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M 6 OAU

CHUONGL NGUON PHAT TLF TRUDNG XUNG CAO VA
CO S6 THIET KE CUPN NAM CHAM

5

1.1 Cac ngu6n tir trucrng tren the gidi

6

1.2 H6 tir trudng xung va cac thOng so ban dau

9

1.3 Co SOT v^t ly li^n quan den phat tir trucrng xung cao

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1.4 Bai toan thi^'t ka'cudn day nam cham
1.4.1

Anh huang cua dang hlnh hoc cuOn day nam cham

1.4.2 Anh hucrng cua nhi6t do do xung dong dien chay qua

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17
19

7

1.4.3

Anh hirong cua ap sua't tir len cu5n day nam cham

1.5 Ket luan chuofng
CHlfONG 2.

22
33

DIEU KHIEN NAP VA PHONG DIEN TRONG
NGUON PHATTLfTRUdNG XUNG CAO

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2.1. Vong didu khien tu dong

37

2.2. Didu khiln di6n tu" va ghep n6i may tinh

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2.3. Mach di6u khi^n SCR vdi tai cam cam khang

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2.3.1. Su tri cua dong dien qua tai cam khang

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"2.3.2. Dong qua d6 qua tai cam khang

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2.4. Chuyen mach Thyristor c6ng sua't \6n

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2.5. Bo tu dien

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2.6. Ket luan chuong

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CHUONG 3.

THUTHAPVAXLTLYTINHIEU

TRONG HE TLf TRUdNG XUNG CAO

3.1. H6 cu6n pick-up

44

44

3.1.1. Phuongphap do cam ung

44

3.1.2. Dae trung tan so

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3.1.3. Anh huomg ciia nhi6t dO d6'n dac tinh cu6n pick-up

48

3.1.4. Anh huong ciaa cac th6ng s5' cu6n pick-up va hinh dang mSu
do den th6' 16i ra cua sensor
3.1.5. Cac loai cu6n day pick-up
3.2. He dien tu thu thap va xir ly tin hieu

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52
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3.2.1. CSu bu trijr va b6 ti^n khud'ch dai vi sai

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3.2.2. Bo tich phan dien tu

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3.2.3. Ba vi phan dien tu

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3.2.4. Cac b6 bie'n d6i A/D va b6 nh6 s6 lifu RAM

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3.3. Thu thap va xu ly s5' li6u bang ghep n6'i may tinh

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3.4. Ke't luan chuang

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CHlfONG 4.

THL/C NGHIEM XAY DL/NG HE TLf KETCfTRl/dNG XUNG CAO

61

4.1

Che tao cuOn nam cham

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4.2

Xay dung khoi nap va phong dien

70

4.2.1. Mach didn cha'p hanh

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4.2.2. Mach di6n cac rcf-le va bien thd'cao ap cOng sua't 16n

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4.2.3. Thyristor va mach tao xung m6i

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4.2.4. Cac dien trof cCng sua't lorn va b6 tu di6n

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4.2.5. Mach I6gic di6u khien

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4.3

xay dung ha thu thap va xu ly s6' Heu

95

4.3.1 Che tao cuOn day pick-up

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4.3.2 Cac mach dien tu thu thap va xu ly tin hidu

99

. 4.3.3 Ghep n5'i he do v6\ may vi tinh qua chudn GPIB
va phSn m6m xu ly so lieu

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4.3,4 Chu^n dO trong he va cac thao luan

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4.4

Ket luan chuang

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CHlfONG 5.

QNG

DUNG HE TL/ KE TLf T R U 6 N G XUNG

TRONG NGHIEN CLfU VAT LIEU TLf

5.1.

M6t s6'ke't qua do su phu thu6c cua ti^ dO vao tir trucrng

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120

5.1.1. Do tir d6 tren m^u b5t dinh huomg

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5.1.2. Cac phep do ti^ do tren mau b6t rdi

121

5.1.3. Xac dinh hieu ung tijf nhiet cua mSu kh6'i
cac hgp cha't Gd5(Ge,.,Si,)
5.2.

Do \.\x trudng di hu6ng bang phuang phap SPD

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129

5.2.1 Phuang phap SPD

129

5^2,2 Thuc nghiem do dac

130

5.2.3 Xir ly s5'tin hieu trong phep do SPD

131

5.3.
5.4.

Do ducmg cong xh trS ciia cac nam cham
Ke't luan chuang

KET LUAN

Cac c6ng trinh lien quan de'n de tai Luan an.

Tai lieu tham kliao
Phu luc

136
141
142


D A N H M U C C A C C H O VIJ^T T A T

Chuf
viet tat

Tieng Anh

Tieng Viet

A/D

Analog to Digital conversion

Bien d6i tuang tu ra s5'

AC

Alternating Current

Dong dien xoay chieu

DC

Direct Current

Dong dien mdt chieu

DIV

Division

D6 chia

FOMP

First Oder Magnetization Process

Xir ly ti^ bac mot

IPS

In-phase Signal

Tin hieu d6ng pha

ISA

Industrial Standard Architecture

Kien true chudn cong nghiep

OPTRON

Chip dieu khien phan each
quang.

OSC

Oscilloscope

PID

Propotional-Integral-Derivative Control Dieu khi^n kieu ty le - tich

Dao dOng ky

phan-vi phan.
PIT

Programmable Interval Timer

Chip dinh thcri kha trinh

PPI

Programmable Peripheral Interface

Chip ghep n6i ngoai vi kha

trinh
PSS

Phase-shift signal

Tin hieu c6 dich pha

RAM

Random Access Memory

Bo nh6 ghi/doc dugc

SCR

Solid-state Conntrolled Rectifier

Cai chinh luu c6 dieu khien
bang mach ran (dugc che'
tao bang vat lieu ban dSn)

SPD

Singular-point detection

Ky thuat phat hien di^m di
thudng,

SQUID

Superconducting Quantum

Thie't bi giao thoa lugng tu

Interferer Device

sieu dSn.

UIB

Universal Interface Board

Ban mach ghep nO'i da nang.

VSM

Vibrating Sample Magnetometer

Tu ke' mSu rung


FTiKR mil ^Au
J hue nghiem trong tiJf trucrng cao mang lai nhieu thdng tin quan trong ve tinh
cha't vat ly cua cac vat lieu. Thuc vay, ttf trudng c6 dO lofn so sanh dugc v6i gia tri
cua tru&ng trao d6i hoac trucrng tinh th^ dSn de'n pha v5 ca'u true tir cua cac phan
mang tuf trong cac vat lieu hgp cha't lien kim loai, Cac chuyen pha tiir gia ben do tach
cac phan vung vdi spin "up" va "down" c6 the thuc hien vdi tir trucrng du Idfn. Cac
hieu iJng lai trong vijng nang lugng ciia cac vat lieu chufa Uran dSn de'n di hucfng tii
khong 16 chi c6 the dugc phat hien v6i cac phep do thuc hien tai tir trucrng cao. Cac
chuyen pha tiif trang thai femion nang hoac trang thai sieu dSn sang trang thai
thucmg cung c6 the dugc gay ra bdi tur trucrng ngoai 16n han nhieu Idn tijr trucrng
thudng diing 6 cac phong thi nghiem. Ngay ca cac nghien cuu gdn lien vdri ling dung
ciia cac "sieu nam cham" che' tao bang cac vat lieu ivc cung chua da't hiem cung can

