIG. 9
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-31-
Assembly
Because of the unique construction of the penertting
voltnetcr the following assenbly procedure is used. The
motor is provided with a clarying ring and is end nounted.
The motor is mounted first, making sure the two lends to
the stator are brought out the front of the chamber ·ad
the two leads to the motor are brought back around the motor.
The flexible c0u;ling uring this time should bc secured to
the shaft of tho motor. The roar bearing housing is next
fastcned to the chambcr, shaft inserted into the counling,
and the cylinder und front bearing housing secured in place.
The cou ling nov may be tightened with an A11en—head wrench
et the opening provided in the rear bearing housing. The
voltrcter may new be boltcd to tnc tank und the roter and
stator ettnch«d fror inside the tank. The voltmeter should
be disasserbled in reverse order.
-g2•
CALIBLKATIOH
Although the generating volhaeter reading is independent
of the ion bean, it ls necessary for ealibratlon purposes to
bombard e target with protons. For this reason a brlcf de-
scription of operation of the eq zipuent ia given.
The first step in _;utting the accelerator into operation
ls to initiate a dlseharge in thc ion source. The lens pro-
duced are cxtracted by application of a 'probe" voltage ln the
dlscharge vessel. The spray voltage is now ra! sed until e pre-
determined voltage between terminal and ground is brought to
equilibrium, with the amount of charge being brought to the
terminal by the charging belt equal to the charge being lost
by the terminal. The ion bc··x is now b·-ing aecelcrnted denn
the tube with the chosen energy. The beam is allowed to fall
upon e quarts disk where it is focused by an eleetrostatlc
lens et the high voltage end of the acceleratlng tube. The
beam mst now be analysen, that 1s, separaten into mass one,
uns two, etc, components. This is done with the magnetic
analyzer•‘8 With propcr adjustment and a reasonable current
thrc gh the magnet eo that the dcsired mass number will be
beat by the magnet, the beam she ld now be at the slit box.
With the bcam implnging on the sllt jaws the coronn feedback
stabilizationl holds the beam on target with the eeslred en-
·33¤-
erg. The spread of energy on the target is nov a function
of the sllt width thro gh which the been passes and the dls-
tance from the magnet to the sllt• The approximate energy
ot the beam is nov known h-cn the knowledge of the nagnetlc
field es determined by the currentJ8 It is now desired tc
determine more exactly the energy correepcmdlng to the gen-
eratlng vcltmeter reading at this vcltagc„
Counting ggaiatul
A
prctons fall upon the target a reactlon may
take place which results in the mission er ga¤ma•reys. It
ls desired to find the "relative yield" of this reactlon,
that is, a number proportional te the ratio of the gonna-
rays euitted from the target te the number ef bombardlng pro-
tons. It is then necessary to measure a quantity proportimal
tc the number of gamma-rays emltted and also a quantity pro-
portional to the number of protons lmpinglng on the targ•t•
A scintillatlen counter was used to deteet the games-
x·ay|•This counter consisted of a so<Eiu¤ iodlde crystal13
end e 6292 Dumont photemultiplier tube. The seintilletiens
caused by the gam:a~rays are arplified by the photomultiplier
tube and the output pulse, after suitable ampliflcation, was
applied to a decade scalcr. Th: dlscrininatcr of the ampll-
fier was set so that the x-ray background ot the accelerater
was not detected. 1'nerefore, the 'background" radlatien wu
-3b-
redueed essentlally to that due to cosnlc radiation.
A qunntity proportional to the n·rher of bombarding
pretons was obtained with the use of a "current integrator'.
The ”current integr tor" wa: of the neon glow t pe. lt een-
sisted of a 150 micrenicrefarad cupaeiter, a 1.2 nagohm re-
slstor and a neon glow lamp. The charge which accnmulated
on the target charget the capacitnnce until the brcakdown
potential of the neon lanp was reachot. The glow tube then
“firod', discharging the capacitor through the reslxtanee,
giving rise to a pulse which was proportional t the charge
ac umulated. The cycle was then repeated. The output pulse
was fad through a preon lifler into a decodc scaler.
Te obtain the rrl tive ‘1eld, it wu: only necessary to
allow the pulses from thc xclntillation counter ana eurr¤nt
lntagratcr to register sinulteneously for n s ecific length
ef tina. By diviping the number ef ¤cale« scintillation
count: by the current integrator counts, the relative yield
is obtained.
