NMR Spectrometer Hardware NMR Spectrometer Hardware

Manoj NaikManoj NaikNMR Facility, TIFRNMR Facility, TIFR

Workshop on NMR & its applicationsWorkshop on NMR & its applicationsTIFR, MumbaiTIFR, Mumbai

November 23, 2009 November 23, 2009

Principle of NMR

Nuclear Magnetic Resonance

ω = γ∗B

A Simplified 60 MHzA Simplified 60 MHzNMR SpectrometerNMR Spectrometer

TransmitterReceiver

Probe

hν

SN

RF Detector Recorder

RF (60 MHz)Oscillator

~ 1.41 Tesla (+ / - ) a few ppm

absorpt ion signal

MAGNETMAGNET

CONTINUOUS WAVE (CW) METHODCONTINUOUS WAVE (CW) METHOD

The magnet ic f ield is “scanned” from a low f ield strength to a higher f ield strength while a constantbeam of radiofrequency (cont inuous wave) is supplied at a f ixed frequency (say 100 MHz).

Using this method, it requires several minutes to plotan NMR spectrum.

THE OLDER, CLASSICAL METHOD

SLOW, HIGH NOISE LEVEL

PULSED FOURIER TRANSFORM PULSED FOURIER TRANSFORM (FT) METHOD(FT) METHOD

THE NEWER COMPUTER- BASED METHOD

The excitat ion pulse, the data collect ion (FID), and the computer- driven Fourier Transform (FT) take only a few seconds.

Most protons relax (decay) from their excited states very quickly (within a second).

The pulse and data collect ion cycles may be repeatedevery few seconds.

Many repet it ions can be performed in avery short t ime, leading to improved signal …..

FASTLOW NOISE

Bloch‘s Laboratory in Stanford 1949

First NMR Signal In1946

NMR in 1964

HFX90

NMR Spectrometer in 1970NMR Spectrometer in 1970

AM console

NMR Spectrometer in 1985NMR Spectrometer in 1985

Routine NMR Spectrometer in 2000Routine NMR Spectrometer in 2000

NMR Spectrometer Schematic

Spectrometer Layout

NMR Spectrometer hardware componentsNMR Spectrometer hardware components

1. Magnet1. Magnet2. RT Shims2. RT Shims3. Field Frquency Lock3. Field Frquency Lock4. Probes4. Probes5. Transmitters5. Transmitters6. Preamplifiers6. Preamplifiers7. Receiver7. Receiver8. Digitiser8. Digitiser9. Host Computer9. Host Computer

Type of Magnets

1: Permanent Magnet: Weak

2: Electromagnet: Bulky & Power Consuming

3: Superconducting Magnet: Compact

Superconducting Magnet

• Compact & Efficient• Ability to support high current density• Niobium-titanium for low field < 9 Tesla• Niobium tin for high field : expensive,brittle• Multifilamentary embedded in cu matrix• For better stability & less diamagnetism• Operated at 4.20K upto 700MHz• Operated at 20K above 700MHz

Magnet Coil

Cryostat Cutview

800 MAGNET CRYOSTAT Adjustment Screw for

Needle ValveQuench Valves

Pump Cryostat arrangement

Supercon magnet

• SC material Al5 + NbTi• Proton frequency 800.13 MHz• Central field 18.79 Tesla• He capacity 1200 litres (350+850)• Hold time > 56 days• Liq. N capacity 450 litres

System Liquid Helium Liquid Nitrogen

Boil offrate

Refill Volume Total Volume

Boil off rate

Refill volume Total Volume

500 MHz 35 ml/hour 100 Lit/3month

286 Lit 400 ml/hour 200 Lit/21days 286 Lit

600 MHz 35 ml/hour 80Lit/2month

195 Lit 250 ml/hour 135 Lit/21days 200 Lit

700 MHz 45ml/hour 162Lit/5month

257 Lit 455ml/hour 229Lit/21days 286 Lit

800 MHz 220 ml/hour 200Lit. /month

1200 Lit 750 ml/hour 250 Lit/15days 400 Lit

Cryogenics data for the NMR magnets

RT Shims

• Homogenous field essential for good lineshape • Variation in Magnetic field with Position• NMR frequency is proportional to field results

in distorted lineshape• To create homogenous field Shim coils are

placed in vicinity of sample • Shim currents strength adjusted by looking at

spectra to nullify field gradient

Field Homogeneity

Classification of Shims

• Axial or spinning shims … Z1,Z2,Z3,Z4…• Non-axial or non spinning shims … X,Y, XY

NMR Probes

NMR Probe

NMR probes

• HR Probes with ATM• High Resolution Probes with Automatic

Tuning and Matching(ATM) 

• 5mm TXI … 1H/13C/15N/2H• 5mm BBI … 1H/2H/ BB

Cryoprobe

• The CryoProbe is a high-performance cryogenically cooled probe developed for high-resolution applications. It has improved signal/noise (S/N) ratios obtained by reducing the operating temperature of the coil and the pre-amplifier. The dramatic increase in the S/N ratio by a factor of 3-4, as compared to conventional probes, leads to a possible reduction in experiment time of up to 16 or a reduction in required sample concentration by a factor of up to 4.

