Millimeter-Wave Diagnostics for EAST Calvin Domier, Xiangyu Kong, Liubing Yu, Alexander Spear, Shao Che, N.C. Luhmann, Jr. University of California at Davis (UC Davis) Chen Luo, Jinlin Xie, Bingxi Gao, Yilun Zhu, Wandong Liu, Changxuan Yu University of Science and Technology of China (USTC) Liu Yong, Liqun Hu, Han Xiang Institute of Plasma Physics, Chinese Academy of Sciences (ASIPP) 2012 US-PRC Magnetic Fusion Workshop July 10-12, 2012 – La Jolla, CA UC DAVIS P LASMA D IAGNOSTICS G ROUP

Outline  Wideband ECE Radiometer ●32 channel radiometer collects 2nd harmonic X-mode ECE radiation spanning a frequency range of 104 to 168 GHz ●Collaborative effort with the Institute of Plasma Physics, Chinese Academy of Sciences (ASIPP) in Hefei, China  ECE Imaging (ECEI) ●High resolution 2-D ECEI system generates 24x16 images of T e profiles and fluctuations in the EAST plasma ●System spans an RF bandwidth of 14.4 GHz, and is tunable over a frequency range of 102 to 150 GHz ●Collaborative effort with the University of Science and Technology of China (USTC) in Hefei, China

Electron Cyclotron Emission (ECE) ● Electron gyromotion results in Electron Cyclotron Emission (ECE) at a series of discrete harmonic frequencies: ω n =nω ce ● In an optically thick plasma, the ECE radiation intensity is the black body intensity (Rayleigh-Jeans Region): ● In tokamak plasmas, there is a one to one mapping between frequency and radial position due to 1/R dependence of magnetic field B. ω ce  B  1/R ● ECE has become a standard technique to measure T e profiles and fluctuations in magnetic fusion plasmas B R ECE f ce

ECE Heterodyne Radiometer System ● Schematic illustration of the EAST radiometer receiver ● Plasma radiation enters from the left BS1BS2BS GHz GHz GHz GHz 51 GHz To Band 1 59 GHz To Band 2 67 GHz To Band 3 75 GHz GHz To Band 4 Dichroic Plate HDPE Lens Subharmonic Mixer

ECE Heterodyne Radiometer System ● Photograph of the EAST radiometer receiver. ● Plasma radiation enters from the right

Sub-harmonic Receiver ● Each receiver consist of a sub- harmonic mixer pumped by a solid state Gunn oscillator ● ECE radiation is downconverted, amplified by a 2-18 GHz low noise preamplifier placed within the shielded enclosure ● Three translation stages provide full alignment capability, with a vertical stage mounted within and a horizontal stage mounted below the enclosure box, and an axial (focusing) stage mounted underneath a focusing lens placed in front of the receiver

ECE Radiometer Optical Design Receiver 1 Receiver 2 Receiver 3 Receiver 4 Frequency Range (GHz) Simulation Wavelength (mm) Distance from window to focal plane (mm) Beam radius at focal (mm) Spot size (HPBW in mm) Collimating lens radius (mm) Focusing lens radius (mm)400

ECE Radiometer Focal Plane Patterns

ECE Radiometer Electronics ● The output of each receiver is amplified further using a second low noise 2-18 GHz pre-amplifier, and is divided into two parts ● One half is lowpass filtered and feeds the four lower frequency channels, while the other half feeds the four higher frequency channels ● A four-wave power divider splits each of these signals again, with the resultant 8 channels all passing through individual bandpass filters (~500 MHz wide) before getting rectified by coaxial detectors and connecting to an 8-channel video amplifier/filter board

ECE Radiometer Response Curves

2-D ECE Imaging (ECEI) ● Technological advancements allow an extension of well- established principles of heterodyne radiometry. ● Real-time T e down to <1% or µ-sec time resolution ● Up to 1 cm 2 spatial resolution ● 2-D localized measurements using wideband IF electronics and single sideband detection. f ce R R

Double Downconversion Approach (1) A characteristic frequency plot for the EAST tokamak (B T =2.1 T) is shown left, showing X-mode ECE spanning 94 GHz to >160 GHz Mixers Detectors Antennas Mixers LP Filters LO LO n Notch Filter ADCs Plasma Optics Dichroic Plate LO 1