Caligratigg Exrcrircnt
Host of the light olments are known to yield gaxua-
rays when they are bemberded with protoas. The intensitr of
gunma•ray radlatlon free next light elencnt: exhibit reso-
nance phenomena; near resonance the amount of garca-rar
radiation is much grratrr than fer neighbering energiee.
For example, in the bombardhent ot fluorinc with protons,
-35-
resonances are known to occur at encrgles of .3*-60 Mev and
.*+86 Hev in addition to other well known rescnnnces.22 To
lllustrate hxrther, examining the yleld from protons on fluo-
rine, it would be expected that the yield would increase with
lncreasing energy until the energy ot .3*+0 Hev was reached.
Increesing the mergy beyond this would result in decreasing
yleld until the next resonance ls approached. This of course
ls the case it the target is a thin target. Let us consider
what would happen lf the target is thicker. If a proton hav-
ing an energy slightly greater than .3*+0 Hcv lmplnges ax such
a target lt will have a lover probabillty of being captured
by the first layer of ateuxxs than one of energy of .3*+0 Hav.
Ext as lt penetrates the target lt will lose energy by calli-
sione with electrons and the probebillty of capture increases.
The net result than is a shitting of the aaxlmxm of the yield
curve to higher energies. If the target ls thick enough to
stop all the protons the yield curve will edxibit no naxlmm
at all but will level off at the highest value of the yleld.
The position of resonance is taken to he half way up the yield
curve. These so called "thick target" yields arc well known
and are suitable for calibraticn purposes.
Thick target yiclds of tlxxorine were obtained and the
calibration ot the generating voltneter made from them. A
typical yield run was made in the following manner. hu gen-
-36-
erating vcltmetcr eelcctor switch was placed in the "Ca1"
positim. Alter a. fefinito recycling pattern ef the magnet
to minimiu hysteresis effects the ren net current was brought
to a dcsired current to bend the mass one c ¤„omnt of the
beam with approxinntely e predetermined energy. The vcltage
ol the accelerntcr was rai:ed until the bcen was seen to be
lrzplnging on the target. Slxmltaneous ecuating ef game-ray
end lntegrator ccunts were made tor two minutes and the rele-
tive yleld oalculated. The gcncratirrg voltneter was read
during the time period. The magnet current was read by
reading the potential ..rop acrosu a standard .01 ohm resis-
tance in series with the nagnct with a Leeds and Zlorthrup type
K-1 potentiometer. hc magnet currcrzt was then ralsed .05 ul-
peres und simultaneous reading taken again. This process vu
repcated until the :.eai;~c<; yield spectr n uns cbtained.
Buulu
T’he .3*•0 Hev and .*+86 Mev resonances ol fluorine were
obtained. The yield curve nay be seen in Figure 11. The
.3*•0 Hev und .*+86 Mev 1·e.;onancos corras ond to generatlng
voltmeter reading: of 36.0 und 56.3 percent cf scale range
on the one million vclts range. Since the voltnetcr should
be linear it was felt that it was only necessary to obtalu
two p.·1¤ts tc establish calibration. The calibraticn curve
ot the generetlng voltneter may bé seen in Figure 12. M
-37.
use of this curve a reiterstlon process was made by |witch•
ing from the "Cal" position to the "Pull" position of the
scale selcctor and the meter was sdjusted umtll full scale
deflection in the "Full" position sho· ld correspond to one
million volts. This curve may also be seen in Figure 12.
The dotted line from the origin to ovne million volts is the
idealized calibrstion curve. The distance between the cell.
brated "full scale" curve and this idealised curve represente
the actual error reading interpretlng the voltage nom the
meter directly. This error should amount to within five
pcrcent ln half scale deflection with decreasing error fo!
higher reading on the one million volts range. On the tvo
nilllon vclts range the error should not exoeed plus or minus
three perocnt being a minimum near half soale• If it ls
necessary to recallbrate the meter, good results should be
obtained ln the following manner. With the been on target
and the current in the magnet 5.0+ amperes, the generating
voltmeter ehe ld read 38 and 32 percent scale reading om the
'Gal" and "Fnll" positions ot the seele selecter respeotively
on the one million volts range•
@
@
#+0-
Hüllen!