CO tijf trucrng ra't Idn di nap tir cac nam cham nay hoac d^ dat dugc mot ducrng tir trS
dSy du ciia chung. So v6i tir trudng trai da't {5.10'^ Tesla) va ti^ trucrng cua cac nam
cham thong thucmg trong phong thi nghiem {0,1 - 2 Tesla) thi cac ngu6n tijr trucrng
v6i cucmg do han 10 Tesla dugc coi la ngu6n tiif trucrng cao [47].
De tao cac ngu6n rw" trudng tinh c6 d6 \dn tren 10 Tesla cSn phai c6 cac phuang
tien phiic tap va dat gia. Thi du, ne'u dung phuang phap Bitter phai tao ra nhutig he
di^u khi^n ngu6n dien c6 nang lugng hang MJ va c6ng sua't len i6i hang MW ciing
cuon day nam cham kh6ng 16 dugc lam lanh dac biet bang he cap nude ap sua't cao.
Ne'u dirng phuang phap cu6n day sieu dSn phai c6 he ca'p He-li long. Trong ca hai
trucrng hgp tren, ngudi ta chi tao dugc cac tijf trudng tinh cue dai tren dudi 20 Tesla.
Phuang phap tao cac tit trudng xung, thi du dua tren nguyen tac nap dien cho bo
tu dien nang lugng Idn r6i phong dien ra't nhanh qua cudn day nam cham dien cam,
cho phep tranh dugc nhung dSu tu dat gia neu tren ma lai tao dugc cac xung tir


trudng c6 bien d6 len tdi hang tram Tesla. Do vay, ngay ca b cac nude tien tien hien
nay deu c6 xay dung cac trung tam nghien ciJu s\s dung tiJf trudng xung cao.
,

Vdi kha nang kinh te' ciia cac phong thi nghiem d Viet nam hien nay chua cho
phep xay dung dugc cac ngu6n tir trudng cao theo kieu tir trudng tinh, trong khi do
do yeu cSu nghien cihi cac vat lieu tijr hien dai, cSn c6 ngay nhiJng ngu6n tijf trudng
cao nhu vay. Chinh ky thuat xung cd th^ dap u:ng dugc yeu cdu nay khi dugc dijng
de tao ra cac xung tir trudng c6 bien dd tren 10 Tesla nhung khoang thdi gian t6n tai
chi cd mili giay de'n 1 giay. R6 rang vdi m6t he tit trudng xung nhu vay thi bien d6
xung \.\x trudng van dat dugc rat Idn trong khi nang lugng chi cSn ca vai chuc KJ va
do dd ve mat kinh te' cac he tuf trudng xung c6 gia thanh cha'p nhan dugc ddi vdi
nude ta.
Hien c6 2 phuang phap tao cac tit trudng xung cao, dd la phuang phap pha huy
(destructive) va phuang phdp khong pha huy (non-destructive). Phuang phap pha

huy dijng d^ tao cac ngu6n ti^ trudng xung cao han 100 Tesla trong mot khdng gian
CO cac dudng sure tir bi nen lai do mdt cii n6; thdi gian t6n tai xung chi ca micrd giay
trudc khi vach ngan khdng gian do va cac vat ben trong bi vu n6 pha huy hoan toan.
Phuang phap khdng pha huy dirng mot ddng dien Idn phong qua cac cuOn dien cam
nham tao ra ben trong loi ciia chung mdt tiJf trudng xung cao cd gia tri nho hem 100
Tesla. Cac cudn nam cham nay g6m mdt vdng hoac nhieu vdng, dugc sir dung nhieu
ISn va cho cac xung tijf trudng dai tir vai mili giay de'n hang giay.
Muc dich cua ban Luan an la nham xay dung dugc mot he tit ke tic trudng xung

cao din tien tai Viet nam. He phai phuc vu dugc cho cdng tac nghien cuu va dao tao
tai cac trudng Dai hoc, cac Trung tam nghien curu trong linh vuc khoa hoc cdng
nghe \i vat lieu tijf hien dai.
Noi dung va phuong phap nghien cihi: Luan an dugc tien hanh bang cac
phuang phap nghien cuu thuc nghiem. Luan an g6m cac ndi dung sau:
1. T6ng quan cac nghien ciJu ly thuye't va thuc nghiem tren the' gidi tai nhOng va'n
de lien quan de'n viec phat v^ do dac cac thdng s6 ciia vat lieu tijf d tijf trudng
cao.


2. Thie't ke' va xay dung mdt he tij: ke' i\x trudng xung cao, day la he d5u tien thudc
loai nay d Viet nam. He g6m 2 khd'i;
(a) Khdi phdt tit trudng xung dugc xay dung bang phuang phap napphong qua bd tu dien. Khd'i dugc dieu khien tu ddng bang dien tir va
ky thuat ghep nd'i vi tfnh. Cac xung tijf trudng cd gia tri cue dai tren 20
Tesla, dd dai xung tit 3 de'n tren 30 mili giay, ddng nha't trong mdt
viing do tai d'ng day c6 dudng kinh de'n 25 mm.
(b) Khdi do cdc thdng sd vat ly ciia cac vat lieu tijf (dugc dat trong tijf
trudng nay) bang cac phuang phap thu thap, xir ly tin hieu tuang tu va
sd' ke't hgp vdi ky thuat ghep nd'i may vi tinh.
Cac thie't ke' ve phSn cufng va phSn mem dugc tien hanh tai Khoa Vat ly trudng Dai hgc Khoa hoc tu nhien - Dai hoe Qud'c gia Ha noi (DHKHTNDHQGHN), tai Vien Vat ly thuc nghiem - Dai hoc Tong hgp Ky thuat Vien
(Cdng hoa Ao) va tai Trung tam Qud'c te' Dao tao ve Khoa hoc vat lieu

(ITIMS). Cac linh kien va vat lieu quan trong trong he do dugc nhap ngoai
hoac dugc che' tao trong nude theo mfiu thiet ke' ciia tac gia va nhdm nghien
ciiu. He dugc che' tao, lap rap, do dac kiem tra tai Phdng thi nghiem Tijf trudng
xung cao - Trung tam ITIMS.
3. Do thir cac he mSu vat lieu tijf, dac biet la cac lien kim loai dat hiem - kim loai
chuyen tiep bang cac phep do khac nhau nham khang dinh cac tinh nang ciia he
tir ke' tij: trudng xung cao da dugc xay dung.
Cac mSu do dugc che' tao va kiem tra bang cac phuang phap lien quan khac tai
Khoa vat ly, DHKHTN-DHQGHN; Dai hgc Tdng hgp ky thuat Vien; Trung
tam ITIMS; Trung tam Khoa hoc tu nhien va Cdng nghe Qud'c gia, Dai hoc
Tong hgp Birmingham (Anh) va Dai hoc Tong hgp Amsterdam (Ha Ian).
• Bd' cue ciia Luan an bao g6m 5 chucmg, trong dd:
Chuang 1 la phSn tong quan ve cac ngu6n phat tir trudng cao va ti^ trudng
xung cao; nhirng va'n di tinh toan ly thuyet cung nhu thuc nghiem che tao


cudn nam cham da dugc khao sat lam tiln d6 cho viec xay dung chuang
trinh thie't ke' tdi uu hoa cudn day nay.
Chuang 2 va 3 de cap tdi cac bai toan thie't ke' he dilu khien nap-phdng
dien trong klid'i phat xung tijf trudng cao va he thu thap xir ly tin hieu trong
khdi do cac thdng sd' vat ly ciia vat lieu tijf dat trong ti^ trudng dd.
Chuang 4 trinh bay cac thuc nghiem da dugc tie'n hanh xay dung he tii
trudng xung cao. Thdng sd, chi tieu ky thuat ciia cac bd phan trong he sau
khi lap rap da dugc do dac cung nhu cac van de chu^n dd tir trudng va tir
dd da dugc bao cao.
Ndi dung ciia chuang 5 la thuc nghiem do dac cac mau vat lieu tir da dugc
tie'n hanh tren he tij ke' tijr trudng xung cao nham kiem tra va khang dinh
tinh diing dan va do tin cay ciia he do, Cac phuang phap do, ke't qua va
thao luan cho cac phep do dac da dugc trinh bay.