Quasi-optical notch filter prevents transmission of a narrow band of frequencies to protect against stray 140 GHz ECRH Mixers Detectors Antennas Mixers LP Filters LO LO n Notch Filter ADCs Plasma Optics Dichroic Plate LO 1 Double Downconversion Approach (2)

Dichroic plate ensures single sideband operation: effect of f cutoff = 110 GHz plate shown left Mixers Detectors Antennas Mixers LP Filters LO LO n Notch Filter ADCs Plasma Optics Dichroic Plate LO 1 Double Downconversion Approach (3)

Antennas receive broadband ECE, downconvert by f LO (at or near f cutoff ), and amplified: example shows f LO =110 GHz combined with 2-20 GHz amplifiers Mixers Detectors Antennas Mixers LP Filters LO LO n Notch Filter ADCs Plasma Optics Dichroic Plate LO 1 Double Downconversion Approach (4)

Downconverted 2-20 GHz signals are split into n bands and downconverted a second time by frequencies f LO1 through f LOn in the GHz range: shown left are two such channels f (GHz) Mixers Detectors Antennas Mixers LP Filters LO LO n Notch Filter ADCs Plasma Optics Dichroic Plate LO 1 Double Downconversion Approach (5)

Final step is to lowpass filter the n band signals, reducing the radial spot size and providing sharp band edges suitable for cross correlation studies f (GHz) Mixers Detectors Antennas Mixers LP Filters LO LO n Notch Filter ADCs Plasma Optics Dichroic Plate LO 1 Double Downconversion Approach (6)

ECEI Imaging Array

Conventional ECEI: 8-Channel RF Layout 7.9/7.0 GHz 8.8/7.6 GHz 2.5/3.32 GHz 3.4/4.0 GHz 4.3/4.6 GHz 5.2 GHz 6.1/5.8 GHz 7.0/6.4 GHz dB 6-bit Attenuator Filters Power Dividers Mixers

New for EAST: 16-Channel RF Layout 9.7 GHz 10.6 GHz 11.5 GHz 12.4 GHz 13.3 GHz 15.1 GHz x2 8.0 GHz dB 20 dB 6-bit Attenuator 14.2 GHz 20 dB HPF Mixers Doubler To Lower 8 channels GHz Input

ECEI Optical Design ● Zoom optics can control the vertical spacing between antenna elements over a factor of 2X, from mm to as high as mm ● Focuser lens determines the beam waist position within the plasma, can be set to -26.7cm ≤ r ≤ +55.2cm in the narrowest zoom configuration ECEI Array Plasma Edge Vacuum Window Toroidal Corrective Lens Zoom Optics Focuser Toroidal Colliminating Lens Beam Waist

Lexan Optical Enclosure Boxes

● In narrow zoom, the Gaussian beams are focused at the plasma edge (left), and at its deepest location (right). ● Focused on the magnetic axis, the image plane is adjusted from narrow zoom (left) to wide zoom (right). ECEI Gaussian Beam Simulations Narrow, Edge Narrow, Deepest Narrow, Magnetic Axis Wide, Magnetic Axis

● The full diffractive characteristics of beam energy passing through system apertures is revealed through the use of numerical techniques employing Beam Propagation Method (BPM). ● Plotted here are the focal plane patterns at the magnetic axis in the narrow zoom position for the edge (left) and center (right) channels. ECEI Beam Energy Simulations

ECEI Focal Plane Measurements ● Focal plane scans using a translatable scattering rod (functions as a line source) confirm good imaging performance ● Shown above are the E-plane (vertical) focal plane patterns of the centermost 8 channels, with fitted gaussians (─) superimposed over raw data (─)

ECEI Installed on EAST ECEI Electronics Cabinet ECEI Optics BWO

ECEI Installed on EAST

ECEI Electronics on EAST ● ECEI electronics consist of power supply/controllers and ECEI modules (8 per rack) ● ECEI electronics and high speed digitizers placed in shielded rack ● All 384 ECEI signals can be simultaneously sampled at 2 MHz for 6 sec DAQ