• Linear behavior in power response • Gradient capability • CryoProbes are available as Triple Resonance, Enhanced Dual, Quad

Nucleus Probes, or Dual Inverse configurations at 400 MHz and higher

• All high resolution probes have a 2H lock circuit

Cryoplatform

• The CryoPlatform's main purpose is to provide the cooling infrastructure needed for the operation of cryogenic probes.

• Components of the CryoPlatform consists of a CryoCooling Unit and a Helium Compressor. The Cryocooling Unit, the heart of the cooling system is a Gifford McMahon cryocooler which is driven by pressurized helium supplied by the helium compressor. Cooling CryoProbes is accomplished with a closed-looped helium gas flow via a flexible transferline. The CryoCooling unit has dedicated electronics control and monitors the entire system during all phases of operation. It has an automatic error handling and safety shutdown functions.

Cryoplatform

Variable temperature

• In general– stable temperature (during experiment)– Controlled air flow over sample – Cooler and Heater are used to control the sample temperature- Thermocouple are used to sense sample

temp.

Low temperature

Moderately low: BCU-05 cooling unitHR- and MAS-Version (pressure)cools gas stream typically by 65 Ktemperature range: approx. -15°C to +50°C

really low: heat exchangerMAS version for VTN, WVT, DVTHR version for DVTcooling down of heat exchanger only underdry N2 gas

VT gas

N2 from boil-off device:dry, oil freelow pressure fluctuation inert

! Caution !! Look after fresh air !

! O2 warning system where required !

Compressed gas from compressor:pay attention to dew point and oil content (0.0 %)condensation of O2 at low temperaturerisc of oxidation at high temperaturepressure fluctuation

Probe and magnet protection

transfer tube

shimsystem “frame cooling“

NO ice nor heat at O-rings!

Probe and magnet protection

flush gas (ambient temperature) forshimsystem probehead (“frame cooling“)transfertube

critical parameters:high temperature: shim foils: T ≤ 70 °Clow temperature: in case of icing of O-rings risc of leakage of vacuum and quench!

Slow heating and cooling!

For heating and cooling consider thermal burden on probe

using a ramp of 6 to 10 degrees per minute is recommended

AQS REF-22 Block Diag.

d1

PW

FIDd1

SelectiveExcitation

NCO0 NCO2 NCO3 NCO0NCO1

NoFrequency F1+ ∆ F F1 Lo = F1 + 22MHz

NoFrequency

Simple Pulse SequenceSimple Pulse Sequence

NCO0Zero AmplitudeZero Frequency

NCO1W1 AmplitudeW1 Frequency

NCO2W2 AmplitudeW2 Frequency

NCO3W3 AmplitudeW3 Frequency

16x16 bit

MULTIPLIERDAC

CONVERTER

UPX

DIGITALCONTROLFROMFCU3

MODWn

Frequency MULT

RFOUT

SHAPEDDS

NCO = Numeric Controlled Oscillator.DDS = Direct Digital Synthesis.

ϕW1 1

ϕW1 2

ϕW1 3Σ

ϕW2 1

ϕW2 2

ϕW2 3Σ

ϕW3 1

ϕW3 2

ϕW3 3Σ ϕ Information

13-23MHz 3-1100MHz

Example of a 10-bit ROM tableExample of a 10-bit ROM table

0

2 = 6 4 K1 6

U P D O W N

U P D O W NI N V E R T E DS I G N

( b i t 1 6 )

( b i t 1 5 )

1 6 K( 1 4 b i t )

O n l y t h e f i r s t 1 / 4 o f t h e c o m p l e t e s i n e p e r i o d i s i n t h e R O M .T h e o t h e r q u a r t e r s a r e o b t a i n e d b y s y m m e t r y .

ROM table for 16 bitROM table for 16 bit

Phase Coherent:

Phase Continuous:

Phase Resetted:

NCO1 NCO2 NCO1

NCO1 NCO2 NCO1

NCO1 NCO2 NCO1 NCO2

Reset Reset

F1 F1+ ∆ F F1

F1 F1+ ∆ F F1 F1+ ∆ F

Flexible Frequency GenerationFlexible Frequency Generation

Blockdiagram of the SGUBlockdiagram of the SGU

TIMING

Pulse Duration: Minimum 50ns

Delay Duration: Minimum 50ns

Resolution 12.5ns

FREQUENCY

Range 3-1100MHz

Bandwidth of each Channel 3-1100MHz

Resolution <0.005Hz or 34bit

Switching Time

<+-2.5MHz Steps < 300ns

Timing and Frequency SpecificationsTiming and Frequency Specifications

PHASE

Phase resolution < 0.006° or 16bit

Phase switching time < 300ns

AMPLITUDE

Modulation (MOD) Range 96dB or 16bit

Resolution < 0.01dB up to 54dB

< 0.05dB up to 60dB

Level (MULT) Range 90dB

Resolution 0.1dB

Amplitude Switching Time 50ns

Next Event: Phase + Amplitude 100ns

Phase and Amplitude SpecificationsPhase and Amplitude Specifications

Amplifier

Amplifier

• overshoot– measured in % of pp voltage

• only little for short pulses

• ripple– measured in % of pp voltage

• only little for short pulses– low frequency ripple:

» comes from insufficient power supply– high frequency ripple:

» comes from RF impurities

• droop– measured in % of pp voltage

• important for long pulses and pulse trains

Characterisation of Pulse ShapesCharacterisation of Pulse Shapes

• on/off ratio– measured in dB

• important for noise reasons

• rise and fall time– from 10 % to 90 % ca. 100 ns

• not much of a concern, because it is determined by the narrowest component (which is the probe)

Characterisation of Pulse ShapesCharacterisation of Pulse Shapes

Transmitter Specification

Amplifier

Probe

Multiplexer

Preamplifier

Controller

Preamplifier designPreamplifier design

Top: wiring of amplifier, probe, and receiver (preamplifier)bottom left: switching under influence of a pulse (> 700 mV)bottom right: switching under influence of an NMR signal

Passive RF switchingPassive RF switching

Linear Pre-amp Specification

Receiver

RX22 Receiver:

Intermediate Frequency IF 22MHz. FID input from Preamplifier. Receiver output is audio frequency Channel A and B (quadrature) into digitizer.

RX22 Receiver:

Intermediate Frequency IF 22MHz. FID input from Preamplifier. Receiver output is audio frequency Channel A and B (quadrature) into digitizer.

Quadrature Detection

Digital to Analogue Conversion (ADC)

RXAD

• Does four main function … To amplify signal from HPPR Demodulation of RF signal to AF range To match the input range of ADC To digitize quadrature signal• Specification … Frequency range: 5…1072MHz Gain range: ………… 93dB in 1dB steps ADC resolution ……. 200KHz …. 20Bit 5MHz …….16Bit Data rate ….560Mbits/s

0-62.5kHz-100kHz 62.5kHz 100kHz

SAMPLING WINDOW

DIGITALFILTER20 kHz

ANTI-ALIASINGANALOGFILTER125 kHz

FkHz

Image

SWH Oversampling200 kHz

SWH2

Signal fullysuppressed

by Digital Filter SWH2

(After Decimation)

SWH(Before

Decimation)

CONVENTIONALANALOGFILTER

SW=20 kHz

10kHz-10kHz

Digital FilteringDigital Filtering

Digital Receiver Unit does following fucntion

Interface to two ADC channel

Capture peak values for ‘receiver gain adjust (rga)’

Automatic DC offset calibration (AutoZeroCompensation), digital phase control, Digital quadrature detection, Digital filtering & Decimation of NMR signals, accumulation and acquisition &

Data transfer to workstation via ethernet

Diagnosis & access to the DRU relies on HTTP & HTML enabling service access just by any web browser

DRU

AQS Avance AV OneBay

AQS CCU10

AQS CCU10 Block Diag.

CCU10 Specification

• RISC based cpu operating @ 100MHz• Ethernet link @ 100MHz half duplex• 10 RS232 CHANNEL• 2 RS485 CHANEL• 64Mb DRAM

Timing Control Unit TCU3

• to synchronize and control the timing of the RCU, FCU’s and GCU• to send frequency information to the FCUs via the F bus• to generate various front panel switching signals used in external amplifiers, QNP Pneumatic Unit, BSMS, etc.• to provide the RCU and GCU with a 40MHz TTL clock signal• to generate the RCUGO signal for the RCU and the AQS signal for the GCU

The TCU3 is used ….

• The timing of the TCU3 is implemented using an 80MHz internal clock (this signal is generated on board from the 20MHz of the REF22 board)

TCU3

Frequency Generation Unit

• Digital control of all aspects of frequency, phase and amplitude• Real-time control of all gating signals generated on the SGU• LVDS (low voltage differential signal) link between the FCU3 and SGU• The FCU3 can be viewed as the digital section of the SGU• One FCU3 contains four independent channels• No jumper-settings required due to auto configuration• No on-board DDS generation - this is performed by the SGU

FCU3

FCU / SGU LVDS Interface

Twisted Pair4x7 bit at 20MHz

560Mbit/s

20MHz(50ns)

Low Voltage Differential Signaling

FCU3 SGU

NMR Consol

The RF Part