CHlfONG 1.

NGUON PHAT TLf TRLTONG XUNG CAO
VA CO S6 THIET KE CUON NAM CHAM

Mot he tiJC keh& ky d6u bao g6m 2 khO'i: kh6'i phat tut trucrng va khd'i do lucmg
cac thdng s6' cua vat heu dat trong tir trucmg do nhu so d6 khd'i hinh 1.
,
Khoi phat tCr trudng


Co cau
Cd cau
dieu khien
chuyen
va
—>
hoa nang
tich luy
luong
nang lUdng

Bo
cam
bien

—>

thu thap
va XLf ly
so lieu

Buong do chifa mau dat
trong vung tCr trudng

Hinh LI

Sa d6 chung cua m6t tir ke'

Kh6'i phat tiif truing g6m cac ca ca'u di6u khien qua trinh tich luy va chuyen hoa
cac ngu6n nang lugng (thi du nhu nang lugng ngu6n dien thanh ph6', nang lugng do
mdt vu nd sinh ra ...) thanh nang lugng tir c6 d5 Idn cSn thiet trong mOt khOng gian
CO th^ tich xac dinh, MSu vat lieu dugc dat trong kh6ng gian do. Khoi do g6m cac
cam bie'n c6 nhiem vu bie'n d6i cac th6ng s6' c^n do cua mSu (thi du nhu tir d5) thanh
cac tin hieu dien ty le r6i dua vao b6 thu thap xu ly tin hieu. Trong cac tir ke' hien dai
hSu he't cac qua trinh dieu khien va do luc^ng ke tren deu dugc xir ly bang may tinh
qua cac chuong trinh phSn mem. Cac tin hieu thudng dugc so hoa va dugc xir ly s6
nham nang cao d5 tin cay va tfnh linh hoat cua he do.
V6\ cac tir ke do dac b dai \.\i trucrng tha'p va cue tha'p nhu tijf ke' xoan, tijf ke' mau
rung, ti^ ke' giao thoa lugng tu sieu dan SQUID v.v... doi hoi c6 nhung ngu6n phat tir
trucmg tinh ra't 6n dinh va cac thie't bi do cue nhay. Trong khi do cac tijf ke' tijr trucmg
cao nhu tii ketic trudng xung cao lai cSn phai tao ra dugc nhirng xung dong dien cue
lorn va thie't bi do phai dam bao thu thap va xiT ly dugc cac th6ng s6 cua he trong mot
thcri gian t6n tai xung ra't ngan.


Do dai phat tijf trucmg trong tu nhien va nhan tao de'n nay trai ra ra't r5ng, nhu se
noi du6i day, nen viec nghien cu:u thie't ke' mOt he tir ke' cu the phai xua't phat tijf

nhung yeu cSu cu th^ ciia cac nghien cu:u vat lieu ti^ c6 tinh de'n cac dinh hudng ve
mat ly thuye't. Do nhGng linh kien va phuang tien xay dung he do con ra't dat nen
dieu kien kinh te' ciia m6i phong thf nghiem, m6i qu6'c gia cung la m5t nhan t5' quan
trong phai tfnh de'n trong m6t chie'n luge c6 the mof r6ng tfnh nang ky thuat cua he
do trong tuang lai. Dudi day se diim l^n lugt tijfng khia canh v^ mat ly thuye't lien
quan de'n viec thie't ke' m6t ngu6n phat i\X trucmg xung cao cho he tijr ke'.
1.1.

CAC

N G U 6 N TIJ TRUCJNG

TRfiN THE GICJI

GiO'ng nhu nhiet dO va ap sua't, ti^ trucmg la m6t trong cac thOng s6 ca ban dugc
dirng d^ thay d6i trang thai vat ly ciia vat lieu. Viec ma rOng dai bie'n doi ciia tir
tru6ng tac dOng len d6'i tugng do trong nghien cuu se dSn t6i cac phat minh mdi va
da dong gop nhieu cho cac hieu bie't ca ban trong vat ly cha't ran. Cac ngu6n phat tij"
trucmg CO sSn trong tu nhien va nhan tao. Hinh 2 la biJc tranh ve do Idn ciia cac
nguon tCf trudng trong dai tir lO"''* den 10^ Tesla [14].
Cac ngu6n ti^ trudng nhan tao dung cho nghien ciJu vat lieu tij* cd the dugc phan
thanh cac ngudn tijf trudng tinh, gia tinh va tijf trudng xung.
a. Tit trudng tinh: g6m cac loai sau.
-

Cdc nam cham dien mot chieu: la cac cudn day dien cam cd loi sat hoac hgp
kim sat. Nhung nam cham dien Idn nhu b Bellevue (Phap) cd tir trudng ca 4,3
Tesla, nang 120 ta'n, tieu thu cdng suat 93 KW [14]. Nhirng nam cham loai nay
trong cac phdng thi nghiem nghien curu vat lieu tir ngay nay dugc thay the' dSn
bang nam cham cd cudn day sieu dSn vdi kfch thudc va trong lugng nho han.

-

Nam cham sieu dan: cudn day nam cham dugc che tao bang cac vat lieu cd
tfnh sieu dan tai cac nhiet do tren 4,2K tdi 77K cung nhu cd tir trudng tdi han
vugt qua 10 T. ISThd cd mat do ddng dien cao nen da xua't hien nhung nam cham
sieu dan tren thi trudng cd ti^ trudng len tdi 20 T.