A generating vclueter capable ot measuring one, two,
or tour mllllm volts has ben designed and oonetrueted tor
une with the Virginia Polytochuie Institute elaetroetatie
eceelerator. The voltmeter ie e grouuded ahutter typo, the
reetitied output ot which is measured by e vecmm tube v¤lt·
meter. ‘l'he voltmeter wu calibrated by kamm uucleur reso-
mmcoe of fluorine. '1'ho callbretiou showed the meter to he
eocurate to within tive peroent at hal! ecale deflectim ¤¤
the cue mulln volts range md lese than plus or minus three
poromt cu the two million volts range,
.1+1..
aßllultäßünuütl
The author wishes to thank Dr. T. N. Hahn, Jr. tor his
inspiration, guidanee and gansrous advice during thispro•
jeet. He also wishes to express his appreoiation to ,- 1
-tor his many untirlng oonsideraticms. He especially
wishea to thank-tor his advice sad hal) in
the aaohining ot the voltneter. Since any work done on the
aooslerator is always the result of group effort, it is in
this oapaoity that the author wishes to thank all the staff
and graduate school uho have helped in this initial effort•
.b2.
BIm.10GRA1HY
1. Ball G., Unpublished H.S. Thesis, Virginia Iolytechnic
metlzuze, 1 57.
2. Bonner, T. W. and Evans, J. E., Phys. Rev., 73, 666
(19k8).
3. Ghao C. Y. Tellcstrup, A. V. Fovlcr W. A. und
Lmalzsea, Ö. c., (bye. Rev., 79, 108 (1950).
M. Elnore W. C. und Jands, H., Eloctgonics, p. 52, McGraw
H111 (19M9).
5. Gernt E. J. Herb R. G. and Parkingson D. B. Phys.
¤.v.,'sM, 6M1 (193f).’ ’
6. Gunn, Ä., Ihys. Rev., H0, 307 (1932).
7. Harnuell G. I. and Van Voorhis, S. N., Rev. Sci. Inst.,M, 6Mo (1933).
8. Haxby, R. 0., Shoupp, U. Y., Stcphcns, H. E. und Wells,
I. H., Ihys. Rev., 56, 1035 (19h0).
9. Henerson, J. E., Goss, V. H. and Rose, J. B., Rev. Sci.
mst., 6, 63 (1935).
10. Herb R. G. Kerst, D. W. and Hcxibben, J. L., Ehys. Rev.
:1, 691 (1937).
11. Herb, R. G. Iarkingson, D. B. und Kerst, D. U., Phys.
Rev., 51, 75 (1937).
12. Herb R. G. Jnowdon, J. C. and Gala, 0., Ihys. Rev.,
vs,§¤613.
n¤rsta6ex·, R., Ihys. Rev., 75, 796 (19*4).
1h. Korn, B. D., Private Corvunicatien.
15. Kirkpatrick, I., Rev. Jci. Inst., 3, M30 (1932).
16. Kirkpatrick, 1. ana Hiyako, I., Äev. dei. Inst., 3, 1
(1932).
17. Lauritscn, T., Luuritsen, C. C. and Fovlcr, H. A., Phys.
Rev., 59, 2h1 (19%1).
J;}-
18. ¤11v•r, ¤. H. ¤¤,)uh11shs«1 1:.8. Thss1s, v1x·g1n1a Po1y•
t•chx11c Inst15ute, 1956.
19. P *.1.11 ·>11 D. B. Ilcrb :1. G. G ::11; E. J. and
raäiibbä, 5. L., Ähys. Äsv., 55, ghz (1938).°
20. Wan, J. L., Uznpublishcd M.S. Thesis, Univusity of Kan-
tucky, 1952.
21. Thomas, H. A., Rev. Sci. Inst., 8, @+8(1937).
22. Tramp J. G., Sattord F. J'. and Vand•
Gruft, H. J.,
nev. 5¤1. mst., 11, 5*+ (who).
23. rz-up J. 0. ma vu.a•
orssrr, 11. J., Phys. nw., 55,
1160 (1939).
zh. 1-WVG M. A. Hsrszsd, L. R. and Dahl, 0., Phys. mv.,*+8. 515 (1955).
25. Van Atta, L. C. Horthrup, D. L., Van Ath C. H. lhd
vu. as 0;·ss::, Ä. J., Phys. mv., h9, 761 (1936).
26. Hella, W. H., Hexhy R. 0., Stephans, I. E. md Shoupp,
w. 1:., Phys. mv., 58, 162 (19*+0).
27. vI1.111sms J. J., Brmbaugh, L. H. amd Tsze, J. F., 13,
202 (19*+2).
The vita has been removed from
the scanned document
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