-

Nam cham Bitter: Cudn day ciia nhirng nam cham nay la nhung dia dong mdng
tach biet cd cac Id trdn ban kinh khac nhau dugc ep vdi nhau. Ca'u true nhu vay
cho phep lam lam lanh dugc nam cham khi cd ddng dien Idn chay qua. Mot


tai 0,1 de'n 1 giay [13] Tai day, ddng dien mdt chi^u DC bie'n d6i tirng budc len
tdi cudng dd ra't cao dugc ca'p cho cudn nam cham day cud'n. Cudn day nay
dugc l^m lanh bang khf Neon long. Ddng dien mdt chilu dugc tao bdi viec
chinh luu cd dilu khi^n ddng dien xoay chi^u AC ciia mdt tram ca'p dien thanh
phd' cd nang lugng len tdi 3 MJ. Day Ih. mdt he ra't phufc tap va dat gia.
c. Tu: trudng xung: dac diim ciia cac ngudn phat tir trudng loai nay la chi cSn cd
nang lugng nho nhung v5n cho phep nhan dugc cac xung tiJf trudng cd dinh cao
do thdi gian t6n tai ciia xung ngln. Tijf trudng xung cd th^ dugc tao ra bdi mdt
trong hai phuang phap:
-

Phuang phdp phd huy: he chi tao dugc mdt xung ti^ trudng cao duy nha't trong
khoang thdi gian ra't ngan r6i sau dd toan bd he do mSu trong khdng gian tijf
trudng bi pha huy hoan toan. Phuang phap nay sir dung nguyen ly nen cac
dudng siic tijf ciia mdt tir trudng ban din ben trong mdt thanh binh (vach ngan)

each tijr. Ne'u van td'c nen cao, thf du dijng ap sua't nen la do luc tac dung len
thanh binh dugc sinh ra bdi mdt vu n6 , thi mat dd tijf thdng se tang len ra't
nhanh trong qua trinh n6 dSn tdi tao dugc mdt xung tijf trudng cue cao trong
khdng gian da bi thu hep lai do thanh binh bi nen [21]. Vdi van td'c nen thanh
binh cao c5 1 km/giay; he cho phep bie'n d6i tiJ trudng ban dSu trong binh len
tdi hang tram Tesla trong vdng chi cd cd micrd giay. Thf du v^ loai nay la he tao
ti^ trudng pha huy tai phdng thf nghiem Megagauss d Vifn Vat ly cha't ran, Dai
hoc T6ng hgp Tokyo cho mdt xung tir trudng len tdi 500 Tesla, thdi gian t6n tai
4 micrd giay trong khdng gian cd dudng kinh 10 mm [30].

-

Phuang phdp tqo tit trudng xung khong phd huy: He cd th^ tao ra cac xung tir
trudng cho nhi^u ISn do. Day la phuang phap dan gian va kinh te', phii hgp vdi
di^u kien ciia cac phdng thf nghifm thdng thudng tren the' gidi va d Viet nam.
Nguyen ly ciia phuang phap dugc thuc hien thanh cdng din tien bdi Kapitza
nam 1924 [17] khi sir dung qua trinh phdng dien tfch tren mdt bd tu dien qua
cudn day nam cham dien cam cd dien trd nho. VI sau nay, nhUng cdng trinh
tie'p theo ciia Allain (1968), Chikazum (1969) va Jordaan (1973) cung cho


rihiJng tCr trudng xung len tdi 50 Tesla [1], [6], [16]. Bang 1.1 la liet ke tdm tat
mdt vai ngudn phat tijf trudng xung cao khdng pha huy tren the' gidi [9].
Bang 1.1 Mdt sd nguon ti)t trudng xung cao tren the gidi.
Ph6ng thf nghiem

Vien H&n iam KH B^c iDai hoc Tdng hop Humbodit (DLTC)
Dai hoc Tong hop Bristol (Anh)

Do dai
Ndng The nap TCrtrifdng Dudng kfnh
lirong cure dai dinh
trong cuon day xung
[KJ]

[KV]

m

[mm]

[msl

340
50
400

5
2.5
5
20
7.5
3
5
10
7
4
5
1

5
7
5
2.5
5
3
7.1

50
50
27
40
26
30
60
60
50
65
55
32

22
10
12
20
28
15
17
24
20

13
15
13
22
22
22
25

3.5
2
5
10
52
5
6.5
7.5
5
3,4
6
3
2-5
10
0.6
3
6
4
150

Dai hoc T6ng hop Osaka (Nhat)

1500

Dai hocl< Tdng hop Dublin (Ireland)
Dai hoc Tdng hop Kobe (Nhat)

290
24

Dai hoc Tdng hop Leuven (Bi)

1200

Dai hoc Tdng hi?p Los Alamos (Hoa ky)

1100

Dai hoc Tdng hdp Oxford (Anh)

800
210
180
30
75
800
30
75

Hoc vidn ky thuat Massachusetts (Hoa ky)
Dai hoc Tdng hop Kurchatov (Nga)
Dai hoc Tdng hop Qudc gia Moscow (Nga)

Dai hoc Tdng hdp St. Petersburg (Nga)
Dai hoc Tdng hdp Sydney (Australia)
Dai hoc Tdng hop Parma (Italy)
Dai hoc Tdng hop ky thuat Vien (Ao)
Dai hoc Tong hdp Wroclaw (Ba Ian)

300
70

Dai hoc Tdng h^p Zaragoza (Tay ban nha)

1200

Dai hoc Tdng hdp Tokyo

35-40

60
34
43
55
47
31

16
10-22

30

Qua bang nay ta th^'y viec danh gia "siJ'c manh" ciia cac ngudn tir trudng xung

cao phii thudc vao nang luong cue dai nap tren tu. Nang luong nay ty le vdi dien
dung va ty le vdi binh phtrofng the' nap cue dai tren bd tu dien. Khi cac thdng sd con
lai la khdng d6i, dd dai xung ty le vdi nang luong. Budng do chu'a cac mSu dugc dat
trong khdng gian t6n tai xung ti^ trudng. Khdng gian nay ty le vdi dudng kinh trong
cudn day nam cham. Dudng kinh cudn day cang Idn cang khd dat dugc gia tri cao
ciia tijr trudng dinh d tam cudn day. Qua day cijng tha'y chua cd mdt co sd nao d
viang Ddng Nam A cd trong danh sach xay dung he ti^ ke' tijf trudng xung cao dugc
liet ke.
1.2.

Hfe TIJ T R I T O N G X U N G VA CAC T H O N G S6 BAN DAU


10

Can cur vao xu hudng dang ph6 bie'n hien nay tren the' gidi va dieu kien d Viet
nam, Luan an da chgn hudng nghien ciiu 1^ xay dung he tiif ke' tir trudng xung cao
khdng pha huy. Tiir day ta se goi van tat 1^ he tit ke tu: trudng xung cao hay he tit
trudng xung cao.
Nhung ly do chinh d^ chon phuang an nay la nhu sau. Ta biet rang cac ngudn
phat tuf trudng nhan tao hien nay da dat tdi tren 500 Tesla, trong khi cac he phat tir
trudng tinh chi cho dugc cudng dd tiJf trudng tren dudi 20 Tesla vdi cac nam cham
phiic tap va dat gia. De'n thdi di^m bat din thuc hien Luan an nay, d Viet nam chi
cd cac ngudn tijf trudng tinh trong cdng nghiep va phdng thf nghiem cd cudng dd
nho hcfn 6 Tesla. Trong khi dd, nhi^u nghien cuu vat lieu tir hien dai lai thudng ddi
hoi nhung ngudn tCf trudng cao han trong dai tiif trudng de'n 10, 20 va tdi tren
40 Tesla. Va'n di dat ra vdi cac phdng thi nghiem nghien cuu vat lieu ih la phai tao
dugc nhung ngudn tuf trudng cao vdi trang thie't bi khdng qua dat. Chinh cac ngudn
phat tiif trudng xung loai khdng pha huy da giup giai quye't dugc va'n d^ nay khi chi
yeu cin mdt ngudn tich tu nang lugng nho vin cho phep phat ra mdt xung tir trudng

Idn trong thdi gian tdn tai ngin. Ta't nhien do thdi gian t6n tai ngan nen se keo theo
nhang yeu cin dac biet v^ thu thap va xir ly sd' lieu trong qua trinh do cac thdng sd'
ciia vat lieu, va'n d^ nay da dugc giai quye't mot each thuan Igi trong nhirng nam gin
day do su phat tri^n cua ky thuat ghep nd'i may vi tfnh.
Nhu tren da ndi, d^ nhan duac

f\/bch i^fieij khien

tir trudng xung thi c^n thie't phai cd
mdt ca ca'u tfch luy nang lugng dien

-tfo—I
Kl
R,

K2

d^ rdi chuyen hoa thanh nang lugng
tir. Phuang phap thdng dung la dirng
mach nap-phdng qua tu dien nhu sa
d6 hinh 1.3. Qua mach di^u khi^n,

Hinh 1.3 So d6 dan gian nguydn ly nap phdng
dien di tao tif trudng xung trong long cuon
day nam cham L.

cdng tac dien tir Kl khi ddng se cho
phep nap din din (trong mdt vai phut) dien tfch tir ngudn dien mdt chilu manh S cho
bd tu dien C qua trd han che' ddng R^ de'n mdt the' Uc mong mud'n. Khi ddng cdng
tac K2, tu C se phdng mdt xung ddng dien rat Idn qua cudn nam cham L di tao ra

11

trong loi khdng khf ciia nd mdt xung tiir trudng manh vdi thdi gian t6n tai ngan. Ban
cha't cua qua trinh nky tuy chi Ih dao ddng tu do trong khung RLC nhung lai xay ra
vdi cac thdng sd' ra't khac nghidt: the' ban d^u dugc nap tren bd tu tir vai tram de'n vai
ng^n vdn cho mdt nang lugng dugc tfch tu tir vai chuc KJ tdi hang tram KJ va khi
dugc phdng qua mdt tai dien cam cd trd thuSn R ra't nho cd m/2 se cho ddng cue dai
tiif vai ng^n len de'n vki chuc ngan ampe trong khoang thdi gian c5 mili giay.
Do dd viec xay dung khd'i phat tir trudng xung cao lien quan tdi 2 bai toan Idn,
do Ik: bM todn thie't ke' cudn day nam cham v^ bai toan thie't ke' he d'lin khien nap phdng dien qua cudn day nay. Nang lugng cin nap tren bd tu, ty le vdi CU^ 12 (vdi
U la the' nap tren bd tu), phu thudc vao gia tri dinh xung tir trudng va dudng kfnh
trong cudn day nam cham. Gia tri dinh va dudng kfnh trong cudn day cang Idn,
nang lugng nap tren tu cang cin phai Idn. Viec lua chon cac thdng sd' ban dau nhu
dien dung bd tu, the' nap cue dai, ddng phdng dien cue dai, do Idn va dd dai ciia
xung tuf trudng cung nhu dudng kfnh trong cudn day tuy thudc vao yeu cin nghien
cihi vat lieu, kha nang ky thuat va kinh te'ciia phdng thf nghiem.
Gia thanh ciia cac trang thie't bi xay dung he tif trudng xung cao tuy la tha'p han so
vdi cac he tir trudng tinh cao nhung cung la Idn so vdi di^u kien kinh phf han hep
cua Viet nam (thi du, gia mdt bd tu dien cd Idp each dien thin film 24 mF/3500V
cung cd vai chuc de'n hang tran ngan dd la My, v.v..). Do vay tren ca sd cac nghien
c\t\x ly thuye't v^ vat lieu tir hien dai va kha nang kinh te' ctia de tai xay dung he tir
trudng xung tai Trung tam ITIMS; cac thdng sd' ban din dugc chon nhu sau:
-

Dudng kfnh trong cudn nam cham do cac thdng sd' vat ly cua cac mSu la 25
mm, dugc quye't dinh chfnh bdi dudng kfnh ciia dudi binh dewar bang thuy
tinh chiia Ni-ta long diing cho do mSu tai cac nhiet dd tha'p tdi 77K.

-

Dudng kfnh trong cua cudn nam cham nap tir la 50 mm de thoa man cac nhu
cin nap tiif cac chi tie't Idn trong cdng nghiep va phdng thf nghiem (ta't nhien tir
trudng cue dai trong cudn nam cham nay se tha'p han tai cac cudn do k^ tren
do dudng kfnh trong Idn han).

-

Cac m5u edn do cd kfch thudc cue dai hinh tru dudng kfnh 5 mm, chi^u cao
4 mm, dat trong khdng gian cd he sd' ddng nha't cua tir trudng la nho han 1%.


12

-

Dai nhiet dd do tir nhiet dd Ni-ta long 77K de'n nhiet dd phdng 300K.

-

Cac xung tiif trudng cd gia tri dinh cue dai tdi tren 20 Tesla, dang xung mdt
ban chu ky hoac tokn bd mdt chu ky hinh sin cd bien dd giam din. Gia tri
cudng dd tuf trudng bie'n ddi tir duang sang am dam bao thoa man cac phep do
tijr dd hoac do dudng cong tir tre cua cac mSu vat lieu tir. Thdi gian tdn tai
xung tiif 3 mili giay de'n tren 30 mili giay. Gidi han dudi ciia gia tri nay dugc
quye't dinh bdi viec tranh hieu ling ddng xoay (eddy current) trong cac m3u
chiia kim loai. Gidi han tren tuy thudc vao nang lugng tfch luy cue dai tren bd
tu (ty le vdi dien dung va the' nap cue dai).

-

Viec lua chon giGa dien dung va the' nap cue dai tren bd tu dugc quye't dinh
nhu sau. Mac du nang lugng cua bd tu ty le vdi binh phuang cua the' nap
nhung do dac di^m khf hau im udt tai Viet nam va gia thanh cua cac chuyen
mach dien tiJ nhu thyristor cd the' va ddng hoat ddng cao la ra't dat nen dien ap
nap cue dai chi dugc chon la 2.500 Vdn. Vi vay bd tu dugc chon la loai tu
each dien gia'y cd dien ap chiu dung la 3.500 Vdn va tdng dien dung la 24 mili
Fara + 10%. Nhu vay, nang lugng cua bd tu khi dugc tfch dien vdi the' cao
nha't la:

Wc=-CUl^=-x24J0-^x2500^

1.3.

=^ 75 KJ

CAC CO SCf VAT L V LIEN QUAN D^N QUA TRINH PHAT TlT

TRU^CJNG XUNG CAO.
Nhac lai rang mdt trong nhihig muc dich ciia Luan an la xay dung ngudn phat tir
trudng xung trdn 20 T bang phuang phap khdng pha huy trong long cac cudn nam
cham cd nhi^u Idp day. Ca sd dd thie't ke' cac nam cham loai nay nhu thdng thudng
dugc xua't phat t& he phuang trinh Maxwell va trudng hgp rieng cua nd la cac dinh
luat Kirchoff. Nhu da bie't, he phuang trinh sdng dien tir Maxwell cd dang:
rotH

^ J ^ —dt

(1.1)

13

rotE^-^

(1.2)
dt

divB

= 0

(1.3)

divD

= g,,

(1.4)

d day, H Ik vecta cudng dd tir trudng cd thu* nguyen [A/m]; J la vecta mat dd
ddng dien [A/m^] ; Dla vecta dien dich [C/m^]; B la vecta cam ling tir ITesla] va
Pid la mat dd dien tfch tu do [C/m^j.
Trong trudng hgp tdng quat, giira cac vecta B wh H, D vk E dugc lien he vdi
nhau qua cac cac ten-xa dien (e) va tiir (|i):
D

=(8)i

(1.5)

B

=iii)H

(1.6)

wk

d day (e) = 8 0 (e)r;

(f^) = m) (^)r • Cac dien tir th^m tuang ddi (e)^ va {[i\ cd

thd la cac ham phtic tap phu thudc vao toa dd, cdn SQ = 8,854J0'^

Flm va

1^0 = 471.10'^ Him la cac dien th^m va tif th^m tuang ddi cua chan khdng.
Khi kfch thudc L^ cua viang cin khao sat nho han nhieu chidu dai budc sdng X
(Ls «

X), cd thd bd qua ddng dien dich (/^ = ^Idt)

so vdi ddng dien dSn va

phuang trinh 1.1 trd thanh:
rot H = J

(1.7)

Ap dung dinh ly Stock , tfch phan phuang trinh tren dd'i vdi mat S dugc bao bdi
dudng khep kfn C,- cd:

jrotHdS = JHdL = p dS
S

C/

(1.8)

5

{jdS chinh la ddng dien Is di qua mat S nen:
5

JHdL = Is

(1.9)


14

Phuang trinh n^y la dinh luat Am-pe trong dang tfch phan. Bang each tuang tu,
tijr phuang trinh (1.2) cd thd nhan dugc dang tfch phan cua dinh luat cam ling
Faraday:

JEdL = -—I'BdS
c,

(1.10)

dt

Hai phuang trinh (1.9) va (1.10) la ca sd dd tfnh toan cho cac may phat tir trudng
cao trong thuc nghiem. Tif day tha'y rang, de cd duac tit trudng cao cdn phai cd mot
ca cau tqo duac mot ddng dien Idn chay qua mot cuon day nam cham. Ddng dien
nay cd thd la ddng mdt chidu cd dd Idn khdng ddi trong thdi gian du dai tai cac he tit
trudng tinh hoac ddng dien xung cd bien dd bie'n ddi tir khdng len mdt gia gia tri cue
dai rdi lai vd khdng trong thdi gian ngan tai he tit trudng xung. Viec phat tir trudng
xung cao la mdt bai toan dti phiic tap vi nd lien quan tdi mdi trudrig ddn va ti^: trudng
khong ditng. Dd dai cua cac xung tif trudng va gia tri bien dd cua cam d'ng tir
Bf^ = /Jof^M 1^ hsi ^?c trung quan trong cua mdt xung tiif trudng cao. Trong qua trinh
phat xung tir trudng, cac hieu ling vd dp sudt titvk tieu tan nhiet phai dugc chu y tdi.
Khi phat ra xung tuf trudng cao, trong vat lieu cudn day nam cham xua't hien su bie'n
thien nhiet dd cung nhu ap sua't tir bang //o^^/2 rat Idn. Vdi nhirng nguon tiif trudng
xung len tdi tren 80 Tesla (cd td'c dd tang tir trudng
dat tdi 10^ Tesla /giay) se gay ra mdt ap sua't tren bd
mat vdng day ra't Idn cd ap sua't trong Idng qua da't.
Khi tir trudng vugt qua 100 Tesla,

ap sua't nay

nhanh chdng dugc truydn vao vat dSn va cd thd xay
ra cac sdng xung kfch pha huy cudn day [21].
Luc tac dung len vat dSn cd mat dd ddng / chay
qua khi dat nd trong tuf trudng B \k:

F=JxB

(1.11)

Dd dan gian, chi khao sat trudng hgp khi tir
trudng xung tac dung len ban dien mat dan nhu

Hinh L4 Tuang tac cua
xung tir trudng vdi ban
dien vat d3n.


15

hinh 1.4. Sir dung cdng thufc lien he giOa tir trudng va ddng di^n (1.7) va cdng thiJc
(1.11) ta cd ap sua't trong vat dSn la:
•

„ P(x.t) = - f^B.dx
^ ax

= P, - ^fJoH'(x.l)
2

(1-12)

trong dd PQ la ap sua't ciia tuf trudng tren bd mat vat dSn.
P, = ^//oZ/VO,/; = ^B'(0,t)/;j,

(1.13)

Ke't qua nay khdng phu thudc vao ban cha't cua ddng dien. Trong vat dSn se hoac

la cd ddng dien dSn tao ra tuf trudng xung hoac ddng cam ling dudi tac dung ciia tif
trudng ngoai khdng dijfng. Dd chenh lech (gradien) ap sua't ben trong vat dSn tai vi
trf X tfnh tiif bd mat vat dSn la:
—
dx

= '^,HdH/dx

(1-14)

Bdi vi phin chinh ciia ap sua't tijf tap trung trong vung dSn ma tiif trudng tha'm vao
nen trong thuc te' vdi mdt dd chfnh xac du Idn, dd tha'm sau cua tir trudng dugc coi
la bang bd day cua Idp ngodi da Sd6i vdi mdt vat lieu da cho d tdn sd' sdng o) tuang
ling vdi thdi gian bie'n ddi cua tir trudng H(t):
6 = -^Ip^cofi^^^

d day p la dien trd sua't cua vat din.

Khao sat mdt vat d5n dudi dang mdt hinh tru rdng cd dudng kfnh ngoai va trong
\in lugt la r2 va /-;; vdi r2 >> r;. Gia sir cd mdt tif trudng dugc sinh ra ben trong hinh
tru nay cd dd tha'm sau d nho han nhidu bd day ciia thanh d'ng Ar =/-2 - r/. Khi tdn
tai xung tiif trudng, phSn ben ngoai cua hinh tru chi la ca ca'u ca khi dd giir phSn ben
trong (bdi Idp vat lieu dky) va hien trang nay hoan toan tuang duang vdi bai toan va
cham cua cha't khf dudi ap sua't P = fJoH^ 12 trong mdt d'ng cd thanh dii day [22].
Ung sua't ca khf xua't hien trong Idp vd cd thd dugc bidu didn dudi dang:

n
a'-\

\ +a

^'-,

(1.15)


16

a. =
CJc =

(1.16)

\-a

a'-\
a,-a^

a2

0

a

1

(1.17)

-11/-

d day, a; , cr^ , 05 \in lugt la d'ng sua't theo cac phuang tie'p tuye'n, ban kfnh va
phuang dich ehuydn; a = r2l rj. Gia tri cue dai a; dat dugc d bd mat ben trong cua
hinh tru, tai vi tri r = rj. Ke't luan nay la quan trong dd'i vdi su trinh bay tie'p sau bdi
vi vat lieu bi pha huy d thdi didm khi ma irng sua't dich chuyen d trong nd vugt qua
do bdn gidi han cua vat lieu. Khi H = 4.10^ A/m; PQ = I.IO^ Pascal trong khi gia tri
gidi han bi pha huy ciia ddng la a;, = 4,2. 10^ Pascal.
Viec phat tijf trudng cao va cue cao cGng lien quan tdi sU bie'n thien nhiet dd mdt
each du ddi trong Idp dSn dien. Ne'u nhu bd qua su trao ddi nhiet giira cac Idp nay va
cac phin cdn lai cua vat din sau khoang thdi gian tdn tai xung dien thi budc nhay
vot vd nhiet dd AT d Idp ngoai da dugc tfnh theo cdng thiJc sau:
cDoAT^

^H^/2,

(1.18)

O day, c la nhiet dung rieng khi ap sua't khdng ddi; DQ la mat dd chat. Thf du sau
cho tha'y dd Idn cua hieu d'ng nay, khi Cp ~ 0,4 J Ig.do (dd'i vdi ddng) vk H = 8.10^
Aim thi AT cd 1100 X^ mac du da bd qua sU tang dien trd cua vat lieu theo nhiet dd.

1.4. BAI TOAN THI^T Kfi' C U O N DAY NAM CHAM
Gia tri dinh cua tiif trudng cao phat ra dugc quye't dinh bdi ddng dien chay qua
cudn nam cham va ddng nay bi han che' bdi cac thudc tfnh cua vat lieu lam cudn
day, dd dSn dien va siic bdn cua cudn day. Luc Lorentz tren mdt dan vi thd tfch ty le
vdi tfch ciia mat dd ddng J va cam ung tir B tai virng do ddng dd sinh ra. Luc nay tao
ra mdt ap sua't ty le vdi J^ (hoac B^) trong cudn day va lam xua't hien ling sua't tuang
d'ng. Ung sua't nay se tang len nhanh chdng theo cudng do cua tiif trudng va de'n mdt
gia tri gidi han nao dd (gidi han sd-c bdn cua vat lieu) cudn day se bi pha huy. Trong
qua trinh chay qua cudn day, xung ddng dien cue Idn cung se dd't ndng cac vdng

17

day. Su tang nhiet dd nay cung ty le vdi P vk ciing de'n mdt gidi han nao dd se lam
hong cudn day.
Nhu vay, thie't ke' cudn day nam cham chfnh la viec tfnh toan td'i uu cac thdng
sd lien quan tdi hinh dang cudn day, kfch thudc va loai vat lieu day dSn v.v..khi cho
trudc cac sd lieu yeu cin ban din nhu tir trudng ddi hoi cue dai, dudng kfnh trong,
dd ddng nha't cua trudng va dd dai xung. Khdng may rang, dd dSn dien cua day dSn
thudng lai ty le nghich vdi dd bdn ca hoc cua vat lieu lam day. Vi vay viec td'i uu
hoa cudn day ciing ddng nghia vdi viec chon day dSn the' nao dd cd mdt su nhan
nhugng giiJa viec vira dam bao cd mdt cudn nam cham bdn viJng va on dinh cdng
nhu cd tfnh dSn dien dii cao.
Cd 3 nhan td' tac ddng tdi viec thie't ke' cudn day nam cham la: anh hudng cua
dang hinh hoc cudn day, cua su tang nhiet dd va ap sua't tir.

1.4.1.

Anh huong cua dang hinh hoc cuon day nam cham

Viec tfnh toan dua tren cac thdng sd ban kfnh
trong r;, ban kfnh ngoai /-2, chidu cao b va sd'

2b

vdng day A^ nhu trong hinh 1.5. Cac thdng sd a
va fl dugc dinh nghia nhu sau:

a = r2lrj va

k

P^blrj

2r,

Theo Gauster va Parker [10], cam d'ng tif d
tam cudn day cd thd duac tfnh theo mat dd ddne
•^
'
. .
6
d i e n / bang:

B=

IJ^XJrj^

jj. , , ^ r^^ .t.^
^-L- i .
Hinh L5 Cac thdng sd hinh hoc
ciia cudn day.

In

(1.20)

7 + V^ + p'
vdi X la he sd la'p ddy bang ty sd thd tfch day dSn tren thd tfch cudn day.
Ne'u nhu bd qua su bien ddi nhiet do cua cudn day khi phat xung thi cam d'ng tir

lien he vdi cdng sua't dSn W (bang I,„„JJ,„„, 12) nhu sau:

B=

v.,G(a,^)^W'K/pr,

(1.21)
€;,1 !-!C

TRllNGT

w

: 1 '

i


18

v6i p la dien trd sua't riSng cua day dSn v^

Gfa,p; = —

P

2n\ a ~1

(1.22)

in

Ham G(a,j3) c6 gia tri cue dai bang 0,179 khi a = 5 va y9 = 2. Noi each khac, v6i
m6t e6ng sua't nha't dinh, tiif trucmg se la cue dai khi cae cac thdng s6 avh /3 (quyS't
dinh hinh dang cudn day) dugc chon nhu vay.
Theo Montogomery [27] dien cam cuon day dugc tfnh nhu sau:
L^r,N'd(a,^)

(1.23)

Parkinson va Mulhall [31] da tfnh gSn dung ham 0:
-1-/

IJfi(l+ay
8P

4P

a+1

(1.24)

2/3

Vdi p la dien trd sua't, thi dien trd ciia cum day dugc tfnh nhu sau:

R =pnrj(a

,N
+ l)-=

A

n(a + l)lN'
p-- - —
2 (a-1) p r,X

(1.25)

Hang so thdi gian ciia cudn day bang:
L
^~

R

,

^^^^ot-f7

^0 ^ rf (a'- m1 + 0,225
4p

^^^a-7 ^ ^^a-7
+ 0,64
+ 0,42

P

a+7

(1.26)

P

Thd tfch V ciia day cud'n duac tinh qua cac tham sd' avk P nhu sau:
V = 2;rr/ (ct^-l)p= nrj(a -¥l)NAI X

(1.27)

Trong hin he't trudng hgp, hinh dang cudn day quye't dinh de'n dd ddng nha't ciia
trudng. Trir viec anh hudng nho den he sd la'p day thi thie't dien ciia day dSn khdng
anh hudng gi ddn hidu sua't ciia cudn day bdi vi nd khdng tac ddng den hang so thdi
gian. Nd chi quydt dinh de'n the' va ddng cin dd tfch nang lucmg cho cudn day ma
thdi. Vdi mdt bd tu cd gia tri dien dung da cho, thdng sd nay quyet dinh de'n dd dai
va dang ciia xung ddng.


19

Dd tfnh toan ddng cue dai phai giai he phuang trinh gdm: phuong trinh vi phan
RLC trong mach phdng dien d hinh 1.3 vdi thdng sd R ciia cudn day nam cham phu
thudc vao nhiet dd va phuang trinh truydn nhiet.

L ^ + [R^+R(T)]^Ul
dt

dt

=0

dr(t)^r(t)R(t)

dt

(1.28)

L
(1.29)

D,Vc(t)

d day c(t) la nhiet dung rieng ciia vat lieu lam cudn day.
He phuang trinh nay dugc giai bang phuang phap sd

1.4J Anh hudng ciia nhiet do do xung dong dien chay qua cuon day
Xung ddng dien chay qua cudn day nam cham se sinh ra nhiet. Cd thd coi qua
trinh trao ddi nhiet xay ra trong cudn day la qua trinh doan nhiet. Vd nguyen tac,
thudc tfnh nhiet cd thd dugc md ta bdi he hai phuang trinh vi phan (1.28) va (1.29)
kd tren. Trong dd, RQ va R(T) la cac ph^n dien trd khdng phu thudc va phu thudc vao
nhiet dd cua mach, T la nhiet dd ciia day dSn, DQ la mat dd chat lam cudn day, V va
c(t) la thd tfch va nhiet dung rieng ciia day dan.
Coi mat dd ddng / la khdng ddi trong cudn nam cham cd khdi lugng M, gin
dung cd thd cho nang lugng Joule trir trong cudn day tuang duang vdi lugng nhiet
toa ra, ta cd phuang trinh can bang nhiet nhu sau [14]:

h)'dt=y-^dr

(1.30)

Trong dd p la dien trd sua't ciia day dSn.
Ne'u dien trd ciia cudn nam cham dii Idn de'n muc cd thd bd qua cac phin tir ky
sinh khac trong mach dien cd lien quan thi khi thuc hien dugc dieu kien sau se

khdng xay ra su ndng chay day dSn khi cd xung ddng di qua nd:
h'dt
0

< IJT„,Tf)

«

\c(T)
To

^dT
P


20

vdi To va Tf Ik nhiet dd tai cac thdi didm din va cud'i xung. / la mat dd ddng
dien chay qua cudn day; /^ dugc goi la ddng tich phdn chi phu thudc vao tfnh cha't
ciia vat din va cac nhiet dd d^u va nhiet dd cud'i.
Can cii vao ke't qua ma tac gia cdng
trinh [18] dSn ra tren hinh 1.6 tha'y
rang viec lam lanh so bd cudn nam
cham cd thd la mdt trong nhirng
phuang phap tang ddng tfch phan , do

Tf^

T^'lQOy

chay va dd bdn ciia kim loai dugc sir
dung lam cudn day lai phai dugc tfnh
de'n khi cudn day dugc hoat ddng d

%u

soa
-r^_-4-

Ofi

dd tang dugc bien dd ciia xung tir
trudng. Luc nay, viec tang gidi han luu

sol

IDOQ

*T

t

1.5

Ifrj,.A'cm^

Hinh 1.6 Sir phu thudc cac nhiet dd
cud'i Tf ciia cudn day ddng vao dong tfch
phan vdi cac nhiet dd ban ddu TQ khac
nhau, khi cho dong chay qua no vdi mat

ddd6ng/fr)[18].

nhiet dd tha'p. Thudng cudn nam cham dugc nhiing vao Nita long trudc khi ban
xung, do vay nhiet dd din TQ = 77K.
Nhiet dd trung binh ciia nam cham cd thd dugc xac dinh bang each do dien trd
ciia cudn day phu thudc vao thdi gian, khi dan gian coi su phu thudc ciia p va nhiet
dung c vao nhiet dd T la tuydn tfnh [14]:
p(T) = Po[l+k,(T-To)
c(T) =Co [l +

(1.31)

kc(T-ToI

vdi po vd CQ la dien trd sua't va nhiet dung rieng ciia day d 77K.
Co = 12,45 Jl moLK ; po = 0,175 .10'^ n.m
kj^ = 0,0329 IK
kc = 3,636. lO'^/K
Su truydn nhiet dugc md ta bdi phuong trinh sau:
dE/dt = -kv(n.gradT)

1.32)

6 day, E la nang lugng nhiet; k la he sd dSn nhiet va via viing xay ra dSn nhiet.


21

Nghi6m thdng thucmg c6 dang la:
/gradT/„ = aE"'

(1-33)

a va m la cac tham s6' xac dinh su tich luy nang lugng cue dai v6i di^u kien ddu
E(t = 0) = Eo.
Khi n ^ 7 :

r 1

mt)=---+

112

+-

k^

2

(1.34)

E(t)

^QCQ

I-n

E(t) =

kvat

+

1-m

m-l

(1.35)

(1-m)

jl'(t)R(t)dt

khi n - 1

mt)=—+

J
—j +
kc

112

1 ^

(1.36)

\P(t)R(t)dtexp(-kvat)
^0 k-c 0

Thay zlT vao phuang trinh (1.31), p (T(t)} cd the tfnh dugc mdt each gian tie'p
qua nhiet dd. Tac gia [14] da chi ra cac gia tri ly thuye't va thuc nghiem ciia nhiet do
cudn day va nang lugng E phu thudc vao the' nap tren tu Uc qua mdt trudng hgp tren
bang 1.2. Cudn day dugc khao sat cd r^= 1,2 cm, r2= 2,15 cm, L = 8,5 cm. Cac ke't
qua tren bang cho tha'y cd th^ nhan dugc nhiet do ciia cudn day tai thdi diem cudi
xung tir trudng bang each tren khi coi xung nay dot ndng doan nhiet cuon day.
Bang 12

Cac gia tri ly thuye't va gia tri do dugc ciia nhiet d6 cudi va
tfch phan nang lugng Joule phu thudc vao the' nap tren tu dien ^c t i4]
Gid trj do

Gia trj ly thuyet

Uc

T,[K]

E

Tr[K]

E

325

79,2

2.2. 10'

78,2

1.163. 10'

650

82,5

5,55. 10'

80.5

4.658 . 10^

1000

90,0

1,33. 10'

86.8

1.102. 10'

1325

100,0

2,39. 10'

95.4

1.934. 10'

1650

115,5

4.06. 10'

112.0

2.999. 10'

2000

135.5

6.47 . 10'

133.3

4,407 . 10'


22

Ddng xoay (eddy current) la'y trung binh tren toan hi day Idp ngoai da d ciia mdt
mat dSn phang. Cac phep tfnh xa'p xy tin sd tha'p khi gia thie't ddng xoay dugc phan
bd tuye'n tinh theo khoang each tinh tir be mat dan cho tha'y su ddng gdp nhiet cua

nd tdi cudn day cung nhu su anh hudng tdi dang xung ddng dien la khdng dang k^
[24].

1.4.3

Anh huong cua ap suat tir len cuon day nam cham

Viec tfnh tai ca khf trong cudn day nam cham loai nay la mdt bai toan phirc tap
vi gap phai mdt loat nhirng dO kien cin thie't ban d^u khdng th^ biet chfnh xac. Dd la
su phan bd ling sua't dia phuang trong cudn day bi chi phdi bdi cac luc lam bien
dang cue bd. Mddun dan hdi ciia cac vat lieu hdn hgp dSn dien va each dien tao nen
cudn day v^ nguyen tac la khdng bie't dugc. Ngoai ra trong cudn day cd nhieu Idp
phai chu y tdi su truydn ap sua't tiir Idp day nay tdi Idp day khac. Khi xung ddng dien
chay qua cudn day nam cham, nd se gay ra cac thanh phdn luc nhu hinh 1.7 chi ra.
Thanh phdn theo ban kfnh ciia tiir trudng H^ gay nen cac luc thanh phin F„ nen cudn
nam cham theo hudng true cudn day. Chung dat tdi cac gia tri cue dai gSn tam cudn
day va bia trijf nhau bang khdng trong mat phang di qua tam va vudng gdc vdi true
cudn day. Ne'u nhu cac vdng day dugc ep sat vdi nhau thi cac luc nen dugc tang len
tijr vdng nay tdi vdng kia va dat tdi gia tri cue
dai tai mat phang di qua tam cudn day. Viec
tfnh toan su nen nay la cin thie't khi cac vdng
day dugc phan each nhau bdi cac Idp each dien
tuang ddi m^m. Trong trudng hgp nay khi thie't
ke' phai nghi tdi d^ tranh lam hong chiing. Cac
luc hudng theo true thudng nho han ti^ 5 de'n 10
lin cac luc F, hudng theo phuang ban kfnh
cudn day. Cac luc nay la do su tuang tac giua
thanh phin ciia tir trudng H rat Idn hudng theo
hudng true vdi chfnh ddng dien chay qua cudn
day eay nen tijr trudng dd. Trong thuc te', thudne

cu6n nam cham